High temperature during early grain‐filling stage is one of the serious abiotic stresses limiting maize yield in the North China Plain. Nitrogen (N) fertiliser has an important role in promoting crop growth, especially under abiotic stresses. However, its contribution to alleviating heat stress (HS) inhibition on maize photosynthesis during early grain‐filling stage is still unclear. Experiments with three N rates (LN, low nitrogen; MN, medium nitrogen; HN, high nitrogen) and two temperature (HS, heat stress; CK, ambient temperature as control) regimes were conducted to examine the effects of increasing N supply on photosynthesis, N assimilation, antioxidant system, and hormones homeostasis of maize during early grain‐filling stage using two maize hybrids Xianyu335 (XY335, heat‐sensitive) and Zhengdan (ZD958, heat‐tolerant). HS negatively affected photosynthesis of both two hybrids, exhibited lower net photosynthetic rate, chlorophyll content and activities of Rubisco and phosphoenolpyruvate carboxylase (PEPC) compared with CK, and then decreased dry matter accumulation of maize, with a lesser extent for ZD958 than XY335. However, increasing N supply alleviated the adverse effects of HS on maize photosynthesis due to improved N assimilation capacity. Under HS condition, greater N content and higher activities of glutamine synthetase and glutamate synthase in maize ear leaf were found in treatment of HN compared with LN and MN. HN with higher N assimilation capacity directly increased the net photosynthetic rate due to improved chlorophyll content, activities of Rubisco and PEPC and antioxidant capacity. HS‐induced abscisic acid (ABA) accumulation was also repressed by HN, and then enhanced the stomatal conductance and transpiration rate to maintain higher photosynthetic capacity compared with LN and MN. Moreover, the positive effects of increasing N supply on maize photosynthesis under HS condition exhibited a larger extent for XY335 than ZD958. As a result of improved photosynthesis and N assimilation capacity by adequate N supply, maize accumulated more biomass under HS, especially for heat‐sensitive hybrid.

中文翻译：

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氮供应通过改善氮同化缓解灌浆早期玉米光合作用的热应激


灌浆前期高温是限制华北平原玉米产量的严重非生物胁迫之一。氮肥对于促进作物生长具有重要作用，尤其是在非生物胁迫下。然而，其在缓解灌浆早期玉米光合作用热应激（HS）抑制方面的贡献仍不清楚。进行了三种施氮量（LN，低氮；MN，中氮；HN，高氮）和两种温度（HS，热应激；CK，环境温度作为对照）方案的实验，以研究增加氮供应对光合作用的影响使用两种玉米杂交种先玉335（XY335，热敏）和郑单（ZD958，耐热）在灌浆早期玉米的氮同化、抗氧化系统和激素稳态。 HS对两个杂交品种的光合作用均产生负面影响，与CK相比，其净光合速率、叶绿素含量以及Rubisco和磷酸烯醇丙酮酸羧化酶(PEPC)的活性较低，进而降低了玉米的干物质积累，其中ZD958的程度小于XY335。然而，增加氮供应由于提高了氮同化能力而减轻了HS对玉米光合作用的不利影响。 HS条件下，与LN和MN处理相比，HN处理玉米穗叶中氮含量更高，谷氨酰胺合成酶和谷氨酸合成酶活性也更高。具有较高氮同化能力的HN由于叶绿素含量、Rubisco和PEPC活性以及抗氧化能力的提高而直接提高了净光合速率。 HS诱导的脱落酸（ABA）积累也被HN抑制，然后增强气孔导度和蒸腾速率，以维持比LN和MN更高的光合能力。此外，在HS条件下增加施氮量对玉米光合作用的积极影响在XY335上表现出比ZD958更大的程度。由于充足的氮供应提高了光合作用和氮同化能力，玉米在HS下积累了更多的生物量，特别是对于热敏性杂交种。