Microplastics Trigger Soil Dissolved Organic Carbon and Nutrient Turnover by Strengthening Microbial Network Connectivity and Cross-Trophic Interactions

Increasing microplastic (MP) inputs in agricultural soils have gained global attention for their ecological effects, especially on soil organic carbon (SOC) and nutrient turnover. However, the microbial mechanism underlying MP-induced SOC and nutrient dynamics remains poorly understood. Here, we investigated the impacts of two common MPs (polyethylene and polyvinyl chloride) on microbial hierarchical groups (bacteria, fungi, and protists) and the cascading effects on dissolved organic carbon (DOC) and nutrient dynamics in two typical agricultural soils (Mollisol and Ultisol). Our results showed that MP inputs consistently reduced NO₃^--N concentration but increased the content of DOC and specific dissolved organic matter (DOM) components. Despite divergent responses of microbial hierarchical groups to MPs, MP inputs consistently strengthened the connectivity and cross-trophic associations of microbial multitrophic networks. Protistan nodes belonging to Cercozoa, Ciliophora, and Chlorophyta played essential roles in maintaining network connectivity in MP-treated soils. The enhanced network connectivity and cross-trophic associations primarily explained variations in soil DOC and nutrient turnover. These findings collectively indicate that MP inputs trigger DOC and nutrient turnover by enhancing the potential multitrophic interactions and species connectivity within soil micro-food webs. Our study provides novel insights into the ecological consequences of MP pollution on microbial hierarchical interactions and microbially mediated biogeochemical cycling.