Ecophysiology of plants as affected by environmental and biotic factors.
I have also been involved with other projects where my role has been determining plant response to phylogenetic, climatic and soil conditions. These have included:
Optimising bioactive metabolites in Pelargoium sidoides
Pelargoiums contain a bioactive compound umkalin which is used to treat respiratory and gastro-intestinal infections. This has resulted in the over-exploitation of wild stocks and prompted a study into identifying geographical populations with high umkalin contents and determining if high contents could be maintained in cultivated plants subject to various treatments.
White A, Davies-Coleman M and Ripley BS (2008) The wild-harvest and cultivation of Pelargonium sidoides: Measuring and optimising umckalin concentration. South African Journal of Botany 74: 260-267.
White A (2006) The effect of geography, cultivation and harvest technique on the umkalin concentration and growth of Pelargonium sidoides (Geraniaceae). MSc, Rhodes University.
Microevolution of and ecophysiology of Chrysanthemoides.
Preliminary DNA research suggested that there are several sub-species of Chrysnathemoides and it appears as if these may be correlated with distinct climates. We determined if the different sub-species had different ecophysiological characteristics and whether these were maintained when plants were grown under the same conditions. These characteristics gave insight to the forces driving the microevolution of Chrysanthemoides.
Barker NP, Von Senger I, Howis S, Zachariades and Ripley BS (2004) Plant phylogeography based on rDNA ITS sequence data: two examples from the Asteraceae. “Plant species-level systematics: patterns, processes and new applications” Edited by FT Bakker, LW Chatrou, B Gravendeel & PB Pelser . Koeltz, Königstein. Regnum Vegetabile: 142.
The effects of smoke on whole plant photosynthesis.
Smoke contains active ingredients that have powerful effects on seedling germination and physiology. Our work has shown that brief exposures to smoke also affect whole plant physiology and smoke elicits both a stomatal response and has direct effects on photosynthetic carboxylation processes.
Gilbert ME and Ripley BS (2002) The effect of smoke on the gas exchange of Chrysanthemoides monilifera. South African Journal of Botany 68: 525-531.
Alleviating phosphorus stress using mycorrhizae.
Mycorhizae have been shown to increase plant phosphorus uptake under conditions of low soil P. Our research assessed the effects of different inoculants on photosynthesis and biomass accumulation. Results indicated that the major effect was on the chlorophyll content and number of function reaction centres per leaf area and that such effect translated both into photosynthetic performance at the level of gas exchange and biomass accumulation. Results showed that the fluorescence technique was more sensitive for monitoring effect than either the gas exchange or biomass measurement.
Ripley BS, Redfern SP and Dames JF (2004) Photosynthetic and Growth Characteristics of Sorghum inoculated with fertilised with two levels of phosphorus. South African Journal of Science 100: 616-618.
The biofertilisation of crops with Azolla.
Azolla filiculoides is an invasive aquatic fern that can be put to good use as a bio-fertiliser. This research showed that dry-land wheat responds positively to bio-fertilisation with Azolla and quantified the optimal application rates that gave results comparable to the use of N,P,K fertiliser applied at typical rates.
BS Ripley, Kiguli LN and Barker NP (2003) Azolla filiculoides as a biofertiliser of wheat under dryland soil conditions. South African Journal of Botany 69: 295 – 300.