Effects of microplastic degradability and concentrations on antibiotic resistance genes between soil and phyllosphere

Microplastics have emerged as significant environmental pollutants and notably facilitated the spread of antibiotic resistance genes (ARGs); however, their impacts and underlying mechanisms remain poorly understood. So, this study investigated the effects of different types of microplastics (biodegradable microplastics; PGA and non-degradable microplastics; HDPE) and their concentrations (0.5 %, 1.0 %, and 1.5 % w/w) on ARGs distribution and transfer between soil and the phyllosphere, utilizing a greenhouse germination experiment. The results demonstrated that microplastic addition altered the characteristics of ARGs in both soil and phyllosphere. PGA, in particular, had a more pronounced effect on ARGs abundance in the phyllosphere. In soil, ARGs abundance were jointly regulated by both microplastic type and concentration: PGA exerted a stronger influence at lower concentrations, while HDPE had a greater effect at higher concentrations. Regardless of type or concentration, microplastic addition reduced microbial network modularity, leading to substantial shifts in ARGs community structure in both soil and phyllosphere. Notably, microplastic addition at 1 % concentration yielded the highest ARGs diversity in soil. Structural equation model revealed that microplastic types and concentrations influenced ARGs transfer via distinct pathways by changing soil physicochemical properties and microbial diversity. Specifically, PGA increased soil electrical conductivity (EC) and dissolved organic carbon (DOC) to influence ARGs, while HDPE primarily affected ARGs through alterations in soil pH, available phosphorus (AP), and available potassium (AK). These findings can offer important insights into the mechanisms by which microplastics influence ARGs dissemination in terrestrial ecosystems.