Microplastic Pollution Is Associated with Fragmentation and Environmental Sensitivity of Marine Planktonic Microbial Communities

The effects of increasing marine microplastic (MP) pollution on the microbial community structure and function remain uncertain, particularly under natural conditions. Specifically, our study focuses on free-living marine microbial communities (0.8–5 μm) rather than plastisphere biofilms. Here, we systematically evaluated differences in microbial community responses to environmental gradients across MP concentration regimes on the basis of a response modulation analysis framework (RMAF). In this framework, co-occurrence network analysis, random forest modeling, and SHapley Additive exPlanations (SHAP) and partial dependence-based interpretation methods are integrated to quantify changes in microbial sensitivity and ecological interactions. Through the use of Tara Oceans metagenomic data, we analyzed seven functional gene categories and species diversity across MP concentration gradients. High-MP environments (with concentrations exceeding 5,500 items·km –2 ) were characterized by a notable decrease in nondominant taxa (from 17–21% to 6.53–9.45%) alongside increased dominance of abundant species. The functional profiles showed higher abundance levels of genes involved in carbon, nitrogen, and sulfur cycling. The results of network analysis indicated reduced connectivity and increased fragmentation, suggesting weakened ecological interactions and decreased system stability. Microbial communities in high-MP environments exhibited increased sensitivity to environmental drivers, characterized by response centralization and niche compression, suggesting a narrower range of environmental responses. MPs were associated with high microbial functional activity and potential indications of low ecosystem resilience.