Abstract: A widely cultivated inbred Japonica rice (Oryza sativa L.) Wuyunjing 23 was grown at two levels of CO₂ (ambient and elevated CO₂ concentration) and two temperature regimes (ambient and elevated temperature) by using a free air CO₂ enrichment (FACE) technology. The diurnal courses (i.e., at 09:00, 11:00, 13:00, 15:00 and 17:00) of leaf photosynthesis at different growth stages of rice were measured, namely 61, 75, 92, 109 and 118 days after transplanting (DAT). Net photosynthetic rate (P_n) and leaf water use efficiency (WUE) of rice on 61 DAT increased nearly 40% by elevated CO₂ concentration (200 μmol·mol^-1 more than ambient CO₂). The increment significantly decreased with the advance of the growth stages, and even disappeared at the late grainfilling stage. A consistent trend of decrease was detected on stomatal conductance (G_s) and transpiration rate (T_r) at different time points on 75, 92 and 109 DAT under elevated CO₂ concentration, and the greatest reduction reached 14% and 5% for G_s and T_r, respectively. Elevated CO₂ concentration had no significant effect on the ratio of intercellular to air CO₂ concentration (C_i/C_a) and stomatal limitation value (L_s) during the early rice growth season, but significantly increased C_i/C_a at the last three growth stages in the range of 4%-8%, resulting in decreases in L_s in the range of 10%-27%. Average temperature increase of 1 ℃ had a positive effect on P_n, G_s, T_r and WUE at the early rice growth stages, but negative effects were found at the late grain filling stages. No clear CO₂ by temperature interaction was detected for most of the measured photosynthetic traits except P_n on 61 DAT. The above results suggested that the elevated atmospheric CO₂ level had a greater effect than the elevated temperature on photosynthetic parameters of Wuyunjing 23. The elevated CO₂ induced photosynthetic down-regulation on rice was observed at two temperature regimes.

Key words: N utilization efficiency., rice, ammonia volatilization, loss-controlled urea