Effects of biochar and compost on microbial community assembly and metabolic processes in glyphosate, imidacloprid and pyraclostrobin polluted soil under freeze thaw cycles

Biochar and organic compost are widely used in agricultural soil remediation as soil immobilization agents. However, the effects of biochar and compost on microbial community assembly processes in polluted soil under freezingthawing need to be further clarified. Therefore, a freezethaw cycle experiment was conducted with glyphosate (herbicide), imidacloprid (insecticide) and pyraclostrobin (fungicide) polluted to understand the effect of biochar and compost on microbial community assembly and metabolic behavior. We found that biochar and compost could significantly promote the degradation of glyphosate, imidacloprid and pyraclostrobin in freezethaw soil decrease the half-life of the three pesticides. The addition of immobilization agents improved soil bacterial and fungal communities and promoted the transformation from homogeneous dispersal to homogeneous selection. For soil metabolism, the combined addition of biochar and compost alleviated the pollution of glyphosate, imidacloprid and imidacloprid to soil through up-regulation of metabolites (DEMs) in amino acid metabolism pathway and down-regulation of DEMs in fatty acid metabolism pathway. The structural equation modeling (SEM) results showed that soil pH and DOC were the main driving factors affecting microbial community assembly and metabolites. In summary, the combined addition of biochar and compost reduced the adverse effects of pesticides residues. Glyphosate, imidacloprid, and pyraclostrobin are a globally used herbicide, insecticide, and fungicide, respectively. However, many reports have shown that their residues have a significant, negative impact on the soil environment. Freezethaw cycles change their mode of action, which in turn threatens soil ecology. This study comprehensively analyzed the effects of biochar and compost on microbial community assembly processes and metabolic pathways in polluted soil under freezethaw conditions. These findings are conducive to our understanding of the relationship between soil microbial communities and metabolites and provide new ideas for the remediation of pesticide-polluted soil in seasonally frozen soil areas.