Photosynthetic acclimation to elevated atmospheric CO₂ concentration ([CO₂]) accompanies decreased leaf nitrogen (N) content. Elevated air temperatures may enhance crop N nutrient content. Whether enhanced leaf N content at high temperatures relieves photosynthetic acclimation to high [CO₂] in rice is unclear, so we investigated the effects of elevated [CO₂] (eC; ambient [CO₂]+200 μmol mol⁻¹ CO₂ and ambient temperature), elevated air temperature (eT; ambient+1 °C), and elevated temperature and [CO₂] together (eT + eC; ambient+1 °C +200 μmol mol⁻¹ CO₂) compared to ambient [CO₂] and temperature (Ambient) on photosynthetic and physiological parameters, biomass, and N accumulation and distribution throughout rice grain filling stages in 2015 and 2016. Net leaf photosynthesis (P_n) increased under eC, but the magnitude of P_n increase decreased as grain filling progressed, which was exacerbated under eT + eC. The total leaf N (TLN) content decreased by 7.1 % and increased by 4.7 % on average during the whole grain filling stage under eC and eT compared with Ambient, respectively. However, increasing TLN under elevated temperature did not offset the TLN reduction under [CO₂] enrichment, similar to the effects of elevated [CO₂] and air temperature on chlorophyll (Chl) and carotenoid (Caro) content. The percentage decrease in Rubisco content was larger under individual changes or the combined elevation of [CO₂] and air temperature than the percentage change in TLN under eC. Meanwhile, the maximum rate of Rubisco carboxylation at 25 °C (V_cmax25) and the maximum rate of electron transport driving RuBP regeneration at 25 °C (J_max25) declined significantly under eT + eC. V_cmax25 had a positive relationship with Rubisco content, and J_max25 had a positive relationship with Chl and Caro content. At the crop level, eC enhanced biomass but reduced N distribution in leaves. Furthermore, the decrease in biomass had a greater effect than the increase in TLN under eT, reducing N distribution in leaves. Photosynthetic acclimation was mainly due to the reduction in TLN and crop N distribution and the increased reduction in leaf N distribution to Rubisco under eT + eC. Therefore, an air temperature increase of approximately 1 °C exacerbated photosynthetic acclimation under eC. These results further elucidated the photosynthesis responses in rice to future climate conditions.

光合适应大气中CO ₂浓度升高（[CO ₂ ]）伴随着叶片氮（N）含量降低。升高的气温可能会增加作物的氮素含量。尚不清楚高温下叶片氮含量的增加是否能缓解水稻对高[CO ₂ ]的光合适应，因此我们研究了升高[CO ₂ ]（eC;环境[CO ₂ ] +200μmolmol ^-1 CO ₂和环境温度），升高的空气温度（eT；环境+1°C）以及升高的温度和[CO ₂ ]一起（eT + eC；环境+1°C +200μmolmol ^-1 CO ₂）_[2 ]和温度（环境温度）对2015年和2016年整个水稻籽粒充实阶段的光合和生理参数，生物量和氮积累和分布的影响。在eC下，净叶片光合作用（P _n）增加，但随着增加，P _n增加的幅度减小籽粒充实进行，在eT + eC下加剧了。与Ambient相比，在eC和eT下，整个籽粒灌浆期的总叶N（TLN）含量分别降低7.1％和平均4.7％。然而，升高的温度下增加的TLN没有偏移下的TLN还原[CO ₂ ]的富集，类似的升高的影响[CO ₂]和空气温度对叶绿素（Chl）和类胡萝卜素（Caro）含量的影响。在单独变化或[CO ₂ ]和空气温度的综合升高下，Rubisco含量的降低百分比大于在eC下TLN的百分比变化。同时，在eT + _eC下，在25°C时Rubisco羧化的最大速率（V _cmax25）和在25°C时驱动RuBP再生的电子传输的最大速率（J _max25）显着下降。V _cmax25与Rubisco含量呈正相关，而J _max25与Chl和Caro含量呈正相关。在作物水平上，eC增强了生物量，但减少了叶片中的氮分布。此外，在eT下，生物量的减少比TLN的增加具有更大的影响，从而减少了叶片中的N分布。在eT + eC下，光合作用的适应主要是由于TLN和农作物N分布的减少以及向Rubisco的叶片N分布的增加的减少。因此，大约1°C的空气温度升高会加剧eC下的光合作用。这些结果进一步阐明了水稻对未来气候条件的光合作用响应。