HR: 11:35h
AN: B52A-06    [Abstracts]
TI: Autotrophic and Heterotrophic Controls over Winter Soil Carbon Cycling in a Subalpine Forest Ecosystem
AU: * Monson, R K
EM: Russell.Monson@colorado.edu
AF: University of Colorado, Department of Ecology and Evolutionary Biology, Boulder, CO 80309 United States
AU: * Monson, R K
EM: Russell.Monson@colorado.edu
AF: University of Colorado, Cooperative Institute for Research in Environmental Science, Boulder, CO 80309 United States
AU: Scott-Denton, L E
EM: Laura.Scott@colorado.edu
AF: University of Colorado, Department of Ecology and Evolutionary Biology, Boulder, CO 80309 United States
AU: Lipson, D A
EM: dlipson@sciences.sdsu.edu
AF: San Diego State University, Department of Biology, San Diego, CA 92182 United States
AU: Weintrub, M N
EM: Michael.Weintraub@colorado.edu
AF: University of Colorado, Department of Ecology and Evolutionary Biology, Boulder, CO 80309 United States
AU: Rosenstiel, T N
EM: Todd.Rosenstiel@colorado.edu
AF: University of Colorado, Department of Ecology and Evolutionary Biology, Boulder, CO 80309 United States
AU: Schmidt, S K
EM: Steve.Schmidt@colorado.edu
AF: University of Colorado, Department of Ecology and Evolutionary Biology, Boulder, CO 80309 United States
AU: Williams, M W
EM: Mark.Williams@colorado.edu
AF: University of Colorado, Department of Geography and Institute for Arctic and Alpine Research, Boulder, CO 80309 United States
AU: Burns, S P
EM: Sean.Burns@colorado.edu
AF: University of Colorado, Department of Ecology and Evolutionary Biology, Boulder, CO 80309 United States
AU: Burns, S P
EM: Sean.Burns@colorado.edu
AF: National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305 United States
AU: Delany, A E
EM: delany@ucar.edu
AF: National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305 United States
AU: Turnipseed, A A
EM: turnip@ucar.edu
AF: National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305 United States
AB: Studies were conducted at the Niwot Ridge Ameriflux site to understand wintertime soil carbon cycling and its control over ecosystem respiration. Wintertime respiration in this ecosystem results in the loss of 60-90% of the carbon assimilated the previous growing season. Thus, an understanding of the controls over winter carbon cycling is required to understand controls over the annual carbon budget. Trees were girdled to prevent the transport of photosynthates to the rhizosphere. In plots with non-girdled trees a large mid-winter pulse of sucrose was observed to enter the soil. In plots with girdled trees, no sucrose pulse was observed. Trees of this ecosystem are not photosynthetically active during the winter, leading us to conclude that the sucrose pulse is due to the death of fine roots that had accumulated sucrose the previous autumn. The sucrose pulse is potentially utilized by a novel winter community of microbes. Using DNA fingerprinting we discovered that the dominant isolates from the winter soils were from Jathinobacter, whereas the summer isolates were from Burkholderia. The winter community was capable of high rates of respiration and exponential growth at low temperatures, whereas the summer community was not. Our winter observations also indicated high activity of N-acetyl-ƒ-glucosaminidase, one of the principal enzymes involved in chitin degradation. The presence of such high chitinase activities implicates decomposing fungal biomass as a principle source of CO₂ beneath the snow pack. Using a novel in situ, beneath-snow CO₂ measurement system, we observed unprecedented Q₁₀ values for winter respiration, being 98 and 8.44 x 10⁴ for the soil next to tree boles or within the open spaces between trees, respectively. These high Q₁₀ values are likely the result of fractional changes in the availability of liquid water below 0°C and responses of microbial biomass to changes in the liquid water fraction. Using six-years of eddy covariance data, we showed that interannual variation in winter ecosystem respiration is positively correlated to interannual variation in the spring snow depth. Years with a with a deeper spring snow pack exhibited higher soil temperatures, and concomitantly higher soil respiration rates. Given the recently reported decadal-scale trend in decreasing snow pack in the Western U.S., which is coupled to warm climate anomalies, our observations indicate the potential for higher wintertime soil carbon sequestration due to lower winter ecosystem respiration rates in subalpine forests. Our studies of processes beneath the winter snow pack demonstrate that contrary to previous assumptions, winter biogeochemical processing of soil organic matter is an important component of ecosystem carbon budgets. Despite low temperatures and an inactive plant rhizosphere, winter microbial communities and exoenzymes appear to be active, carbon substrates appear to be in relatively high abundance and soil respiration rates appear to be sensitive to seasonal and interannual winter climate variability.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0419 Biomineralization
DE: 0428 Carbon cycling (4806)
DE: 0463 Microbe/mineral interactions
DE: 0465 Microbiology: ecology, physiology and genomics (4840)
SC: Biogeosciences [B]
MN: Fall Meeting 2005