Mechanism of the Synergistic Effect of Combined Fe₂O₃ and MoS₂ Nanoparticles on the Soybean Biological Nitrogen Fixation

This study investigated the synergistic effects of co-applied molybdenum disulfide nanoparticles (MoS₂-NPs) and iron oxide nanoparticles (Fe₂O₃-NPs) on biological nitrogen fixation in soybean (Glycine max L.), and clarified the underlying regulatory mechanism via multi-omics analysis. A greenhouse pot experiment was conducted with sterilized vermiculite as the cultivation substrate, and iron- and molybdenum-free low-nitrogen nutrient solution was supplied throughout the growth period. The experiment set up 8 treatment groups with gradient Mo:Fe mass ratios via root application of the two nanomaterials. The most pronounced synergistic effect occurs at a Mo:Fe ratio of 1:2 (corresponding to 40 mg/kg MoS₂-Nanoparticles and 80 mg/kg Fe₂O₃-Nanoparticles), increasing nodule nitrogenase activity by 26.07% and 29.72% compared with sole MoS₂-nanoparticles group and sole Fe₂O₃-nanoparticles group. Transcriptomic and metabolomic analyses demonstrated that, in the early stages of nodule formation (15 d), the synergistic effect promotes nodule development by influencing amino acid content and carbon metabolism within the nodules. While in the middle (30 d) and late (45 d) nodulation stages the synergistic action mainly regulated the biosynthesis of isoflavones, the nodulation signaling molecules, and modulated the levels of plant hormones including (S)-abscisic acid, gibberellin A1 and jasmonic acid in root nodules, thereby maintaining nodule structure and activity. Our study identifies key molecular nodes of this synergistic regulation, offering novel insights for nanomaterial applications to improve legume nitrogen fixation and advance sustainable agriculture and nanofertilizers.