Melatonin (MT) is involved in physiological processes in plants under abiotic stress. In this study, we investigated the effects of melatonin on maize photosynthetic and antioxidant capacities under salinity stress. Our findings indicated salinity stress significantly inhibited maize growth. However, exogenous MT promoted maize growth and antioxidant capacity. Superoxide dismutase, peroxidase, and catalase increased by 138.8, 38.7, and 32.0%, respectively, while H2O2 and malondialdehyde decreased by 23 and 31%, respectively. Exogenous MT also improved maize photosynthesis under salinity stress. Net photosynthetic rate, transpiration rate, and stomatal conductance increased by 134, 67.2, and 46.3%, respectively. Maximum quantum yield of PSII photochemistry, effective quantum yield of PSII photochemistry, photochemical quenching coefficient, and electron transport rate increased by 5.8, 70.4, 65.3, and 41.0%, respectively. Therefore, our findings suggested exogenous MT significantly ameliorated maize physiological and photosynthetic adaptation under salinity stress, thereby providing helpful guidance for maize cultivation in areas of high salinity. Highlights • Exogenous melatonin (MT) mediated physiological and photosynthetic adaptation in sweet corn • Exogenous MT maintained the balance of ROS metabolism under salinity stress • Exogenous MT ameliorated salinity-induced damages of sweet corn seedlings et al. 2020). Several studies have reported a significant decline in growth and biomass yield of plants under salinity stress (Ahanger et al. 2018, Alam et al. 2019). The effects of salinity stress on photosynthesis have several outcomes. A decrease in stomatal conductance leads to a decrease in carbon dioxide assimilation. Moreover, salinity stress is associated with a decrease in chlorophyll (Chl) content,
