Microbial Perspective: Regulatory Mechanisms of Interactions Between Microplastics and Dissolved Organic Matter on Greenhouse Gas Emissions in Aquatic Ecosystems.

Microplastic (MP) pollution may influence aquatic greenhouse gas (GHG) emissions by altering dissolved organic matter (DOM)-microbe coupling, yet reported effects remain inconsistent across ecosystems and exposure regimes. Here, we synthesized evidence from 16 studies to quantify the net effects of MPs on CO2, CH4, and N2O fluxes under ambient DOM conditions. Our meta-analysis indicates that MP exposure significantly increases CO2 emissions and decreases N2O fluxes, whereas CH4 responses show a non-significant positive trend with high variability. Exposure duration and polymer identity emerge as key moderators, indicating that MP effects are context-dependent rather than uniform. Short-term exposure tends to suppress carbon mineralization, whereas long-term exposure is more often associated with GHG production, consistent with a time-dependent trajectory potentially shaped by polymer aging. Mechanistically, this pattern may reflect initial DOM adsorption and humification that reduce substrate availability, followed by the release of bioavailable MP-derived compounds that may stimulate microbial respiration, methanogenesis, and denitrification. Overall, MPs reshape aquatic carbon and nitrogen cycling within the overarching framework of DOM, which may ultimately influence GHG emissions under certain conditions. These findings provide a quantitative basis for reconciling conflicting observations and improving predictions of the climate relevance of MP pollution in aquatic ecosystems.