[Impact of Microplastics in Sediments on Microbial Carbon Cycling Functions in Qinhuai River]

Microplastics （MPs）， as emerging contaminants， have attracted widespread attention in recent years. Microorganisms， as key regulators of the cycling of elements such as carbon， are sensitive to MPs pollution. Urban river sediments are sinks for environmental MPs and also important habitats for microbial communities. MPs pollution may bring ecological risks to urban rivers by affecting the structure and function of microbial communities. To examine the impact of MPs on microbial carbon cycle functions， this study investigated the sediments from the Qinhuai River， a typical urban river. Sediment samples were collected in October 2024， and MPs analysis combined with metagenomic sequencing was performed to characterize MPs pollution and its effects on microbial community structure and carbon cycling functional genes in both sediments and the plastisphere. The results showed a 100% detection rate of MPs in sediments， with an average abundance （based on dry weight） of （520.56±202.01） n·kg^-1. MPs were predominantly between 200-300 μm and 1 000-2 000 μm， transparent in color， and exhibited fibrous or fragmental morphologies. Metagenomic analysis revealed significant differences in microbial community structure between the plastisphere and sediments， with higher abundance of Methanomicrobia in the plastisphere， potentially driving the significant enrichment of methane metabolism genes （Wilcoxon rank-sum test， P<0.05）. The Mantel test further indicated that the abundance of carbon cycling genes in the plastisphere was significantly correlated with total nitrogen and a specific MP polymer type （epoxy resin） （P<0.05）. This study uncovered the mechanism by which MPs shape distinct ecological niches and modulate microbial carbon cycling in urban river sediments， providing a scientific basis for evaluating the ecological impacts of MPs.