Microbial metabolism influences microplastic perturbation of dissolved organic matter in agricultural soils

Abstract An estimated 258 million tons of plastic enter the soil annually. Joining persistent types of microplastic, there will be an increasing demand for biodegradable plastics. There are still many unknowns about plastic pollution by either type, and one large gap is the fate and composition of dissolved organic matter released from microplastics as well as how they interact with soil microbiomes in agricultural systems. In this study, polyethylene microplastics, photoaged to different degrees, and virgin polylactic acid microplastics were added to agricultural soil at different levels and incubated for 100 days to address this knowledge gap. We find that upon microplastic addition, labile components of low aromaticity were degraded and transformed, resulting in increased aromaticity and oxidation degree, reduced molecular diversity, and changed nitrogen and sulfur contents of soil dissolved organic matter. Terephthalate, acetate, oxalate, and L-lactate in dissolved organic matter released by polylactic acid microplastics and 4-nitrophenol, propanoate, and nitrate in dissolved organic matter released by polyethylene microplastics were the major molecules available to the soil microbiomes. The bacteria involved in the metabolism of dissolved organic matter released by microplastics are mainly concentrated in Proteobacteria, Actinobacteriota, and Bacteroidota, and fungi are mainly in Ascomycota and Basidiomycota. Our study provides an in-depth understanding of the microbial transformation of dissolved organic matter released by microplastics and its effects of dissolved organic matter evolution in agricultural soils.