The outlook for C4 crops in future climate scenarios

Abstract

Several C4 crops dominate a large percentage of current agriculture due to the array of physiological benefits provided by C4 photosynthesis over the ancestral C3 photosynthesis, such as high productivity, resource use efficiency and stress tolerance. It is therefore imperative that we understand both how these crops will fare under future climate scenarios, and how we can further utilise C4 crops to help achieve future food security thresholds. The heightened water use efficiency of C4 plants suggests they may take a more prominent role in agriculture across the world to alleviate some of the future stress on fresh water supplies. However, as temperatures increase, they will begin to exceed the temperature optima of C4 crops such as Zea mays (maize) in key growing areas, which will shape the agricultural landscape of Z. mays and alternative C4 crops. Elevated CO2 has little direct effect on C4 plants due to the carbon concentrating mechanism, however, under water stressed conditions elevated CO2 does provide some drought tolerance to C4 plants due to decreased transpiration. However, the limited positive effects of elevated CO2 will likely not outweigh the stress of increased temperature and reduced water availability. Nevertheless, C4 crops are expected to play a major role in maintaining future food security due to their superior physiological attributes. Looking forward, two approaches to maintain or advance production of C4 crops seem feasible: (1) continued improvement of current crop lines via marker-assisted breeding, cutting-edge gene editing techniques and beneficial farming practices. This could allow current cropping practices to continue into the future without reduced yields. (2) Changes in the geographic distribution of C4 crops. As environments become more suitable, C4 crops will likely be introduced into those areas, while areas currently dominated by C4 crops may require alternative, more resilient species to maintain economic value