Vault permafrost tunnel, Alaska, inoculation study

Laboratory incubations are a common method for determining greenhouse gas production potentials from thawed permafrost soils. However, soils within these incubations usually maintain their in situ organic matter and microbial communities, which is not representative of conditions following permafrost thaw in natural settings. We anaerobically incubated sediments collected from a 12-m yedoma profile in Interior Alaska (Vault permafrost tunnel) to examine: (i) interaction between thawed substrate (FT-ICR-MS) and microbial community composition (16S RNA) and function (metagenomics); (ii) how mixing modern CH4-producing communities with microbial communities present in frozen permafrost affects community composition and function following thaw; and (iii) subsequent effects on anaerobic CO2 and CH4 production. We used three treatments— (i) control treatments of unaltered thawed sediment samples; (ii) inoculated treatments where thawed sediment samples were inoculated with surface sediment collected from an adjacent thermokarst lake, which contained modern CH4-producing communities (Methanobacteriales, Methanomicrobiales, and Methanosarcinales); and (iii) sterilized inoculated treatments where thawed sediment samples were inoculated with the same surface sediment that had been autoclaved to remove active microbial communities. Metagenomic sequencing of 10 samples was conducted to further evaluate the differing priming effect responses to the same inoculate in the 9.0 m and 12.0 m yedoma depths.