Effects of Exogenous Antioxidant Melatonin on Physiological and Biochemical Characteristics of Populus cathayana × canadansis ‘Xin Lin 1’ under Salt and Alkaline Stress

Salt and alkaline stress is one of the important problems restricting agricultural production and afforestation projects. This kind of stress will greatly limit the growth and development of forest trees. Recently, melatonin has been gradually realized as a strong kind of antioxidant due to its important regulatory and protective roles in the process of plant growth and development. This study takes Xin Lin 1 (Populus cathayana × canadansis ‘Xin Lin 1’) as the research object, and measures the changes of physiological indexes at different time points to verify the alleviation effect of melatonin under salt and alkaline stress. In this experiment, plants have different behaviors in the face of different levels of exogenous melatonin. Among them, low concentrations of melatonin (50 μM and 100 μM) were more helpful to reduce the levels of MDA and osmotic regulators in leaves. At this level, the SOD and CAT content in the leaves increased significantly. Melatonin at 800 μM was more inclined to induce POD, but its activity was not significantly induced. Overall, melatonin contributes to the secretion of ABA in plants and has a tendency to inhibit the content of SA. It is worth mentioning that the 100 μM melatonin treatment was more conducive to the secretion of IAA. To sum up, this experiment proves that melatonin has a dose effect in alleviating stress.