Remediation effects of straw combined with microbial agents on cinnamon soils with varying degradation based on metagenomics and untargeted metabolome.

Microbial agents show potential for improving soil quality and crop yield. However, in the context of different soil degraded degrees, the effects of straw combined with microbial agents on soil microbial communities and their associated metabolic processes remain insufficiently explored. Here, we conducted pot experiments using cinnamon soils at three degradation levels (highly, moderately, and non-degraded), applying straw alone or straw combined with microbial agents during alfalfa cultivation. In this study, we combined metagenomic sequencing and untargeted metabolomics to study the effects of straw and straw combined with microbial agents on soil quality and plant biomass, and metabolites as well as on the network complexity and stability of soil microbial communities. Our findings showed that both straw and straw-microbial agent combinations enhanced the soil quality and alfalfa yield, as well as on the complexity and stability of bacterial networks in highly degraded soils. Meanwhile, the straw-microbial agent combination significantly altered key metabolic pathways (e.g., steroid hormone biosynthesis, cofactor biosynthesis, and nucleotide metabolism) and differentially regulated metabolites (e.g., amino acids/peptides, organosulfur compounds, and alkaloids) compared to straw alone, with distinct effects observed across degradation levels. Overall, the microbial community and their metabolites shaped by straw and straw combined with microbial agents promoted the remediation of degraded soils, ultimately enhancing soil quality and plant biomass. These findings advance the understanding of straw and microbial agents as a synergistic remediation strategy for modulating soil microbial communities and offer practical insights for soil health restoration.