Microbiome-metabolite signaling drives aluminum stress alleviation in soybean under intercropping and selenium...

Aluminum (Al) toxicity and soil-borne pathogens severely constrain legume productivity in acidic soils, yet the signaling mechanisms underlying intercropping-mediated stress alleviation remain insufficiently understood. Here, we investigated whether soybean-sorghum intercropping under Al stress (SSAl), alone or combined with selenium nanoparticles (SSAl + Se), modulates rhizosphere signaling networks and plant defense responses. Integrated 16S rRNA microbiome sequencing and rhizosphere metabolomics were employed to decipher microbe‒metabolite interactions associated with Al detoxification and disease suppression. Compared with monoculture soybean under Al stress (MSAl), SSAl and SSAl + Se significantly reduced Al accumulation (16.9% and 57.4%, respectively) and Fusarium wilt incidence (10.9% and 34.4%, respectively), accompanied by enhanced root growth. These treatments attenuated oxidative stress, as evidenced by decreased O₂^-, H₂O₂, and malondialdehyde (MDA) levels, while stimulating antioxidant enzyme activities (SOD, POD, and APX), indicating reinforcement of redox homeostasis. In the rhizosphere, NH₄⁺-N and available K levels increased, with NH₄⁺-N positively correlated with urease activity and negatively correlated with Al accumulation, suggesting nitrogen-mediated modulation of Al dynamics. Microbiome analysis revealed enrichment of beneficial taxa, including Streptomyces, Intrasporangium, and Sphingomonas, which are positively associated with antimicrobial and stress-related metabolites such as 15-methyl palmitate, lactucin, and sordarin. These coordinated shifts in the microbial community structure and metabolite profiles indicate that the activation of rhizosphere chemical signaling restricts pathogen proliferation and enhances Al detoxification. Collectively, our findings demonstrate that selenium nanoparticles potentiate intercropping-induced rhizosphere reprogramming, linking redox regulation, nitrogen transformation, and microbiome-metabolite signaling to improve aluminum stress tolerance and disease resistance in soybean. This study provides mechanistic insight into how nano-enabled agronomic strategies influence plant signaling networks under edaphic stress.