Application of Fe₃O₄@SiO₂ nanoparticles improves the soil properties, growth performances, physiological and biochemical responses of nettle under water stress

This study investigated whether Fe₃O₄@SiO₂ nanoparticles (Fe-NPs) can alleviate drought stress and improve plant performance and soil function in Urtica dioica L. under water-limited conditions . A factorial greenhouse experiment was conducted with four Fe-NPs concentrations (0, 0.5, 0.75, and 1% w/w) and three irrigation regimes (100%, 75%, and 50% field capacity). The underlying hypothesis was that Fe-NPs enhance iron availability and stress tolerance mechanisms, thereby improving growth, physiological stability, and phytochemical production under drought. Fe-NPs application significantly enhanced soil physicochemical attributes, including water retention, porosity, hydraulic conductivity, and nutrient availability, while promoting microbial activity and enzyme functions. In plants, Fe-NPs mitigated drought-induced growth inhibition by increasing shoot and root biomass, chlorophyll content, relative water content, and water-use efficiency. Biochemical analyses showed that application of Fe₃O₄@SiO₂ nanoparticles increased antioxidant enzyme activities (SOD, CAT, POD), enhanced osmolyte accumulation (proline) and secondary metabolites (phenolics and flavonoids), elevated abscisic acid levels, and reduced lipid peroxidation (MDA), indicating that Fe-NPs improved oxidative stress tolerance under drought. Optimal responses were consistently observed at 0.75% Fe-NPs, particularly under moderate drought. Correlation and principal component analyses highlighted the integrated effects of Fe-NPs in enhancing soil fertility, physiological stability, and stress resilience. Multivariate analyses confirmed the integrative role of Fe-NPs in enhancing physiological resilience and stress adaptation. These findings demonstrate that Fe-NPs act as multifunctional agents that improve nutrient availability, water status, and antioxidant defenses, offering a sustainable nanotechnological approach to bolster plant growth and productivity under drought stress. • Fe₃O₄@SiO₂ nanoparticles improved soil quality, nutrients, and microbial activity under drought. • Nanoparticles enhanced growth, chlorophyll, leaf water content, and water-use efficiency. • Antioxidant enzymes and osmolytes increased, reducing oxidative damage and lipid peroxidation. • Phytochemical levels, including phenolics and flavonoids, were significantly enhanced. • The 0.75% Fe‑NP treatment gave the best physiological and phytochemical responses under drought.