The role of exogenous melatonin in modulating root morphology and physiological response to drought in soybean seedlings

Abstract This study investigated how melatonin helps soybean seedlings grow in drought conditions by studying root morphology and physiological characteristics in the 'Suinong 26' variety. The experiment started at the V2 stage with water control and melatonin spraying. Three treatments were established: drought stress (D), drought stress with melatonin spraying (D + M), and normal water supply as control. The study compared the effects of melatonin spraying on the growth of soybean seedling roots and shoots. Compared to control, D treatment inhibited soybean seedling growth significantly. D + M treatment increased root length, volume, and dry weight on days 10 and 20. Root activity and antioxidant enzyme activities, as well as sugar and protein contents, also increased on days 3, 6, and 9. Root morphological and physiological indicators were significantly improved, correlating positively with shoot photosynthesis and dry matter accumulation. Melatonin spraying enhances soybean seedling growth under drought stress by regulating root characteristics and key physiological factors, leading to improved photosynthesis, shoot development, and dry matter accumulation.