Response of acetochlor degradation and bacterial community in black soil to the application of vermicompost

Acetochlor (ACE), one of the widely used herbicides in northeastern China, has raised concerns due to its residual presence in the soil. In this study, a pot experiment was conducted to investigate the effects of adding vermicompost on the degradation efficiency and pathways of acetochlor in black soil under dark conditions. The results showed that the vermicompost addition increased the degradation rate of acetochlor, shortened its degradation half-life, and altered the composition of the bacterial community. The influence of vermicompost on bacterial community diversity is minimal, but it can increase the relative abundance of acetochlor degradation bacteria, promoting the collaboration between exogenous and indigenous bacteria to enhance acetochlor utilization. GC-MS analysis revealed the formation of seven metabolites during the acetochlor degradation process, including 2-chloro-N-(2-ethyl-6-methylphenyl) acetamide, 2-ethyl-6-methylaniline, 4-amino-3-ethyl-5-methylpheno, 2-ethyl-6-methylcychexa-2,5-diene-1,4-diol, 2-ethyl-6-methylcychexa-2,5-diene-1,4-dione, N-(2-ethyl-6-methylphenyl)hydroxylamine and 1-ethyl-3-methyl-2-nitrobenzene. The synergistic action of Sphingomonas, Rhodococcus, Bacillus, Arthrobacter, Methylobacillus, and Streptomyces probably lead to the gradual decomposition of acetochlor into H₂O and CO₂. Comparative analysis of functional genes in the KEGG metabolic pathways showed upregulation of hyaB/hybC, hyaA/hybO, nfsA, nfnB/nfsB, and nemA in the soil treated with vermicompost. These functional genes could promote -NHOH conversion to -NO₂. Additionally, redundancy analysis revealed that soil organic matter and pH were the main driving factors for bacterial community variation. These findings suggest that vermicompost can be used as a bioremediation measure to reduce acetochlor in black soil.