Effect of Melatonin on Concentrations of Some Elements and Solubility Substance in Vigna radiata (L.) R. Wilczek Plant Affected by Drought Stress

Melatonin, a well-known plant growth regulator, has gained attention for its multifaceted role in enhancing plant resilience to environmental stresses. A field experiment was conducted during the 2021–2022 growing season in the Botanical Garden of the Department of Biology at the College of Education for Pure Sciences, Ibn Al-Haitham, University of Baghdad, to investigate the effects of foliar spray with varying concentrations of melatonin (0, 50, 100, 150, and 200 ppm) on mung bean (Vigna radiata L.) under drought stress condition. Drought conditions were simulated through three irrigation intervals: every 5 days (control), 10 days, and 15 days. The results indicated that extending the irrigation interval significantly reduced levels of critical plant characteristics, including nutrient and carbohydrate content. However, foliar application of melatonin at increased concentrations effectively mitigated drought stress, enhancing the rates of nitrogen, potassium, phosphorus, protein, and carbohydrate contents in mung beans. Melatonin at 150 ppm proved most effective, leading to notable increases of 75.19% in soluble protein, 47.1% in carbohydrate content, 8.3% in nitrogen content, and 41.4% in potassium content compared to control plants. In contrast, drought stress reduced potassium, protein, and carbohydrate levels by 41.3%, 42.2%, and 11.0%, respectively. These findings highlight melatonin's substantial mitigating effects on nutrient losses and stress-related declines in plant health.