Seagrass meadows are acknowledged as blue carbon ecosystems, yet they are also ideal habitats for methane (CH4) release, offsetting their ability to mitigate climate change. The global CH4 fluxes in seagrass meadows remain highly uncertain due to regional and species biases, and the microbial mechanisms driving methane release are poorly understood. Here, we investigated CH4 air-sea fluxes, sediment CH4 emission potential and microbes involved in CH4 release using geochemical techniques combined with qPCR and Illumina sequencing in a temperate Zostera japonica and Zostera marina mixed meadow. The CH4 air-sea fluxes fluctuated from -0.42 to 11.42 μmol·m-2·d-1, showing a strong seasonal variation. CH4 emission potential was significantly higher in seagrass vegetated sediments (10.34 ± 2.72 nmol·g-1·d-1) than in the adjacent bare sediments (1.55 ± 1.15 nmol·g-1·d-1), primarily attributed to variations in sediment organic matter content. Diverse methanogens occurred in the seagrass meadow, with Methanolobus dominating in seagrass sediments, while Methanococcoides, Methanosarcina, and Methanoculleus being prevalent in bare sediments. Meanwhile, a variety of methylotrophic groups were detected, including aerobic Gammaproteobacteria, anaerobic Desulfobacterota and Methylomirabilota, as well as archaea Candidatus Methanoperedens. The co-occurrence of these functional groups implied the presence of complex CH4 production and oxidation pathways, which regulated the CH4 budget in the seagrass ecosystems. Taken together, our findings enhance the comprehension of the methane emission process and driving mechanism in seagrass ecosystems.
Keywords: Driving mechanism; Methane flux; Methane oxidation; Methanogen; Seagrass meadow.
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