Bimetallic Zn–Mn Nanocomposites Using Peganum harmala for Alleviating Salinity Stress in Sporobolus ioclados

The synthesis of nanoparticles via the green route is the safest and most effective method, as it preserves both economic and environmental safety standards to evaluate their novel role as foliar application, mitigating salt stress (350 and 450 mM NaCl) in halophytic grass Sporobolus ioclados. Salinity is a major abiotic stress that severely constrains plant growth and productivity in arid and semi-arid environments. Analysis of ZnO and MnO Nanoparticles and ZnMn nanocomposites relied on X-ray diffraction, UV spectroscopy, and scanning electron microscopy methods. UV spectroscopy confirmed the absorption characteristics of ZnO NPs at (290 nm-360 nm), MnO NPs at (290 nm), and ZnMn oxide nanocomposites (292 nm, 360 nm), indicating the successful synthesis of nanomaterial. Salinity (350 and 450 mM NaCl) had a significant negative impact on vegetative growth and biochemical parameters of S. ioclados (p < 0.05). Foliar application of Zinc oxide nanoparticles alleviated the impact by promoting growth and biochemical parameters with an approximate increase of 25–40% compared to salt-stressed plants. ZnO NPs offered the best growth results, with the longest shoots (76.67 cm) and roots (52.33 cm), and the highest flower count of 11. Manganese oxide nanoparticles observed maximum height (140.67 cm) followed by ZnMn oxide nanocomposites (139.67 cm), while the most biomass was noted (25.67 g), compared to (25.33 g) when nanocomposites were sprayed under salt stress. MnO NPs (0.25 g) resulted in the maximum increase in peroxidase activity (3.88 ± 0.44), which exhibited robust soluble proteins (2.367 ± 0.321) and phenolic contents (2.065 ± 0.082). Nanocomposite treatments significantly enhanced biochemical responses under salt stress, with the highest total soluble proteins (2.37) indicating improved antioxidant defence. Our results expand the current understanding that Peganum harmala extract is rich in phytochemicals and effective for the synthesis of green nanoparticles, which improves salinity tolerance and plant productivity. This study demonstrates, for the first time, that foliar nanoparticles and nanocomposites enhance the productivity potential of halophytic grasses under extreme stress by establishing a highly efficient, dual-element biogenic synthesis route, offering a scalable approach to restore marginal lands in arid regions.