The life history of selected coastal foredune species of South Africa
- Authors: Knevel, Irma Cornelia
- Date: 2002
- Subjects: Sand dune plants -- South Africa Sand dune ecology -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4207 , http://hdl.handle.net/10962/d1003776
- Description: South African dune fields are severely threatened by human expansion and in the long run the stabilisation of many dunes will be necessary. The alien grass Ammophila arenaria is the most important drift sand stabiliser at present in South Africa. Although not invasive, the current impact of A. arenaria on the dune systems of South Africa is considerable, and thus the stabilising benefit of the grass seemed to may be outweighed by its negative consequences. It is therefore preferable to use indigenous sand stabilising species. In order to define guidelines for the application of indigenous plants for stabilisation, their autecology should be studied first to enhance the chance of successful stabilisation results. The main aim of the present thesis was to gather information on the life history processes of selected indigenous, sand stabilising foredune species. To investigate the growth of foredune pioneer species, the common pioneer Scaevola plumieri was followed over a three-year period to determine the growth season and leaf phenology. Soil-borne pathogens are known to influence the growth and vegetation dynamics of foredune species. To examine this effect on the South African foredunes the rhizosphere soil and the roots of several species were studied. To test the effect of the nematode fauna on succeeding plant species a transplantation experiment was carried out. The seed stage is the only life-cycle stage that can survive unfavourable conditions. Therefore, the seed ecology of several foredune species was studied extensively to determine the reproductive season, the seed production, the fate of seeds after shedding (germination, seawater dispersal), germination requirements and seed bank strategy. Seeds of the species Arctotheca populifolia, Ipomoea pes-caprae, Myrica cordifolia, and Scaevola plumieri were subjected to germination trials, field observations on seedling survival, and scarification and stratification experiments. This was done to obtain information about the germination requirements and to determine the reproductive season and growth season. The seed bank strategy of the foredune species, as well as the seed bank density, was determined by extensive sampling along the Cape coast. The species S. plumieri thrived under sand accretion situations, which makes it a good candidate for stabilisation purposes. The growth of S. plumieri was seasonal, with the highest leaf production during spring and summer. The stem position on the foredune had a strong effect on the overall performance of S. plumieri , with the stems situated on the landward face of the foredune showing higher leaf and seed production. Theiii nematode survey of soil and roots of several foredune species showed that all plant species featured a specific nematode fauna in the rhizosphere soil and the roots. The specific nematode fauna affected the growth of foreign plant species in the transplantation experiment, resulting in a lower root and/or shoot biomass production. Most of the foredune species produce seeds from spring to late summer. For S. plumieri the position of the stem on the dunes, as well as the predation of unripe seeds affected the number of seeds produced. The highest production was found for the landward faced stems. The S. plumieri seeds were able to float on seawater for at least three months without losing viability, as was observed for seeds of I. pes-caprae. The seeds of M. cordifolia, however, sank after a few days, but their viability was not affected. The rhizome fragments of A. arenaria and S. virginicus floated for 120 days, whereas the fragments of E. villosa sunk after one day. The viability of S. virginicus fragments was affected by the duration in seawater by an increase in sprouting time. The seeds of all species tested germinated readily under controlled conditions, except S. plumieri seeds which required a long lag-phase before germination. In the field the seeds of A. populifolia, I. pes-caprae and S. plumieri germinated, producing many seedlings. Only the seedlings of A. populifolia and S. plumieri survived. Of the species found in the foredunes 57% was represented in the soil seed bank. For most species, the seeds that were found in the seed bank showed viability of at least 40%. Many of the seeds found were older than one year, suggesting a short-term persistent seed bank. The present study is a start in filling the gap in information on dune pioneer and foredune species. The conclusion was that in general all species in the present study were easy to grow under controlled conditions, and thus could be used for stabilisation purposes. When the more rapidly growing pioneer species are planted in combination with succeeding foredune species, a functional and aesthetic ecosystem could be created.
- Full Text:
- Date Issued: 2002
- Authors: Knevel, Irma Cornelia
- Date: 2002
- Subjects: Sand dune plants -- South Africa Sand dune ecology -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4207 , http://hdl.handle.net/10962/d1003776
- Description: South African dune fields are severely threatened by human expansion and in the long run the stabilisation of many dunes will be necessary. The alien grass Ammophila arenaria is the most important drift sand stabiliser at present in South Africa. Although not invasive, the current impact of A. arenaria on the dune systems of South Africa is considerable, and thus the stabilising benefit of the grass seemed to may be outweighed by its negative consequences. It is therefore preferable to use indigenous sand stabilising species. In order to define guidelines for the application of indigenous plants for stabilisation, their autecology should be studied first to enhance the chance of successful stabilisation results. The main aim of the present thesis was to gather information on the life history processes of selected indigenous, sand stabilising foredune species. To investigate the growth of foredune pioneer species, the common pioneer Scaevola plumieri was followed over a three-year period to determine the growth season and leaf phenology. Soil-borne pathogens are known to influence the growth and vegetation dynamics of foredune species. To examine this effect on the South African foredunes the rhizosphere soil and the roots of several species were studied. To test the effect of the nematode fauna on succeeding plant species a transplantation experiment was carried out. The seed stage is the only life-cycle stage that can survive unfavourable conditions. Therefore, the seed ecology of several foredune species was studied extensively to determine the reproductive season, the seed production, the fate of seeds after shedding (germination, seawater dispersal), germination requirements and seed bank strategy. Seeds of the species Arctotheca populifolia, Ipomoea pes-caprae, Myrica cordifolia, and Scaevola plumieri were subjected to germination trials, field observations on seedling survival, and scarification and stratification experiments. This was done to obtain information about the germination requirements and to determine the reproductive season and growth season. The seed bank strategy of the foredune species, as well as the seed bank density, was determined by extensive sampling along the Cape coast. The species S. plumieri thrived under sand accretion situations, which makes it a good candidate for stabilisation purposes. The growth of S. plumieri was seasonal, with the highest leaf production during spring and summer. The stem position on the foredune had a strong effect on the overall performance of S. plumieri , with the stems situated on the landward face of the foredune showing higher leaf and seed production. Theiii nematode survey of soil and roots of several foredune species showed that all plant species featured a specific nematode fauna in the rhizosphere soil and the roots. The specific nematode fauna affected the growth of foreign plant species in the transplantation experiment, resulting in a lower root and/or shoot biomass production. Most of the foredune species produce seeds from spring to late summer. For S. plumieri the position of the stem on the dunes, as well as the predation of unripe seeds affected the number of seeds produced. The highest production was found for the landward faced stems. The S. plumieri seeds were able to float on seawater for at least three months without losing viability, as was observed for seeds of I. pes-caprae. The seeds of M. cordifolia, however, sank after a few days, but their viability was not affected. The rhizome fragments of A. arenaria and S. virginicus floated for 120 days, whereas the fragments of E. villosa sunk after one day. The viability of S. virginicus fragments was affected by the duration in seawater by an increase in sprouting time. The seeds of all species tested germinated readily under controlled conditions, except S. plumieri seeds which required a long lag-phase before germination. In the field the seeds of A. populifolia, I. pes-caprae and S. plumieri germinated, producing many seedlings. Only the seedlings of A. populifolia and S. plumieri survived. Of the species found in the foredunes 57% was represented in the soil seed bank. For most species, the seeds that were found in the seed bank showed viability of at least 40%. Many of the seeds found were older than one year, suggesting a short-term persistent seed bank. The present study is a start in filling the gap in information on dune pioneer and foredune species. The conclusion was that in general all species in the present study were easy to grow under controlled conditions, and thus could be used for stabilisation purposes. When the more rapidly growing pioneer species are planted in combination with succeeding foredune species, a functional and aesthetic ecosystem could be created.
- Full Text:
- Date Issued: 2002
Changes in carbohydrate concentration and amylolytic activity in germinating maize
- Authors: Breen, C M
- Date: 1969
- Subjects: Corn -- Research Corn -- Analysis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4251 , http://hdl.handle.net/10962/d1007680
- Description: Changes in the concentration of some carbohydrates and in amylolytic activity have been followed during germination of Zea. Mays L. var. Hickory King and var. Early Pearl. Assay techniques have been developed which permitted assay of individual grains. Thus during the investigation both groups and individual grains were used as samples. The use of groups permitted control of assay technique. Length of radicle, coleoptile and lateral roots were recorded in order to permit quantitative estimation of correlation between growth and the concentration of the various carbohydrates. Initially, during the study of changes in the carbohydrate concentration in Hickory King grains, total reducing sugar, sucrose and dextrin concentrations were estimated. However, the results obtained for changes in dextrin concentration, although reproduceable, thereby indicating reliable assay technique, presented a confusing picture and, in view of the apparent importance of sucrose and reducing sugar concentration, assay of dextrin concentration was discontinued in a subsequent study of Early Pearl. Instead changes in total reducing sugar, sucrose and glucose concentrations were followed. The results revealed that there is very considerable variability in physiological activity between grains subjected to the same germination conditions. However, all, irrespective of variety, follow the same basic metabolic pattern during germination. The trends observed were: (i) Reducing sugar accumulates slowly during the first 72-96 hours germination, but thereafter accumulation is very rapid, although concentration may decrease towards the end of the gestation period. (ii) Glucose follows a similar pattern to reducing sugar, accumulating slowly during the early stages of germination, followed by a period of rapid increase in concentration, which may decrease towards the end of the germination period. (iii) Sucrose concentration in dormant grains is fairly high, but it decreases markedly during the first 96 hours germination. This is followed by a phase of sucrose accumulation. (iv) Dextrin concentration shows two peaks. Initial level is low, but it accumulates rapidly during the first 72 hours. The level decreases between 72 and 120 hours but increases when the germination period is increased to 192 hours, after which there is a marked decrease. It was impossible, from the data relating to the study of individual grains, to discern a trend in dextrin concentration. With the exception of dextrin, about which there is little information, the results are in general agreement with the literature. Investigation of correlation between the various carbohydrates and between these and growth revealed that: (i) reducing sugar concentration and growth are positively correlated ; (ii) glucose concentration and growth are positively correlated; (iii) sucrose and reducing sugar concentrctions are negatively correlated during the initial stages of germination; (iv) sucrose and glucose concentrations are negatively correlated during early germination; (v) glucose and reducing sugar are positively correlated; (vi) in general, correlation between growth and concentration of the carbohydrates studied, decreases during the later periods of germination. These observations suggested that growth was, at least during the early stages of germination, dependent on the level of reducing sugar, and more particularly on the level of glucose, and that sucrose is the principal source of reducing sugar during this period. The relationship between amylase activity (total alpha- and beta-amylase activity) and reducing sugar concentration tends to be curvilinear, which suggests that amylolytic activity produces relatively little reducing sugar during early gennination, even though amylase activity and growth may be positively correlated. The results suggest, contrary to the observations of previous workers, that alpha-amylolytic activity may be present in dormant grains and that maize is not characterised by low levels of beta-amylase activity during germination. From the observations it is concluded that the initinl accumulati on of reducing sugar is the result of sucrose hydrolysis, and therefore sucrose is an importnnt metabolite durjng early germination. Amylolytic activity contributes little reducing sugar durlng the initia1 stages of germinatIon but that after approximately 72 hours it represents the major source of reducing sugar.
- Full Text:
- Date Issued: 1969
- Authors: Breen, C M
- Date: 1969
- Subjects: Corn -- Research Corn -- Analysis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4251 , http://hdl.handle.net/10962/d1007680
- Description: Changes in the concentration of some carbohydrates and in amylolytic activity have been followed during germination of Zea. Mays L. var. Hickory King and var. Early Pearl. Assay techniques have been developed which permitted assay of individual grains. Thus during the investigation both groups and individual grains were used as samples. The use of groups permitted control of assay technique. Length of radicle, coleoptile and lateral roots were recorded in order to permit quantitative estimation of correlation between growth and the concentration of the various carbohydrates. Initially, during the study of changes in the carbohydrate concentration in Hickory King grains, total reducing sugar, sucrose and dextrin concentrations were estimated. However, the results obtained for changes in dextrin concentration, although reproduceable, thereby indicating reliable assay technique, presented a confusing picture and, in view of the apparent importance of sucrose and reducing sugar concentration, assay of dextrin concentration was discontinued in a subsequent study of Early Pearl. Instead changes in total reducing sugar, sucrose and glucose concentrations were followed. The results revealed that there is very considerable variability in physiological activity between grains subjected to the same germination conditions. However, all, irrespective of variety, follow the same basic metabolic pattern during germination. The trends observed were: (i) Reducing sugar accumulates slowly during the first 72-96 hours germination, but thereafter accumulation is very rapid, although concentration may decrease towards the end of the gestation period. (ii) Glucose follows a similar pattern to reducing sugar, accumulating slowly during the early stages of germination, followed by a period of rapid increase in concentration, which may decrease towards the end of the germination period. (iii) Sucrose concentration in dormant grains is fairly high, but it decreases markedly during the first 96 hours germination. This is followed by a phase of sucrose accumulation. (iv) Dextrin concentration shows two peaks. Initial level is low, but it accumulates rapidly during the first 72 hours. The level decreases between 72 and 120 hours but increases when the germination period is increased to 192 hours, after which there is a marked decrease. It was impossible, from the data relating to the study of individual grains, to discern a trend in dextrin concentration. With the exception of dextrin, about which there is little information, the results are in general agreement with the literature. Investigation of correlation between the various carbohydrates and between these and growth revealed that: (i) reducing sugar concentration and growth are positively correlated ; (ii) glucose concentration and growth are positively correlated; (iii) sucrose and reducing sugar concentrctions are negatively correlated during the initial stages of germination; (iv) sucrose and glucose concentrations are negatively correlated during early germination; (v) glucose and reducing sugar are positively correlated; (vi) in general, correlation between growth and concentration of the carbohydrates studied, decreases during the later periods of germination. These observations suggested that growth was, at least during the early stages of germination, dependent on the level of reducing sugar, and more particularly on the level of glucose, and that sucrose is the principal source of reducing sugar during this period. The relationship between amylase activity (total alpha- and beta-amylase activity) and reducing sugar concentration tends to be curvilinear, which suggests that amylolytic activity produces relatively little reducing sugar during early gennination, even though amylase activity and growth may be positively correlated. The results suggest, contrary to the observations of previous workers, that alpha-amylolytic activity may be present in dormant grains and that maize is not characterised by low levels of beta-amylase activity during germination. From the observations it is concluded that the initinl accumulati on of reducing sugar is the result of sucrose hydrolysis, and therefore sucrose is an importnnt metabolite durjng early germination. Amylolytic activity contributes little reducing sugar durlng the initia1 stages of germinatIon but that after approximately 72 hours it represents the major source of reducing sugar.
- Full Text:
- Date Issued: 1969
Physico-chemical and substructural studies on Nudaurelia capensis β virus
- Authors: Struthers, J Keith
- Date: 1974
- Subjects: Imbrasia cytherea , Insects -- Viruses , RNA viruses , DNA
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4075 , http://hdl.handle.net/10962/d1007327 , Imbrasia cytherea , Insects -- Viruses , RNA viruses , DNA
- Description: From Introduction: The pine emperor moth, Nudaurelia cytherea capensis Stoll is an insect which, during the larval stage, causes extensive defoliation of the pine tree, Pinus radiata in the Cape province. These insects are susceptible to a virus disease, which on occasions causes large scale mortality. Five nonoccluded viruses have been shown to infect the pine emperor moth, and of these, one found in the greatest concentration, Nudaurelia capensis β virus (NβV) has been characterised to the greatest extent. This virus has been shown to contain RNA, to be isometric with a diameter of 36 mm, and to have a molecular weight of 16 million. The virus occurs in all stages of the insect's development, and by fluorescent antibody staining has been shown to develop in the cytoplasm of the host's cells. There have in recent years been a number of reports describing nonoccluded RNA viruses which appear to be similar to NβV. These are the viruses isolated from the moths Gonometa podocarpi and Antheraea eucalypti, and the one from the citrus red mite, Panonychus citri. These viruses have not been as extensively characterised as NβV, so the extent of the similarity between them and NβV is not known. However it would appear as if their discovery collectively heralds the emergence of a distinct new grouping within the nonoccluded RNA viruses of insects. This work reports the isolation and further characterisation of N. capensis β virus, its protein and nucleic acid.
