Photosynthesis: Food, Fuel and Global Change
Feeding the world’s current population already requires 15% of the total net primary productivity of globe’s land area and that will need to increase to 25% in order to meet the projected increase in agriculture demand this century. This near doubling of food production will have to be accomplished during a time in which there will be ever increasing demand on cultivated lands for the production of bioenergy crops and biofuels and will have to accomplished in the face of a changing global environment that has already resulted in decreasing global yield of some of the world’s most important crops.
Much effort has been devoted to linking models of climate and crop growth to project future changes in global crop yields and food supply across. Projections from the Intergovernmental Panel on Climate Change suggest that increased temperature and decreased soil moisture, which would otherwise reduce crop yields, will be offset by the direct fertilization effect of rising carbon dioxide concentration ([CO2]). Crops sense and respond directly to rising [CO2] through photosynthesis, and this is the basis for the fertilization effect on yield. In C3 plants, mesophyll cells containing RuBisCO are in direct contact with the intercellular air space that is connected to the atmosphere via stomatal pores in the epidermis.
Hence, in C3 crops, rising CO2 increases net photosynthetic CO2 uptake because RuBisCO is not CO2-saturated in today's atmosphere and because CO2 inhibits the competing oxygenation reaction leading to photorespiration. However, the stimulation of photosynthesis and yield in C3 crops grown under agricultural conditions at [CO2] expected for 2050 are only half that expected. We have shown that three major reasons that C3 crops are not responding optimally to higher [CO2] is that: 1) photosynthesis is not adapted for the higher [CO2], 2) mitochondrial respiration is markedly stimulated and 3) other global change factors suppress the photosynthetic response.