Magnesium nanoparticles enhance growth and reshape the rhizosphere microbial community in soybean (Glycine max L.)

Magnesium (Mg) is an essential macronutrient in plants, vital for photosynthesis, enzyme activation, protein synthesis, and carbon metabolism. This study evaluated the effects of magnesium oxide nanoparticles (MgO NPs) on growth, physiological performance, and rhizosphere microbial composition in soybean (Glycine max L.). Field experiments identified 200 mg L^-1 MgO NPs as the optimal treatment, increasing stem diameter (27.70 %), biomass (25.24 %), and grain yield (27.47 %) compared with the control. MgO NPs enhanced photosynthetic pigment and gas exchanges without inducing oxidative stress. Compared with conventional Mg fertilizers (MgSO₄, MgO, MgCl₂, EDTA-Mg), MgO NPs more effectively promoted Mg accumulation in plant tissues, increased activities of sucrose synthase, and sucrose phosphate synthase, and upregulated sugar transport-related genes, thereby facilitating source-sink carbon partitioning. These changes led to elevated seed sucrose content and improved oleic acids (11.59 %). Furthermore, MgO NPs reshaped rhizosphere bacterial communities by enriching beneficial taxa, including Firmicutes (16.74 %), Bacteroidota (9.12 %), Paenibacillus (12.50 %), and Bradyrhizobium (7.89 %), while preserving overall microbial diversity. These results demonstrate that MgO NPs function as an efficient Mg source, simultaneously enhancing yield, nutritional quality, and rhizosphere health of soybean.