- Full Text:
- Date Issued: 1974
- Authors: Struthers, J Keith
- Date: 1974
- Subjects: Imbrasia cytherea , Insects -- Viruses , RNA viruses , DNA
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4075 , http://hdl.handle.net/10962/d1007327 , Imbrasia cytherea , Insects -- Viruses , RNA viruses , DNA
- Description: From Introduction: The pine emperor moth, Nudaurelia cytherea capensis Stoll is an insect which, during the larval stage, causes extensive defoliation of the pine tree, Pinus radiata in the Cape province. These insects are susceptible to a virus disease, which on occasions causes large scale mortality. Five nonoccluded viruses have been shown to infect the pine emperor moth, and of these, one found in the greatest concentration, Nudaurelia capensis β virus (NβV) has been characterised to the greatest extent. This virus has been shown to contain RNA, to be isometric with a diameter of 36 mm, and to have a molecular weight of 16 million. The virus occurs in all stages of the insect's development, and by fluorescent antibody staining has been shown to develop in the cytoplasm of the host's cells. There have in recent years been a number of reports describing nonoccluded RNA viruses which appear to be similar to NβV. These are the viruses isolated from the moths Gonometa podocarpi and Antheraea eucalypti, and the one from the citrus red mite, Panonychus citri. These viruses have not been as extensively characterised as NβV, so the extent of the similarity between them and NβV is not known. However it would appear as if their discovery collectively heralds the emergence of a distinct new grouping within the nonoccluded RNA viruses of insects. This work reports the isolation and further characterisation of N. capensis β virus, its protein and nucleic acid.
- Full Text:
- Date Issued: 1974
The anatomy and ecophysiology of Mariscus congestus from three different habitats in the Albany and Bathurst districts of the Eastern Cape, investigated under field and laboratory conditions
- Authors: Sonnenberg, Bernd Jürgen
- Date: 1992
- Subjects: Cyperaceae -- South Africa , Plant anatomy , Plant physiology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4229 , http://hdl.handle.net/10962/d1003798 , Cyperaceae -- South Africa , Plant anatomy , Plant physiology
- Description: An investigation of the anatomy and gas exchange characteristics of Mariscus congestus in three different habitats was undertaken in order to establish whether M. congestus from the three different habitats displayed any ecotypic responses when placed in a new similar environment. It was hoped that the results of this investigation would yield evidence that would support the ecotype concept similar to the investigations of Milner and Hiesey (1964), Green (1969) and Slayter and Ferrar (1977). On the basis of the site leaf anatomy, M. congestus investigated at the coast (site 1) differed in many respects from the inland plants (sites 2 and 3). These differences suggest that the coastal plants may have undergone a slight ecotypic divergence from the inland plants. The anatomical investigation also suggested that the leaves of M. congestus from all three sites may either be C₄ NADP-ME or PCK and that all had typical Chlorocyperiod anatomy. The habitat microclimates at sites 1-3 had different light and water regimes. There were no significant differences between the 12 month temperature environments of the three sites. There was however, a minor difference between the coastal (high temperature) and the inland (lower temperature) sites. M. congestus at the three sites had significantly different CO₂ assimilation rates, transpiration and stomatal conductance in response to the differing habitat microclimates. The water use efficiency of the sites were however, similar. Site 1 attained the highest CO₂ assimilation rates, transpiration, stomatal conductance, and water use efficiency and site 3 the lowest. Under similar conditions the gas exchange data for the potted plants indicated that M. congestus from the different sites was typically C₄. The optimal photosynthetic temperatures of all the sites was above 30°C and they did not show significant inhibition of CO₂ assimilation by different oxygen concentrations. The results of the laboratory investigation of the potted plants suggested that the only site-specific (ecotypic) response of M. eongestus was the light intensity at which the plants from the different sites were light saturated. The light and temperature response of field plants under field conditions was not comparable to the light and temperature response of potted plants under laboratory conditions. This may have been due to the field results being obtained under differing water and soil nutrient regimes. The potted plants may also have had a reduced root mass compared to their field counterparts and the potted plants may have also have become root bound. Under field conditions the plants had differing light saturation points and optimal photosynthetic temperatures compared to the potted plants. This investigation thus did not support the hypothesis stated in this thesis. The data in this investigation thus may indicate that plants with as diverse habitats as Mariscus congestus that are removed from their natural habitats display rapid changes in gas exchange characteristics in response to their new microclimates, with few ecotypic physiological characteristics of the old habitat being retained.
- Full Text:
- Date Issued: 1992
- Authors: Sonnenberg, Bernd Jürgen
- Date: 1992
- Subjects: Cyperaceae -- South Africa , Plant anatomy , Plant physiology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4229 , http://hdl.handle.net/10962/d1003798 , Cyperaceae -- South Africa , Plant anatomy , Plant physiology
- Description: An investigation of the anatomy and gas exchange characteristics of Mariscus congestus in three different habitats was undertaken in order to establish whether M. congestus from the three different habitats displayed any ecotypic responses when placed in a new similar environment. It was hoped that the results of this investigation would yield evidence that would support the ecotype concept similar to the investigations of Milner and Hiesey (1964), Green (1969) and Slayter and Ferrar (1977). On the basis of the site leaf anatomy, M. congestus investigated at the coast (site 1) differed in many respects from the inland plants (sites 2 and 3). These differences suggest that the coastal plants may have undergone a slight ecotypic divergence from the inland plants. The anatomical investigation also suggested that the leaves of M. congestus from all three sites may either be C₄ NADP-ME or PCK and that all had typical Chlorocyperiod anatomy. The habitat microclimates at sites 1-3 had different light and water regimes. There were no significant differences between the 12 month temperature environments of the three sites. There was however, a minor difference between the coastal (high temperature) and the inland (lower temperature) sites. M. congestus at the three sites had significantly different CO₂ assimilation rates, transpiration and stomatal conductance in response to the differing habitat microclimates. The water use efficiency of the sites were however, similar. Site 1 attained the highest CO₂ assimilation rates, transpiration, stomatal conductance, and water use efficiency and site 3 the lowest. Under similar conditions the gas exchange data for the potted plants indicated that M. congestus from the different sites was typically C₄. The optimal photosynthetic temperatures of all the sites was above 30°C and they did not show significant inhibition of CO₂ assimilation by different oxygen concentrations. The results of the laboratory investigation of the potted plants suggested that the only site-specific (ecotypic) response of M. eongestus was the light intensity at which the plants from the different sites were light saturated. The light and temperature response of field plants under field conditions was not comparable to the light and temperature response of potted plants under laboratory conditions. This may have been due to the field results being obtained under differing water and soil nutrient regimes. The potted plants may also have had a reduced root mass compared to their field counterparts and the potted plants may have also have become root bound. Under field conditions the plants had differing light saturation points and optimal photosynthetic temperatures compared to the potted plants. This investigation thus did not support the hypothesis stated in this thesis. The data in this investigation thus may indicate that plants with as diverse habitats as Mariscus congestus that are removed from their natural habitats display rapid changes in gas exchange characteristics in response to their new microclimates, with few ecotypic physiological characteristics of the old habitat being retained.
- Full Text:
- Date Issued: 1992
The anatomy and distribution of the cyperaceae in the Eastern Cape region of South Africa
- Authors: Sonnenberg, Bernd Jürgen
- Date: 2005
- Subjects: Cyperaceae Cyperaceae -- Anatomy Cyperaceae -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4228 , http://hdl.handle.net/10962/d1003797
- Description: The principal objective of this investigation, was to collect the family Cyperaceae and to study their leaf, bract and culm anatomy. The second was to examine the collection for unique structures or forms, whilst a third was to classify the Cyperaceae according to their photosynthetic structures and types. Distribution of the Cyperaceae within the broad region defined as the Eastern Cape would be influenced by rainfall pattern. It was expected that C₃ species would predominate in more mesic environments and habitats, whilst the C₄ species would be found in drier less favourable habitats. Collection within the region (November 1993 to late January 1997), yielded 106 species, totalling some 600 specimens. Both sub-families of the Cyperaceae (Caricoideae and Cyperoideae), eight tribes (Abildgaardieae, Cariceae, Cypereae, Hypotvtreae, Rhynchosporeae, Shoeneae, Sirpeae and Slerieae) and twenty five genera were found to be present. Sixty percent of the species were C₃ and forty percent were C₄. Sixteen new species, which had not been collected within the boundaries of the region previously were also found. Over 43 percent of the species collected had unique anatomical characteristics that appeared to be influenced by habitat and or climate influenced. These are the characters influenced by hydromorphic, mesomorphic and xeromorphic environments. These anatomical characters: Thickness of leaves and bracts; thickness of the adaxial and abaxial epidermis of the leaves and bracts; flush, sunken and raised stomata; presence or absence of bulliform cells; presence and distribution of sclerenchymatous structures; presence or absence of a hypodermis; presence or absence of cavities in the leaves, bracts and culms; mesophyll or ground tissue structure, and the presence or absence of secretary structures. A few noteworthy anatomical characters that are influenced by climate are present in Cladium mariscus subsp. jamaicense (Schoeneae), the Cariceae, the Cypereae and the Sclerieae. Within Cladium mariscus subsp. jamaicense the pseudo-dorsiventral leaves and bracts, as well as the large lamina cavities, containing trans-lamina girders are unique. Papillate epidermal cells are limited to the tribe Cariceae. In the Cypereae many of the species lack bulliform cells and hypodermal layers. In Pycreus cooperi (Cypereae) the vascular bundles of the leaves and bracts, appear to be stacked in rows, that are inter-spaced with lamina cavities. In the Sclerieae the mesophyll structure is specific to the species level. Unique anatomical characteristics were also present in the leaves, bracts and culms of the genus Carpha. In this genus distinctive lateral vascular bundles were present abutting the large bundles and/or midrib bundle. The most distinctive anatomical characteristics that could be used to separate the members of the Cyperaceae were the structures and associated structures related to the photosynthetic pathway. The Eastern Cape Cyperaceae could be divided into three distinct groups based on photosynthetic structure, namely one C₃, a C₄ and a potential C₃-C₄ intermediate group. The C₃ group was found to have non-radiate mesophyll and an outer parenchymatous sheath with small chloroplasts (Cariceae, Cyperaceae [in part], Hypolytreae (Chrysithrix capensis], Rhynchosporeae [R. brownii], Schoeneae, Scirpeae and Sclerieae). The C₄ group has radiate mesophyll and an inner parenchymatous sheath with enlarged chloroplasts (Kranz or PCR sheath). The C₄ species are present in tribes Abildgaardieae, Cypereae (in part) and Rhynchosporeae (R. barrosiana). In the Eastern Cape, a few species with C₃ anatomy have anatomical characteristics that are similar to the species with C₄ anatomy (Cyathocoma hexandra [bracts], Cyperus tennellus var. tennellus [leaves and bracts], Ficinia bulbosa [leaves], F. dura [leaves and bracts], F. lateralis coastal [leaves and bracts], F. oligantha [bracts], F. pingiour [bracts], F. stolonifera [leaves and bracts], F. tribracteata [leaves and bracts], F. zeyheri [leaves and bracts], Isolepis cernua [leaves and bracts], I. costata var. macra [bracts], Schoenus nigricans [leaves], Scirpus nodosus [bracts] and Tetraria cuspidata [leaves and bracts)). The vascular bundles within this intermediate group, fall within the Hattersleyand Watson (1975) minimal cell lateral count and maximal cell distal count criteria for C₄ grass species. However, no biochemical data exists to see whether they are C₃-C₄ intermediates or whether the Hattersley and Watson (1975) C₄ criteria for grasses applies to smaller, or scutiform Cyperaceae or not. Based on the results presented here, five distinct structural forms/types were found to be present in the C₃, C₄ and C₃-C₄ intermediate groups. The C₃ and the potential C₃-C₄ intermediate species may be divided into two types, based on the number of vascular sheaths present. In the first or A-type, vascular bundles are surrounded by two sheaths and in the more dominant B-type, by three. The A-type was found in the Cypereae (Cyperus denudatus and C. textilis) and most of the Scirpeae. B-type anatomy occurred in the Cariceae, Cypereae (c. difformis, C. pulcher, C. sphaerospermus, C. tennellus var. tennellus and P. mundii), Hypolytreae, Rhynchosporeae (R. brownii), Schoeneae, Scirpeae (Bolboschoenus maritimus, Ficinia cinnamomea, F. fascicularis, F. lateralis both, F. pingiour, the genus Fuirena, I. diabolica, I. fluitans, I. prolifera and Schoenoplectus paludicola) and Sclerieae tribes. Based on the vascular sheath structure, the C₄ species could be divided into three groups, namely bulbostyloid, chlorocyperoid and fimbristyloid, where the bulbostyloid structure occurred in Bulbostylis schoenoides. Cyperus (in part), Kyllinga, Mariscus and Pycreus (except P. mundii) had a chlorocyperoid structure. Genera with fimbristyloid structure were recorded in the genera Abildgaardia, Bulbostylis and Fimbristylis. The bulbostyloid type represents a potential a fifth C₄ anatomical type within the C₄ Cyperaceae. As a result of this observation, it is possible that the C₄ syndrome may have evolved five times in the Cyperaceae and not four as previously suggested by Bruhl and Perry (1995) and by Soros and Dengler (2001). The C₃ Cyperaceae species within the Eastern Cape are more dominant in higher elevation habitats the C₄ species, similar to the C₃ grasses. The only C₄ species that occur at high elevations are those with three sheaths. The C₃ and C₄ species within the region occur in similar low rainfall habitat ranges, where the C₄'s are more dominant in xeric habitats on drier soils than the C₃ species, similar to the grasses. Where more C₃ species occur in higher rainfall habitats than the C₄ species. With the exception of the Afromontane Bulbostylis schoenoides and R. barrosiana, the C₄ species similar to the grasses are dominant in high light and temperature habitats with low rainfall, unlike the C₄ Cyperaceae of Japan and America. Only five species occur in the desert like conditions of the Karoo-Namib biome (Cyperus laevigatus, C. rupestris var. rupestris, I. cernua, M. capensis and M. uitenhagensis), which have less than 250mm of rainfall per annum. Only three species are habitat-specific or may be endemic to a specific area within the Eastern Cape, namely A. capensis, Chrysithrix capensis and R. barrosiana. A. capensis in marshes on the Amatole mountains near Alice and Hogsback. C. capensis to the Tstsikamma mountains of the Wite Els Bosch forests. R. barrosiana to the marshlands of the Cape Morgan coastal Nature reserve at Kei Mouth. The anatomical types of the C₃ and more especially C₄ Cyperaceae are not specifically found in a particular rainfall regime or habitat type, which is contrary to the thesis hypothesis. However, the C₃ species are mostly correlated with hydrophytic to mesic habitats, with the exception of Ficinia and the two sheathed species. Ficinia is dominant in mesic grasslands and halophytic habitats. The two sheathed C₃ species are mostly present in halophytic habitats. The C₄ species are also more dominant in mesic to xerophytic grasslands, as expected in the hypothesis. Where only a few species occur in habitats correlated with increasing rainfall and temperature similar to the C₄ Cyperaceae of Japan and America. It may thus be that the development and evolution of the different C₄ anatomical forms (or phylogenetic forms) within the Cyperaceae may have enabled these species to establish themselves in habitats that were alien to their origins. It may be that the ability to regulate photoassimilate and water transport within the Cyperaceae enables their success in a dynamic and unpredictable climate, such as the Eastern Cape. Many of the anatomical characteristics reported in this thesis and its appendices are unique to the tribes, genera and/or species of the Eastern Cape Cyperaceae and thus may be valuable to future taxonomic classifications of the family. The research presented here should provide a good working platform for future, more detailed research on this often forgotten component of the vegetation.
