Sodium Nitroprusside and Melatonin Improve Physiological Vitality and Drought Acclimation via Synergistically Enhancing Antioxidant Response in Dryland Maize

It is critical to improve the adaptability of plants to drought stress through exogenous addition method. This study explored the combined effects of sodium nitroprusside (SNP) and melatonin (MT) on improving drought resilience in dryland maize. We hypothesized that the joint application of SNP + MT would enhance drought resilience through both above- and below-ground interactions. Maize plants were treated with SNP, MT, and a combination of both under different water stress conditions. The combined treatment was observed to significantly improve chlorophyll contents, water use efficiency (WUE), while reducing oxidative stress markers, compared to separate treatments and controls (CK). These improvements led to enhanced plant biomass and yield productivity under the conditions of drought. Specifically, leaf chlorophyll levels increased averagely by 24.22% under well-watered (WW) conditions, and 27.94% under mild water-stressed (MWS) conditions, respectively. In addition, the content of chlorophyll b increased by 13.27 and 56.32% in WW and MWS, respectively. Particularly, the combined treatment resulted in higher WUE, lower oxidative stress, and higher nutrient content [nitrogen, phosphorus, and potassium (NPK)], contributing to improved plant growth and yield. The examination uncovered noteworthy associations (p < 0.05) between these interventions and physiological characteristics, including heightened WUE, diminished oxidative stress, and augmented nutrient content. These factors contributed to the enhancement of plant production and biomass. The research also investigated the effects of microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN). Therefore, the combined application of SNP and MT can act as a promising strategy to enhance drought tolerance in maize, demonstrating a fine potential to improve crop productivity in drought-prone areas.