Vegetation cover affects the response of greenhouse gas emissions to microplastics in a coastal wetland

Microplastics (MPs) pollution in coastal wetlands has become a major environmental concern. Most studies examining the effects of MPs on greenhouse gas (GHG) emissions in these ecosystems have been limited to laboratory-based incubations. Here, we conducted field-based in situ incubation experiments to explore spatiotemporal patterns of GHG emissions under varying levels of MPs and evaluate the regulatory effects of dissolved organic matter (DOM), microbial communities, and vegetation cover. MPs exposure significantly increased GHG emissions (global warming potential, GWP: +107.46 %) by restructuring microbial networks, enriching key functional microbial taxa, and reducing the bioavailability of DOM while enhancing its electron transfer capacity (p < 0.05). Biodegradable MPs stimulated GHG emissions more than traditional MPs (GWP: 155.87 % vs. 71.16 %), primarily due to the additional organic carbon substrates they provide and their priming effect on microbial metabolism. Vegetation cover altered the direction of carbon dioxide (CO₂) emission responses, increased methane emissions, and affected the mechanistic pathways of nitrous oxide production. Moreover, MPs contributed up to 1.16 Tg of CO₂-equivalent carbon emissions annually in China's coastal wetlands, potentially reducing their carbon sequestration capacity by as much as 15.32 % (∼0.12 % MPs scenarios). This poses a significant threat to the carbon sink function of blue carbon ecosystems. MPs altered GHG emissions by mediating interactions between DOM chemical diversity and microbial structure and function, and vegetation cover affected the response of GHG emissions to MPs. These findings clarify the effects of MPs pollution on GHG emissions in coastal wetland environments.