Foliar iron and zinc applications mitigate salinity stress in Althaea officinalis L.: Effects on yield, antioxidant responses, and mineral composition

Abstract Foliar application of micronutrients may help alleviate the adverse effects of salinity on crop plants. This study evaluated the effects of foliar‐applied iron (Fe) and zinc (Zn) on Althaea officinalis L. grown under saline conditions. A factorial experiment was conducted using three salinity levels (0, 4, and 8 dS m − 1 , imposed with NaCl) and three concentrations of foliar‐applied Fe and Zn (0, 1.5, and 3 mg L − 1 ). Antioxidant‐related traits, mineral composition, total phenolic content (TPC), and 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical‐scavenging activity were subsequently assessed. Salinity significantly reduced flower number and yield, whereas foliar application of Fe and Zn partly alleviated these reductions. Increasing salinity levels increased the activities of catalase, superoxide dismutase, peroxidase, and polyphenol oxidase, as well as TPC and DPPH radical‐scavenging activity. Foliar application of Fe and Zn, particularly at 3 mg L − 1 , was associated with changes in antioxidant enzyme activities, TPC concentration, and the in vitro DPPH radical‐scavenging activity of leaf extracts under saline conditions. Salinity also decreased the concentrations of nitrogen (N), potassium (K), phosphorus (P), calcium (Ca), and manganese (Mn), while increasing sodium (Na + ) concentration. Foliar Fe and Zn applications partly moderated these salinity‐induced changes in mineral composition. Overall, Fe and Zn application under saline conditions was associated with improved flower production, yield, antioxidant‐related responses, phenolic accumulation, and mineral composition in A. officinalis . These findings suggest that foliar Fe and Zn may have potential for improving the performance of A. officinalis under salinity.