- Full Text:
- Date Issued: 2005
- Authors: Sonnenberg, Bernd Jürgen
- Date: 2005
- Subjects: Cyperaceae Cyperaceae -- Anatomy Cyperaceae -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4228 , http://hdl.handle.net/10962/d1003797
- Description: The principal objective of this investigation, was to collect the family Cyperaceae and to study their leaf, bract and culm anatomy. The second was to examine the collection for unique structures or forms, whilst a third was to classify the Cyperaceae according to their photosynthetic structures and types. Distribution of the Cyperaceae within the broad region defined as the Eastern Cape would be influenced by rainfall pattern. It was expected that C₃ species would predominate in more mesic environments and habitats, whilst the C₄ species would be found in drier less favourable habitats. Collection within the region (November 1993 to late January 1997), yielded 106 species, totalling some 600 specimens. Both sub-families of the Cyperaceae (Caricoideae and Cyperoideae), eight tribes (Abildgaardieae, Cariceae, Cypereae, Hypotvtreae, Rhynchosporeae, Shoeneae, Sirpeae and Slerieae) and twenty five genera were found to be present. Sixty percent of the species were C₃ and forty percent were C₄. Sixteen new species, which had not been collected within the boundaries of the region previously were also found. Over 43 percent of the species collected had unique anatomical characteristics that appeared to be influenced by habitat and or climate influenced. These are the characters influenced by hydromorphic, mesomorphic and xeromorphic environments. These anatomical characters: Thickness of leaves and bracts; thickness of the adaxial and abaxial epidermis of the leaves and bracts; flush, sunken and raised stomata; presence or absence of bulliform cells; presence and distribution of sclerenchymatous structures; presence or absence of a hypodermis; presence or absence of cavities in the leaves, bracts and culms; mesophyll or ground tissue structure, and the presence or absence of secretary structures. A few noteworthy anatomical characters that are influenced by climate are present in Cladium mariscus subsp. jamaicense (Schoeneae), the Cariceae, the Cypereae and the Sclerieae. Within Cladium mariscus subsp. jamaicense the pseudo-dorsiventral leaves and bracts, as well as the large lamina cavities, containing trans-lamina girders are unique. Papillate epidermal cells are limited to the tribe Cariceae. In the Cypereae many of the species lack bulliform cells and hypodermal layers. In Pycreus cooperi (Cypereae) the vascular bundles of the leaves and bracts, appear to be stacked in rows, that are inter-spaced with lamina cavities. In the Sclerieae the mesophyll structure is specific to the species level. Unique anatomical characteristics were also present in the leaves, bracts and culms of the genus Carpha. In this genus distinctive lateral vascular bundles were present abutting the large bundles and/or midrib bundle. The most distinctive anatomical characteristics that could be used to separate the members of the Cyperaceae were the structures and associated structures related to the photosynthetic pathway. The Eastern Cape Cyperaceae could be divided into three distinct groups based on photosynthetic structure, namely one C₃, a C₄ and a potential C₃-C₄ intermediate group. The C₃ group was found to have non-radiate mesophyll and an outer parenchymatous sheath with small chloroplasts (Cariceae, Cyperaceae [in part], Hypolytreae (Chrysithrix capensis], Rhynchosporeae [R. brownii], Schoeneae, Scirpeae and Sclerieae). The C₄ group has radiate mesophyll and an inner parenchymatous sheath with enlarged chloroplasts (Kranz or PCR sheath). The C₄ species are present in tribes Abildgaardieae, Cypereae (in part) and Rhynchosporeae (R. barrosiana). In the Eastern Cape, a few species with C₃ anatomy have anatomical characteristics that are similar to the species with C₄ anatomy (Cyathocoma hexandra [bracts], Cyperus tennellus var. tennellus [leaves and bracts], Ficinia bulbosa [leaves], F. dura [leaves and bracts], F. lateralis coastal [leaves and bracts], F. oligantha [bracts], F. pingiour [bracts], F. stolonifera [leaves and bracts], F. tribracteata [leaves and bracts], F. zeyheri [leaves and bracts], Isolepis cernua [leaves and bracts], I. costata var. macra [bracts], Schoenus nigricans [leaves], Scirpus nodosus [bracts] and Tetraria cuspidata [leaves and bracts)). The vascular bundles within this intermediate group, fall within the Hattersleyand Watson (1975) minimal cell lateral count and maximal cell distal count criteria for C₄ grass species. However, no biochemical data exists to see whether they are C₃-C₄ intermediates or whether the Hattersley and Watson (1975) C₄ criteria for grasses applies to smaller, or scutiform Cyperaceae or not. Based on the results presented here, five distinct structural forms/types were found to be present in the C₃, C₄ and C₃-C₄ intermediate groups. The C₃ and the potential C₃-C₄ intermediate species may be divided into two types, based on the number of vascular sheaths present. In the first or A-type, vascular bundles are surrounded by two sheaths and in the more dominant B-type, by three. The A-type was found in the Cypereae (Cyperus denudatus and C. textilis) and most of the Scirpeae. B-type anatomy occurred in the Cariceae, Cypereae (c. difformis, C. pulcher, C. sphaerospermus, C. tennellus var. tennellus and P. mundii), Hypolytreae, Rhynchosporeae (R. brownii), Schoeneae, Scirpeae (Bolboschoenus maritimus, Ficinia cinnamomea, F. fascicularis, F. lateralis both, F. pingiour, the genus Fuirena, I. diabolica, I. fluitans, I. prolifera and Schoenoplectus paludicola) and Sclerieae tribes. Based on the vascular sheath structure, the C₄ species could be divided into three groups, namely bulbostyloid, chlorocyperoid and fimbristyloid, where the bulbostyloid structure occurred in Bulbostylis schoenoides. Cyperus (in part), Kyllinga, Mariscus and Pycreus (except P. mundii) had a chlorocyperoid structure. Genera with fimbristyloid structure were recorded in the genera Abildgaardia, Bulbostylis and Fimbristylis. The bulbostyloid type represents a potential a fifth C₄ anatomical type within the C₄ Cyperaceae. As a result of this observation, it is possible that the C₄ syndrome may have evolved five times in the Cyperaceae and not four as previously suggested by Bruhl and Perry (1995) and by Soros and Dengler (2001). The C₃ Cyperaceae species within the Eastern Cape are more dominant in higher elevation habitats the C₄ species, similar to the C₃ grasses. The only C₄ species that occur at high elevations are those with three sheaths. The C₃ and C₄ species within the region occur in similar low rainfall habitat ranges, where the C₄'s are more dominant in xeric habitats on drier soils than the C₃ species, similar to the grasses. Where more C₃ species occur in higher rainfall habitats than the C₄ species. With the exception of the Afromontane Bulbostylis schoenoides and R. barrosiana, the C₄ species similar to the grasses are dominant in high light and temperature habitats with low rainfall, unlike the C₄ Cyperaceae of Japan and America. Only five species occur in the desert like conditions of the Karoo-Namib biome (Cyperus laevigatus, C. rupestris var. rupestris, I. cernua, M. capensis and M. uitenhagensis), which have less than 250mm of rainfall per annum. Only three species are habitat-specific or may be endemic to a specific area within the Eastern Cape, namely A. capensis, Chrysithrix capensis and R. barrosiana. A. capensis in marshes on the Amatole mountains near Alice and Hogsback. C. capensis to the Tstsikamma mountains of the Wite Els Bosch forests. R. barrosiana to the marshlands of the Cape Morgan coastal Nature reserve at Kei Mouth. The anatomical types of the C₃ and more especially C₄ Cyperaceae are not specifically found in a particular rainfall regime or habitat type, which is contrary to the thesis hypothesis. However, the C₃ species are mostly correlated with hydrophytic to mesic habitats, with the exception of Ficinia and the two sheathed species. Ficinia is dominant in mesic grasslands and halophytic habitats. The two sheathed C₃ species are mostly present in halophytic habitats. The C₄ species are also more dominant in mesic to xerophytic grasslands, as expected in the hypothesis. Where only a few species occur in habitats correlated with increasing rainfall and temperature similar to the C₄ Cyperaceae of Japan and America. It may thus be that the development and evolution of the different C₄ anatomical forms (or phylogenetic forms) within the Cyperaceae may have enabled these species to establish themselves in habitats that were alien to their origins. It may be that the ability to regulate photoassimilate and water transport within the Cyperaceae enables their success in a dynamic and unpredictable climate, such as the Eastern Cape. Many of the anatomical characteristics reported in this thesis and its appendices are unique to the tribes, genera and/or species of the Eastern Cape Cyperaceae and thus may be valuable to future taxonomic classifications of the family. The research presented here should provide a good working platform for future, more detailed research on this often forgotten component of the vegetation.
- Full Text:
- Date Issued: 2005
An investigation on the effect of Russian wheat aphid (Diuraphis noxia Kurdjumov) population growth and feeding damage on selected barley (Hordeum vulgare L.) cultivars under ambient and elevated CO2
- Authors: Sacranie, Sattar Farouk
- Date: 2016
- Subjects: Russian wheat aphid -- Research -- South Africa Barley -- Disease and pest resistance -- South Africa Callose Aphids
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/50311 , vital:25975
- Description: The Russian wheat aphid (RWA) (Diuraphis noxia Kurdjumov) is a major pest of cultivated small grains. It is particularly devastating because of is high reproductive rate which results in the growth of large populations which become damaging to its host plants. Development of resistant barley (Hordeum vulgare L.) cultivars is complicated as resistance is polygenic. As a result, the industry remains at risk now that the RWA has spread throughout South Africa. It has, as recently as, 2013, been identified in the SW Cape, which was previously geographically isolated. This is South Africa‟s principle barley growing region. Now a potentially huge problem exists. Therefore, it is imperative that an alternative to pesticide use is found. Testing potential innate resistance in barley cultivars is thus, critical. In this thesis, I present data on four barely cultivars where I have examined their resistance/ lack of resistance to three known RWA biotypes, RWASA1, RWASA2 and RWASA3. The barley varieties used were two economically important South African malt barley cultivars (S5 and SSG 564) along with two potentially RWA resistant Afghan accessions (CIho 4125 and CIho 4159). The RWA biotype population growth rates on each of the plants were determined over a 14 day period. The aim was to establish baseline data of the effects of RWA population growth on the host plants under ambient CO2 (380 – 400 ppm) conditions. The extent of RWA feeding damage was investigated at the cell level by examining saliva deposition and cell disruption using Transmission Electron Microscopy; at the tissue/vascular level using fluorescence microscopy, to determine the extent of callose formation; at a whole leaf level by recording percent chlorosis and leaf roll; and finally, at a whole plant level by measuring biomass loss.The experiments were repeated under elevated CO2 (450 ppm) to model any changes in RWA/plant interaction with respect to future climate change. The effects of an elevated CO2 environment and RWA feeding on host plant foliar N and C:N ratio were compared to ambient CO2 conditions, to provide a clearer picture of the potential nutrient drain that a feeding RWA colony exacts on its host. Of the varieties tested, the CIho accessions performed better than the two SA barley cultivars as the CIho accessions appeared to express a mild antibiosis resistance response as RWA populations, particularly those of RWASA1, were smaller than those observed on either S5 or SSG 564. In addition, less damage was evident in the two CIho accessions due to RWA feeding. II RWASA2 was the most virulent of the three RWA biotypes tested, followed by RWASA3 while RWASA1 was the least virulent. Under elevated CO2 conditions, RWA feeding damage was exacerbated but the trend of biotype virulence remained the same. Higher aphid population sizes were recorded under elevated CO2, meant that even the more resistant CIho accessions were overcome by the increased demand made by the larger aphid colonies on the host plants. The % foliar N data showed that under elevated CO2 aphid-free control plants had increased N levels in their leaves. Increased “food” supply (as shown by the increased N levels) therefore allowed significantly larger aphid populations to develop on the plants exposed to elevated CO2, due to improved nutrient status of the phloem sap taken up by RWA. The knock-on effect of a higher aphid population was increased cell disruption as a result of extensive probing, extensive formations of wound callose, with the result that phloem damage impeded nutrient flow through the vascular tissues which contributed to chlorosis and (eventually plant) death. The major conclusion from this study is that even a mild CO2 elevation resulted in an increase aphid population which may pose a severe and very real threat to a barley crop. Therefore, without effort to identify and deploy resistant barley cultivars, it could well be possible that future barley cultivation in South Africa may no longer be viable.
- Full Text:
- Date Issued: 2016
- Authors: Sacranie, Sattar Farouk
- Date: 2016
- Subjects: Russian wheat aphid -- Research -- South Africa Barley -- Disease and pest resistance -- South Africa Callose Aphids
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/50311 , vital:25975
- Description: The Russian wheat aphid (RWA) (Diuraphis noxia Kurdjumov) is a major pest of cultivated small grains. It is particularly devastating because of is high reproductive rate which results in the growth of large populations which become damaging to its host plants. Development of resistant barley (Hordeum vulgare L.) cultivars is complicated as resistance is polygenic. As a result, the industry remains at risk now that the RWA has spread throughout South Africa. It has, as recently as, 2013, been identified in the SW Cape, which was previously geographically isolated. This is South Africa‟s principle barley growing region. Now a potentially huge problem exists. Therefore, it is imperative that an alternative to pesticide use is found. Testing potential innate resistance in barley cultivars is thus, critical. In this thesis, I present data on four barely cultivars where I have examined their resistance/ lack of resistance to three known RWA biotypes, RWASA1, RWASA2 and RWASA3. The barley varieties used were two economically important South African malt barley cultivars (S5 and SSG 564) along with two potentially RWA resistant Afghan accessions (CIho 4125 and CIho 4159). The RWA biotype population growth rates on each of the plants were determined over a 14 day period. The aim was to establish baseline data of the effects of RWA population growth on the host plants under ambient CO2 (380 – 400 ppm) conditions. The extent of RWA feeding damage was investigated at the cell level by examining saliva deposition and cell disruption using Transmission Electron Microscopy; at the tissue/vascular level using fluorescence microscopy, to determine the extent of callose formation; at a whole leaf level by recording percent chlorosis and leaf roll; and finally, at a whole plant level by measuring biomass loss.The experiments were repeated under elevated CO2 (450 ppm) to model any changes in RWA/plant interaction with respect to future climate change. The effects of an elevated CO2 environment and RWA feeding on host plant foliar N and C:N ratio were compared to ambient CO2 conditions, to provide a clearer picture of the potential nutrient drain that a feeding RWA colony exacts on its host. Of the varieties tested, the CIho accessions performed better than the two SA barley cultivars as the CIho accessions appeared to express a mild antibiosis resistance response as RWA populations, particularly those of RWASA1, were smaller than those observed on either S5 or SSG 564. In addition, less damage was evident in the two CIho accessions due to RWA feeding. II RWASA2 was the most virulent of the three RWA biotypes tested, followed by RWASA3 while RWASA1 was the least virulent. Under elevated CO2 conditions, RWA feeding damage was exacerbated but the trend of biotype virulence remained the same. Higher aphid population sizes were recorded under elevated CO2, meant that even the more resistant CIho accessions were overcome by the increased demand made by the larger aphid colonies on the host plants. The % foliar N data showed that under elevated CO2 aphid-free control plants had increased N levels in their leaves. Increased “food” supply (as shown by the increased N levels) therefore allowed significantly larger aphid populations to develop on the plants exposed to elevated CO2, due to improved nutrient status of the phloem sap taken up by RWA. The knock-on effect of a higher aphid population was increased cell disruption as a result of extensive probing, extensive formations of wound callose, with the result that phloem damage impeded nutrient flow through the vascular tissues which contributed to chlorosis and (eventually plant) death. The major conclusion from this study is that even a mild CO2 elevation resulted in an increase aphid population which may pose a severe and very real threat to a barley crop. Therefore, without effort to identify and deploy resistant barley cultivars, it could well be possible that future barley cultivation in South Africa may no longer be viable.
