Engineered magnesium-straw biochar nanocomposite mitigates cadmium toxicity through oxidative stress management and rhizosphere ecological regulation in soybean

Cadmium (Cd) contamination in agricultural soils represents a critical threat to food security and human health through crop bioaccumulation. This study investigated the effectiveness of engineered magnesium-biochar nanocomposites (Mg-BNCs) in mitigating Cd toxicity in soybean ( Glycine max L.) cultivation systems. Mg-BNCs were synthesized through two-stage ball milling of rapeseed straw and Mg citrate before and after pyrolysis, producing nanoscale particles with 16.8 nm average size and 32.74% magnesium content. The greenhouse experiment results demonstrated that Mg-BNCs significantly enhanced plant growth parameters, increasing plant length by 26.5%, fresh weight by 36.3%, and dry weight by 38.2% compared to Cd-stressed controls. The nanocomposites effectively reduced oxidative stress by decreasing hydrogen peroxide and malondialdehyde levels by 33.2% and 33.8%, respectively, while enhancing antioxidant enzyme activities. Photosynthetic efficiency was restored through improved chlorophyll content and gas exchange parameters. Notably, Mg-BNCs reduced Cd accumulation by 75.0% in shoots and 64.2% in roots, while enhancing plant Mg uptake in plants. Mg-BNCs application was associated with shifts in rhizosphere microbial community composition, including higher relative abundances of several beneficial taxa such as Sphingomonas , Bacillus , and Gemmatimonas . These changes occurred concurrently with improved plant performance under Cd stress. Metabolomic profiling identified 887 metabolites, with Mg-BNCs modulating key pathways including pyrimidine metabolism, oxidative phosphorylation, and photosynthesis. These findings establish Mg-BNCs as a promising sustainable solution for agricultural remediation, functioning through multi-faceted mechanisms encompassing reduced Cd bioavailability and plant uptake, oxidative stress mitigation, photosynthetic enhancement, and rhizosphere ecological regulation.