Effects of Field Application of Sewage Sludge Aerobic Fermentation Products on Antibiotic Resistance Gene Prevalence in Pakchoi (Brassica chinensis L.)
To investigate the effects of applying sewage sludge aerobic fermentation products on antibiotic resistance genes (ARGs) in the rhizosphere soil and phyllosphere of pakchoi (Brassica chinensis L.), field experiments were conducted with three treatments: sludge product (sludge group), chemical fertilizer (fertilizer group), and no fertilizer (control). Antibiotic residues, abundances of ARGs and mobile genetic elements (MGEs) were measured in rhizosphere soil and phyllosphere, and microbial community composition and virulence factor (VF) contributions were annotated via metagenomics. Results showed that antibiotic concentrations in rhizosphere soil were generally higher than in phyllosphere. Compared with control, sludge application increased soil antibiotic content by 12.70%, whereas fertilizer increased it by only ~3%, indicating a more significant exogenous input from sludge. At the resistance level, total ARG abundances in rhizosphere soil and phyllosphere of the sludge group increased by 25.47% and 73.08%, respectively, relative to control, with concurrent increases in beta-lactam resistance genes and MGEs such as integron intI1. Sludge application may enhance integron-mediated gene capture and horizontal transfer potential, driving resistance risk accumulation in both phyllosphere and rhizosphere soil. Conversely, fertilizer application reduced ARG abundances by 53.40% in rhizosphere soil and 13.50% in phyllosphere compared with control, consistent with decreased microbial community abundance and diversity, suggesting that reduction of host bacteria and dissemination vectors was a key reason. In community structure, Proteobacteria dominated the phyllosphere, while Chloroflexi dominated rhizosphere soil. Correlation networks identified Sphaerobacter thermophilus and Aggregatilinea lenta positively correlated with multiple ARGs (r≈0.95–1.00), whereas Solirubrobacter sp. CPCC_204708 was negatively correlated (r≈−0.91). Virulence factor contributions followed trends similar to ARGs. Sludge fermentation products simultaneously increased ARG prevalence and related risk indicators in both rhizosphere soil and phyllosphere of pakchoi, providing a reference for risk identification and safe application of sludge fermentation products in agriculture.