HR: 09:15h
AN: B21C-06    [Abstracts]
TI: The Degree of Permafrost Thawing Determines Arctic Tundra Carbon Balance
AU: * Vogel, J G
EM: jvogel@ufl.edu
AF: Univ. of Florida-Botany, 220 Bartram Hall, Gainesville, FL 32611, United States
AU: Schuur, E A
EM: tschuur@ufl.edu
AF: Univ. of Florida-Botany, 220 Bartram Hall, Gainesville, FL 32611, United States
AU: Sickman, J
EM: james.sickman@ucr.edu
AF: Univ. of California-Riverside Dept. of Environmental Sciences, 212 Science Laboratories 1, Riverside, CA 92521, United States
AU: Lee, H
EM: hannalee@ufl.edu
AF: Univ. of Florida-Botany, 220 Bartram Hall, Gainesville, FL 32611, United States
AU: Trucco, C
EM: christiantrucco@hotmail.com
AF: Univ. of Florida-Botany, 220 Bartram Hall, Gainesville, FL 32611, United States
AB: In interior Alaska, we measured gross photosynthesis (GP), ecosystem respiration (ER), and net ecosystem exchange (NEE) near a permafrost monitoring borehole that has recorded an increase in permafrost temperatures during the last 22 years. From May 2004 to May 2006, ecosystem C exchange measurements were made with static and automatic chambers in a moist acidic tundra ecosystem. A gradient in degree of permafrost thaw was used to select three sites (Minimal, Moderate and Severe Thaw) that corresponded to an increase in thermokarst occurrence. Between June 1 and August 30, the Severe and Moderate Thaw sites had significantly greater C uptake (GPP) (p<0.05) than the Minimal Thaw site. This growing season GP correlated with aboveground productivity. However, greater winter ER from the Severe Thaw site caused it to be a source (negative NEE, -128 g C m-2) of carbon over three years. The Moderate Thaw site was a carbon sink (52 g C m- 2), while the Minimal Thaw site was near carbon neutral (-7 g C m-2). In the spring and fall, carbon uptake correlated with the occurrence of plant functional groups (sedges, evergreen shrubs) that maintain green foliage and can photosynthesize under cold conditions. Both of these functional groups decreased inside thermokarst. In the winter, the Severe Thaw site lost 34% more C than the other two sites, likely due to warmer deep soil temperatures. As permafrost thaw proceeds, increasing ecosystem C loss may occur during the winter, spring, and fall due to the unique biotic and abiotic characteristics of thermokarst.
DE: 0428 Carbon cycling (4806)
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0475 Permafrost, cryosphere, and high-latitude processes (0702, 0716)
DE: 0476 Plant ecology (1851)
DE: 0486 Soils/pedology (1865)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting