Shifting microbiology and carbon loss across a thawing permafrost wetland-to-lake mosaic landscape
Tuesday, 16 December 2014: 4:45 PM
Understanding the fate of carbon (C) in thawing permafrost is an unresolved challenge of modern biogeochemistry and climate change. The associated C pools are large (~1700 PgC), and their dynamics under thaw are complex: old C decomposes as it is liberated from thawing permafrost as CO2 or CH4, even as new C accumulates due to thaw-initiated ecological succession. The interconnected wetland and aquatic landscapes commonly associated with thaw are critically important to tracing C fate, with a significant fraction cycling through lake sediments. Microbes mediate C loss across this landscape, but a mechanistic microbes-to-emissions scaling is missing. Our team is investigating in situ changes in C cycling and microbiology across a thawing permafrost mosaic palsa-bog-fen-lake landscape, at Stordalen Mire (68°21′N, 19°02′E) in Arctic Sweden. At this site, wetlands and lakes each account for roughly half of total landscape emissions (eg Wik et al 2013). Along the thaw gradient, vegetation shifts from ericaceous shrubs to mosses and sedges, and then aquatic plants, while organic matter becomes increasingly reduced and labile, with evidence of greater humification rates and faster decomposition (Hodgkins et al 2014). C gas emissions peak in the fen habitat, with increasing relative production ratios of CH4 to CO2 (McCalley et al in review, Hodgkins et al 2014). The microbial communities mediating these transformations and losses are markedly complex, and change dramatically across the landscape. Notable community shifts include high abundances of an undescribed group of Caldiserica in intact and freshly-thawed permafrost, and of newly-identified family of hydrogenotrophic methanogens (Methanoflorentaceae) (Mondav and Woodcroft et al., 2014) in bog and fen, as well as anaerobic methane oxidizers of the ANME-2d lineage present in the lake sediments. Methanogenesis shifts both isotopically and by lineage-abundance from hydrogenotrophy in the bog to a mixture with acetoclasty in the fen. Unraveling the interconnections of microbial lineages and carbon transformations is ongoing.