Shifting microbial communities dynamically mediate the effect of permafrost thaw on isotopic composition of atmospheric methane
Abstract
Increasing methane (CH4) emission from thawing permafrost is expected to increase atmospheric methane concentrations and constitute an important positive feedback to climate change. However, the dependence of this feedback on ecological changes in the microbial communities that produce CH4 is largely unknown. To study the effects of microbial community ecology on isotopic composition of atmospheric CH4, we combined high frequency measurements of the carbon isotopic signatures of CH4 emissions with microbial community profiling via 16S rRNA amplicon sequencing along a permafrost thaw gradient in northern Sweden. We found that different stages of thaw were associated with different microbial communities and isotopic compositions. Early thaw microbial communities were dominated by methanogens with hydrogenotrophic metabolism, emitting isotopically light CH4 (δ13C ~ -80‰), while communities in fully thawed environments contained a greater proportion of methanogens utilizing acetoclastic pathways, and emitted CH4 that was less depleted in 13C (δ13C ~ -65‰). To assess the potential global implications of the observed thaw-induced changes in microbial metabolism and associated CH4 isotope dynamics, we used a simple box model of atmospheric mixing. We found that if thaw-induced patterns in CH4 isotopes generally match our observations, then CH4 emissions from thawing permafrost will likely produce shifts in the isotopic composition of global atmospheric CH4. These changes will be more negative than those typically assumed by current atmospheric model-based inversion studies, which assume that the carbon isotopic signature of biogenic CH4 emissions is fixed at -60 or -65‰. This isotopic difference would lead to a 2-4 fold overestimation of the amount of CH4 released from thawing permafrost and a corresponding underestimation of emissions from non-wetland sources. We conclude that microbial community ecology may be a significant but neglected mechanism in the effect of permafrost thaw on atmospheric composition.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.B54B..07S
- Keywords:
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- 0400 BIOGEOSCIENCES;
- 0315 ATMOSPHERIC COMPOSITION AND STRUCTURE Biosphere/atmosphere interactions;
- 0465 BIOGEOSCIENCES Microbiology: ecology;
- physiology and genomics