Mechanisms for sulfadiazine effective mitigation in biochar-amended soil: From antibiotic resistance to soil microbial community composition and function

Sulfonamide residues in soil have the potential to affect soil microbial community and promote the dissemination of antibiotic resistance. Biochar is a strong candidate for soil enhancement, however, its feasibility and mechanisms in controlling the burden of antibiotic resistance and restoring soil quality under antibiotic contamination require systematic evaluation. Thus, a pot experiment using Anthrosol soil amended with 3 % woody biochar was conducted to evaluate the efficacy in mitigating the inhibition of plant growth, antibiotic resistance genes (ARGs) proliferation, and microbial community disruption at an environmentally relevant (feedlot-adjacent soil equivalence) and a tenfold elevated concentration. Results showed that biochar effectively alleviate the inhibitory effects of sulfadiazine on photosynthesis and sustain ryegrass growth comparable to uncontaminated control. Structural equation model analysis demonstrated that biochar can control ARGs occurrence in soil effectively through both direct and indirect effects. Amplicon sequencing and untargeted metabolomics results indicated that biochar exhibited a limited restorative effect in mitigating high-dose sulfadiazine-induced disturbances to soil microbial community composition and functional profiles, relating to the significant decrease in microbial biomass and the diminished microbial carbon metabolism capability. All these findings provide a systematic evaluation of the efficacy and potential limitations of biochar in remediating sulfonamide-contaminated soils, offering valuable understanding for agricultural soil management.