Eco-safe potential of FITC-tagged nFeO in enhancing alfalfa-rhizobia symbiosis and salt stress tolerance via physicochemical and ultrastructural modifications

Salt stress severely limits global crop productivity by disrupting ionic balance, physiological processes, and cellular ultrastructure, particularly in salt-sensitive forages like alfalfa (Medicago sativa L). Addressing this issue requires environmentally feasible and innovative strategies. This study investigated the comparative potential of Nano-FeO and FeSO₄ (30 mg kg^-1) soil supplements with rhizobium on alfalfa salt tolerance employing morphological, physicochemical, and cellular approaches. The results demonstrated that FITC-nFeO and rhizobium significantly reduced Na⁺ uptake, enhanced K⁺ accumulation, and improved the Na⁺/K⁺ ratio in alfalfa roots and shoots relative to FeSO₄. Scanning electron microscopy illustrated that FITC-nFeO ameliorated root ultracellular structure and leaf stomatal functionality, facilitating improved gaseous exchange characteristics and photosynthetic performance. Confocal laser scanning microscopy confirmed FITC-tagged nFeO adhesion to roots, supported by transmission electron microscopy findings of preserved chloroplast ultrastructure under FITC-nFeO and rhizobium application. FITC-nFeO also mitigated oxidative damage of ROS, as evidenced by reduced hydrogen peroxide, electrolyte leakage, and thiobarbituric acid reactive substances (TBARS) content, through enhanced antioxidant enzyme activities. Overall, in comparison to FeSO₄, FITC-nFeO with rhizobium retrieved the salt-induced damages in alfalfa by promoting morpho-physiological and ultracellular integrity. This study highlights the role of nanotechnology in enhancing the resilience of forages on salt-contaminated soils, paving the way for eco-friendly remediation strategies.