Soybean is usually grown under rain-fed conditions, and long-term drought stress often occurs with short-term heat stress. This study aimed to investigate changes in the photosynthetic characteristics of subtending leaves and their relationships with pod development under short-term heat, long-term drought and their combined stresses. Short-term heat stress lasted for 5 days began at R5 stage, and long-term drought stress lasted from R5 stage until maturity, respectively. No significant effect was observed on pod development under short-term heat stress alone due to unaffected net photosynthetic rate after treatment and PSII recovery after the heat stress release. Except that the reduction of sucrose content had been brought forward from 12 to 5 days after treatment under combined stresses, application of combined stresses caused similar responses to long-term drought stress alone on the photosynthetic characteristics of subtending leaves and pod development, but more pronounced under combined stresses. Reduced pod weight and seed weight per pod under long-term drought stress alone or combined stress due to a decrease in the net photosynthetic rate and production of sucrose and starch, especially after 19 days of treatment. Findings from this study demonstrate that under combined stress, long-term drought stress had a dominant effect on the photosynthetic performance of subtending leaves and pod development over short-term heat stress; moreover, even short-term heat stress also exacerbates the negative effects of long-term drought stress.

中文翻译：

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高温、干旱和复合胁迫下对生叶片光合特性及其与大豆荚果发育的关系

大豆通常在雨养条件下生长，长期干旱胁迫往往伴随着短期热胁迫。本研究旨在探讨短期高温、长期干旱及其复合胁迫下对生叶片光合特性的变化及其与荚果发育的关系。分别从R5期开始持续5天的短期热胁迫，从R5期开始持续至成熟期的长期干旱胁迫。由于处理后的净光合速率和热胁迫释放后的 PSII 恢复未受影响，单独短期热胁迫下对荚果发育没有观察到显着影响。除了蔗糖含量的减少在联合应激处理后 12 天提前到 5 天外，联合胁迫的应用在对向叶片和豆荚发育的光合特性上引起了与单独的长期干旱胁迫相似的反应，但在联合胁迫下更为明显。由于净光合速率以及蔗糖和淀粉产量的降低，特别是在处理 19 天后，在单独长期干旱胁迫或联合胁迫下，豆荚重量和每个豆荚的种子重量减少。这项研究的结果表明，在复合胁迫下，长期干旱胁迫对短期热胁迫对对叶和豆荚发育的光合性能有显着影响；此外，即使是短期的热胁迫也会加剧长期干旱胁迫的负面影响。