In the last years globally, daily night-time low temperatures have increased more than twice compared with maximum temperatures. There is little evidence about maize growth and yield responses to high night temperature (HNT) under field conditions. In this study, we aimed to (i) evaluate the effect of HNT during post-flowering on kernel number (KN), crop growth rate expressed in chronological days and thermal units (CGR_D and CGR_TU, respectively), radiation use efficiency (RUE), night respiration (Rn), net photosynthesis (Amax), chlorophyll fluorescence and cell membrane stability (CMS), and (ii) identify associations among the measured physiological traits. Two hybrids (Te, temperate; and St, subtropical) were exposed to two thermal conditions from R1 + 2d to R1 + 16d: (i) HNT from 1900 to 0700 h, and (ii) ambient night temperature (ANT). The HNT resulted in reductions in KN (8%), CGR_D (11%), and CGR_TU (19%), with non-significant changes in kernel weight and grain yield. Reductions in KN were better explained by drops in CGR_TU than in CGR_D. Under HNT, Amax significantly decreased (p < 0.05; 17%, among experiments and hybrids) with insignificant changes in CMS and chlorophyll fluorescence. HNT caused a larger effect on Rn in Te (+40%) than in St. We found a strong negative relationship between Rn and Amax, indicating that high Rn might exhibit an indirect effect on Amax, altering carbon balance and growth.

中文翻译：

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玉米开花后夜间高温会增加夜间呼吸并减少光合作用、生长和籽粒数量

在过去的几年中，全球每日夜间低温与最高温度相比增加了两倍以上。几乎没有证据表明玉米在田间条件下的生长和产量对夜间高温 (HNT) 的反应。在这项研究中，我们旨在 (i) 评估 HNT 在开花后对籽粒数 (KN)、以实际天数表示的作物生长速率和热单位 (CGR _D和 CGR _{TU ) 的影响}，分别），辐射利用效率（RUE），夜间呼吸（Rn），净光合作用（Amax），叶绿素荧光和细胞膜稳定性（CMS），以及（ii）确定测量的生理特征之间的关联。两个杂交种（Te，温带；和 St，亚热带）暴露于从 R1 + 2d 到 R1 + 16d 的两种热条件：（i）从 1900 到 0700 小时的 HNT，和（ii）环境夜间温度（ANT）。HNT 导致 KN (8%)、CGR _D (11%) 和 CGR _TU (19%) 减少，而籽粒重量和籽粒产量没有显着变化。_{与 CGR D}相比， CGR _TU的下降更好地解释了 KN 的减少。在 HNT 下，Amax 显着下降 ( p < 0.05; 17%，在实验和杂交种中）CMS 和叶绿素荧光变化不大。HNT 在 Te (+40%) 中对 Rn 的影响比在 St 中更大。我们发现 Rn 和 Amax 之间存在很强的负相关关系，这表明高 Rn 可能对 Amax 产生间接影响，从而改变碳平衡和增长。