- Title
- Tolerance of salt marsh ecotone species to salinity and inundation
- Creator
- Matabane, Rebotile
- Subject
- Geobiology
- Subject
- Plant ecology Plant ecophysiology
- Date Issued
- 2018
- Date
- 2018
- Type
- Thesis
- Type
- Masters
- Type
- MSc
- Identifier
- http://hdl.handle.net/10948/22409
- Identifier
- vital:29967
- Description
- Ecophysiology studies help understand and predict the response of coastal ecosystems to changes in environmental factors and complement modelling and mapping studies that often do not take into account the physiological tolerances of the biota. Along the South African coastline predicted sea level rise will shift the tidal front and result in larger submerged areas. The frequency and magnitude of inundation and subsequent salinity stress is expected to influence the survival and distribution of salt marsh. An understanding of the effects of sea level rise on plant growth and survival is required to predict, manage and adapt to climate change. The aim of this study was to investigate the response of the salt marsh ecotone species Disphyma crassifolium (L.) L. Bol. to salinity and submergence stress and to measure in situ spatial and temporal changes in vegetation cover and its environmental drivers in the Swartkops Estuary in South Africa.Three greenhouse experiments assessed morphological and physiological responses to salinity and inundation treatments on D. crassifolium. The first experiment used three inundation levels (dry, tidal and waterlogged) and five salinity treatments (0, 8, 18, 35 and 45 ppt) and ran for six weeks. The second experiment also had three inundation levels (dry, waterlogged and completely submerged) and five salinity treatments (0, 8, 18, 35 and 45 ppt) and ran for 12 weeks. The third experiment investigated the response of a narrower range of salinity treatments under dry conditions only; namely 0, 5, 10, 15, 20, 25, 30 and 35 ppt and ran for seven weeks. Experiment 1 showed that D. crassifolium growth decreased with an increase in salinity. Optimum growth occurred at lower salinity treatments of 0 to 18 ppt under dry conditions. Plant height and leaf succulence was the highest at 0 ppt (12.4 ± 1.2 cm and 94.9 ± 0.6 % respectively). The number of leaves produced were the highest at 0 ppt (47.7 ± 8.9 number of leaves) and 8 ppt (59.6 ± 6.3 number of leaves). The root/shoot ratio for dry treatment plants was significantly lower (p < 0.005, n=12) than that of waterlogged and tidal-treated plants. This was as a result of more leaves being produced in dry treatments. In Experiment 2 D. crassifolium plants died after one month of submergence regardless of the salinity. Once again optimum growth occurred at salinity of 0 to 18 ppt under the dry treatment. Within the waterlogged treatment, 0 and 8 ppt treated plants developed adventitious roots and started flowering after two weeks.The electrolyte leakage increased with salinity, however the waterlogged plants had significantly higher electrolyte leakage compare to the dry treated plants. Within the waterlogged treatment electrolyte leakage was at the highest at 18 ppt (36.5 ± 4.2 %) and lowest at 0 ppt (26.1 ± 3.3 %). Photosynthetic pigments showed significant difference across the two inundation states. However, chlorophyll and carotenoids concentrations did not differ significantly with an increase in salinity in each treatment. D. crassifolium tolerated stress through accumulation of solutes that increased in concentration with salinity treatment. The proline concentration ranged between 23.1 to 102 mM while the glycinebetaine concentration ranged between 36.6 and 120 mM. Experiment 3 showed that growth was highest at salinity < 20 ppt. The highest growth based on plant height was measured at 0 and 10 ppt. Spatial and temporal changes in the salt marsh terrestrial boundary was investigated in situ at two sites in the Swartkops Estuary using three line transects per site extending from the terrestrial boundary to the supratidal salt marsh. Plant cover abundance was measured seasonally along with sediment moisture content, electrical conductivity, redox potential, organic content and sediment particle size. There were five sampling trips between April 2016 to July 2017, representing autumn, winter and summer. The transects at Sites 1 and 2 were divided into three zones; a Drosanthemum zone (dominated by Drosanthemum parvifolium (Haw.) Schwantes at the beginning of the transect), a Sarcocornia zone (in the middle of the transect and dominated by Sarcocornia pillanssii (Moss) A.J. Scott) and a Disphyma zone at the end of the transect in the supratidal marsh (dominated by Disphyma crassifolium). There was no significant seasonal change in vegetation cover except in Site 1 during Winter 2016 when Isolepis sp. appeared and was dominant in the middle of the transects. Sediment assessed from each of the zones showed physicochemical ranges within the typical ecotone sediment characteristics. Moisture content ranged between 0.6 and 30.9 % at Site 1 and between 3 and 33.8 % at Site 2. Electrical conductivity ranged between 0.9 and 10.2 mS cm-1 at Site 1 and between 1.4 and 17.8 mS cm-1 at Site 2. Organic content ranged between 1.9 and 16 % at Site 1 and between 3.9 and 16.3 % at Site 2. Redox potential ranged between 208 and 406.7 mV at Site 1 and between 202.7 and 389.67 mV at Site 2. Sediment particle size consisted of sand (>70%), silt (>15%) and clay (<10%). The aim of this study was to provide insight on the effects of salinity and inundation on the morphology and physiology of D. crassifolium occurring in the salt marsh terrestrial boundary and to assess its spatial and temporal changes over time. The research suggests that D. crassifolium is more sensitive to inundation than salinity. Furthermore the succulent was found in the field to be dominant in conditions which the glasshouse experiments showed to be its optimum growth. That is, in dry sediments with salinity of < 18 ppt. Therefore, if these conditions change (sediment moisture and salinity), the cover abundance of D. crassifolium could significantly change in the field.
- Format
- x, 135 leaves
- Format
- Publisher
- Nelson Mandela University
- Publisher
- Faculty of Science
- Language
- English
- Rights
- Nelson Mandela University
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