Yield, dry matter distribution and photosynthetic characteristics of rice under elevated CO2 and increased temperature conditions

Abstract Carbon dioxide (CO2)-induced stimulation of the leaf net photosynthetic rate (Amax) is projected to further increase with increasing temperature. Although the impact of rising temperature or CO2 on leaf photosynthesis parameters and dry matter (DM) accumulation and distribution has been widely investigated, less research has been conducted to evaluate the combined effects of these climate change factors on rice in field sites. In this study, the effects of the combination of two levels of CO2 (390 μmol mol−1 and 590 μmol mol-1) and two levels of temperature (no increase and increase of ˜1.5 °C) on the Amax, respiration rate (Rd), leaf biochemical parameters, DM accumulation and distribution and yield of rice were tested in a free air CO2-enrichment (FACE) system. Elevated CO2 dramatically increased DM accumulation before heading; however, rising temperature alone or in combination with CO2 concentration enrichment remarkably reduced DM at the heading stage compared to that under ambient conditions. Therefore, rising temperature leads to a decrease in rice yield, regardless of whether it occurs alone or in combination with high CO2 concentration. The negative effect of rising temperature alone or in combination with elevated CO2 was attributed to a reduced leaf area index, as both treatments had minor or positive effects on Amax and Rd. Increases in Amax and Rd under the combination of elevated CO2 and temperature were linked to improvements in the maximum carboxylation rate of Rubisco (Vc,max) and the maximum electron transport rate (Jmax). Furthermore, the increase in both CO2 and temperature significantly increased Amax compared to that under elevated CO2. Alleviation of the decrease in leaf nitrogen and Rubisco content by the increase in both CO2 and temperature compared to that observed with elevated CO2 alone accounted for the increase in Vc,max and Jmax. These results suggest that future climate conditions will be advantageous for leaf photosynthesis but not for the growth and yield of rice.