Diverse Arctic lake sediment microbiota shape methane emission temperature sensitivity

Northern post-glacial lakes are a significant and increasing source of atmospheric carbon (C), largely through ebullition (bubbling) of microbially-produced methane (CH 4 ) from the sediments 1 . Ebullitive CH 4 flux correlates strongly with temperature, suggesting that solar radiation is the primary driver of these CH 4 emissions 2 . However, here we show that the slope of the temperature-CH 4 flux relationship differs spatially, both within and among lakes. Hypothesizing that differences in microbiota could explain this heterogeneity, we compared site-specific CH 4 emissions with underlying sediment microbial (metagenomic and amplicon), isotopic, and geochemical data across two post-glacial lakes in Northern Sweden. The temperature-associated increase in CH 4 emissions was greater in lake middles—where methanogens were more abundant—than edges, and sediment microbial communities were distinct between lake edges and middles. Although CH 4 emissions projections are typically driven by abiotic factors 1 , regression modeling revealed that microbial abundances, including those of CH 4 -cycling microorganisms and syntrophs that generate H 2 for methanogenesis, can be useful predictors of porewater CH 4 concentrations. Our results suggest that deeper lake regions, which currently emit less CH 4 than shallower edges, could add substantially to overall CH 4 emissions in a warmer Arctic with longer ice-free seasons and that future CH 4 emission predictions from northern lakes may be improved by accounting for spatial variations in sediment microbiota.