Correlation analysis of heavy metal, antibiotics accumulation, and antibiotic resistance genes induced by long-term biogas slurry application.

Biogas slurry (BS), as product of animal manure fermentation, is often used as a fertilizer in farmland. However, the long-term application impact on the soil remains not fully understood. Studies have shown that although long-term application of BS does not lead to excessive antibiotic residues in the soil, it increases the abundance of antibiotic resistance genes (ARGs) and promotes their transfer among potential hosts. The complex co-occurrence of bacteria and ARGs implies enhanced horizontal gene transfer, and the increased abundance of the intl1 gene supports this change. Moreover, the distribution of antibiotic-resistant bacteria and ARGs is closely related to the duration of application. Meanwhile, tetracyclines and fluoroquinolones antibiotics, as well as ARGs, are significantly enriched in soils irrigated with BS, and various potentially pathogenic bacterial genera are present. In addition, the application of BS can increase the soil organic carbon stock and alter the soil bacterial and fungal communities. Long-term application of BS results in the accumulation of tetracyclines and the enrichment of ARGs in the soil. It also has an impact on the diversity of soil microbial functional genes. These findings provide a basis for the formulation of relevant policies and sustainable soil management.