8. Life at the Freezing Point: Global Change and Permafrost Microbiology

One quarter of the earth’s terrestrial surface is underlain by permafrost, or perennially frozen soils. Permafrost soils contain approximately 25% to 50% of the total global soil carbon pool (Schuur and others, 2008), nearly double the atmospheric carbon reservoir. Recent studies have shown that much of this frozen carbon is highly labile (Waldrop and others, 2010), and as permafrost continues to thaw (Osterkamp and Romanovsky, 1999), the stored carbon becomes increasingly available for microbial metabolism. Decomposition of this carbon may produce globally significant quantities of carbon dioxide (CO₂) and methane (CH₄), thereby providing a positive feedback between climate change and the altered biogeochemistry of northern ecosystems. Permafrost soils in interior Alaska, southern Canada, and central/southern Asia are critically poised, just below the freezing point of water (Osterkamp and Romanovsky, 1999), a thermal state in which, although technically still frozen, microbial activity continues.

The fate of carbon residing in permafrost soils depends on a number of physical factors, including the thermal properties of soils (which affect heat flow rates), its disturbance regime (which controls changes in physical properties), and hydrologic regime (where soil-water interactions can rapidly thaw permafrost). Yet the mechanism of permafrost carbon decomposition and greenhouse gas production operates primarily through the microbial loop: enzyme production, carbon and nutrient assimilation, growth, and food web interactions. Thus the ultimate fate of carbon residing in permafrost soils depends critically upon microbial activity in near frozen soils, their diversity and abundance, and their metabolic capacities for degrading and oxidizing carbon.

Our understanding of the diversity of microbial life in this extreme habitat is still very limited (Graham and others, 2011). Until recently, it was thought that microorganisms in permafrost were dead or dormant. However, in the last decade, studies have shown that microbial communities in permafrost are capable of growth and activity at subzero temperatures, likely because some liquid water still exists even when the temperature is below zero (Waldrop and others, 2010). Recent studies by our group have shown that microbial communities are active in frozen permafrost soils, but the diversity and abundance of microorganisms inhabiting permafrost can be low (Machelprang and others, 2011).  We need to understand how these communities, or specific functional members of the community, might respond to thawing soils as a result of climate change.

Thawing of permafrost can be a gradual process where permafrost thaws vertically from the surface or an abrupt process where the land subsides resulting in the formation and expansion of thermokarst bogs. The creation of thermokarst bogs is particularly important because arctic wetlands can produce up to 10 percent of all global methane emissions, even though northern soils are frozen at the surface for most of the year. The biogeochemical processes that regulate carbon flow in high-latitude thawed soils may hold the keys to understanding the sensitivity and strength of high-latitude feedbacks to global climate change. Newly thawed wetland soils rapidly establish a balance of carbon flow that couples primary productivity to continued heterotrophic decomposition of thawed peat and subsequent methane production and consumption in surface layers. Many of these processes are controlled by complex redox processes, such as humic substance reduction and syntrophic microbial metabolism, that have only recently been considered. The role of carbon quality, macronutrients, temperature, pH, and hydrologic constraints on thermokarst peatland biogeochemical processes are still poorly understood.

We seek a postdoctoral researcher to develop a study around the composition, structure, and metabolic activity of the permafrost microbial community, its response to permafrost thaw, and advancing new techniques to study life and biogeochemical processes in permafrost soils and thawed permafrost or thermokarst bogs. The Mendenhall Fellow can utilize established research sites at the Bonanza Creek Long Term Ecological Research (LTER) Station outside of Fairbanks, Alaska. This site is currently instrumented to measure continuous fluxes of greenhouse gases using flux towers and autochambers, along with continuous monitoring of environmental data such as atmospheric and soil climate. Work at such sites will allow the researcher to collaboratively answer questions at the ecosystem scale; at the same time, the researcher will be expected to develop small-scale microbial techniques and experiments that will further our knowledge of microbially driven biogeochemical processes in these complex environments. Methodologies could include isotopic labeling of soil microorganisms or microbial mediated processes with heavy water (¹⁸O), carbon (¹³C), or nitrogen (¹⁵N). One could use ¹³C and/or ¹⁴C to study carbon turnover or carbon flow pathways, metagenomic analysis and proteomics to study regulation of metabolic systems, microbial thermal properties, and (or) studies of novel pathways including CO₂ or humic acid reduction, critical yet understudied pathways affecting greenhouse gas production. These techniques can elucidate previously uncharacterized metabolic pathways and processes occurring in deep, cold, carbon rich environments of the northern permafrost region.

