HR: 1330h
AN: B32A-0376    [PDF]
TI: Temperature Acclimation in the Terrestrial Biosphere and Implications for Global Climate-Carbon Cycle Feedbacks
AU: * King, A W
EM: kingaw@ornl.gov
AF: Environmental Sciences Division Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831 United States
AU: Post, W M
EM: postwmiii@ornl.gov
AF: Environmental Sciences Division Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831 United States
AU: Wullschleger, S D
EM: wullschlegsd@ornl.gov
AF: Environmental Sciences Division Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831 United States
AU: Gu, L
EM: lianhong-gu@ornl.gov
AF: Environmental Sciences Division Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831 United States
AU: Erickson, D J
EM: ericksondj@ornl.gov
AF: Cpmputer Science and Mathematics Divison Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831 United States
AU: Thompson, S L
EM: thompson59@llnl.gov
AF: Atmospheric Science Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550 United States
AB: Simulations with general circulation models that include an interactive global carbon cycle indicate a positive feedback between climate change and atmospheric CO$_2$ concentration. Both future climate change and CO$_2$ concentrations are higher in the coupled climate-carbon cycle simulations than in simulations without the coupling. Most of the increase in CO$_2$ concentration can be attributed to terrestrial biospheric response to changes in climate, with increases in ecosystem respiration in response to increasing temperature being a major factor. However, these simulations do not allow for ecosystem acclimation to warmer temperatures. Field and laboratory observations show that plants and microbial communities often respond (i.e., acclimate) to elevated temperatures with a decline in the rate at which respiration increases with temperature. For the same change in temperature, respiration with acclimation is lower than respiration without acclimation. Thus temperature acclimation of ecosystem respiration will tend to reduce the magnitude of the climate-carbon cycle feedback. We are investigating the implications of temperature acclimation for climate-carbon cycle feedbacks in coupled climate-carbon models. We identified alternative temperature acclimation responses supported by empirical evidence for both autotrophic (plant) $R_a$ and heterotrophic (microbial) respiration $R_h$. We implemented these responses in a global terrestrial biogeochemsitry model (GTEC 2.0) and an global integrated terrestrial biosphere model (IBIS 2.5). We present simulations of CO$_2$ released in ecosystem respiration in response to future climate change simulated by a general circulation model (PCM). Our results raise scientific questions about the rates at which acclimation occurs and the form of temperature response functions. However, they also suggest that acclimation or other differences in temperature dependencies may not be significant in coupled climate-carbon simulations. Rather, dramatic feedbacks in the form of large modeled carbon releases in $R_h$ may indicate extreme temperature increases, catastrophic ecosystem failure, or anomalous accumulation of terrestrial carbon stocks. The choice of temperature dependency should carefully consider temperature response in the range of historically prevailing temperatures. Functional differences in the range of 10-35 C are likely more important than differences under warmer, but rarely experienced, conditions. Differences in how carbon stocks are modeled will also influence model response to temperature, often mitigating differences in temperature dependency. Zero-order models of decomposer respiration will likely show more sensitivity to temperature dependency than first-order models. Model response will also vary in important ways with differences in the partitioning of total soil organic carbon among various soil carbon pools.
DE: 0315 Biosphere/atmosphere interactions
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2003 Fall Meeting