Effects of Bioavailability and Microbial Community on the Degradation of Atrazine in Sewage Sludge Biochar-Amended Soils

Biochar, as an emerging biotechnology, has been widely used in the remediation of soil organic pollution, mainly by promoting the abundance of related degrading bacteria in soil. In this study, we explored the influence of sewage sludge biochars pyrolyzed at different temperatures of 300–700 °C (SSB₃₀₀-SSB₇₀₀) and addition rates (1% and 5%) on the atrazine biodegradation in soils. After a 21-day incubation, the application of 5% SSB₃₀₀ significantly increased soil catalase (CAT), urease activity, dissolved organic carbon (DOC), and electrical conductivity (EC). However, biochar amendment exhibited inhibitory effects on atrazine degradation in soils. The atrazine degradation ratio decreased with decreasing pyrolysis temperature and increasing addition rates. Further analysis found that there were two possible reasons for the significant decline of atrazine biodegradation in SSB₃₀₀ groups: (1) SSB₃₀₀ demonstrated higher adsorption capacity for atrazine compared to SSB₅₀₀ and SSB₇₀₀ and reduced atrazine bioavailability due to its stronger hydrophobic nature and more abundant surface functional groups; and (2) the SSB₃₀₀ significantly decreased the abundances of dominant atrazine-degraders (Arthrobacter and Pseudomonas) and atrazine-degrading genes (atzA, atzB, and trzN).