Some important questions that may be addressed by research under this opportunity are:

1. Who is active below freezing and what metabolic activities are occurring?
2. What are the consequence of reduced diversity and abundance of microorganisms in permafrost soils to the production of greenhouse gases?
3. How do microbial communities affect the vulnerability of permafrost C to climate change?
4. What chemical and biological factors regulate CO₂ and CH₄ production and consumption in deep cold thermokarst bogs and fens?

References
Graham, D.E., Wallenstein, M.D., Vishnivetskaya, T.A., Waldrop, M.P., Phelps, T.J., Pfiffner, S.M., Onstott, T.C., Whyte, L.G., Rivkina, E.M., Gilichinsky, D.A., Elias, D.A., Mackelprang, R., VerBerkmoes, N.C., Hettich, R.L., Wagner, D., Wullschleger, S.D., and Jansson, J.K., 2011, Commentary: Microbes in thawing permafrost: The unknown variable in the climate change equation: The ISME Journal, v. 5, no. 11,| doi:10.1038/ismej.2011.163.

Mackelprang, R., Waldrop, M.P., DeAngelis, K.M., David, M.M., Chavarria, K.L., Blazewicz, S.J., Rubin, E.M., and Jansson, J.K., 2011, Deep metagenome sequencing illuminates rapid permafrost response to thaw: Nature, v. 480, p. 368–371.

Osterkamp, T.E., and Romanovsky, V.E., 1999, Evidence for warming and thawing of discontinuous permafrost in Alaska: Permafrost and Periglacial Processes, v. 10, p. 17–37.

Schuur, E.A.G., Bockheim, J., Canadell, J.G., Euskirchen, E., Field, C.B., Goryachkin, S.V., Hagemann, S., Kuhry, P., Lafleur, P.M., Lee, H., Mazhitova, G., Nelson, F.E., Rinke, A., Romanovsky, V.E., Shiklomanov, N., Tarnocai, C., Venevsky, S., Vogel, J.G., and Zimov, S.A., 2008, Vulnerability of permafrost carbon to climate change: Implications for the global carbon cycle: Bioscience, v. 58, p. 701–714.

Waldrop, M.P., Wickland, K.P., III, R.W., Berhe, A.A., Harden, J.W.,and Romanovsky, V.E., 2010, Molecular investigations into a globally important carbon pool: Permafrost-protected carbon in Alaskan soils: Global Change Biology, v. 16, p. 2543–2554.

 

Proposed Duty Station: Menlo Park, CA

Areas of Ph.D.: Soil science, microbiology, geochemistry, biogeochemistry, ecology (candidates holding a Ph.D. in other disciplines but with knowledge and skills relevant to the Research Opportunity may be considered).

Qualifications: Applicants must meet one of the following qualifications: Soil Scientist, Research Microbiologist, Research Chemist, Research Hydrologist, Research Ecologist

(This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)

Research Advisors :Mark Waldrop, (650) 329-5005, mwaldrop@usgs.gov; Burt Thomas; (650) 329-5482, burt_thomas@usgs.gov; Kimberly Wickland (303) 541-3072, kpwick@usgs.gov; Janet Jansson (Lawrence Berkeley Laboratory, Department of Energy), (510) 486-7487, jrjansson@lbl.gov

Human Resources Office contact: Candace Azevedo, (916) 278-9393, caazevedo@usgs.gov

Summary of Opportunities