Abstract
Summary The purpose of this study was to test for direct inhibition of rice canopy apparent respiration by elevated atmospheric carbon dioxide concentration ([CO 2 ]) across a range of short‐term air temperature treatments. Rice (cv. IR‐72) was grown in eight naturally sunlit, semiclosed, plant growth chambers at daytime [CO 2 ] treatments of 350 and 700 μmol mol −1. Short‐term night‐time air temperature treatments ranged from 21 to 40 °C. Whole canopy respiration, expressed on a ground area basis ( R d ), was measured at night by periodically venting the chambers with ambient air. This night‐time chamber venting and resealing procedure produced a range of increasing chamber [CO 2 ] which we used to test for potential inhibitory effects of rising [CO 2 ] on R d . A nitrous oxide leak detection system was used to correct R d measurements for chamber leakage rate ( L ) and also to determine if apparent reductions in night‐time R d with rising [CO 2 ] could be completely accounted for by L . The L was affected by both CO 2 concentration gradient between the chamber and ambient air and the inherent leakiness of each individual chamber. Nevertheless, after correcting R d for L , we detected a rapid and reversible, direct inhibition of R d with rising chamber [CO 2 ] for air temperatures above 21 °C. This effect was larger for the 350 compared with the 700 μmol mol −1 daytime [CO 2 ] treatment and was also increased with increasing short‐term air temperature treatments. However, little difference in R d was found between the two daytime [CO 2 ] treatments when night‐time [CO 2 ] was at the respective daytime [CO 2 ]. These results suggest that naturally occurring diurnal changes in both ambient [CO 2 ] and air temperature can affect R d . Because naturally occurring diurnal changes in both [CO 2 ] and air temperature can be expected in a future higher CO 2 world, short‐term direct effects of these environmental variables on rice R d can also be expected.