Rice Responses to Elevated CO2 Concentrations and High Temperatures

Abstract

Long-term CO2 enrichment experiments under various temperature conditions on “Akihikari” rice were conducted using Temperature Gradient Chambers (TGCs) over 4 growing seasons (1992-1995). Measurements were made of crop biomass production, yield, and water use efficiency (WUE), and also of single leaf photosynthesis and transpiration, to evaluate interactive effects of CO2 and temperature on those attributes. Temperature conditions created in the TGC ranged from 21-30°C on average over entire growth season.Doubling CO2 concentration increased total biomass at maturity by 26% on average. The relative enhancement rate in biomass by doubling CO2 tended to increase slightly with a rise in temperature. The doubling CO2 upward shifted the optimum temperature for single leaf photosynthesis by 5°C. Also it increased yield under near outdoor temperature conditions to a similar extent as the dry matter production. However, the yield decreased drastically with a temperature increase both under the ambient and the doubling CO2, due to spikelet sterility induced by high temperature at the flowering period. Doubling CO2 treatments enhanced WUE by 34% on average over the entire range of temperature conditions. The enhancement rate in WUE was maximal (49%) at 26°C, and decreased with a temperature rise at a rate of 7% per°C. These results suggest that interactive effects of CO2 and temperature on various processes of crop production are key issues for understanding and evaluating crop production under global climate change.