Diverse Arctic lake sediment microbiota shape methane emission temperature sensitivity

Abstract

37Northern post-glacial lakes are a significant and increasing source of 38 atmospheric carbon (C), largely through ebullition (bubbling) of microbially-39 produced methane (CH 4 ) from the sediments 1 . Ebullitive CH 4 flux correlates 40 strongly with temperature, suggesting that solar radiation is the primary driver of 41 these CH 4 emissions 2 . However, here we show that the slope of the temperature-42 CH 4 flux relationship differs spatially, both within and among lakes. 43Hypothesizing that differences in microbiota could explain this heterogeneity, we 44 2 compared site-specific CH 4 emissions with underlying sediment microbial 45 (metagenomic and amplicon), isotopic, and geochemical data across two post-46 glacial lakes in Northern Sweden. The temperature-associated increase in CH 4 47 emissions was greater in lake middles-where methanogens were more 48 abundant-than edges, and sediment microbial communities were distinct 49 between lake edges and middles. Although CH 4 emissions projections are 50 typically driven by abiotic factors 1 , regression modeling revealed that microbial 51 abundances, including those of CH 4 -cycling microorganisms and syntrophs that 52 generate H 2 for methanogenesis, can be useful predictors of porewater CH 4 53 concentrations. Our results suggest that deeper lake regions, which currently 54 emit less CH 4 than shallower edges, could add substantially to overall CH 4 55 emissions in a warmer Arctic with longer ice-free seasons and that future CH 4 56 emission predictions from northern lakes may be improved by accounting for 57 spatial variations in sediment microbiota. 58 59 Main text 60At high latitudes, lakes and ponds are recognized as a large and 61 understudied source of methane (CH 4 ) 1,3,4 , a radiatively important trace gas. 62Post-glacial lakes (formed by glaciers and receding ice sheets, leaving mineral-63 rich sediments) represent the largest lake area at high latitudes 5 . Because of 64 their areal extent, these lakes contribute to approximately two-thirds of the 65 model-predicted natural CH 4 emissions above 50° N latitude 1 . Their 66 geochemistry and emissions are distinct from thermokarst lakes formed by 67 permafrost thaw 6 . With warming, permafrost thaw, and predicted increased 68 middle sediments in Inre Harrsjön. Carbon quality, as assessed by visual 130 comparisons of organic matter composition, revealed coarse, less decomposed 131 detritus gyttja (organic-rich, peat-derived mud) in the edge sediments of both 132 lakes, while middle sediments were characterized by fine-grained, generally 133 more decomposed detritus gyttja 15 . Thus, higher temperature responsiveness 134 occurred where there was lower potential substrate quality, suggesting that 135 substrate differences do not readily explain differences in CH 4 emission 136

Physicochemical Drivers of Microbial Community Structure in Sediments of Lake Hazen, Nunavut, Canada

“…However, the microbial communities inhabiting polar lake sediments are still poorly characterized, and what drives community composition is relatively unknown. Although over the past few years several studies taking place in the polar regions have used next-generation sequencing to characterize microbial communities (Stoeva et al, 2014 ; Emerson et al, 2015 ; Hauptmann et al, 2016 ; Schütte et al, 2016 ; Wang et al, 2016 ; Mohit et al, 2017 ; Thaler et al, 2017 ), data on sediment microbial communities in these environments is still sparse. The available data are also biased toward small lakes and thaw ponds, thus underrepresenting large arctic lakes.…”

Evidence for non‐methanogenic metabolisms in globally distributed archaeal clades basal to theMethanomassiliicoccales

“…In previous work, a MAG recovered from subarctic lake sediment metagenomes in northern Sweden, referred to here as SAL16, was characterized taxonomically as a member of the archaeal order Methanomassiliicoccales (Emerson et al ., 2020). However, despite being 95% complete, the MAG lacked genetic evidence for methanogenesis, which was unusual, given that all previously identified Methanomassiliicoccales were thought to be methanogens (Borrel et al ., 2014; Söllinger et al ., 2015).…”

“…Previous work suggested that a MAG, referred to here as subarctic lake (SAL) 16 (SAL16), assembled from methanogenic sediments of a subarctic lake in northern Sweden, lacked methanogenesis genes, despite being assigned as a Methanomassiliicoccales based on the genomic information and RDP assignment of the assembled and binned 16S rRNA gene (Bin 16 in Emerson et al, 2020). To further investigate whether these missing genes were the result of incomplete genome binning or were likely to be a true lack of methanogenic capabilities, MAGs were identified that were closely related to SAL16 in the Genome Taxonomy Database (GDTB; https://gtdb.ecogenomic.org/ tree) release 86 archaeal tree, including those which were also in the Ca.…”

Sink or Source: Alternative Roles of Glacier Foreland Meadow Soils in Methane Emission Is Regulated by Glacier Melting on the Tibetan Plateau

“…Our results showed that the methanogens in LXZ glacier foreland soils were dominated by Methanomassiliicoccales (49%) and Methanomicrobiales (24%), which are consistent with those recovered from the NamCo wetland ( Deng et al, 2019 ), Zoige wetland ( Zhang et al, 2008 ), and Qilian Mountain alpine permafrost soils ( Wang et al, 2020 ). Methanomassiliicoccales has been identified from a wide range of environments, such as tropical peat swamp forest soils ( Too et al, 2018 ), lake sediment ( Emerson et al, 2020 ), and alpine cave soils ( Jurado et al, 2020 ). Methanomassiliicoccales is phylogenetically distant from other methanogen orders, and belongs to a large evolutionary branch composed of many non-methanogenic archaea ( Borrel et al, 2014 ).…”