- • Increasing our understanding of the factors regulating seasonal changes in rice canopy carbon gain (Cgain: daily net photosynthesis – night respiration) under elevated CO2 concentrations ([CO2]) will reduce our uncertainty in predicting future rice yields and assist in the development of adaptation strategies.
- • In this study we measured CO2 exchange from rice (Oryza sativa) canopies grown at c. 360 and 690 µmol mol−1[CO2] in growth chambers continuously over three growing seasons.
- • Stimulation of Cgain by elevated [CO2] was 22–79% during vegetative growth, but decreased to between −12 and 5% after the grain-filling stage, resulting in a 7–22% net enhancement for the whole season.
- • The decreased stimulation of Cgain resulted mainly from decreased canopy net photosynthesis and partially from increased respiration. A decrease in canopy photosynthetic capacity was noted where leaf nitrogen (N) decreased. The effect of elevated [CO2] on leaf area was generally small, but most dramatic under ample N conditions; this increased the stimulation of whole-season Cgain. These results suggest that a decrease in Cgain enhancement following elevated CO2 levels is difficult to avoid, but that careful management of nitrogen levels can alter the whole-season Cgain enhancement.