Linking Sediment Microbial Communities to Carbon Cycling in High-Latitude Lakes

Abstract:

It is well recognized that thawing permafrost peatlands are likely to provide a positive feedback to climate change via CH₄ and CO₂ emissions. High-latitude lakes in these landscapes have also been identified as sources of CH₄ and CO₂ loss to the atmosphere. To investigate microbial contributions to carbon loss from high-latitude lakes, we characterized sediment geochemistry and microbiota via cores collected from deep and shallow regions of two lakes (Inre Harrsjön and Mellersta Harrsjön) in Arctic Sweden in July, 2012. These lakes are within the Stordalen Mire long-term ecological area, a focal site for investigating the impacts of climate change-related permafrost thaw, and the lakes in this area are responsible for ~55% of the CH₄ loss from this hydrologically interconnected system. Across 40 samples from 4 to 40 cm deep within four sediment cores, Illumina 16S rRNA gene sequencing revealed that the sedimentary microbiota was dominated by candidate phyla OP9 and OP8 (Atribacteria and Aminicenantes, respectively, including putative fermenters and anaerobic respirers), predicted methanotrophic Gammaproteobacteria, and predicted methanogenic archaea from the Thermoplasmata Group E2 clade. We observed some overlap in community structure with nearby peatlands, which tend to be dominated by methanogens and Acidobacteria. Sediment microbial communities differed significantly between lakes, by overlying lake depth (shallow vs. deep), and by depth within a core, with each trend corresponding to parallel differences in biogeochemical measurements. Overall, our results support the potential for significant microbial controls on carbon cycling in high-latitude lakes associated with thawing permafrost, and ongoing metagenomic analyses of focal samples will yield further insight into the functional potential of these microbial communities and their dominant members.