THE ORIGIN OF A C4 SPECIES? EVOLUTION AND ATMOSPHERIC INTERACTIONS IN C3 AND C4 SUBTYPES OF ALLOTEROPSIS SEMIALATA

The genetic origins of C₄ photosynthesis and the environmental drivers of its success are major unresolved questions in evolutionary biology. How did this complex genetic trait evolve in more than 30 independent groups? And how did changes in atmospheric CO₂, climatic warmth and the seasonality of rainfall interact with the ecological success of C₄ species? Here we investigate the origin, evolution and environmental interactions of C₄ photosynthesis in Alloteropsis semialata, the only species yet discovered with C₃ and C₄ subspecies. We present the first findings from a long-term study of this unique African grass, utilizing complimentary molecular genetic, physiological and ecological approaches to address evolutionary problems. Molecular genetic techniques test the hypothesis of an allopolyploid origin for the C₄ subspecies, the wholesale acquisition of C₄ genes in the C₃ subtype by hybridisation followed by chromosome doubling. Experiments using controlled environment systems analyse the extent to which physiological advantages of the C₄ subtype over its C₃ counterpart in sub-ambient CO₂ and warm temperatures translate into growth, reproduction and survival responses. Finally, field transplant and irrigation experiments at an arid site in South Africa test the seasonal physiological and growth responses of C₃ and C₄ subtypes to temperature and rainfall. By integrating the results of these experiments, we aim to produce an in-depth understanding of C₄ evolution in A. semialata, thereby uncovering mechanisms of more general importance for the evolution and expansion of C₄ plants.