Thawing arctic permafrost contains 30-50% of global soil carbon and is expected to drive substantial alterations to carbon (C) cycling that will accelerate climate change. As permafrost thaws, old C may decompose and be released as carbon dioxide (CO2) and methane (CH4, a more potent greenhouse gas). However, thawing soil can also increase C inputs to the soil from plant litter when perennial shrub communities transition to faster-growing annual wetland plants. The impact of these changes on the C balance depend not only on total C inputs, but also on their influence on priming and microbial community composition. Here, we investigate the role of permafrost thaw in altering patterns of microbial decomposition of fresh plant litter and the associated impact on C gas emissions.
We incubated 13C-enriched plant material from sedge and moss plants (Eriophorum and Sphagnum) with arctic peats from pre- and post-permafrost thaw areas under near-in situ conditions. We measured the isotopic composition of CO2 and CH4 fluxes to partition between unlabeled soil and labeled litter-induced decomposition. To characterize the microbiota responsible for litter decomposition and gas production, we sampled microbial DNA from incubations and used density-fractionation to identify enriched taxa in the metagenomes.
Results/Conclusions
Gas fluxes showed rapid release of enriched C from litter decomposition taking place in three distinct phases. Priming effects depended on thaw phase and gas species (CO2 vs CH4) with strong negative priming of CO2 but positive priming of CH4 in post-thaw habitats only. Microbial analyses indicated litter utilization by a broad range of organisms but particularly strong growth of a few key taxa. In particular, Paludibacteraceae appeared to be a dominant player in litter decomposition in post-thaw habitats. We conclude that changes in litter inputs to thawing permafrost-associated soils alters the pattern of microbial decomposition and will heavily impact the fate of C stored in these soils.