Large mulch film residues are more unfavourable to the reduction of soil antibiotic resistance genes induced by organic fertilisation than small mulch film residues

Abstract

Plastic film mulching and organic fertilisation result in the coexistence of mulch film residues of multiple sizes and antibiotic resistance genes (ARGs) in farmlands. However, the differential effects of large and small low-density polyethylene mulch film (LDPEM) and biodegradable mulch film (BDM) residues on ARGs have not yet been studied. In this study, we investigated the dynamic variations in soil ARGs induced by organic fertiliser application under treatments with different LDPEM and BDM residue sizes. The results indicated that the target ARGs could be divided into six clusters according to their variation characteristics with sampling time. The reduction rates of most target ARGs, including ermC, aadA-01, qacEdelta1-01, sul1, sul2, tetM-01, tetM-02 and tetPA in treatments with large mulch film residues were lower than those with small mulch film residues for both LDPEM and BDM, which resulted from the higher average degree and positive correlation ratio in the networks between the soil bacterial community and ARGs. The results of structural equation modelling indicated that soil bacterial communities directly affected soil ARGs, with a path coefficient of −0.6428. Soil physicochemical properties and soil enzyme activities affected soil ARGs through the soil bacterial community with path coefficients of 0.24 and 0.28, respectively. The results of the present study emphasise that the environmental impact of large mulch film residues should not be ignored.