[Effects of Microplastic Pollution on Microbial Activity and Carbon Metabolism Function in Soil]

Clarifying the ecological effects of microplastics （MPs） in soil is a frontier problem in environmental science research. A 60-d microcosmic culture experiment was conducted using soil with three relative abundances （2%, 5%, and 10%, MPs/soil）, of traditional MPs polystyrene （PS） and biodegradable MPs polylactic acid （PLA）. Additionally, the changes in microbial activity and carbon metabolism function in the soil after cultivation were analyzed. The results showed that： After cultivation with MPs, the soil pH decreased and the content of dissolved organic carbon （DOC） in the soil significantly increased. The addition of MPs significantly reduced the activities of catalase and polyphenol oxidase in the soil and the reduction degree was related to the concentration of MPs. However, the addition of PLA significantly enhanced the activity of soil urease, while PS had no significant effect on urease activity. The addition of MPs led to a decrease in the carbon metabolism ability of soil microbial communities. The carbon metabolism ability of soil microorganisms cultured with PS was higher than that of those cultured with PLA. The inhibitory effect of both on soil carbon metabolism was positively correlated with their concentration. The concentrations of PS （10%） and PLA （10%） had the strongest inhibitory effect on soil microbial carbon metabolism ability, with a decrease of 63.91% and 82.27%, respectively. PLA had a greater impact on soil microbial activity and carbon metabolism than that of PS because PLA in soil degraded easily to produce harmful dissolved organic matter and smaller plastic particles. The research results provide a theoretical basis for clarifying the ecological effects of MPs in soil and basic data for future development of standards related to soil MPs pollution.