ABSTRACT
Improving photosynthesis in rice: from small steps to giant leaps R. F. Sage, University of Toronto, Canada; and Shunsuke Adachi and Tadashi Hirasawa, Tokyo University of Agriculture and Technology, Japan
1 Introduction
2 Demand functions in C3 plants: biochemical limitations
3 Supply functions in C3 plants: diffusion limitations
4 Strategies for improving photosynthetic performance
5 Future trends and conclusion
6 Where to look for further information
7 References
There is currently much interest in improving crop yields to meet projected demands for agricultural commodities, which are expected to roughly double by 2050 (Tilman et al., 2011; Ray et al., 2013). The growth in projected demand results from a combination of increase in food requirements due to population growth, changing economic and social conditions that favour meat consumption, and the cultivation of new biofuel and fibre crops (Ray et al., 2012; Long et al., 2015). In addition, productivity enhancements will need to compensate for yield stagnation due to soil erosion, salinization, higher fertilizer costs, urbanization and climate change-induced stress (Sheehy and Mitchell, 2011; Ray et al., 2012). As a crop of warm climates with high water requirements, rice is particularly vulnerable to yield losses in future climates; for example, for each 1°C rise in mean minimum temperature during the growing season, rice yields are predicted to decline by 10% (Peng et al., 2004). Much of the increase in production can be realized through improved crop management, introduction of new varieties with superior disease resistance and elevated CO2 concentrations. These options are not expected to fully meet future demand because they are approaching their respective limits of effectiveness, at least in developed nations (Sheehy and Mitchell, 2011). The success of new breeds, modern fertilization regimes, pesticide use and scientific management has enabled crop production to approach yield ceilings determined by available sunlight, local climate and the ability of rice plants to convert solar radiation into usable biomass (Sheehy et al., 2007;
Sheehy and Mitchell, 2011). As a crop approaches its yield ceiling, traditional improvement strategies will encounter diminishing returns, and it will become necessary to raise the ceiling to significantly enhance yield. To increase yield ceilings, improvements are required in the efficiency at which photosynthesis converts solar energy into biomass (Sheehy and Mitchell, 2011).
