Zinc Sulfate‐Mediated Modulation of Growth, Physiology, Yield, and Metabolome in Capsicum annuum L. Under Salinity Stress

Salinity stress is a major global constraint to agriculture, limiting plant growth and productivity. Exogenous application of ZnSO₄ offers a potential strategy to mitigate its detrimental effects owing to zinc's vital role in plant metabolism. A preliminary screening using varying concentrations of ZnSO₄·7H₂O (0.025%, 0.05%, 0.1%, 0.2%, and 0.5%) under 50 and 100 mM NaCl in Capsicum annuum L. identified 0.1% as the most effective dose, while 0.5% caused phytotoxicity. To validate these findings, a pot experiment was conducted under natural conditions to evaluate the physio-chemical, ultrastructural, yield and metabolomic responses of Capsicum annuum L. to 0.1% and 0.5% ZnSO₄ under salinity stress. The results revealed that 0.1% ZnSO₄ significantly enhanced stomatal aperture and density, chlorophyll content, photosynthetic efficiency, and relative water content, leading to improved biomass and yield. Untargeted quantitative UHPLC-HRMS metabolomics showed upregulation of phenylpropanoids, amino acids, and fatty acid amides, indicating enhanced antioxidant defense and metabolic signaling for stress tolerance. Conversely, 0.5% ZnSO₄ disrupted cellular homeostasis, increased ROS accumulation and impaired energy metabolism, reflecting oxidative damage. Overall, these findings underscore how Capsicum annuum L. dynamically perceives and responds to salinity and exogenous ZnSO₄ via coordinating physio-chemical performance and molecular signaling to achieve ecological resilience.