期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2022
卷号：119
期号：9
DOI：10.1073/pnas.2106628119
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Significance
Seagrass meadows colonize shallow coastlines around the world and represent sites of intense carbon cycling. Due to their capacity to produce methane, seagrass ecosystems constitute net sources of methane to the atmosphere. Here, we identify key processes and microorganisms responsible for methane formation in seagrass-covered sediments in the Mediterranean Sea. Our work shows that methane is solely formed from methylated compounds that are produced and released by the plant itself. Due to the persistence of these compounds in buried plant material, microbial methane production continues long after the death of the living plant. These results provide a comprehensive understanding of methane production in seagrass habitats, thereby contributing to our knowledge on these important blue carbon ecosystems.
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 µmol CH
4 ⋅ 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.
