Increasing microplastic abundance drives deterministic assembly of soil microbial communities and suppresses energy metabolism

Microplastic (MP) pollution has emerged as a global environmental issue, yet its effect on soil microbial energy metabolism and community assembly in agricultural ecosystems remains unclear. In this study, we analyzed agricultural soil samples collected from 15 sites in riparian zones within a typical watershed in Southwest China to quantify the level of contamination by MPs and the microbial community structure and function. We conducted an in-depth evaluation of the regulatory effects of MPs on microbial functional genes and community composition. The results indicated that the abundance of MPs in the soil ranged from 7.2 to 31.6 particles per gram of soil. A high abundance of MPs significantly suppressed the expression of key genes involved in oxidative phosphorylation (nuoB, nuoD, and nuoI) and carbohydrate-degrading enzymes (GT35, GH13_11, GH13_9, and CBM48), indicating the impairment of energy metabolic functions. Neutral model and normalized stochasticity ratio analyses demonstrated that an increasing abundance of MPs weakened neutral dispersal processes while strengthening environmental filtering, resulting in decreased community similarity and elevated species turnover rates. Proteobacteria and Actinobacteria were the most sensitive phyla to pollution stress from MPs. This study elucidates how MPs in agricultural soils pose potential risks to ecological functions by damaging microbial energy metabolism and reshaping the microbial community. • Anning River farmland soils contained MPs in concentrations ranging from 7.2 to 31.6 n/g. • Increased abundance of MPs inhibits microbial oxidative phosphorylation. • Proteobacteria and Actinobacteria show high sensitivity to MP stress. • Increased abundance of MPs promotes deterministic assembly of microbial communities.