Nano-iron modulates salt stress responses in Lycium barbarum via enhanced nutrient uptake, antioxidant defense, and phenolic metabolism.

While goji berry (Lycium barbarum) exhibits moderate to high salt tolerance, prolonged or high salinity can still impair its growth, water relations, and metabolism, especially in arid and saline regions. Despite its agronomic and pharmaceutical value, the combined effects of salinity and foliar-applied nano-iron remain largely unexplored. This study investigated the interactive impacts of salinity (0, 150, and 300 mM NaCl) and foliar nano-iron (0, 15, and 30 µM Fe-NPs) on physiological performance, nutrient dynamics, antioxidant responses, and secondary metabolite accumulation in hydroponically grown goji berry under controlled greenhouse conditions. Treatments were arranged in a factorial design with three replicates. Salinity significantly reduced biomass, chlorophyll content, and relative water content, while increasing oxidative damage indicators such as malondialdehyde, hydrogen peroxide, and electrolyte leakage. Foliar nano-iron, particularly at 15 and 30 µM, mitigated these effects by enhancing antioxidant enzyme activities (catalase, ascorbate peroxidase, guaiacol peroxidase, superoxide dismutase), promoting osmolyte accumulation, and improving membrane stability. Furthermore, nano-iron improved nutrient homeostasis under salt stress. At 150 mM NaCl, Fe-NPs increased uptake of key macronutrients (N, P, K⁺) and micronutrients (Fe2⁺, Zn2⁺), while reducing harmful Na⁺ and Cl⁻ accumulation. However, these benefits were diminished under severe salinity (300 mM), likely due to stress-imposed nutrient uptake limitations. HPLC profiling identified nine major polyphenolics, including six phenolic acids and three flavonoids. Moderate salinity (150 mM NaCl) reduced most compounds, whereas nano-iron, particularly at 30 µM, enhanced chlorogenic acid and quercetin, with modest effects on rutin. These compound-specific shifts, together with increases in PAL activity, total phenolics, flavonoids, and antioxidant capacity, indicate selective activation of the phenylpropanoid pathway under nano-iron supplementation. These findings highlight the potential of foliar nano-iron application to improve crop resilience and phytochemical quality in saline environments, though field validation under soil-based systems remains necessary.