What are southern Cape renosterveld geophytes storing in their underground organs?

Bachelor Thesis


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University of Cape Town

Geophytes have been extremely successful in the Cape Floristic Region of South Africa, because they possess underground storage organs adapted to unpredictable climates. This study analysed the storage reserves of geophyte species from the southern Cape renosterveld, to determine if reserve concentrations varied with storage organ size and if different storage organ types (bulbs, corms, tubers and secondary thickening) store unique reserve concentrations. Plant species collected were analysed for water content (gig fresh weight), nitrogen percentage (mass spectrometry), phosphorus percentage (dry-ashing extraction method) and starch content (Megazyme Total Starch Assay Kit, which follows an enzymatic procedure). Bulbs (mean = 30.89mm) and tubers (18.65mm) were found to have significantly larger widths than corms (11.13mm) and secondary thickening (7.00mm). Secondary thickening contained significantly less water than the other storage organ types (28.13%). Bulbs (83.81%) contained significantly more water than corms (68.33%). There were no observable differences in N, P and starch for the four storage organ types, although there was high variability. There were no substantial correlations between any of the reserves and storage organ width. The size variation is most likely due to annual versus perennial life cycle. Variability in water content is presumably due to microhabitat variation, and structures to prevent water loss. The average nutrient concentrations (nitrogen and phosphorous) were similar for all storage organ types possibly because all of the species are growing in a homogenous renosterveld environment. The results of this investigation were not entirely meaningful because they were a snapshot of a very dynamic system. Suggestions for further research include: considering time of year and age of geophytes when sampling, analysing local soils and assessing the variety of different carbohydrates and nutrients stored. Furthermore, the potential for phylogenetic signal, ecological similarity of species because they are phylogenetically related, could be explored.