Biogenic Iron Oxide Nanoparticles Confer Induced Pre‐sowing Drought Tolerance in Glycine max via Enhanced Soil‐Plant Physiological Responses

ABSTRACT Drought stress severely affects soybean ( Glycine max L.) growth and productivity by disrupting physiological and metabolic processes. This study evaluated the potential of biogenic iron oxide nanoparticles green synthesised using Pistacia khinjuk L. leaf extract to improve soybean tolerance to water deficit. The iron oxide nanoparticles were characterised using ultraviolet–visible spectroscopy, scanning electron microscopy, Fourier‐transform infrared spectroscopy and X‐ray diffraction. The nanoparticles were applied to soil at concentrations of 0, 25, 50, 75 and 100 ppm under well‐watered conditions at 100% pot capacity and drought‐stressed conditions at 70% pot capacity. Drought stress reduced germination by 22.6%, plant growth by 18.7%–25.0%, and chlorophyll content by 20.5%. Meanwhile, soil application of iron oxide nanoparticles, particularly at 75–100 ppm, improved germination, plant growth and photosynthetic pigment content. Nanoparticle treatments also enhanced enzymatic and non‐enzymatic antioxidant defences and reduced malondialdehyde accumulation, hydrogen peroxide content and electrolyte leakage by up to 49.8%, 43.2%, and 46.7%, respectively. Net photosynthesis, stomatal conductance, relative water content, plant iron accumulation, soil microbial biomass carbon and dehydrogenase activity were also improved. Multivariate analyses indicated strong positive relationships among antioxidant activity, water status, photosynthetic performance and plant growth, whereas oxidative damage indicators were negatively associated with these traits. Overall, soil‐applied biogenic iron oxide nanoparticles improved soybean physiological resilience under controlled drought conditions. However, field‐scale validation and long‐term environmental assessment are required before practical agricultural application.