Permafrost thaw subjects previously frozen soil organic carbon (SOC) to microbial degradation to the greenhouse gases carbon dioxide (CO2) and methane (CH4). Emission of these gases constitutes a positive feedback to climate warming. Among numerous uncertainties in estimating the strength of this permafrost carbon feedback (PCF), two are: (i) how mineralization of permafrost SOC thawed in saturated anaerobic conditions responds to changes in temperature and (ii) how microbial communities and temperature sensitivities change over time since thaw. To address these uncertainties, we utilized a thermokarst-lake sediment core as a natural chronosequence where SOC thawed and incubated in situ under saturated anaerobic conditions for up to 400 years following permafrost thaw. Initial microbial communities were characterized, and sediments were anaerobically incubated in the lab at four temperatures (0 °C, 3 °C, 10 °C, and 25 °C) bracketing those observed in the lake's talik. Net CH4 production in freshly-thawed sediments near the downward-expanding thaw boundary at the base of the talik were most sensitive to warming at the lower incubation temperatures (0 °C to 3 °C), while the overlying sediments which had been thawed for centuries had initial low abundant methanogenic communities (< 0.02%) and did not experience statistically significant increases in net CH4 production potentials until higher incubation temperatures (10 °C to 25 °C). We propose these observed differences in temperature sensitivities are due to differences in SOM quality and functional microbial community composition that evolve over time; however further research is necessary to better constrain the roles of these factors in determining temperature controls on anaerobic C mineralization.
Bibliographical noteFunding Information:
We thank P. Anthony, S. Billings, A. Bondurant, J. Cherry, M. Engram, N. Haubenstock, F. Horn, T. Howe, K. Martinez-Cruz, P. Lindgren, A. Saborowski, C. Schädel, A. Sepulveda-Jauregui, and M. Zhang for assistance in data collection and/or analysis; C. Knoblauch, V. Romanovsky, M. Zhang, and three anonymous reviewers for their feedback on earlier versions of this manuscript; and S. Skidmore for granting access to Vault Lake. Funding for J.K.H. and K.M.W.A. was provided NSF ARC-1304823 and ARC-1500931 and NASA ABoVE NNX15AU49A . M. W. was supported by the NSF ARCSS-1500931 . G.G. was additionally supported by ERC 338335 . The Helmholtz Gemeinschaft (HGF) is acknowledged for funding the Young Researcher's Group of S.L. ( VH-NG-919 ). Additional funding for J.K.H. was provided under STAR Fellowship Assistance agreement no. FP-91762901-0 awarded by the US Environmental Protection Agency (EPA). The publication has not been formally reviewed by the EPA. The views expressed in this publication are solely those of the authors and the EPA does not endorse any products or commercial services mentioned.
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- Lake sediments
- Temperature sensitivity
PubMed: MeSH publication types
- Journal Article