HR: 1340h
AN: B23D-1605    [Abstracts]
TI: Microbial decomposer communities in Alaskan permafrost soils and their response to thaw
AU: * Waldrop, M P
EM: mwaldrop@usgs.gov
AF: US Geological Survey, 345 Middlefield Rd. MS 962, Menlo Park, CA 94025, United States
AU: Wickland, K
EM: kpwick@usgs.gov
AF: US Geological Survey, Denver Federal Center, Denver, CO 80225,
AU: Wickland, K
EM: kpwick@usgs.gov
AF: US Geological Survey, 3215 Marine St, Boulder, CO 80303, United States
AU: Harden, J
EM: jharden@usgs.gov
AF: US Geological Survey, 345 Middlefield Rd. MS 962, Menlo Park, CA 94025, United States
AU: Striegl, R
EM: rstriegl@usgs.gov
AF: US Geological Survey, 3215 Marine St, Boulder, CO 80303, United States
AU: Aiken, G
EM: aiken@usgs.gov
AF: US Geological Survey, Denver Federal Center, Denver, CO 80225,
AB: Permafrost protected soil carbon in boreal forest ecosystems represents a significant portion of the approximately 500 Gt C in the soil organic matter of boreal regions. The magnitude of this thermally-protected carbon pool makes it a particularly important to the global C cycle within the context of global climatic change. Permafrost has acted as a C sink for thousands of years yet currently has been warming at a rate of 1°C per decade, making the C contained within it potentially available for decomposition. Thawing permafrost opens a latch into a globally important C reservoir that could be released to the atmosphere (as CO₂) and rivers (as dissolved organic carbon, DOC), affecting greenhouse warming and aquatic chemistry. A gap in our current knowledge is the extent to which permafrost-protected C is available for microbial metabolism once soils thaw. Current indications are that organic matter contained within permafrost is relatively labile since it is not protected from decomposition by physical protection or humification mechanisms. However, we have little understanding of the microbiology of permafrost soils, which could significantly affect the rate of decomposition of permafrost C after thaw. Our aim was to use quantitative molecular techniques to examine the abundance of microbial decomposer functional groups in permafrost soils, the enzymes they encode, and their rates of respiration under both aerobic and anaerobic conditions in a simulated summer thaw at 5°C. We compared microbial and chemical characteristics of active layer and permafrost soils from black spruce stands in three distinct geographic regions: Coldfoot, Hess Creek, and Smith Lake, AK. We chose these regions because they span a range of permafrost conditions from shallow active layers and mineral-associated permafrost layers to thick active layers and deep organic permafrost soils. Soil carbon and nitrogen concentrations did not differ between active layer and permafrost soils within sites, and neither did the relative abundance of total bacteria and methanogens. In contrast, total fungal abundance and basidiomycete abundance was strongly reduced in permafrost soils. We tested whether the reduction in fungal abundance in permafrost soils could affect the turnover of soil carbon in thawed permafrost. We incubated soils under aerobic and anaerobic conditions at 5°C for 3 months. We are currently examining the changes in microbial respiration and enzyme activities that result from the incubation, as well as microbial population shifts. We are testing the hypothesis that low fungal biomass in permafrost soils will reduce the rate of decomposition of organic matter during summer thaw.
UR: http://carbon.wr.usgs.gov/
DE: 0428 Carbon cycling (4806)
DE: 0448 Geomicrobiology
DE: 0465 Microbiology: ecology, physiology and genomics (4840)
DE: 0475 Permafrost, cryosphere, and high-latitude processes (0702, 0716)
DE: 0486 Soils/pedology (1865)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting