Effects of manure application and tetracycline contamination on soil enzyme activity and tetracycline resistance genes in soils: Effects of vegetation

While manure improves soil quality, it can also be a significant source of antibiotics and antibiotic resistance genes (ARGs), especially for manures with high concentrations of antibiotics. We conducted a pot experiment with/without culturing pakchoi in soils with three manure application amounts and four TC contamination levels to evaluate how vegetation affects the persistence of tetracyclines (TCs) and tetracycline resistance genes (TRGs) in manure-amended soils and identify key microbial taxa driving ARG dissemination under TC contamination. After cultivation for 35 days, soil samples were collected and analyzed for residual TCs, soil enzyme activities, and TRG (including tetA , tetB/P , tetC , tetG , tetM , tetO , tetW , tetT , and tetX ) and class 1 integron-integrase gene ( intI1 ). The results revealed that vegetation decreased the oxytetracycline (OTC) and chlortetracycline (CTC) residues by 55.60 % and 38.59 %, respectively; however, it increased TC from 0.3988 mg/kg to 0.6422 mg/kg in high amounts of TC-manure treatments. Manure application improved the soil polyphenol oxide (S-PPO) activity (up to 134.06 % in high-amount manure treatments without vegetation). The tetC abundance decreased with the TC and/or manure treatments. In contrast, the abundance of tetM , tetO , and tetX increased, especially in the vegetation group with large amounts of manure, indicating that the main resistance mechanisms might be changed. Spearman’s correlation analysis, PCA, and network analysis revealed that manure-borne microorganisms had positive correlations with intI1 and multiple TRGs, and Xanthomonadaceae might play an important role in TRG dissemination. Moreover, vegetation changed the structure of soil microorganisms and the main host of TRGs, suggesting that vegetation changed their diffusion route. These results elucidate the role of vegetation in soil ecology under TC-manure conditions and emphasize the effect of the key taxa to manage ARG risks in agricultural activities. • Vegetation stabilized soil enzyme activities under TC stress compared to non-vegetated soil. • TC-manure co-exposure exerted strong microbial toxicity. • Vegetation shifted the TRG transmission route, amplified by manure. • Vegetation enhanced TRG absolute abundances while reducing relative abundances.