Table_3_Exogenous Melatonin Modulates Physiological Response to Nitrogen and Improves Yield in Nitrogen-Deficient Soybean (Glycine max L. Merr.).xls

Melatonin (MT) is a key plant growth regulator. To investigate its effect at different growth stages on the yield of soybean under nitrogen deficiency, 100 μM MT was applied to soybean supplemented with zero nitrogen (0N), low nitrogen (LN), and control nitrogen (CK) levels, during the plant vegetative growth (V3) and filling (R5) stages. This study revealed that the application of MT mainly enhanced the nitrogen fixation of plants by increasing the root nodule number and provided more substrates for glutamine synthetase (GS) under 0N supply. However, under the LN supply, more ammonium was assimilated through the direct promotion of nitrate reductase (NR) activity by MT. MT enhanced the activity of ammonium-assimilation-related enzymes, such as GOGAT and GDH, and the expression of their coding genes, promoted the synthesis of chlorophyll and amino acids, and increased the photosynthetic capacity under nitrogen deficiency. Exogenous MT directly upregulated the expression of genes involved in the photosynthetic system and stimulated dry-matter accumulation. Thus, MT alleviated the inhibitory effect of nitrogen deficiency on soybean yield. This mitigation effect was better when MT was applied at the V3 stage, and the seed weight per plant increased by 16.69 and 12.20% at 0N and LN levels, respectively. The results of this study provide a new theoretical basis to apply MT in agriculture to improve the resilience of soybean plants to low nitrogen availability.

褪黑素（Melatonin，MT）是一类关键的植物生长调节物质。为探究其在不同生育期对缺氮条件下大豆产量的调控效应，本研究在大豆营养生长期（V3）与籽粒灌浆期（R5），分别对施加零氮（0N）、低氮（LN）及正常氮（CK）水平的大豆喷施100 μM浓度的MT。本研究结果表明，在零氮供给条件下，MT主要通过增加根瘤数目强化植株固氮能力，为谷氨酰胺合成酶（glutamine synthetase，GS）提供更多底物；而在低氮供给条件下，MT可直接促进硝酸还原酶（nitrate reductase，NR）活性，从而加速更多铵态氮的同化进程。MT还可提升铵态氮同化相关酶（如谷氨酸合酶GOGAT、谷氨酸脱氢酶GDH）的活性及其编码基因的表达水平，促进叶绿素与氨基酸的合成，增强缺氮环境下植株的光合能力。外源施加的MT可直接上调光合系统相关基因的表达，并促进干物质积累。综上，MT可缓解缺氮胁迫对大豆产量的抑制作用，且在V3期喷施的缓解效果更为显著：在零氮与低氮条件下，单株籽粒重量分别提升16.69%与12.20%。本研究结果为MT在农业生产中的应用提供了全新的理论基础，有助于提升大豆植株对低氮养分环境的抗逆适配能力。