Melatonin, a ubiquitous molecule found in almost all organisms, is considered an important regulator in plant growth. However, little is known about the interactive effect of melatonin and arbuscular mycorrhizal (AM) fungi on plant resistance against soil salinity and alkalinity. To fill in such a gap in knowledge, we conducted three experiments to explore (1) whether exogenous melatonin and an AM fungus had interactive effects on plant response to saline-alkaline stress, (2) whether the influence of melatonin on mycorrhizal plant stress tolerance was attributable to effect on the AM fungus, and (3) whether the effect of melatonin application was due to changes in soil salinity and alkalinity. We found interactive effects between melatonin and the AM fungus on alleviating ROS burst, decreasing malondialdehyde content and protecting Leymus chinensis photosynthetic activity through activation of antioxidant enzyme and gene expression (superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase) in plant shoots and roots. Our results showed that exogenous melatonin promoted spore germination and hyphal length of the AM fungus under Petri-dish conditions. However, exogenous melatonin application did not exhibit significant effects on soil salinity and alkalinity. This study provides an insight into the beneficial effects of exogenous melatonin on saline-alkaline stress tolerance in mycorrhizal L. chinensis through regulating antioxidant systems, protecting photosynthetic activity, and promoting associated AM fungal growth without changing soil salinity and alkalinity. It also reveals potential applications of exogenous melatonin and AM fungi for the restoration of saline-alkaline degraded grassland.

中文翻译：

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外源褪黑素和根瘤菌根内辐射作用对羊草生理盐水耐盐性的影响。

褪黑激素是在几乎所有生物体中普遍存在的分子，被认为是植物生长的重要调节剂。但是，关于褪黑素和丛枝菌根（AM）真菌对植物抵抗土壤盐分和碱度的相互作用的影响知之甚少。为了填补知识上的空白，我们进行了三个实验以探索（1）外源褪黑素和AM真菌是否对植物对盐碱胁迫的反应具有交互作用，（2）褪黑素是否对菌根植物胁迫耐性具有影响归因于对AM真菌的影响，以及（3）褪黑素施用的影响是否归因于土壤盐度和碱度的变化。我们发现褪黑素和AM真菌之间的相互作用可减轻ROS爆发，降低丙二醛含量并保护羊草通过激活抗氧化酶和植物芽和根中的基因表达（超氧化物歧化酶，过氧化氢酶，抗坏血酸过氧化物酶和谷胱甘肽还原酶）而具有光合作用。我们的结果表明，在培养皿条件下，外源褪黑素促进了AM真菌的孢子萌发和菌丝长度。但是，外源褪黑素的施用对土壤盐分和碱度没有显着影响。这项研究提供了洞悉褪黑素对菌根的L.盐碱耐性的有益作用的见解。通过调节抗氧化剂系统，保护光合作用，促进相关的AM真菌生长，而不会改变土壤盐度和碱度。它还揭示了外源褪黑素和AM真菌在恢复盐碱退化草地方面的潜在应用。