- Full Text:
- Date Issued: 2016
The effect of elevated CO₂ on Phaseolus vulgaris L. cv Contender
- Authors: Mjwara, Jabulani Michael
- Date: 1997
- Subjects: Plants -- Effect of carbon dioxide on Kidney bean
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4215 , http://hdl.handle.net/10962/d1003784
- Description: The response of Phaseolus vulgaris L. cv. Contender grown in controlled environmental conditions, at either ambient or elevated (360 and 700 μmol mol ̄¹, respectively) CO₂ concentrations ([CO₂]), was monitored from 10 days after germination (DAG) until the onset of senescence. Elevated CO₂ had a pronounced effect on total plant height (TPH), leaf area (LA), dry weight (DW) accumulation and specific leaf area (SLA). All of these were significantly increased by elevated [CO₂] with the exception of SLA, which was significantly reduced. Except for higher initial relative growth rates (RGR) in CO₂-enriched plants, RGR did not differ significantly between the two CO₂ treatments throughout the remainder of growth period. While growth parameters clearly differed between CO₂ treatments, the effects of CO₂ on many physiological processes including net assimilation rate (NAR), Rubisco activity, and some foliar nutrient concentrations were largely transient. For example, CO₂ enrichment significantly increased NAR, but from 20 DAG onward, NAR declined to levels measured on plants grown under ambient CO₂. Similarly, the decline in both foliar N concentration and Rubisco activity in CO₂-enriched plants after 20 DAG was significantly greater than the decline observed for ambient CO₂ plants. Soluble leaf protein and total chlorophylls (a+b) were also significantly reduced in plants grown under elevated CO₂. Chlorophyll (a/b) ratios increased with time underelevated CO₂, indicating that the rate of decline of chlorophyll b was higher than that of chorophyll α. No significant changes in total carotenoid (x+c) levels were observed in either CO₂ treatment. Under enhanced CO₂, the foliar concentrations of K and Mn were increased significantly, while P, Ca, Fe and Zn were reduced significantly. However, changes in Mg and Cu concentrations were not significant. High CO₂-grown plants also exhibited pronounced leaf discoloration or chlorosis, coupled with a significant reduction in leaf longevity. The levels of non-structural carbohydrates (sucrose, glucose, fructose and starch) and nitrogenous compounds (nitrogen, total soluble proteins and free amino acids) were determined for leaves and developing seeds of P. vulgaris. Leaf tissue of elevated CO₂-grown plants accumulated significantly higher levels of both soluble sugars and starch. Leaf ultrastructure revealed considerable erilargement of starch grain sizes with surface areas more than five times larger compared to those of control plants. No apparent differences in structure and membrane integrity of chloroplasts in both CO₂ treatments were noted. Although ambient CO₂-grown plants had comparatively low levels of non-structural carbohydrates (NSC), they accumulated significantly higher levels of nitrogenous compounds. The levels of NSC were consistently higher in seeds of plants grown under elevated CO₂. In comparison to plants grown at elevated [CO₂], pods and seeds of ambient CO₂-grown plants had significantly larger pools of free amino compounds and N. Stomatal conductance (gs) declined significantly, as expected for plants grown under elevated CO₂. This was accompanied by a decline in transpiration rates (E). Reduced gs and E led to high AlE ratio, which meant improved water use efficiency (WUE) values for CO₂-enriched bean plants. Leaf carbon isotope discrimination (∆) against the heavier isotope of carbon (¹³C), has been used to select for high WUE in C₃ plants. In plants grown at elevated CO₂ concentration, ,1 was significantly reduced. Although ∆ was negatively correlated with WUE in both CO₂ treatments, the correlation was steeper and highly negative for CO₂-enriched plants. These results indicate underlying differences in gas-exchange physiology, including stomatal responses between ambient and elevated CO₂-grown plants. Photosynthetic acclimation was investigated using the response of assimilation to internal carbon dioxide concentration (A/C₁ curves). At early stages of growth, the initial slope of the A/C₁ response curve did not differ with CO₂ treatment. In contrast, CO₂-saturated photosynthetic rate (Amax) was significantly higher in plants grown under elevated versus ambient CO₂ at 15 DAG. However, at subsequent stages of growth both the initial slope and Amax declined in bean plants grown in elevated CO₂. Apparent carboxylation efficiency (ACE, estimated from the initial slope of A/C₁ response) values followed a similar trend and were significantly reduced in CO₂-enriched plants. These results indicate that acclimation or negative adjustment of photosynthesis may have been caused by a combination of both stomatal and biochemical limitations. Bean plants grown under conditions of elevated atmospheric CO₂ flowered 3 to 4 days earlier, and produced significantly more flowers and pods than plants grown at ambient conditions. Plants grown at elevated CO₂ aborted 22 and 20% more flowers and pods, respectively, than plants grown at ambient CO₂. Elevated CO₂ also significantly increased the number of tillers or lateral branches produced by plants, which contributed to a significant increase in pod number and seed yield in these plants. Although plants grown at elevated CO₂ produced on average 8 seeds per pod, while plants grown under ambient CO2 conditions produced 5 seeds per pod, the greater number of seeds was offset by lower seed weights in plants grown under _ elevated CO₂. Thus, despite high seed yield in beans grown under elevated CO₂, the harvest index (HI) did not change significantly between CO₂ treatments.
- Full Text:
- Date Issued: 1997
- Authors: Mjwara, Jabulani Michael
- Date: 1997
- Subjects: Plants -- Effect of carbon dioxide on Kidney bean
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4215 , http://hdl.handle.net/10962/d1003784
- Description: The response of Phaseolus vulgaris L. cv. Contender grown in controlled environmental conditions, at either ambient or elevated (360 and 700 μmol mol ̄¹, respectively) CO₂ concentrations ([CO₂]), was monitored from 10 days after germination (DAG) until the onset of senescence. Elevated CO₂ had a pronounced effect on total plant height (TPH), leaf area (LA), dry weight (DW) accumulation and specific leaf area (SLA). All of these were significantly increased by elevated [CO₂] with the exception of SLA, which was significantly reduced. Except for higher initial relative growth rates (RGR) in CO₂-enriched plants, RGR did not differ significantly between the two CO₂ treatments throughout the remainder of growth period. While growth parameters clearly differed between CO₂ treatments, the effects of CO₂ on many physiological processes including net assimilation rate (NAR), Rubisco activity, and some foliar nutrient concentrations were largely transient. For example, CO₂ enrichment significantly increased NAR, but from 20 DAG onward, NAR declined to levels measured on plants grown under ambient CO₂. Similarly, the decline in both foliar N concentration and Rubisco activity in CO₂-enriched plants after 20 DAG was significantly greater than the decline observed for ambient CO₂ plants. Soluble leaf protein and total chlorophylls (a+b) were also significantly reduced in plants grown under elevated CO₂. Chlorophyll (a/b) ratios increased with time underelevated CO₂, indicating that the rate of decline of chlorophyll b was higher than that of chorophyll α. No significant changes in total carotenoid (x+c) levels were observed in either CO₂ treatment. Under enhanced CO₂, the foliar concentrations of K and Mn were increased significantly, while P, Ca, Fe and Zn were reduced significantly. However, changes in Mg and Cu concentrations were not significant. High CO₂-grown plants also exhibited pronounced leaf discoloration or chlorosis, coupled with a significant reduction in leaf longevity. The levels of non-structural carbohydrates (sucrose, glucose, fructose and starch) and nitrogenous compounds (nitrogen, total soluble proteins and free amino acids) were determined for leaves and developing seeds of P. vulgaris. Leaf tissue of elevated CO₂-grown plants accumulated significantly higher levels of both soluble sugars and starch. Leaf ultrastructure revealed considerable erilargement of starch grain sizes with surface areas more than five times larger compared to those of control plants. No apparent differences in structure and membrane integrity of chloroplasts in both CO₂ treatments were noted. Although ambient CO₂-grown plants had comparatively low levels of non-structural carbohydrates (NSC), they accumulated significantly higher levels of nitrogenous compounds. The levels of NSC were consistently higher in seeds of plants grown under elevated CO₂. In comparison to plants grown at elevated [CO₂], pods and seeds of ambient CO₂-grown plants had significantly larger pools of free amino compounds and N. Stomatal conductance (gs) declined significantly, as expected for plants grown under elevated CO₂. This was accompanied by a decline in transpiration rates (E). Reduced gs and E led to high AlE ratio, which meant improved water use efficiency (WUE) values for CO₂-enriched bean plants. Leaf carbon isotope discrimination (∆) against the heavier isotope of carbon (¹³C), has been used to select for high WUE in C₃ plants. In plants grown at elevated CO₂ concentration, ,1 was significantly reduced. Although ∆ was negatively correlated with WUE in both CO₂ treatments, the correlation was steeper and highly negative for CO₂-enriched plants. These results indicate underlying differences in gas-exchange physiology, including stomatal responses between ambient and elevated CO₂-grown plants. Photosynthetic acclimation was investigated using the response of assimilation to internal carbon dioxide concentration (A/C₁ curves). At early stages of growth, the initial slope of the A/C₁ response curve did not differ with CO₂ treatment. In contrast, CO₂-saturated photosynthetic rate (Amax) was significantly higher in plants grown under elevated versus ambient CO₂ at 15 DAG. However, at subsequent stages of growth both the initial slope and Amax declined in bean plants grown in elevated CO₂. Apparent carboxylation efficiency (ACE, estimated from the initial slope of A/C₁ response) values followed a similar trend and were significantly reduced in CO₂-enriched plants. These results indicate that acclimation or negative adjustment of photosynthesis may have been caused by a combination of both stomatal and biochemical limitations. Bean plants grown under conditions of elevated atmospheric CO₂ flowered 3 to 4 days earlier, and produced significantly more flowers and pods than plants grown at ambient conditions. Plants grown at elevated CO₂ aborted 22 and 20% more flowers and pods, respectively, than plants grown at ambient CO₂. Elevated CO₂ also significantly increased the number of tillers or lateral branches produced by plants, which contributed to a significant increase in pod number and seed yield in these plants. Although plants grown at elevated CO₂ produced on average 8 seeds per pod, while plants grown under ambient CO2 conditions produced 5 seeds per pod, the greater number of seeds was offset by lower seed weights in plants grown under _ elevated CO₂. Thus, despite high seed yield in beans grown under elevated CO₂, the harvest index (HI) did not change significantly between CO₂ treatments.
- Full Text:
- Date Issued: 1997
A quantitative investigation of the absorption of certain cations by whole plants and plant tissues
- Cresswell, Christopher Frederick
- Authors: Cresswell, Christopher Frederick
- Date: 1959 , 2014-07-24
- Subjects: Cations -- Absorption and adsorption , Plant tissues
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4262 , http://hdl.handle.net/10962/d1013335
- Description: Introduction: Part 1. Greenhouse studies were conducted to investigate the absorption of sodium, potassium, calcium and magnesium by lemon seedlings. The plants were grown in controlled nutrient solutions and analysis of the plant material was made to determine the relationship between the four cations in the different plant organs. Results of the experiment may be summarized as follows:- The occurrence of leaf burn appeared to be associated with a low calcium content, together with a high sodium, potassium or sodium + potassium content. The development of the seedlings was shown to be markedly influenced by the level of calcium supply and to a much lesser degree by the level of potassium supplied. The concentration of sodium, potassium, calcium and magnesium in the stem and leaf varied with position of the tissues on the main axis. The level of sodium was found to influence the distribution of sodium in the leaves, and the sodium content of the leaf, stem and root tissues gave a good reflection of the level of sodium supplied. The effect of the sodium treatment on the uptake of potassium appeared to be dependent on the calcium content of the tissues. Sodium treatment was found not to affect the leaf calcium content. In the stem and root tissues the calcium content was reduced when the calcium level in the nutrient medium was low, and increased the calcium content of these two tissues at the higher level of calcium supply. The sodium supply was shown to reduce the leaf magnesium only slightly, and its affect on the magnesium content of the stem and root tissues was shown to be dependent on the level of calcium supplied. The potassium content of the leaves, stems and roots increased when the supply of potassium was raised. Increasing the potassium level in the nutrient supply was found to cause a very slight reduction in the sodium content of the leaf, but did not affect the sodium content of the stem and root. Potassium did not affect the calcium content of the leaves and increased the stem calcium when sodium was not present in the nutrient media in high concentrations. In the roots potassium only increase the calcium content at the upper level of calcium supply. The magnesium content of the leaf and stem tissues was reduced as the potassium supply was increased. In the roots the general trend was for the magnesium content to increase when the level of potassium treatment was raised. The calcium content of all the plant parts increased with a rise in the calcium supply, the stem and root tissues having a greater percentage increase than the leaves. The sodium content of the plant tissue was reduced as the level of calcium supply was raised. The leaf potassium content decreased with a higher calcium level of supply. In the stem and roots the potassium content was increased by doubling the calcium supply. The calcium treatment had no influence on the magnesium content of the foliage, but in the stem and root tissues a decrease in magnesium content resulted from an increase in the calcium supply. Part II Potato tuber tissue and carrot root tissue were used as experimental material in the investigation of sodium9 potassium9 and calcium uptake by storage tissue. It was shown that when the tissue disks are transferred from distilled water to a solution of salts there is a rapid initial uptake of cation which is neither particularly selective, nor related to metabolism, but dependent on the external concentration. On the other hand, the prolonged active accumulation of cation exhibits selectivity. Potassium absorption by potato tuber tissue was shown to be stimulated by sodium9 whereas the potassium and calcium absorption by carrot root tissue was shown to be reduced by sodium. Similarly the sodium absorption by the carrot root tissue was reduced by potassium, thus suggesting that the cations compete with one another for the same absorption mechanism.
- Full Text:
- Date Issued: 1959
- Authors: Cresswell, Christopher Frederick
- Date: 1959 , 2014-07-24
- Subjects: Cations -- Absorption and adsorption , Plant tissues
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4262 , http://hdl.handle.net/10962/d1013335
- Description: Introduction: Part 1. Greenhouse studies were conducted to investigate the absorption of sodium, potassium, calcium and magnesium by lemon seedlings. The plants were grown in controlled nutrient solutions and analysis of the plant material was made to determine the relationship between the four cations in the different plant organs. Results of the experiment may be summarized as follows:- The occurrence of leaf burn appeared to be associated with a low calcium content, together with a high sodium, potassium or sodium + potassium content. The development of the seedlings was shown to be markedly influenced by the level of calcium supply and to a much lesser degree by the level of potassium supplied. The concentration of sodium, potassium, calcium and magnesium in the stem and leaf varied with position of the tissues on the main axis. The level of sodium was found to influence the distribution of sodium in the leaves, and the sodium content of the leaf, stem and root tissues gave a good reflection of the level of sodium supplied. The effect of the sodium treatment on the uptake of potassium appeared to be dependent on the calcium content of the tissues. Sodium treatment was found not to affect the leaf calcium content. In the stem and root tissues the calcium content was reduced when the calcium level in the nutrient medium was low, and increased the calcium content of these two tissues at the higher level of calcium supply. The sodium supply was shown to reduce the leaf magnesium only slightly, and its affect on the magnesium content of the stem and root tissues was shown to be dependent on the level of calcium supplied. The potassium content of the leaves, stems and roots increased when the supply of potassium was raised. Increasing the potassium level in the nutrient supply was found to cause a very slight reduction in the sodium content of the leaf, but did not affect the sodium content of the stem and root. Potassium did not affect the calcium content of the leaves and increased the stem calcium when sodium was not present in the nutrient media in high concentrations. In the roots potassium only increase the calcium content at the upper level of calcium supply. The magnesium content of the leaf and stem tissues was reduced as the potassium supply was increased. In the roots the general trend was for the magnesium content to increase when the level of potassium treatment was raised. The calcium content of all the plant parts increased with a rise in the calcium supply, the stem and root tissues having a greater percentage increase than the leaves. The sodium content of the plant tissue was reduced as the level of calcium supply was raised. The leaf potassium content decreased with a higher calcium level of supply. In the stem and roots the potassium content was increased by doubling the calcium supply. The calcium treatment had no influence on the magnesium content of the foliage, but in the stem and root tissues a decrease in magnesium content resulted from an increase in the calcium supply. Part II Potato tuber tissue and carrot root tissue were used as experimental material in the investigation of sodium9 potassium9 and calcium uptake by storage tissue. It was shown that when the tissue disks are transferred from distilled water to a solution of salts there is a rapid initial uptake of cation which is neither particularly selective, nor related to metabolism, but dependent on the external concentration. On the other hand, the prolonged active accumulation of cation exhibits selectivity. Potassium absorption by potato tuber tissue was shown to be stimulated by sodium9 whereas the potassium and calcium absorption by carrot root tissue was shown to be reduced by sodium. Similarly the sodium absorption by the carrot root tissue was reduced by potassium, thus suggesting that the cations compete with one another for the same absorption mechanism.
