Selenium nanoparticles synthesized using the native Saudi Arabian succulent Aizoon canariense enhance salinity tolerance in maize and soybean

Salinity limits crop productivity by disrupting water relations, ion homeostasis, photosynthesis and cellular redox balance. This study investigated whether selenium nanoparticles green-synthesized using Aizoon canariense extract could improve salinity tolerance in maize ( Zea mays L.) and soybean ( Glycine max L.). Maize was exposed to 0, 75 or 150 mM NaCl and soybean to 0, 50 or 100 mM NaCl, followed by treatment with 0, 0.5, 1.0 or 1.5 mg Se L⁻¹ SeNPs. A. canariense extract and sodium selenite were included as comparative controls. Severe salinity reduced total dry mass by 54.5% in maize and 54.4% in soybean and was accompanied by impaired water status, pigment loss, restricted gas exchange, Na⁺ accumulation, nutrient deficiency and oxidative damage. SeNP application alleviated these effects in a concentration-dependent manner, with 1.0 mg Se L⁻¹ producing the most consistent response. At this concentration, total dry mass increased by 46.0% in severely stressed maize and 45.3% in soybean, while net photosynthesis increased by 55.1 and 60.4%, respectively, relative to the untreated saline controls. SeNPs also improved relative water content and membrane stability, reduced electrolyte leakage, restricted shoot Na⁺ accumulation and restored K⁺, Ca²⁺, Mg²⁺, N and P nutrition. These improvements were associated with enhanced accumulation of compatible solutes and greater activities of superoxide dismutase, catalase, ascorbate peroxidase, guaiacol peroxidase, glutathione reductase and glutathione peroxidase. H₂O₂, superoxide and malondialdehyde concentrations declined markedly. The plant extract and sodium selenite provided partial protection but were generally less effective than the SeNP formulation. A. canariense -mediated SeNPs enhanced salinity tolerance by coordinating osmotic adjustment, ion regulation, antioxidant defence and photosynthetic recovery, with 1.0 mg Se L⁻¹ identified as the optimum concentration under the present conditions.