Results/Conclusions: Soil C becomes increasingly reduced and labile across the gradient, and this changing substrate quality translates to increasing CH4 emissions and lower emitted CO2:CH4. The CH4 also shifts isotopically from characteristic of hydrogenotrophic production to mixed with acetoclastic production. Notably, only half of the landscape CH4 emissions derive from the Mire’s thaw-associated wetlands, with the other half deriving from adjacent post-glacial lakes via ebullition. Mire-derived CH4 is “young”, while lake CH4 is “old”, revealing the importance of lateral C flow in these systems. The microbial and viral communities mediating these processes are complex, and change dramatically across the landscape. Notable community shifts include high abundances of an undescribed group of Caldiserica in the early stages of permafrost collapse, and of a recently-identified globally-distributed family of hydrogenotrophic methanogens, Methanoflorentaceae, in the bog and fen habitats. Metagenomic sequencing has been used to characterize more than two hundred samples spanning depths and habitat types at Stordalen Mire, and these metagenomes have allowed the assembly of several hundred high-quality population genomes. From these population genomes, we are gaining insights into the C-cycling metabolisms of previously-undescribed, novel, and abundant lineages within the Mire. Targeted metatranscriptomics and metaproteomics are helping identify which of these novel lineages are most metabolically active for processes of interest. Unraveling the interconnections of microbial lineages and C transformations is ongoing.