- Full Text:
- Date Issued: 1959
Growth and photosynthetic responses of Acacia (Vachellia) seedlings to atmospheric CO2 increased from glacial to current concentrations: underlying mechanisms and ecological implications
- Authors: Anderson, Bruce Maurice
- Date: 2020
- Subjects: Acacia vachellia , Acacia vachellia -- Growth , Acacia -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/138182 , vital:37604
- Description: The African Acacia species Vachellia karroo, V. robusta, V. nilotica, and V. tortilis are some of the most invasive species implicated in bush encroachment and woody thickening of historically open savannas in southern Africa. This is partially explained by historic increases in atmospheric CO2 concentrations, which are proposed to have promoted the growth and survivorship of C3 tree seedlings relative to C4 grasses. However, the uniformity of CO2 responsiveness and differences among Vachellia species remain largely undetermined. Here we investigate the growth and photosynthetic responses of four Vachellia species, all implicated in woody encroachment, but originating from distinct climatic niches. Exposing these species to a range of sub-ambient CO2 concentrations (12 – 40 Pa) showed that V. karroo, V. robusta, V. nilotica and V. tortilis all responded strongly and fairly consistently to increasing CO2 concentrations, acting as a ‘functional type’ despite being selected from different geographic regions and having different climatic niches. Combined average net CO2 assimilation rates increased by 130% despite significant, but low levels of down-regulation and decreased stomatal conductance. The increased photosynthetic rates stimulated growth and biomass production in all compartments, with no significant differences in interspecific above and below ground allocation. Growth rates and dry biomass increased by 50% and 186%, respectively, while leaf level water use efficiency (ratio of net CO2 assimilation rate to transpiration rate) increased by an average of 218%. When this was scaled to the whole plant level, this stimulation was decreased to 80%. The decrease was the result of the CO2 stimulated increase in canopy areas, which increased leaf area for water loss. The seedlings’ total number of spinescent physical defenses, as well as the average mass and spine mass fraction also increased with rising CO2. These thicker spines could act as better deterrents against vertebrate browsers. Spine density was unchanged, however, showing that the increased spine numbers were associated with larger seedlings at higher CO2 rather than an increase in the number of spines per stem length. The stimulatory effects of increasing CO2 concentrations since the last glacial maximum and resultant increases in seedling growth and biomass are likely to have had important consequences for the survival and establishment of Acacia seedlings. Tolerance of drought and disturbance has been related to seedling size, hence stimulating the growth rate could confer disturbance tolerance and this tolerance would develop more rapidly with increasing CO2 concentrations. Furthermore, increased nitrogen and water use efficiency have the potential to support seedling establishment in environments where these resources would otherwise be limited at lower atmospheric CO2 concentrations. Resulting in a larger proportion of CO2 fertilization responsive woody seedlings surviving the seedling size classes, and persisting within historically open savannas. Where interspecific differences occurred they are likely to have arisen from adaptation to specific climates where these species are native and selection would have been driven by factors such climate, resource availability, levels of disturbance and competitive interactions. V. karroo had the highest growth rates and strong CO2 driven increases in biomass accumulation, despite having the lowest inherent photosynthetic rates. V. karroo also had the lowest increase in water use efficiency and high transpiration rates could potentially increase access to soil nutrients through mass flow. This species had the highest mean spine mass and showed significant increases in spine mass fraction at elevated CO2 concentrations, which may be important for deterring herbivores. V. robusta’s distribution to the mesic east coast of Africa suggests that water is an important limitation to its distribution. Hence, the CO2 stimulated increase in water use efficiency at both leaf and whole canopy level allows speculation that this may be an important driver of this species’ range expansion, which might continue if increasing levels of CO2 continue to promote water use efficiency. V. nilotica occupies a broad range of habitats, inhabiting large areas of the subtropics both north and south of the equator, with the strongest climatic correlates being the precipitation of the wettest quarter followed by high temperature seasonality. In response to increasing CO2, V. nilotica showed overall strong increases in growth, water use efficiency, and physical defenses. These responses may explain why V. nilotica has been such a successful encroacher in a broad range of habitats where limitations are likely to include multiple climatic factors and disturbances. V. tortilis has the widest distribution of all the species studied, covering broad ranges of Africa and only being excluded from the wettest parts of the equator and driest parts of the deserts. In these experiments this species showed the lowest biomass responsiveness to CO2, but had especially large increases in water use efficiency at both the leaf and canopy level. This may have been an important driver for this species’ encroachment into the more arid parts of its distribution, however this link will need to be verified with further experimentation.
- Full Text:
- Date Issued: 2020
- Authors: Anderson, Bruce Maurice
- Date: 2020
- Subjects: Acacia vachellia , Acacia vachellia -- Growth , Acacia -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/138182 , vital:37604
- Description: The African Acacia species Vachellia karroo, V. robusta, V. nilotica, and V. tortilis are some of the most invasive species implicated in bush encroachment and woody thickening of historically open savannas in southern Africa. This is partially explained by historic increases in atmospheric CO2 concentrations, which are proposed to have promoted the growth and survivorship of C3 tree seedlings relative to C4 grasses. However, the uniformity of CO2 responsiveness and differences among Vachellia species remain largely undetermined. Here we investigate the growth and photosynthetic responses of four Vachellia species, all implicated in woody encroachment, but originating from distinct climatic niches. Exposing these species to a range of sub-ambient CO2 concentrations (12 – 40 Pa) showed that V. karroo, V. robusta, V. nilotica and V. tortilis all responded strongly and fairly consistently to increasing CO2 concentrations, acting as a ‘functional type’ despite being selected from different geographic regions and having different climatic niches. Combined average net CO2 assimilation rates increased by 130% despite significant, but low levels of down-regulation and decreased stomatal conductance. The increased photosynthetic rates stimulated growth and biomass production in all compartments, with no significant differences in interspecific above and below ground allocation. Growth rates and dry biomass increased by 50% and 186%, respectively, while leaf level water use efficiency (ratio of net CO2 assimilation rate to transpiration rate) increased by an average of 218%. When this was scaled to the whole plant level, this stimulation was decreased to 80%. The decrease was the result of the CO2 stimulated increase in canopy areas, which increased leaf area for water loss. The seedlings’ total number of spinescent physical defenses, as well as the average mass and spine mass fraction also increased with rising CO2. These thicker spines could act as better deterrents against vertebrate browsers. Spine density was unchanged, however, showing that the increased spine numbers were associated with larger seedlings at higher CO2 rather than an increase in the number of spines per stem length. The stimulatory effects of increasing CO2 concentrations since the last glacial maximum and resultant increases in seedling growth and biomass are likely to have had important consequences for the survival and establishment of Acacia seedlings. Tolerance of drought and disturbance has been related to seedling size, hence stimulating the growth rate could confer disturbance tolerance and this tolerance would develop more rapidly with increasing CO2 concentrations. Furthermore, increased nitrogen and water use efficiency have the potential to support seedling establishment in environments where these resources would otherwise be limited at lower atmospheric CO2 concentrations. Resulting in a larger proportion of CO2 fertilization responsive woody seedlings surviving the seedling size classes, and persisting within historically open savannas. Where interspecific differences occurred they are likely to have arisen from adaptation to specific climates where these species are native and selection would have been driven by factors such climate, resource availability, levels of disturbance and competitive interactions. V. karroo had the highest growth rates and strong CO2 driven increases in biomass accumulation, despite having the lowest inherent photosynthetic rates. V. karroo also had the lowest increase in water use efficiency and high transpiration rates could potentially increase access to soil nutrients through mass flow. This species had the highest mean spine mass and showed significant increases in spine mass fraction at elevated CO2 concentrations, which may be important for deterring herbivores. V. robusta’s distribution to the mesic east coast of Africa suggests that water is an important limitation to its distribution. Hence, the CO2 stimulated increase in water use efficiency at both leaf and whole canopy level allows speculation that this may be an important driver of this species’ range expansion, which might continue if increasing levels of CO2 continue to promote water use efficiency. V. nilotica occupies a broad range of habitats, inhabiting large areas of the subtropics both north and south of the equator, with the strongest climatic correlates being the precipitation of the wettest quarter followed by high temperature seasonality. In response to increasing CO2, V. nilotica showed overall strong increases in growth, water use efficiency, and physical defenses. These responses may explain why V. nilotica has been such a successful encroacher in a broad range of habitats where limitations are likely to include multiple climatic factors and disturbances. V. tortilis has the widest distribution of all the species studied, covering broad ranges of Africa and only being excluded from the wettest parts of the equator and driest parts of the deserts. In these experiments this species showed the lowest biomass responsiveness to CO2, but had especially large increases in water use efficiency at both the leaf and canopy level. This may have been an important driver for this species’ encroachment into the more arid parts of its distribution, however this link will need to be verified with further experimentation.
- Full Text:
- Date Issued: 2020
Evaluating the physiological, morphological and nutritional effects of elevated atmospheric CO2 and drought on select South African maize cultivars
- Authors: Bopape, Tebadi Mamadiga
- Date: 2021-10
- Subjects: Corn Varieties South Africa , Dry farming South Africa , Corn Effect of atmospheric carbon dioxide on South Africa , Corn Effect of drought on South Africa , Corn Morphology , Corn Nutrition , Corn Physiological effect
- Language: English
- Type: Master theses , text
- Identifier: http://hdl.handle.net/10962/189020 , vital:44807
- Description: Thesis embargoed. Expected Release date October 2022. , Thesis (MSc) -- Faculty of Science, Botany, 2021
- Full Text:
- Date Issued: 2021-10
- Authors: Bopape, Tebadi Mamadiga
- Date: 2021-10
- Subjects: Corn Varieties South Africa , Dry farming South Africa , Corn Effect of atmospheric carbon dioxide on South Africa , Corn Effect of drought on South Africa , Corn Morphology , Corn Nutrition , Corn Physiological effect
- Language: English
- Type: Master theses , text
- Identifier: http://hdl.handle.net/10962/189020 , vital:44807
- Description: Thesis embargoed. Expected Release date October 2022. , Thesis (MSc) -- Faculty of Science, Botany, 2021
- Full Text:
- Date Issued: 2021-10
Some aspects of the autecology of Rhizoclonuium riparium (Roth) Harv. with special reference to its growth in the maturation ponds of the Grahamstown sewage works
- Authors: Snook, Deborah Jane
- Date: 1986 , 2013-03-11
- Subjects: Green algae , Marine algae -- South Africa -- Grahamstown , Estuarine ecology -- South Africa -- Grahamstown
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4236 , http://hdl.handle.net/10962/d1004724 , Green algae , Marine algae -- South Africa -- Grahamstown , Estuarine ecology -- South Africa -- Grahamstown
- Description: During 1982 benthic and floating filamentous algal mats appeared in the maturation ponds of the Grahamstown Sewage Disposal Works. These mats clogged the ponds and reduced the efficiency by which the effluent was purified. As they continued to be a problem despite numerous efforts to remove them, this study was initiated to investigate the alga, establish why it was successful in the pond environment, and how its growth could be controlled. The physico-chemical environment of a representative maturation pond was characterised while laboratory studies were conducted to investigate the growth, photosynthetic and respiratory characteristics in the alga. The alga was identified as Rhizoclonium riparium (Roth) Harv. although its morphological variability was greater than that reported in the literature. Growth and photosynthetic studies indicated that the alga favoured temperatures between 20 and 30⁰C and relatively high light intensity (700μE.m⁻².s⁻¹) and that it was highly productive. In addition, the alga exhibited photoadaptive ability, although it seemed to be sensitive to photoinhibition. Its success in the maturation pond was attributed to the favourable physico-chemical environment, particularly the high transparency of the effluent which allowed the penetration of PAR to the pond floor and to the alga's ability to adapt to the change in environment when it floated from the pond floor to its surface. Although the algal mats contribute to the oxidation of the effuent within the maturation pond, they are generally detrimental to the system because they shade the water column and inhibit wind-induced mixing. Recommendations on methods of controlling of the mats are presented. , KMBT_363 , Adobe Acrobat 9.53 Paper Capture Plug-in
- Full Text:
- Date Issued: 1986
- Authors: Snook, Deborah Jane
- Date: 1986 , 2013-03-11
- Subjects: Green algae , Marine algae -- South Africa -- Grahamstown , Estuarine ecology -- South Africa -- Grahamstown
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4236 , http://hdl.handle.net/10962/d1004724 , Green algae , Marine algae -- South Africa -- Grahamstown , Estuarine ecology -- South Africa -- Grahamstown
- Description: During 1982 benthic and floating filamentous algal mats appeared in the maturation ponds of the Grahamstown Sewage Disposal Works. These mats clogged the ponds and reduced the efficiency by which the effluent was purified. As they continued to be a problem despite numerous efforts to remove them, this study was initiated to investigate the alga, establish why it was successful in the pond environment, and how its growth could be controlled. The physico-chemical environment of a representative maturation pond was characterised while laboratory studies were conducted to investigate the growth, photosynthetic and respiratory characteristics in the alga. The alga was identified as Rhizoclonium riparium (Roth) Harv. although its morphological variability was greater than that reported in the literature. Growth and photosynthetic studies indicated that the alga favoured temperatures between 20 and 30⁰C and relatively high light intensity (700μE.m⁻².s⁻¹) and that it was highly productive. In addition, the alga exhibited photoadaptive ability, although it seemed to be sensitive to photoinhibition. Its success in the maturation pond was attributed to the favourable physico-chemical environment, particularly the high transparency of the effluent which allowed the penetration of PAR to the pond floor and to the alga's ability to adapt to the change in environment when it floated from the pond floor to its surface. Although the algal mats contribute to the oxidation of the effuent within the maturation pond, they are generally detrimental to the system because they shade the water column and inhibit wind-induced mixing. Recommendations on methods of controlling of the mats are presented. , KMBT_363 , Adobe Acrobat 9.53 Paper Capture Plug-in
- Full Text:
- Date Issued: 1986
Environmental and socio-economic effects associated with the planting of Atriplex nummularia Lindl. (Oldman saltbush) in the Karoo
- Authors: Hobson, Colin Desmond
- Date: 1991
- Subjects: Botany, Economic Plant introduction -- South Africa -- Karoo Plants, Cultivated
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: vital:4794 , http://hdl.handle.net/10962/d1001894
- Description: This study examines the environmental and socio-economic effects associated with the planting of Atriplex nummularia Lindl. (Oldman saltbush) in the karoo. This is the first study of its kind on oldman saltbush and serves as an important scoping exercise in assessing the impact of saltbush on its surrounds and in identifying additional aspects which require investigation. The environmental parameters investigated include microclimatic effects, soil induced changes, salinity effects on the germination of selected karoo species and compositional changes in the indigenous plant community within a saltbush plantation. When compared to indigenous karoo plant species oldman saltbush is found to ameliorate soil temperatures and increase surface soil salinity (specifically sodium chloride), on an individual plant basis. Salinity is shown to have a differential effect on the germination of selected karoo shrubs. The indigenous plant community within a forty year old saltbush plantation is impoverished with both density of individuals and species richness being markedly reduced. Saltbush is identified as an unsuitable nurse plant for the majority of karoo shrubs. Farm size in relation to both actual and intended area established to saltbush is considered. The area of saltbush already established in the karoo is considered too insignificant to have any wide socio-economic impact. Farmers who intend planting large areas of their farms to saltbush are in the minority. It is those farmers who already have some saltbush planted, who intend planting more. Ecologically based management guidelines are presented, suggesting practices which minimize the detrimental effects of saltbush on soil salinity and the indigenous plant community. These guidelines are practical and in keeping with the overall objectives of optimum resource utilisation and the national grazing strategy for South Africa.
