Abstract: To explore the effects of exogenous melatonin on antioxidant capacity and nutrient uptake of plants under drought stress, we used Lolium perenne and Medicago sativa potted seedlings for foliar spraying and root application of 100 μmol·L^-1 melatonin, respectively. We measured the biomass, malondialdehyde (MDA) content, relative conductivity, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities, as well as nutrient contents (organic carbon, total nitrogen, total phosphorus) under drought stress. The results showed that the biomass of L. perenne and M. sativa decreased significantly under drought stress, and that external melatonin application could effectively alleviate the inhibitory effect of drought stress on L. perenne and M. sativa. Foliar spray and root application of melatonin under drought stress enhanced L. perenne biomass by 14.5% and 29.6%, and that of M. sativa by 36.6% and 49.1%, respectively. The SOD and POD activities in L. perenne and SOD activity in M. sativa significantly decreased under drought stress, and exogenous melatonin significantly increased SOD, POD and CAT activities in L. perenne and M. sativa, reduced the accumulation of MDA in leaves, caused a significant decrease in the relative conductivity of leaves, and significantly increased antioxidant capacity. Drought stress and exogenous melatonin did not affect organic carbon content of L. perenne and M. sativa. Under drought stress, the contents of N and P in L. perenne leaves and roots and the content of N in M. sativa roots decreased, while the application of melatonin increased the contents of N and P in roots and leaves of L. perenne and M. sativa, indicating that melatonin could regulate the nutrient absorption of L. perenne and M. sativa under drought stress. In conclusion, the melatonin application not only improved the antioxidant capacity of plants, but also regulated nutrient uptake to enhance plant resilience to drought stress. Foliar spraying of melatonin was more effective than root application.

Key words: drought stress, melatonin, nutrient content, oxidation resistance