Microbes drive more carbon dioxide and nitrous oxide emissions from wetland under long-term nitrogen enrichment

Wetlands are frequently regarded as weak carbon dioxide (CO₂) sinks, the largest natural sources of methane (CH₄), and weak sources of nitrous oxide (N₂O). Anthropogenic activities and climate change-induced nitrogen (N) enrichment may affect wetland carbon (C) and N cycling via soil microbes, consequently modifying the original greenhouse gas (GHG) emissions. However, the effects and mechanisms of the duration and rate of N inputs on wetland GHG emissions remain uncertain and controversial. Therefore, this study conducted an in situ field experiment to investigate the effects and driving mechanisms of long-term N enrichment on wetland GHG emissions throughout the 2023 growing season by using the static opaque chambers method. Soil microbial composition and function were also analyzed through metagenomic sequencing. The results showed that N enrichment significantly increased wetland CO₂ emissions, which were associated with the abundance of microbial C-fixing functional genes and the soil C content. Although nitrogen enrichment tended to suppress CH₄ emissions, the effect was not significant. High N enrichment created a powerful wetland N₂O source driven by the abundance of microbial nitrification function genes and microbial species. Vegetation influenced wetland GHG emissions by altering soil carbon content. This study elucidates the response mechanism of wetland GHG emissions to long-term nitrogen enrichment, thereby furnishing a theoretical basis for wetland conservation and nitrogen management.