The impact of enhanced atmospheric CO2 concentrations on the responses of maize and soybean to elevated growth temperatures

Abstract

In this chapter, we argue that responses of plant growth and yield to CO2 enrichment and to elevated growth temperatures are principally mediated by changes in photosynthesis. Crop plants such as soybean, which possess the C3 cycle, exhibit increased photosynthetic rates in response to CO2 enrichment. Conversely, maize, which uses the C4 cycle, is largely unresponsive to enhanced2 concentrations, except during periods of drought. The yield of each crop species can be predicted by their growth at minimum Tmin, maximum Tmax, and optimum Topt temperatures. The Topt is often higher for vegetative than for reproductive growth and if photosynthetic rates of a particular crop species increase, the Topt for vegetative growth usually increases in response to CO2 enrichment. Another factor strongly influencing crop yields is the duration of reproductive growth, which often becomes shorter as growth temperatures increase. Growing season duration of some crops can also be modified by CO2 enrichment. Since reproductive timing in both soybean and maize is sensitive to photoperiod, adaptation of local varieties may need adjustment as temperatures rise. In summary, CO2 enrichment is capable of mitigating the effects of moderately elevated temperatures on yields of certain crop species but not others. Also, for those plants that respond to elevated CO2, the beneficial effects of CO2 enrichment on yield usually diminish as elevated growth temperatures become stressful.