- Full Text:
- Date Issued: 1991
- Authors: Hobson, Colin Desmond
- Date: 1991
- Subjects: Botany, Economic Plant introduction -- South Africa -- Karoo Plants, Cultivated
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: vital:4794 , http://hdl.handle.net/10962/d1001894
- Description: This study examines the environmental and socio-economic effects associated with the planting of Atriplex nummularia Lindl. (Oldman saltbush) in the karoo. This is the first study of its kind on oldman saltbush and serves as an important scoping exercise in assessing the impact of saltbush on its surrounds and in identifying additional aspects which require investigation. The environmental parameters investigated include microclimatic effects, soil induced changes, salinity effects on the germination of selected karoo species and compositional changes in the indigenous plant community within a saltbush plantation. When compared to indigenous karoo plant species oldman saltbush is found to ameliorate soil temperatures and increase surface soil salinity (specifically sodium chloride), on an individual plant basis. Salinity is shown to have a differential effect on the germination of selected karoo shrubs. The indigenous plant community within a forty year old saltbush plantation is impoverished with both density of individuals and species richness being markedly reduced. Saltbush is identified as an unsuitable nurse plant for the majority of karoo shrubs. Farm size in relation to both actual and intended area established to saltbush is considered. The area of saltbush already established in the karoo is considered too insignificant to have any wide socio-economic impact. Farmers who intend planting large areas of their farms to saltbush are in the minority. It is those farmers who already have some saltbush planted, who intend planting more. Ecologically based management guidelines are presented, suggesting practices which minimize the detrimental effects of saltbush on soil salinity and the indigenous plant community. These guidelines are practical and in keeping with the overall objectives of optimum resource utilisation and the national grazing strategy for South Africa.
- Full Text:
- Date Issued: 1991
The autecology of Azolla filiculoides Lamarck with special reference to its occurrence in the Hendrik Verwoerd Dam catchment area
- Authors: Ashton, Peter John
- Date: 1983
- Subjects: Azolla filiculoides -- South Africa -- Gariep Dam Azollaceae Azolla -- South Africa -- Gariep Dam Water ferns -- South Africa -- Gariep Dam Aquatic weeds -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4181 , http://hdl.handle.net/10962/d1003732
- Description: An autecological study of the heterosporous fern Azolla filiculoides Lamarck and its endosymbiotic blue-green alga Anabaena azollae Strasburger, based on a combination of field and laboratory studies, is presented. The taxonomy, morphology and anatomy of the fern-alga association were studied as well as nutritional and physiological aspects of the symbiosis. These studies have defined the habitat and nutritional requirements of the fern and have provided new insights into its reproductive biology, nitrogen metabolism and the nature of the association between the fern and alga. In the catchment area of the Hendrik Verwoerd Dam the availability of suitably sheltered habitat limits the distribution of A. filiculoides while the availability of nutrients, in particular calcium, phosphorus and iron, limits the growth of the fern. The multilayered mats formed by A. filiculoides are essential for spore production, cause dramatic changes in the hydrochemistry of the underlying waters and confer a great competitive advantage on the plant. Methods for the isolation of the fern and algal components of the symbiosis have been developed but recombination of the individual organisms to reform the symbiosis was unsuccessful. The development of the fern is closely linked to that of the alga and the association is maintained throughout the life cycle of the fern. Because of its specific habitat and nutritional requirements, A. filiculoides is unlikely to colonize the open waters of the Hendrik Verwoerd Dam.
- Full Text:
- Date Issued: 1983
- Authors: Ashton, Peter John
- Date: 1983
- Subjects: Azolla filiculoides -- South Africa -- Gariep Dam Azollaceae Azolla -- South Africa -- Gariep Dam Water ferns -- South Africa -- Gariep Dam Aquatic weeds -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4181 , http://hdl.handle.net/10962/d1003732
- Description: An autecological study of the heterosporous fern Azolla filiculoides Lamarck and its endosymbiotic blue-green alga Anabaena azollae Strasburger, based on a combination of field and laboratory studies, is presented. The taxonomy, morphology and anatomy of the fern-alga association were studied as well as nutritional and physiological aspects of the symbiosis. These studies have defined the habitat and nutritional requirements of the fern and have provided new insights into its reproductive biology, nitrogen metabolism and the nature of the association between the fern and alga. In the catchment area of the Hendrik Verwoerd Dam the availability of suitably sheltered habitat limits the distribution of A. filiculoides while the availability of nutrients, in particular calcium, phosphorus and iron, limits the growth of the fern. The multilayered mats formed by A. filiculoides are essential for spore production, cause dramatic changes in the hydrochemistry of the underlying waters and confer a great competitive advantage on the plant. Methods for the isolation of the fern and algal components of the symbiosis have been developed but recombination of the individual organisms to reform the symbiosis was unsuccessful. The development of the fern is closely linked to that of the alga and the association is maintained throughout the life cycle of the fern. Because of its specific habitat and nutritional requirements, A. filiculoides is unlikely to colonize the open waters of the Hendrik Verwoerd Dam.
- Full Text:
- Date Issued: 1983
Photosynthetic gas exchange responses to light, temperature, carbon dioxide and water stress, and changes in photosynthetic pigments to light and water stress in two cultivars of Hordeum vulgare L
- Logie, Malcolme Ronald Ruxton
- Authors: Logie, Malcolme Ronald Ruxton
- Date: 1992
- Subjects: Plants -- Photorespiration , Plants -- Transpiration , Botanical chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4210 , http://hdl.handle.net/10962/d1003779
- Description: The gas exchange responses of two cultivars of Hordeum vulgare L., to light, temperature, CO₂ and water stress were investigated in the laboratory. The optimum temperature for net CO₂ assimilation was found to be 25°C and 22.5°C for cv. Clipper and cv. Dayan respectively. Net CO₂ assimilation was reduced at 30°C in cv. Dayan. At low light intensity the highest quantum yield efficiency was 0.051 mol.mol⁻¹ at 30°C for cv. Clipper, and 0.066 mol.mol⁻¹ at 20°C for cv. Dayan. At the same temperature, cv. Clipper had a higher water use efficiency than cv. Dayan, but stomatal conductance for cv. Dayan was higher than cv. Clipper. Stomatal limitation to CO₂ was lowest at the optimum temperature for CO₂ assimilation in both cultivars. Stomata limited CO₂ assimilation in cv. Clipper to a larger degree than in cv. Dayan. Relative stomatal limitation for cv. Clipper at 25°C was 0.280 ± 0.010, and for cv. Dayan at 22.5°C was 0.028 ± 0.011. Short-term exposure to elevated CO₂ concentrations increased CO₂ assimilation in both cultivars, but more so for cv. Clipper. Transpiration rate at elevated CO₂ partial pressures were higher in cv. Dayan than in cv. Clipper. At very high CO₂ (860 μmol.m⁻²s⁻¹) partial pressure water use efficiency in cv. Clipper was higher than cv. Dayan, but at low CO₂ partial pressures water use efficiency in cv. Dayan was higher than cv. Clipper. Water stress reduced the relative leaf water content and net CO₂ assimilation in both cultivars. Cultivar Dayan was more tolerant to water stress, and CO₂ assimilation in this cultivar was less affected by water stress. In both cultivars water stress increased the concentration of chlorophyll a, chlorophyll b, and chlorophyll a+b. The chlorophyll a:b ratio remained relatively constant throughout the stress period. No correlation between relative leaf water content and total carotenoid concentration was observed.
- Full Text:
- Date Issued: 1992
- Authors: Logie, Malcolme Ronald Ruxton
- Date: 1992
- Subjects: Plants -- Photorespiration , Plants -- Transpiration , Botanical chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4210 , http://hdl.handle.net/10962/d1003779
- Description: The gas exchange responses of two cultivars of Hordeum vulgare L., to light, temperature, CO₂ and water stress were investigated in the laboratory. The optimum temperature for net CO₂ assimilation was found to be 25°C and 22.5°C for cv. Clipper and cv. Dayan respectively. Net CO₂ assimilation was reduced at 30°C in cv. Dayan. At low light intensity the highest quantum yield efficiency was 0.051 mol.mol⁻¹ at 30°C for cv. Clipper, and 0.066 mol.mol⁻¹ at 20°C for cv. Dayan. At the same temperature, cv. Clipper had a higher water use efficiency than cv. Dayan, but stomatal conductance for cv. Dayan was higher than cv. Clipper. Stomatal limitation to CO₂ was lowest at the optimum temperature for CO₂ assimilation in both cultivars. Stomata limited CO₂ assimilation in cv. Clipper to a larger degree than in cv. Dayan. Relative stomatal limitation for cv. Clipper at 25°C was 0.280 ± 0.010, and for cv. Dayan at 22.5°C was 0.028 ± 0.011. Short-term exposure to elevated CO₂ concentrations increased CO₂ assimilation in both cultivars, but more so for cv. Clipper. Transpiration rate at elevated CO₂ partial pressures were higher in cv. Dayan than in cv. Clipper. At very high CO₂ (860 μmol.m⁻²s⁻¹) partial pressure water use efficiency in cv. Clipper was higher than cv. Dayan, but at low CO₂ partial pressures water use efficiency in cv. Dayan was higher than cv. Clipper. Water stress reduced the relative leaf water content and net CO₂ assimilation in both cultivars. Cultivar Dayan was more tolerant to water stress, and CO₂ assimilation in this cultivar was less affected by water stress. In both cultivars water stress increased the concentration of chlorophyll a, chlorophyll b, and chlorophyll a+b. The chlorophyll a:b ratio remained relatively constant throughout the stress period. No correlation between relative leaf water content and total carotenoid concentration was observed.
- Full Text:
- Date Issued: 1992
Natural resources and local management in the Hewu District of the Eastern Cape : limitations to achieving sustainability
- Authors: Nkansa-Dwamena, Yaw
- Date: 1998
- Subjects: Natural resources -- South Africa -- Management , Natural resources -- South Africa -- Eastern Cape -- Management
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4218 , http://hdl.handle.net/10962/d1003787 , Natural resources -- South Africa -- Management , Natural resources -- South Africa -- Eastern Cape -- Management
- Description: The Mceula Commonage Land in the Hewu district lies due northwest of Whittle sea and west of Queenstown in the Eastern Cape. This thesis has two main objectives. Firstly, to survey and analyse the condition of the natural resource. base in the Hewu district with particular reference to water, soil, vegetation and land use. Secondly, to investigate the relationship between scientific approaches to assessing land use degradation and to compare these to the results obtained using a participatory approach of the rural environment of the Hewu district of the Eastern Cape. Random quadrats (4m2) were sampled and corresponding line transects were done with increasing distances from the villages. The Braun-Blanquet method was used to find the cover and abundance of the various species of plants. Data obtained from point sampling along 100 metre line transects was used to assess the condition of the veld using Trollope's technique. Six communities were defined using TWINSP AN, and grazing capacities and veld condition scores of the respective sites were calculated. It was concluded that the six communities were distributed along a gradient of palatable to non palatable grass and grasslike species. Rangelands close to the villages had low veld condition scores and percentage plant cover as opposed to those farther away from the villages. The null hypothesis of no significant difference between the percentage plant cover and condition of the veld close to the villages and farther away from the villages was rejected. Whilst it is urgent to resolve political disputes around land through land distribution, a key issue for the future is sustainability of the natural resource base of South Africa. To attain this, the old traditional methods of research must be supplemented with the participatory method, where the local community becomes fully involved. The central theme of the participatory approach was to investigate the possibility of promoting local management of the natural resources. Workshops were conducted to involve the local community in the project. The community formed six discussion groups that met regularly to discuss environmental issues. The six groups that were formed were: Firewood or woodlot collectors, shepherds / livestock raisers, crop fanners / agriculturists, water collectors, building material / soil collectors and medicinal plant users. The results obtained from the meeting of the discussion groups were used to compare the scientific results obtained from Braun-Blanquet method. Perceptions about their environment, which came out of the results of the discussion groups showed that the local knowledge of the rural community of Mceula was sufficient to train them to manage their environment sustainably.
- Full Text:
- Date Issued: 1998
- Authors: Nkansa-Dwamena, Yaw
- Date: 1998
- Subjects: Natural resources -- South Africa -- Management , Natural resources -- South Africa -- Eastern Cape -- Management
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4218 , http://hdl.handle.net/10962/d1003787 , Natural resources -- South Africa -- Management , Natural resources -- South Africa -- Eastern Cape -- Management
- Description: The Mceula Commonage Land in the Hewu district lies due northwest of Whittle sea and west of Queenstown in the Eastern Cape. This thesis has two main objectives. Firstly, to survey and analyse the condition of the natural resource. base in the Hewu district with particular reference to water, soil, vegetation and land use. Secondly, to investigate the relationship between scientific approaches to assessing land use degradation and to compare these to the results obtained using a participatory approach of the rural environment of the Hewu district of the Eastern Cape. Random quadrats (4m2) were sampled and corresponding line transects were done with increasing distances from the villages. The Braun-Blanquet method was used to find the cover and abundance of the various species of plants. Data obtained from point sampling along 100 metre line transects was used to assess the condition of the veld using Trollope's technique. Six communities were defined using TWINSP AN, and grazing capacities and veld condition scores of the respective sites were calculated. It was concluded that the six communities were distributed along a gradient of palatable to non palatable grass and grasslike species. Rangelands close to the villages had low veld condition scores and percentage plant cover as opposed to those farther away from the villages. The null hypothesis of no significant difference between the percentage plant cover and condition of the veld close to the villages and farther away from the villages was rejected. Whilst it is urgent to resolve political disputes around land through land distribution, a key issue for the future is sustainability of the natural resource base of South Africa. To attain this, the old traditional methods of research must be supplemented with the participatory method, where the local community becomes fully involved. The central theme of the participatory approach was to investigate the possibility of promoting local management of the natural resources. Workshops were conducted to involve the local community in the project. The community formed six discussion groups that met regularly to discuss environmental issues. The six groups that were formed were: Firewood or woodlot collectors, shepherds / livestock raisers, crop fanners / agriculturists, water collectors, building material / soil collectors and medicinal plant users. The results obtained from the meeting of the discussion groups were used to compare the scientific results obtained from Braun-Blanquet method. Perceptions about their environment, which came out of the results of the discussion groups showed that the local knowledge of the rural community of Mceula was sufficient to train them to manage their environment sustainably.
