Sensitivity of soil C loss to temperature sensitivity algorithms that vary with soil C lability

Soil C stocks are sensitive to changes in temperature and it is commonly believed that even minor increases in temperature may lead to large releases of C from soils to the atmosphere. Most of this thought is based on short- term incubation data and model output that implicitly assumes soil C pools are comprised of organic matter fractions with uniform temperature sensitivities. Several lines of evidence suggest that resistant soil C fractions are more sensitive to temperature than resistant soil C fractions, but carbon cycle models typically apply equal sensitivity for both labile and resistant fractions. Based on long-term soil C and 13C laboratory incubation data, we have derived three new temperature response functions that account for differential temperature sensitivities of labile and resistant soil C - one with a direct relationship between soil C resistance to decomposition and temperature sensitivity, and two with curvilinear relationships in which increasing sensitivity responses are transient (i.e., limited to a fraction of the resistant soil C). We test these algorithms against independent laboratory measurements and field soil respiration measurements. We then evaluate predictions of these algorithms against those with uniform temperature sensitivities across different soil C pools. Our preliminary results indicate that the three models are all capable of accurately modeling soil CO2 fluxes in the field, but that the algorithms with a soil C lability-dependant temperature sensitivity most accurately model laboratory responses and predict substantially larger reductions in soil C stocks with a changing climate.