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

ABSTRACT Salinity stress is a major global constraint to agriculture, limiting plant growth and productivity. Exogenous application of ZnSO 4 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 ZnSO 4 ·7H 2 O (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% ZnSO 4 under salinity stress. The results revealed that 0.1% ZnSO 4 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% ZnSO 4 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 ZnSO 4 via coordinating physio‐chemical performance and molecular signaling to achieve ecological resilience.