Evolution and ecology of C4 photosynthetic grasses
One of my main research interests is the comparative ecology and ecophysiology of C3 and C4 grasses. The evolution of the first C4 grasses is likely to have occurred 30 million years ago in response to declining atmospheric CO2 concentrations. However, the expansion of C4 dominated grasslands is much more recent and requires a more complex explanation than that offered by the CO2 starvation hypothesis alone. This has revived an interest in the different responses of C3 and C4 species to abiotic and biotic factors and prompted our interest in investigating C3 and C4 plant responses to atmospheric CO2 supply, nutrients, water-availability, fire, herbivory and their interactions.
C4 photosynthesis in the grasses has multiple origins along various ancestral lines and hence such investigations must account for phylogeny. Our experimental approach has been two-fold: firstly to investigate responses using Alloteropsis semialata,a unique species that has both C3 and C4 subspecies; and then to investigate if the observed responses have more general application by selecting species for comparison from a robust grass phylogeny. Hence, we able to determine if the observed responses are the result of photosynthetic pathway or ancestral lineage.
This project has been a close collaboration with from Dr Colin Osborne from Sheffield University, UK (http://www.shef.ac.uk/aps/staff/acadstaff/Osborne.html) and is ongoing with both NRF and NERC support and opportunities for both MSc, PhD and Postdoctoral studies.
Ibrahim DG, Gilbert ME, Ripley BS and Osborne CP (2008) Seasonal differences between the C3 and C4 subspecies of Alloteropsis semialata are offset by frost and drought. Plant, Cell and Environment 31: 1039-1050.
Osborne CP, Wythe EJ, Ibrahim DG, Gilbert ME and Ripley BS (2008) Low temperature effects on leaf physiology and survivorship in the C3 and C4 subspecies of Alloteropsis semialata. Journal of Experimental Botany 59: 1743-1754.
Cunniff J, Osborne CP, Ripley BS, Charles M and Jones G (2008) Response of wild C4 crop progenitors to sub-ambient CO2 highlights a possible role in the origin of agriculture. Global Change Biology 14: 576-587.
Ripley BS, Abraham TI and Osborne CP (2008) Nitrogen-limitation causes differential partitioning of growth in C3 and C4 subspecies of Alloteropsis semialata. Journal of Experimental Botany 59: 1705-1714.
Ripley BS, Gilbert ME, Ibrahim DG and Osborne CP (2007) Drought constraints on C4 photosynthesis: stomatal limitation and electron sinks in C3 and C4 subspecies of Alloteropsis semialata. Journal of Experimental Botany 58: 1351 - 1364.
Drought resistance: challenging the textbooks. Planet Earth, Summer, 2007, p.8.
Ibrahim DG (2007) The C3 and C4 subspecies of Alloteropsis semialata: phylogenetic relationship and climatic responses. PhD, Sheffield University.
Abraham TI (2007) Photosynthetic and growth response of C3 and C4 subspecies of Alloteropsis semialata to nitrogen supply. MSc, Rhodes University.
Frole KM (2008) Drought responses of C3 and C4 (NADP-ME) Panicoid grasses. MSc, Rhodes University.