Effects of high temperature and CO2 concentration on spikelet sterility in indica rice

The effects of increasing temperature and CO2 concentration on floral sterility were examined for rice (cv. IR 72) using open-top chambers located at the International Rice Research Institute in Los Banes, Philippines. The field-based open-top chamber system was used to simulate four different environments: ambient temperature and CO2 concentration (control); ambient temperature, ambient +300 mu l l(-1) CO2; ambient +4 degrees C temperature, ambient CO2 concentration; ambient +4 degrees C temperature, ambient + 300 mu 1 l(-1) CO2. High temperature during flowering resulted in increased pollen sterility with the degree of sterility exacerbated if rice was exposed to both high temperature and increased CO2 concentration. The critical air temperature for spikelet sterility (as determined from the number of germinated pollen grains on the stigma) was reduced by ca 1 degrees C at elevated concentrations of carbon dioxide. We speculate that this downward shift in critical temperature may be due to the observed increase in air temperature within the canopy at high CO2 concentrations. This increase in air temperature, in turn, may be related to stomatal closure and reduced transpirational cooling in an elevated CO2 environment. Data from this experiment indicate that increasing CO2 concentration could limit rice yield if average air temperature increased simultaneously.