Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 119, Issue 9, Pages -Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.2106628119
Keywords
methane; methanogenesis; seagrass; archaea; blue carbon
Categories
Funding
- Max Planck Society
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Marine coastlines colonized by seagrasses are a significant net source of methane emissions, primarily driven by methylated compounds produced by the plants. Methane production continues even after the plants die off, likely due to the presence of methylated compounds in detached plant leaves and rhizomes. The study also identified gene sequences associated with key methane-producing enzymes in the seagrass sediments, suggesting their involvement in methane metabolism.
Marine coastlines colonized by seagrasses are a net source of methane to the atmosphere. However, methane emissions from these environments are still poorly constrained, and the underlying processes and responsible microorganisms remain largely unknown. Here, we investigated methane turnover in seagrass meadows of Posidonia oceanica in the Mediterranean Sea. The underlying sediments exhibited median net fluxes of methane into the water column of ca. 106 mu mol CH4 . m(-2) . d(-1). Our data show that this methane production was sustained by methylated compounds produced by the plant, rather than by fermentation of buried organic carbon. Interestingly, methane production was maintained long after the living plant died off, likely due to the persistence of methylated compounds, such as choline, betaines, and dimethylsulfoniopropionate, in detached plant leaves and rhizomes. We recovered multiple mcrA gene sequences, encoding for methyl-coenzyme M reductase (Mcr), the key methanogenic enzyme, from the seagrass sediments. Most retrieved mcrA gene sequences were affiliated with a clade of divergent Mcr and belonged to the uncultured Candidatus Helarchaeota of the Asgard superphylum, suggesting a possible involvement of these divergent Mcr in methane metabolism. Taken together, our findings identify the mechanisms controlling methane emissions from these important blue carbon ecosystems.
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