Response of wetland indicator grass species to degree of soil water saturation
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Date
2020-08
Authors
Jaola, Khumo
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Publisher
University of the Free State
Abstract
Different plant species, adapted to life in water-saturated soil conditions, have been used for quite some time as indicators of wetland presence. However, it is not quantitatively known how wet the soil should be to support these wetland plants. This study aimed to investigate the response of wetland indicator grass species to the degree of soil water saturation. There were three key aims to the study: to investigate a procedure to evaluate grass species growth at different degrees of water saturation, to determine at what degree of water saturation obligate and upland wetland plants grow and to propose a degree of water saturation guidelines for quantitative wetland delineation. The study was conducted in glasshouses at the University of Free State, under controlled environmental conditions, Two grass species: Leptochloa fusca (obligate wetland) and Themeda triandra (obligate upland), were selected and transplanted into soil-filled pots. Within these pots the different degrees of water saturation could be monitored making use of the bulk density of the soil. Two separate studies were conducted at different times with different degrees of water saturation. The first study used 60%, 70%, 80% and 90% degrees of water saturation. During this study parameter such as photosynthetic rate, water conductance, intercellular CO2 concentration, and transpiration rate were monitored weekly by using the Licor-6400XL apparatus. A measuring ruler was used to measure leaf length of selected and marked leaves weekly. The second study conducted had four different degrees of saturation (20%, 40%, 60% and 80%) with measurements for the photosynthetic rate, water conductance, intercellular CO2 concentration, and transpiration rate were monitored weekly making use of the Licor-6400XL apparatus. A measuring ruler was used to measure the length of selected and marked leaves weekly. In both studies the parameters for degree of water saturation and the photosynthetic rate, water conductance, intercellular CO2 concentration, and transpiration rate did not show any correlations nor significant differences. In the first study the results obtained from the Chlorophyll a, b, chlorophyll a & b and carotenoid content also did not yield any significant differences or correlations. However, in the first study Leptochloa fusca grew taller than Themeda trianadra indicating that Leptochloa fusca was better adapted to all degrees of water saturation. The second study revealed that Themeda triandra grew taller than Leptochloa fusca at 20% and 40% water saturation. In contrast to this at 60% and 80% water saturation Leptochloa fusca outperformed Themeda triandra and more so at 80% than at 60% saturation. These differences were, however, not statistically significant but the result does seem to indicate that 60% soil water saturation was sufficient to support optimal obligate wetland grass growth. The results obtained might have been influenced by the fact that grasses were grown out of season or that the soil that was used was not optimal to support the grasses, especially wetland grasses. From the results, it could also be inferred that these parameters may not be such good indicators of plant adaptability to different degrees of water saturation as was initially thought. However, further experiments may be done using different soil types, other non-wetland and wetland grasses, as well as conducting the experiments within the growing season of grasses.
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Keywords
Dissertation (M.Sc. (Soil, Crop and Climate Science))--University of the Free State, 2020, Degree of water saturation, Glasshouse, Photosynthetic rate, Transpiration rate, Upland grasses, Wetland grasses