- Full Text:
- Date Issued: 1998
A comparison of the reproductive strategies of key species of a prograding dune system in the Mlalazi Nature Reserve, Natal
- Authors: Todd, Colleen Barbara
- Date: 1995
- Subjects: Sand dune plants -- South Africa -- KwaZulu-Natal -- Mlalazi Nature Reserve , Sand dune plants Comparative studies
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4231 , http://hdl.handle.net/10962/d1003800 , Sand dune plants -- South Africa -- KwaZulu-Natal -- Mlalazi Nature Reserve , Sand dune plants Comparative studies
- Description: The succession on the dunes of the Mlalazi Nature Reserve represents a classical example of primary succession. The reproductive strategies of eight key species were compared to determine some of the mechanisms affecting the community dynamics, at the population level, in the early stages of succession. There is a temporal separation in the flowering and fruiting phenologies. Passerina rigida, Stipagrostis zeyheri and Imperata cylindrica produced small seeds with a low fruit/seed mass ratio within a short cycle. The seeds are suitable for wind-dispersal. The animal-dispersed species; Eugenia capensis, Mimusops caffra and Scaevola plumieri, produced large fleshy seeds with a high fruit/seed mass ratio within cycles of six months and more. Chrysanthemoides monilifera, also an animal-dispersed species, produced a large quantity of small fleshy seeds throughout the year. The fern, Microsorium scolopendrium produced spores throughout the year. The staggered fruiting and flowering phenology ensures a year-round availability of fruit in the dunefield. The key species formed less than half of the species composition of the soil seed bank. The size and range of the soil seed bank differed between the species. P. rigida and S. plumieri formed a high proportion of the seeds in the soil with a wide distribution along the successional gradient. The other species had low soil seed densities with short distribution ranges, or were not present. P. rigida and S. plumieri are easily dispersed species, whereas the other species may have a more restricted and clumped distribution due to the effect of foragers. A high density of P. rigida and E. capensis seeds were found under the parent trees. Only seeds of P. rigida and S. zeyheri were found in the soil in the open. Seeds of P. rigida, S. zeyheri, E. capensis and M. caffra were found under the canopies of P. rigida, E. capensis and M. caffra. No seeds of C. monilifera and I. cylindrica were found in the soil, possibly due to predation. The period of the study (September 1991 to November 1992) was in a dry or drought cycle with only 56.8% of the mean annual rainfall falling. Seed germination and seedling survival of all the species were affected by these dry, warm climatic conditions. The species had seedling densities of less than 4 seeds/m². The environmental conditions along the successional gradient also had an effect on seed germination and seedling survival. Environmental factors of soil pH, light intensity and surface soil temperatures were higher in the open than under canopy. Soil pH and the understorey cover decreased as the light intensity decreased from under the canopy of P. rigida to M. caffra . Litter cover and plant height increased. E. capensis had measurements intermediate to the two species, but had higher surface soil temperatures and plant height than P. rigida. Seedlings of P. rigida in the open and under the canopy of the parent plants had died by the end of the monitoring period. 50% of the seedlings of S. zeyheri under the canopy of P. rigida and M. caffra died. The mortality rate of the seedlings of E. capensis was lower under M. caffra than under the parent plants. I. cylindrica may be propagated vegetatively. However, the mortality of the propagules was greater under the canopy of E. capensis than under P. rigida. M. caffra only germinated under the canopy of E. capensis with a 100% mortality of the seedlings. M. scolopendrium only produced propagules through vegetative propagation under the canopy of E. capensis and M. caffra. The mortality of the young ferns was less than 50% and less under M. caffra than under E. capensis. No seedlings of C. monilifera or S. plumieri were found. The seed distribution range, seed germination requirements and the effect of the environmental conditions on the germination of the seeds and seedling establishment of the species appear to important factors of the reproductive strategies regulating the size of the species populations along the successional gradient.
- Full Text:
- Date Issued: 1995
- Authors: Todd, Colleen Barbara
- Date: 1995
- Subjects: Sand dune plants -- South Africa -- KwaZulu-Natal -- Mlalazi Nature Reserve , Sand dune plants Comparative studies
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4231 , http://hdl.handle.net/10962/d1003800 , Sand dune plants -- South Africa -- KwaZulu-Natal -- Mlalazi Nature Reserve , Sand dune plants Comparative studies
- Description: The succession on the dunes of the Mlalazi Nature Reserve represents a classical example of primary succession. The reproductive strategies of eight key species were compared to determine some of the mechanisms affecting the community dynamics, at the population level, in the early stages of succession. There is a temporal separation in the flowering and fruiting phenologies. Passerina rigida, Stipagrostis zeyheri and Imperata cylindrica produced small seeds with a low fruit/seed mass ratio within a short cycle. The seeds are suitable for wind-dispersal. The animal-dispersed species; Eugenia capensis, Mimusops caffra and Scaevola plumieri, produced large fleshy seeds with a high fruit/seed mass ratio within cycles of six months and more. Chrysanthemoides monilifera, also an animal-dispersed species, produced a large quantity of small fleshy seeds throughout the year. The fern, Microsorium scolopendrium produced spores throughout the year. The staggered fruiting and flowering phenology ensures a year-round availability of fruit in the dunefield. The key species formed less than half of the species composition of the soil seed bank. The size and range of the soil seed bank differed between the species. P. rigida and S. plumieri formed a high proportion of the seeds in the soil with a wide distribution along the successional gradient. The other species had low soil seed densities with short distribution ranges, or were not present. P. rigida and S. plumieri are easily dispersed species, whereas the other species may have a more restricted and clumped distribution due to the effect of foragers. A high density of P. rigida and E. capensis seeds were found under the parent trees. Only seeds of P. rigida and S. zeyheri were found in the soil in the open. Seeds of P. rigida, S. zeyheri, E. capensis and M. caffra were found under the canopies of P. rigida, E. capensis and M. caffra. No seeds of C. monilifera and I. cylindrica were found in the soil, possibly due to predation. The period of the study (September 1991 to November 1992) was in a dry or drought cycle with only 56.8% of the mean annual rainfall falling. Seed germination and seedling survival of all the species were affected by these dry, warm climatic conditions. The species had seedling densities of less than 4 seeds/m². The environmental conditions along the successional gradient also had an effect on seed germination and seedling survival. Environmental factors of soil pH, light intensity and surface soil temperatures were higher in the open than under canopy. Soil pH and the understorey cover decreased as the light intensity decreased from under the canopy of P. rigida to M. caffra . Litter cover and plant height increased. E. capensis had measurements intermediate to the two species, but had higher surface soil temperatures and plant height than P. rigida. Seedlings of P. rigida in the open and under the canopy of the parent plants had died by the end of the monitoring period. 50% of the seedlings of S. zeyheri under the canopy of P. rigida and M. caffra died. The mortality rate of the seedlings of E. capensis was lower under M. caffra than under the parent plants. I. cylindrica may be propagated vegetatively. However, the mortality of the propagules was greater under the canopy of E. capensis than under P. rigida. M. caffra only germinated under the canopy of E. capensis with a 100% mortality of the seedlings. M. scolopendrium only produced propagules through vegetative propagation under the canopy of E. capensis and M. caffra. The mortality of the young ferns was less than 50% and less under M. caffra than under E. capensis. No seedlings of C. monilifera or S. plumieri were found. The seed distribution range, seed germination requirements and the effect of the environmental conditions on the germination of the seeds and seedling establishment of the species appear to important factors of the reproductive strategies regulating the size of the species populations along the successional gradient.
- Full Text:
- Date Issued: 1995
The coastal grasslands of the Eastern Cape west of the Kei River
- Authors: Judd, Rachel Anne
- Date: 1999
- Subjects: Grassland ecology -- South Africa -- Eastern Cape Grasslands -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4203 , http://hdl.handle.net/10962/d1003772
- Description: The grasslands of South Africa are the foundation of commercial and subsistence agriculture yet they are being degraded at an alanning rate. The coastal grasslands of the Eastern Cape are no exception and they suffer added pressure of coastal resort development because of their proximity to an attractive coastline. In order to determine the degree of conservation necessary for any area it is essential to know what species occur there in order to determine if protection from habitat destruction is required. Four aims were defined for this studv. The initial aim was a phytogeographical classification of the grasslands in the coastal region west of the Kei River. This was done by vegetation sampling followed by computer based analysis with TWINSPAN. This analysis defined ten grassland associations. five being located in the area west of the Keiskamma River and five occurring east of it. The associations in the eastern half are termed mesic while those in the western balf are xeric. The second aim was to determine the presence of any underlying ecological gradients affecting the distribution of tbe associations. Indirect gradient analysis was carried out where samples are analysed irrespective of environmental factors. Direct gradient analysis was then carried out using scores per sample of various environmental factors. Environmental factors whicb migbt produce such gradients are both naturally-ocurring and man-induced. Natural factors which were recorded in the field include depth of soil at sample site, soil family, aspect and distance from the shore. An important factor is the land / sea interface. Natural factors analysed in the laboratory include soil pH. conductivity. percent organic matter, calcium, magnesium, phosphate and potassium. Man-induced factors are land use history e.g. Ploughing and grazing. Both direct and indirect gradient analysis were carried out with the computer based programme CANOCO. The third aim of the study was to determine the presence of any successional trends between the ten defined associations. This was done using several characteristics of the associations. Alpha and beta diversity were the first factors compared between associations. The percentage contribution of the Cyperaceae, Fabaceae, Asteraceae and Poaceae to each association was assessed and compared. The presence of various life forms of the species occurring in each association was determined together with the cover abundance of different classes of grass species. These results were then combined and analysed in the light of the results from CANOCO analvsis. They show that the mesic Themeda Iriandra - Anthospermum herhoceum, association which occurs closest to the shore and with the least disturbance is a depauperate form of the mesic climax Themeda triandra association. The mesic Hyparrhenia hirta - Dtheteropogon amplectens association may be a secondary grassland on account of phosphate and potassiun poor soils and land-use. The mesic Hyparrhenia hirta - Themedo triandra association is a slightly degraded form of the climax association due to grazing. The severely disturbed Stenotaphrum secundatum - C'entella coriacea association, which is located close to the shore, is a secondary grassland. Analysis of the xeric associations indicates a clearly defined ordination of associations on the basis of land-use. The Cynodon daclylon - Helictolrichon hirtulum and Sporobolis africanus - Setaria sphacelata associations which occur where ploughed lands have been left to lie fallow are secondary in nature. The Themeda triandra - Ehrharta calycina association is thought to be the closest representati ve of a climax xeric association but the presence of E. calycina indicates that some disturbance has occurred. The vegetation is subject to moderate grazing. The Cynodon dactylon - Ehrharla calycina and Diheleropogon filifolius - Ehrharla calycina associations are subject to varying intensities of trampling and grazing and are degraded forms of the Themeda triandra - Ehrharla calycina association. Because of tbe overriding influence of the land-use gradient separation along gradients of the remaining eight factors was limited. The effect of fire and temporal change in the mesic Themeda triandra and Hyparrhenia hirta - Themeeia trianda associations was assessed via long-term studies at Potter's Pass outside East London. The results show a quick response to burning with a return to 100% cover within six months by both associations. During spring the two associations could not be separated by either TWINSPAN or DECORANA. indicating a temporal shift from the Hyparrhenia hirta - Themeda triandra association to the Themeda triandra association. The fourth and final aim was to identify plants requiring protection from habitat destruction and to make recommendations for further conservation areas and management of the coastal grasslands. Through the collection and identification of as many plants as possible a species checklist was prepared and the status of each was determined through reference to the Red Data Book of threatened and endangered species. Kniphofia rooperi is vulnerable in the Cape and Euphorbia hupleuroides is considered rare in kwazulu-Natal. Ten species are endemic to the Cape and / or South Africa. The richness of the vegetation lies in the presence of species representative of the four major floras which converge in the eastern Cape. i.e. The Cape, NamaKarroo, Tongoland-Pondolaod floras and the Kalahari Highveld Regional Transitional Zone. Suggestions are made for the conservation of the grassland associations at various sites within the study area based on the present area conserved. Less than 2% of the coastline in the study area is conserved and it is felt that the area under conservation should be increased. Management suggestions based on the available literature are given for both farmed and conserved areas. There is a great potential for further studies on grassland dmamics within the areas surveyed. In terms of management, the grasslands require careful examination to determine the most effective season in which to burn if at all. As with most agricultural systems in South Africa. grazing strategies will benefit from further research. Any additional research on the dynamics of these grasslands can only be of benefit to the sustained utilisation of this vital resource.
- Full Text:
- Date Issued: 1999
- Authors: Judd, Rachel Anne
- Date: 1999
- Subjects: Grassland ecology -- South Africa -- Eastern Cape Grasslands -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4203 , http://hdl.handle.net/10962/d1003772
- Description: The grasslands of South Africa are the foundation of commercial and subsistence agriculture yet they are being degraded at an alanning rate. The coastal grasslands of the Eastern Cape are no exception and they suffer added pressure of coastal resort development because of their proximity to an attractive coastline. In order to determine the degree of conservation necessary for any area it is essential to know what species occur there in order to determine if protection from habitat destruction is required. Four aims were defined for this studv. The initial aim was a phytogeographical classification of the grasslands in the coastal region west of the Kei River. This was done by vegetation sampling followed by computer based analysis with TWINSPAN. This analysis defined ten grassland associations. five being located in the area west of the Keiskamma River and five occurring east of it. The associations in the eastern half are termed mesic while those in the western balf are xeric. The second aim was to determine the presence of any underlying ecological gradients affecting the distribution of tbe associations. Indirect gradient analysis was carried out where samples are analysed irrespective of environmental factors. Direct gradient analysis was then carried out using scores per sample of various environmental factors. Environmental factors whicb migbt produce such gradients are both naturally-ocurring and man-induced. Natural factors which were recorded in the field include depth of soil at sample site, soil family, aspect and distance from the shore. An important factor is the land / sea interface. Natural factors analysed in the laboratory include soil pH. conductivity. percent organic matter, calcium, magnesium, phosphate and potassium. Man-induced factors are land use history e.g. Ploughing and grazing. Both direct and indirect gradient analysis were carried out with the computer based programme CANOCO. The third aim of the study was to determine the presence of any successional trends between the ten defined associations. This was done using several characteristics of the associations. Alpha and beta diversity were the first factors compared between associations. The percentage contribution of the Cyperaceae, Fabaceae, Asteraceae and Poaceae to each association was assessed and compared. The presence of various life forms of the species occurring in each association was determined together with the cover abundance of different classes of grass species. These results were then combined and analysed in the light of the results from CANOCO analvsis. They show that the mesic Themeda Iriandra - Anthospermum herhoceum, association which occurs closest to the shore and with the least disturbance is a depauperate form of the mesic climax Themeda triandra association. The mesic Hyparrhenia hirta - Dtheteropogon amplectens association may be a secondary grassland on account of phosphate and potassiun poor soils and land-use. The mesic Hyparrhenia hirta - Themedo triandra association is a slightly degraded form of the climax association due to grazing. The severely disturbed Stenotaphrum secundatum - C'entella coriacea association, which is located close to the shore, is a secondary grassland. Analysis of the xeric associations indicates a clearly defined ordination of associations on the basis of land-use. The Cynodon daclylon - Helictolrichon hirtulum and Sporobolis africanus - Setaria sphacelata associations which occur where ploughed lands have been left to lie fallow are secondary in nature. The Themeda triandra - Ehrharta calycina association is thought to be the closest representati ve of a climax xeric association but the presence of E. calycina indicates that some disturbance has occurred. The vegetation is subject to moderate grazing. The Cynodon dactylon - Ehrharla calycina and Diheleropogon filifolius - Ehrharla calycina associations are subject to varying intensities of trampling and grazing and are degraded forms of the Themeda triandra - Ehrharla calycina association. Because of tbe overriding influence of the land-use gradient separation along gradients of the remaining eight factors was limited. The effect of fire and temporal change in the mesic Themeda triandra and Hyparrhenia hirta - Themeeia trianda associations was assessed via long-term studies at Potter's Pass outside East London. The results show a quick response to burning with a return to 100% cover within six months by both associations. During spring the two associations could not be separated by either TWINSPAN or DECORANA. indicating a temporal shift from the Hyparrhenia hirta - Themeda triandra association to the Themeda triandra association. The fourth and final aim was to identify plants requiring protection from habitat destruction and to make recommendations for further conservation areas and management of the coastal grasslands. Through the collection and identification of as many plants as possible a species checklist was prepared and the status of each was determined through reference to the Red Data Book of threatened and endangered species. Kniphofia rooperi is vulnerable in the Cape and Euphorbia hupleuroides is considered rare in kwazulu-Natal. Ten species are endemic to the Cape and / or South Africa. The richness of the vegetation lies in the presence of species representative of the four major floras which converge in the eastern Cape. i.e. The Cape, NamaKarroo, Tongoland-Pondolaod floras and the Kalahari Highveld Regional Transitional Zone. Suggestions are made for the conservation of the grassland associations at various sites within the study area based on the present area conserved. Less than 2% of the coastline in the study area is conserved and it is felt that the area under conservation should be increased. Management suggestions based on the available literature are given for both farmed and conserved areas. There is a great potential for further studies on grassland dmamics within the areas surveyed. In terms of management, the grasslands require careful examination to determine the most effective season in which to burn if at all. As with most agricultural systems in South Africa. grazing strategies will benefit from further research. Any additional research on the dynamics of these grasslands can only be of benefit to the sustained utilisation of this vital resource.
