Biogeographic limits of C4 engineered rice

Genetic engineers are attempting to meet increased global food demand by rewiring the pathway crops take to convert sunlight and carbon dioxide (CO2) into yield. Most crops use the C3 pathway. C4 photosynthesis uses a biological pump that concentrates CO2, which makes it less resource demanding than C3 photosynthesis. C4 photosynthesis however uses more energy than C3 photosynthesis, so the advantage of C4 crops diminishes as atmospheric CO2 concentrations increase and temperatures decrease. By estimating the trade-off between traditional C3 and engineered C4 rice, we show C4 rice benefits less productive countries in the tropics rather than the largest producers (China, India). These geographic variations in productivity gains diminish under higher CO2 concentrations and coincide with the likely commercial release of C4 rice. Therefore, C4 rice will have little advantage in terms of productivity over C3 rice without global climate change mitigation. The findings agree with previous
studies that projected declines in C4 grasses as CO2 concentrations increase despite the compensating effects of global warming. Researchers are exploring other yield improvement technologies—the benefits of which are also tied to climatic niches that change over time. Determining the limits of these technologies requires the biogeographic approach adopted in our study.