Propagation and stress physiology of selected Subtropical Thicket species : towards increasing biodiversity at rehabilitation sites
- Authors: Louw, Merika
- Date: 2012
- Subjects: Biodiversity conservation , Plant physiology , Stress (Physiology) , Plant propagation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10758 , http://hdl.handle.net/10948/d1021115
- Description: Sundays Thicket and Spekboomveld vegetation in the Eastern Cape have experienced intensive and extensive degradation due to over-browsing by domestic stock. The Subtropical Thicket Restoration Project aims to take advantage of the high carbon sequestration potential of Portulacaria afra (Spekboom) and other Thicket species, to rehabilitate degraded Thicket by restoring biodiversity and ecosystem services, create job opportunities and socio-economic upliftment in local communities, and promote the trade of carbon credits generated by planting and „farming‟ with Spekboom truncheons, rather than domestic stock. Plant material (seeds and length of stem) was sourced from the farm Krompoort, outside Uitenhage in the Eastern Cape. The effectiveness of four different rooting media i.e. plain pool filter sand and 1:1 mixtures of pool filter sand with perlite, potting soil and Thicket soil, on the rooting of ten Thicket species, were tested. Species with the greatest percentage strike and mean root length on stem cuttings were succulent species, Crassula ovata (84 percent strike) and Portulacaria afra (97 percent), as was expected. The application of rooting hormone Seradix© No. 3 did not significantly promote cutting strike or increase mean root length in C. ovata and P. afra. Woody canopy shrub species with the greatest cutting strike and mean root length, overall, were Rhigozum obovatum (24 percent), Lycium cinereum and L. oxycarpum (21 percent), and Searsia longispina (19 percent). These species, as well as Grewia robusta (4 percent), are considered „easy-to-root‟ species, or of sufficient functional value in terms of their spinescence, flower and fruit production, and soil-binding capabilities. Very low percentage strike (<1 percent) and mean root length were achieved in Azima tetracantha, Carissa bispinosa and Gymnosporia polyacantha subsp. polyacantha. These species are considered unsuitable for propagation for rehabilitation purposes. Crassula ovata, L. cinereum, L. oxycarpum, P. afra and S. longispina cuttings produced longer roots when planted in Thicket soil, the same having been found in R. obovatum cuttings planted in perlite. Thicket soil was, therefore, best at promoting cutting strike and root growth in „easy-to-root‟ species. Plain pool filter sand was the only medium in which A. tetracantha, C. bispinosa and G. robusta, cuttings rooted, and perlite the only medium in which G. polyacantha subsp. polyacantha cuttings rooted. Potting soil did not promote significant cutting strike or root growth in any of the species tested. Physiological variables i.e. photosynthetic efficiency (chlorophyll a fluorescence, Fv/Fm) and stomatal conductance (mmol H2O m-2 s-1) were measured for ten Thicket species, including Portulacaria afra. Control plants were watered well once a week, and treatment plants were dried out for 30 days, rewatered on the 30th day and their recovery from drought stress monitored for a further 17 days. Species that responded poorly to drought stress were Gymnosporia buxifolia and Putterlickia pyracantha. In addition to Portulacaria afra, species that showed the fastest recovery and resprout after rewatering, were: Crassula ovata, Ehretia rigida, Grewia robusta, Lycium ferocissimum, Rhigozum obovatum and Searsia longispina. These species produced the smallest decline in volumetric moisture content of soil, and had the lowest decline in photosynthetic efficiency and stomatal conductance during simulated drought. Unlike C. ovata and P. afra, which are CAM or C3-CAM switching species, mortality of transplants will most likely be high, if not total, during transplantation, as this study was done at lower light and temperature, and higher humidity levels than experienced at rehabilitation sites. This study has shown that the reintroduction of propagated woody canopy shrubs and trees into degraded Thicket sites does not appear to be a practical or economical method of actively restoring biodiversity to rehabilitation sites. As woody climax species have been shown to return to sites planted with Spekboom truncheons through „natural regeneration‟ within approximately 50 years, future research efforts should focus on optimising restoration site selection and planting techniques in order to maximize carbon sequestration potential of planted truncheons, which will, in the long term, result in an environment that can support regeneration of the biodiversity to something resembling intact Thicket.
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- Date Issued: 2012
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.
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- Date Issued: 1992