- Full Text:
- Date Issued: 1999
Revising the distribution of mangrove forests in South Africa and changes in growth of mangrove species along a latitudinal gradient
- Authors: Bolosha, Uviwe
- Date: 2017
- Subjects: Mangrove ecology -- South Africa , Mangrove forests -- South Africa , Mangrove plants -- South Africa -- Effect of temperature on
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/7544 , vital:21271
- Description: Mangrove forests are a diverse assemblage of trees and shrubs that are adapted to a saline and tidally inundated environment. The global spread of mangrove species is affected by climate, with most confined to areas that are warmer and moist. At a global scale, temperature limits the distribution of mangrove forests but on a regional scale and local scale, rainfall, river flow and tidal exchange have a strong effect on the distribution and biomass of mangrove forests. Other factors that play a role in limiting growth and distribution of mangroves include accessibility of suitable habitats for growth and also conditions that are suitable for propagule dispersal. The objectives of this study were to review the distribution of mangroves in South Africa and determine the number of extreme temperature events that may limit further distribution and secondly to measure growth rates of mangrove species at Mngazana and Nahoon Estuary and the nutrient pools in the sediment of these forests. In 1982, Ward and Steinke published a list of estuaries where mangroves were present. The current study sampled the population structure, microclimate and level of expansion in two estuaries within and outside of the published range. The minimum, maximum temperature and number of extreme temperature events were measured using iButtons. Mangrove expansion will be limited by minimum temperatures (1.1 ° C) and an increase in extreme temperature events (830) (<5 ° C and 5- 10 ° C) at the latitudinal limits. Expansion of A. marina at Kwelera and Tyolomnqa Estuary was evident but sapling survival was low. Mangroves have expanded within and outside the range proposed by Ward and Steinke (1982), but are limited by physical factors, restricted by the presence of saltmarsh and other estuarine macrophytes and natural disturbance regimes. An increase in population growth was recorded over the years at both Mngazana and Nahoon Estuary. Nutrients, (ammonium, nitrates + nitrites and soluble reactive phosphorus) varied amongst sites and were related to seasonality. Nitrogen in both estuaries was available in the form of ammonium (NH4) and its concentration was generally higher (1.3-76.2 pm) than other forms of nitrogen (0.07-6.3 µm). Soluble reactive phosphorus (SRP) was higher during the wet seasons in both estuaries. An increase in porewater salinity since 2007 (41.3 practical salinity unit (PSU)) was measured at Mngazana and this is a result of freshwater abstraction and low rainfall. A. marina saplings and adults grew significantly faster at Nahoon Estuary (the distributional limit) (11.1 ± 1.1 cm year-¹) compared to Mngazana Estuary (5.3 ± 1.8 cm year-¹). Different mangrove species and forests respond differently to environmental factors and changes in mangrove distribution is expected in South Africa but changes are expected to happen slowly and opportunistically.
- Full Text:
- Date Issued: 2017
- Authors: Bolosha, Uviwe
- Date: 2017
- Subjects: Mangrove ecology -- South Africa , Mangrove forests -- South Africa , Mangrove plants -- South Africa -- Effect of temperature on
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/7544 , vital:21271
- Description: Mangrove forests are a diverse assemblage of trees and shrubs that are adapted to a saline and tidally inundated environment. The global spread of mangrove species is affected by climate, with most confined to areas that are warmer and moist. At a global scale, temperature limits the distribution of mangrove forests but on a regional scale and local scale, rainfall, river flow and tidal exchange have a strong effect on the distribution and biomass of mangrove forests. Other factors that play a role in limiting growth and distribution of mangroves include accessibility of suitable habitats for growth and also conditions that are suitable for propagule dispersal. The objectives of this study were to review the distribution of mangroves in South Africa and determine the number of extreme temperature events that may limit further distribution and secondly to measure growth rates of mangrove species at Mngazana and Nahoon Estuary and the nutrient pools in the sediment of these forests. In 1982, Ward and Steinke published a list of estuaries where mangroves were present. The current study sampled the population structure, microclimate and level of expansion in two estuaries within and outside of the published range. The minimum, maximum temperature and number of extreme temperature events were measured using iButtons. Mangrove expansion will be limited by minimum temperatures (1.1 ° C) and an increase in extreme temperature events (830) (<5 ° C and 5- 10 ° C) at the latitudinal limits. Expansion of A. marina at Kwelera and Tyolomnqa Estuary was evident but sapling survival was low. Mangroves have expanded within and outside the range proposed by Ward and Steinke (1982), but are limited by physical factors, restricted by the presence of saltmarsh and other estuarine macrophytes and natural disturbance regimes. An increase in population growth was recorded over the years at both Mngazana and Nahoon Estuary. Nutrients, (ammonium, nitrates + nitrites and soluble reactive phosphorus) varied amongst sites and were related to seasonality. Nitrogen in both estuaries was available in the form of ammonium (NH4) and its concentration was generally higher (1.3-76.2 pm) than other forms of nitrogen (0.07-6.3 µm). Soluble reactive phosphorus (SRP) was higher during the wet seasons in both estuaries. An increase in porewater salinity since 2007 (41.3 practical salinity unit (PSU)) was measured at Mngazana and this is a result of freshwater abstraction and low rainfall. A. marina saplings and adults grew significantly faster at Nahoon Estuary (the distributional limit) (11.1 ± 1.1 cm year-¹) compared to Mngazana Estuary (5.3 ± 1.8 cm year-¹). Different mangrove species and forests respond differently to environmental factors and changes in mangrove distribution is expected in South Africa but changes are expected to happen slowly and opportunistically.
- Full Text:
- Date Issued: 2017
An anatomical investigation of jointed cactus (Opuntia aurantiaca, Lindley) with germination tests, and observations on the movements of the stomata
- Authors: Archibald, E E A
- Date: 1936
- Subjects: Cactus -- Anatomy , Opuntia , Stomata , Germination
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4264 , http://hdl.handle.net/10962/d1013444
- Description: From Introduction: In 1934 the Government started an active campaign on the eradiction of Jointed Cactus. This plant was causing considerable damage to the farms and commonages of the Eastern Province, and was spreading at an alarming rate. The Officer in Charge of eradication, Mr E. du Toit, was stationed at Grahamstown which is fairly centrally situated in the infested area. In 1935 Dr A. Leemann of the Division of Plant Industry made his headquarters at Rhodes University College.
- Full Text:
- Date Issued: 1936
- Authors: Archibald, E E A
- Date: 1936
- Subjects: Cactus -- Anatomy , Opuntia , Stomata , Germination
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4264 , http://hdl.handle.net/10962/d1013444
- Description: From Introduction: In 1934 the Government started an active campaign on the eradiction of Jointed Cactus. This plant was causing considerable damage to the farms and commonages of the Eastern Province, and was spreading at an alarming rate. The Officer in Charge of eradication, Mr E. du Toit, was stationed at Grahamstown which is fairly centrally situated in the infested area. In 1935 Dr A. Leemann of the Division of Plant Industry made his headquarters at Rhodes University College.
- Full Text:
- Date Issued: 1936
Coastal dune ecology and management in the Eastern Cape
- Authors: Avis, Anthony Mark
- Date: 1993
- Subjects: Sand dune ecology -- South Africa Shore protection -- South Africa Coastal zone management -- South Africa Sand dunes -- South Africa Sand dune plants -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4185 , http://hdl.handle.net/10962/d1003753
- Description: The importance of understanding the ecological functioning of coastal dune systems is emphasized as being fundamental to the correct management of the dune landscape. Dune vegetation along the Eastern Cape coastline, from Cape St Francis in the west to Kei Mouth in the east was described in terms of the distribution and phytochorological affinities of the taxa. At a regional scale species distribution was strongly influenced by both the climate, particularly rainfall, and the phytochorological affinities of the taxa. Seven communities were defined using TWINSPAN, and the interrelationships between these communities in anyone area appeared to be linked to a successional gradient. Dune Slacks are thought to play a key role in this successional sequence, and a temporal study of this community led to a conceptual model of plant succession in these dunefields. Climate, particularly rainfall and wind, are major factors influencing plant succession. Wind-borne sand causes the slacks to migrate in an easterly direction under the influence of the predominantly westerly winds, although easterly winds, mainly in summer months may reverse these trends. Autogenic changes appeared to be important in this succession, and a comparative study of a good example of a primary succession at Mtunzini in Natal was undertaken to elucidate the main mechanism of change. Eight communities that were identified here were concluded to be distnbuted along a gradient of increasing age, with successional changes predictable, linear and directional. Species were grouped in distinct zones along the continuum and edaphic changes (decrease in soil pH, increase in organic matter and exchangeable bases) were related to the community based changes in species composition. The mechanism of change supported the facilitation model of plant succession which is a modification of the original Clementsian concept. Similar results were found in the Eastern Cape, but due to the harsh environment, multiple pathways of succession exist. Data from this study lent support to the model of plant succession developed earlier, and confinned that the dune slacks played an important role in this facilitation by acting as centres of diversity. The foredunes were found to have an indirect role in protecting these slacks from salt spray and sand movement. The central theme of the management studies was to investigate the ecological consequences of recreational pressure within the dune environment. Current levels of beach utilization at East London were lower than other beaches in South Africa, but a general trend of increasing utilization due to sociopolitical changes can be expected. The suitability of questionnaire surveys to assess aspects such as the adequacy of facilities, perceptual carrying capacity and the beach users opinion of natural vegetation and preference for particular beaches was demonstrated. The dune vegetation was found to be sensitive to human trampling, but at current levels, the ecological carrying capacity will not be exceeded since results of the aerial census counts and questionnaire survey revealed that few people entered sensitive zones such as the coastal forest. More detailed long term studies on the susceptibility of dune vegetation to both trampling and off-road vehicle impacts revealed a low resilience of dune plant communities to these effects. Although susceptibility differed between the three communities tested, generally the greatest amount of damage occurred after the first few passages, and vehicles caused a more significant decrease in height when compared to trampling. Recovery rates were slow and low levels of repeated damage were sufficient to retard or prevent the recovery of the plants. Stricter control of vehicle use on beaches is therefore required, and in high use zones the ecological carrying capacity should be increased by providing access tracks if possible, or if not possible, by restricting access. A historical account of the process of dune stabilization showed that although first initiated in 1845, indigenous species were only used in the past three decades. The use of alien species has resulted in problems such as a reduction in the ecological integrity and aesthetic appeal of coastal systems. The techniques applied in the stabilization of drift sands with indigenous vegetation have been successful, as revealed by a quantitative survey of 17 sites in the Eastern Cape. Sites were grouped by multivariate analysis on the basis of their species composition, and variability between sites was dependent on the types of species planted. Selection of suitable species is therefore important and is discussed with respect to their natural distribution along the coast. The long term objective of stabilization should be the creation of functional, diverse, aesthetic ecosystems, since the intrinsic and economic value of the dune landscape for tourism lies therein. However, detailed studies should be undertaken prior to implementing a manipulative process such as dune stabilization, since ecological processes may be disrupted. An understanding of such processes is therefore important if one wishes to effectively manage the dune landscape.
- Full Text:
- Date Issued: 1993
- Authors: Avis, Anthony Mark
- Date: 1993
- Subjects: Sand dune ecology -- South Africa Shore protection -- South Africa Coastal zone management -- South Africa Sand dunes -- South Africa Sand dune plants -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4185 , http://hdl.handle.net/10962/d1003753
- Description: The importance of understanding the ecological functioning of coastal dune systems is emphasized as being fundamental to the correct management of the dune landscape. Dune vegetation along the Eastern Cape coastline, from Cape St Francis in the west to Kei Mouth in the east was described in terms of the distribution and phytochorological affinities of the taxa. At a regional scale species distribution was strongly influenced by both the climate, particularly rainfall, and the phytochorological affinities of the taxa. Seven communities were defined using TWINSPAN, and the interrelationships between these communities in anyone area appeared to be linked to a successional gradient. Dune Slacks are thought to play a key role in this successional sequence, and a temporal study of this community led to a conceptual model of plant succession in these dunefields. Climate, particularly rainfall and wind, are major factors influencing plant succession. Wind-borne sand causes the slacks to migrate in an easterly direction under the influence of the predominantly westerly winds, although easterly winds, mainly in summer months may reverse these trends. Autogenic changes appeared to be important in this succession, and a comparative study of a good example of a primary succession at Mtunzini in Natal was undertaken to elucidate the main mechanism of change. Eight communities that were identified here were concluded to be distnbuted along a gradient of increasing age, with successional changes predictable, linear and directional. Species were grouped in distinct zones along the continuum and edaphic changes (decrease in soil pH, increase in organic matter and exchangeable bases) were related to the community based changes in species composition. The mechanism of change supported the facilitation model of plant succession which is a modification of the original Clementsian concept. Similar results were found in the Eastern Cape, but due to the harsh environment, multiple pathways of succession exist. Data from this study lent support to the model of plant succession developed earlier, and confinned that the dune slacks played an important role in this facilitation by acting as centres of diversity. The foredunes were found to have an indirect role in protecting these slacks from salt spray and sand movement. The central theme of the management studies was to investigate the ecological consequences of recreational pressure within the dune environment. Current levels of beach utilization at East London were lower than other beaches in South Africa, but a general trend of increasing utilization due to sociopolitical changes can be expected. The suitability of questionnaire surveys to assess aspects such as the adequacy of facilities, perceptual carrying capacity and the beach users opinion of natural vegetation and preference for particular beaches was demonstrated. The dune vegetation was found to be sensitive to human trampling, but at current levels, the ecological carrying capacity will not be exceeded since results of the aerial census counts and questionnaire survey revealed that few people entered sensitive zones such as the coastal forest. More detailed long term studies on the susceptibility of dune vegetation to both trampling and off-road vehicle impacts revealed a low resilience of dune plant communities to these effects. Although susceptibility differed between the three communities tested, generally the greatest amount of damage occurred after the first few passages, and vehicles caused a more significant decrease in height when compared to trampling. Recovery rates were slow and low levels of repeated damage were sufficient to retard or prevent the recovery of the plants. Stricter control of vehicle use on beaches is therefore required, and in high use zones the ecological carrying capacity should be increased by providing access tracks if possible, or if not possible, by restricting access. A historical account of the process of dune stabilization showed that although first initiated in 1845, indigenous species were only used in the past three decades. The use of alien species has resulted in problems such as a reduction in the ecological integrity and aesthetic appeal of coastal systems. The techniques applied in the stabilization of drift sands with indigenous vegetation have been successful, as revealed by a quantitative survey of 17 sites in the Eastern Cape. Sites were grouped by multivariate analysis on the basis of their species composition, and variability between sites was dependent on the types of species planted. Selection of suitable species is therefore important and is discussed with respect to their natural distribution along the coast. The long term objective of stabilization should be the creation of functional, diverse, aesthetic ecosystems, since the intrinsic and economic value of the dune landscape for tourism lies therein. However, detailed studies should be undertaken prior to implementing a manipulative process such as dune stabilization, since ecological processes may be disrupted. An understanding of such processes is therefore important if one wishes to effectively manage the dune landscape.
- Full Text:
- Date Issued: 1993