HR: 14:40h
AN: B12E-05    [PDF]
TI: Rapid decomposition of labile soil organic matter inputs obscures sensitivity of heterotrophic respiration to temperature: A model analysis.
AU: * Post, W M
EM: postwmiii@ornl.gov
AF: Oak Ridge National Laboratory, P.O. Box 2008, Bldg 1509 Bethel Valley Road, Oak Ridge, TN 37831-6335 United States
AU: GU, L
EM: lianhong-gu@ornl.gov
AF: Oak Ridge National Laboratory, P.O. Box 2008, Bldg 1509 Bethel Valley Road, Oak Ridge, TN 37831-6335 United States
AU: King, A W
EM: kingaw@ornl.gov
AF: Oak Ridge National Laboratory, P.O. Box 2008, Bldg 1509 Bethel Valley Road, Oak Ridge, TN 37831-6335 United States
AB: Labile carbon, although often a small fraction of soil organic matter (SOM), significantly affects heterotrophic respiration at short time scales because of its rapid decomposition. However, in the current literature, most soil respiration measurements are interpreted without simultaneous information on labile carbon pool dynamics. Sensitivity of soil respiration to temperature is routinely derived directly from field observations and such relationships have been used to extrapolate effects of global change (e.g. warming) on the carbon emission from SOM. Here we used a multi-pool SOM model to demonstrate the impacts of seasonal fluctuations in labile carbon pools. Labile carbon pool sizes varied widely in response to seasonal changes in representative plant material inputs and temperature even though the model was operating at an equilibrium state (in terms of annual means). Convolution of the dynamics of fast turnover carbon pools and temporal progression in temperature led to misrepresentation and misinterpretation of the heterotrophic respiration - temperature relationships estimated from bulk soil CO2 exchanges. Temperature sensitivity was overestimated when the variations of labile carbon pools and temperature were in phase and underestimated when they were out of phase. Furthermore, with normally used observation time windows (weeks to a year), temperature sensitivity was more likely to be underestimated. A distortion of temperature sensitivity (Q10) from 2 (actual, sensitive dependence on temperature) to nearly 1 (false, no dependence on temperature) was shown. Our analysis indicates that cautions must be taken when soil respiration - temperature relationships are evaluated based on bulk soil observations and that sensitivity of soil respiration to temperature estimated directly under field conditions should not be used to predict future carbon cycle climate feedbacks.
DE: 0315 Biosphere/atmosphere interactions
DE: 3210 Modeling
DE: 4806 Carbon cycling
SC: Biogeosciences [B]
MN: 2003 Fall Meeting