Dry matter and nitrogen accumulation and partitioning in rice (Oryza sativa L.) exposed to experimental warming with elevated CO₂

Effects of elevated CO₂ concentration ([CO₂]) and air temperature (T_air) on accumulation and intra-plant partitioning of dry matter (DM) and nitrogen in paddy rice were investigated by performing a pot experiment in six natural sunlit temperature gradient chambers (TGCs) with or without CO₂ fumigation. Rice (Oryza sativa L.) plants were grown in TGCs for a whole season under two levels of [CO₂] (ambient, 380 ppm; elevated, 622 ppm) and two daily T_air regimes (ambient, 25.2°C; elevated, 27.3°C) in split-plot design with triplication. The effects of elevated [CO₂] and T_air on DM were most dramatic for grain and shoot with a significant (P < 0. 05) interaction between [CO₂] and T_air. Overall, total grain DM increased with elevated [CO₂] by 69.6% in ambient T_air but decreased with elevated T_air by 33.8% in ambient [CO₂] due to warming-induced floral sterility. Meanwhile, shoot DM significantly increased with elevated T_air by 20.8% in ambient [CO₂] and by 46.6% in elevated [CO₂]. Although no [CO₂] × T_air interaction was detected, the greatest total DM was achieved by co-elevation of [CO₂] and T_air (by 42.8% relative to the ambient conditions) via enhanced shoot and root DM accumulation, but not grain. This was attributed largely both to increase in tiller number and to accumulation of photosynthate in the shoot and root due to inhibition of photosynthate allocation to grain caused by warming-induced floral sterility. Distribution of N (both soil N and fertilizer ¹⁵N) among rice parts in responding to climatic variables entirely followed the pattern of DM. Our findings demonstrate that the projected warming is likely to induce a significant reduction in grain yield of rice by inhibiting DM (i.e., photosynthates) allocation to grain, though this may partially be mitigated by elevated [CO₂].