Microbial Community Dynamics Dominate Greenhouse Gas Production in Thawing Permafrost

The Science

Northern permafrost ecosystems are changing rapidly, with rising temperatures causing the transition of many previously frozen environments to wetlands. As permafrost thaws, the trapped organic carbon is accessible to decomposition by microbes and can be released to the atmosphere as greenhouse gases (GHGs). Understanding of these communities is limited, especially the specific nature of processes that impact rates of carbon decomposition and the balance of the carbon dioxide (CO₂) versus methane (CH₄) released to the atmosphere. Although both gases are GHGs, CH₄ is much more potent in the short term, so understanding the microbial mechanisms driving these large-scale processes would significantly improve predictions of possible climate change impacts.

An interdisciplinary team of researchers led by the University of Arizona has examined microbial community dynamics at a site in northern Sweden that occupies a natural temperature gradient. Northern portions of this site are frozen permafrost while southern areas are thawed fens. Over several years, the team measured CO₂ and CH₄ production along the gradient, examined isotopic signatures of gases characteristic of distinct microbial processes, and correlated the data with measured shifts in microbial community composition and abundance. Only small amounts of GHGs were released from frozen permafrost, but in progressively more thawed sites, CH₄ was the dominant product released. The team was able to link these observations with extensive shifts in microbial community composition, revealing a reproducible succession pattern of different types of CH₄-producing microbes (methanogens) across the thaw gradient. Surprisingly, a single methanogen species, Candidatus Methanoflorens stordalenmirensis, was dominant in recently thawed sites and its relative abundance strongly correlated with the magnitude and specific type of CH₄ produced at any given site.

The Impact

The striking dominance of a single microbial species in mediating a large-scale carbon cycle process is highly unusual and provides an opportunity to more effectively track and predict the impacts of climate change across an entire region. The team has begun to incorporate integrated datasets on biogeochemical process measurements and microbial community patterns into ecosystem-scale models of carbon cycle processes. This effort represents a significant advance in understanding and more accurately representing critical biogeochemical processes in permafrost that are performed by microbes, improving predictions of climate change impacts on these delicate ecosystems and their potential atmospheric consequences.

Principal Investigator

Carmody McCalley
University of Arizona

BER Program Manager

U.S. Department of Energy, Biological and Environmental Research (SC-33)
Biological Systems Science Division
[email protected]

References

McCalley, C. K., B. J. Woodcroft, S. B. Hodgkins, R. A. Wehr, E.-H. Kim, R. Mondav, P. M. Crill, J. P. Chanton, V. I. Rich, G. W. Tyson, and S. R. Saleska. 2014. “Methane Dynamics Regulated by Microbial Community Response to Permafrost Thaw,” Nature 514, 478-81. DOI: 10.1038/nature13798.