Methane Consumption by Microbes in High Arctic Soils
As global climate change warms Arctic ecosystems, organic carbon locked in frozen soils thaws and becomes susceptible to decomposition by microbes. Major uncertainties remain regarding what fraction of this carbon will be released as carbon dioxide (CO2) versus methane (CH4), especially in different types of environments. Both CO2 and CH4 act as greenhouse gases, but with different intensities and residence times in the atmosphere. Various microbes can either produce methane (methanogens) or consume it (methanotrophs), so understanding the roles played by these organisms in different Arctic habitats is critical in determining potential outcomes of warming scenarios. In a recent study, a collaborative team of researchers used a combination of systems biology tools and biogeochemical process measurements to examine methanogenic and methanotrophic microbes in soils on Axel Heiberg Island in the Canadian high Arctic. In a surprising finding, the low nutrient mineral soils found on the island acted a methane sink, actively removing CH4 from the atmosphere. Metagenomic profiling of core samples taken from these soils identified a specific subclass of high-affinity methanotrophs capable of growth on very low CH4 concentrations. Targeted metatranscriptomic and metaproteomic profiling demonstrated that these organisms are not only present in these samples, but are actively expressing the genes and protein involved in high-affinity CH4 uptake. In a series of microcosm experiments using intact soil cores from the island, the team subjected the samples to warming and moisture additions consistent with current climate change projections for the region. Although rates of CH4 production by methanogens increased in deeper layers of the samples, there was no net release of CH4, suggesting that it was completely consumed by methanotrophs and converted to CO2. These results are very different from observations in more nutrient-rich permafrost ecosystems, where warming typically results in significant CH4 releases. As predictions of climate change impacts continue to improve, these findings highlight the importance of understanding the complex set of interrelationships between microbial community members and habitat-specific environmental conditions.
Lau, M. C. Y., B. T. Stackhouse, A. C. Layton, A. Chauhan, T. A. Vishnivetskaya, K. Chourey, J. Ronholm, N. C. S. Mykytczuk, P. C. Bennett, G. Lamarche-Gagnon, N. Burton, W. H. Pollard, C. R. Omelon, D. M. Medvigy, R. L. Hettich, S. M. Pfiffner, L. G. Whyte, and T. C. Onstott. 2015. “An Active Atmospheric Methane Sink in High Arctic Mineral Cryosols,” The ISME Journal, DOI: 10.1038/ismej.2015.13.