Combined effects of elevated [CO2] and high night temperature on carbon assimilation, nitrogen absorption, and the allocations of C and N by rice (Oryza sativa L.)

To estimate the combined effects of elevated [CO2] and night temperature on C assimilation, N absorption, and their allocations in rice organs, we conducted a pot experiment in controlled-environment chambers with [CO2] at 380 or 680 ppm, night temperatures of 22 or 32 °C, and a 32 °C day temperature. Whole-plant C and N concentrations were unaffected by elevated [CO2] and high night temperature, while C assimilation and N absorption increased significantly under both elevated [CO2] and high night temperature with a significant interaction of [CO2] and high night temperature. C assimilation increased under high night temperatures despite the higher C loss to night respiration. Regarding to part organs of rice, high night temperature significantly increased living leaf N concentration and area (by 7.8% and 14.5%, respectively), and enhanced photosynthetic capacity at last stage of rice growth. Elevated [CO2] did not affect C and N allocations between ear and stem during reproductive growth, but high night temperature significantly decreased C and N allocation to the ears. Because high night temperatures limited the translocation of C and N to the ear, they will reduce the stimulatory effect of elevated [CO2] on rice yield in the future if both [CO2] and temperature continue to increase.