Temperature response of wheat decomposition is more complex than the common approaches of most multi-pool models

The temperature response of heterotrophic soil respiration is crucial for a reliable prediction of carbon dynamics in response to climatic changes. Most multi-pool models describe the temperature dependence of carbon decomposition by a response function which uniformly scales the decomposition constants of all carbon pools. However, it is not clear whether the temperature response does, indeed, conform to such a simple formulation. In this study, we analysed measured CO2 efflux from wheat decomposition experiments under six different temperatures (5, 9, 15, 25, 35 and 45 degrees C). Data were interpreted by assuming that litter could be sub-divided into two pools, a labile and a more recalcitrant one, that would each decay exponentially. We found that the observed patterns of carbon loss were poorly described if we used the same relative temperature response functions for the decomposition of both pools and assumed the same chemical recalcitrance (expressed as the ratio of labile and recalcitrant pool sizes) at all temperatures. Data prediction could be significantly improved by using different temperature response functions for the decomposition of the two different organic matter fractions. Even better data prediction could be achieved by assuming that chemical recalcitrance varied with temperature. The data could also be well described by the more sophisticated carbon-dynamic models RothC and CenW/CENTURY, again, provided that the ratio of litter fractions in the initial input material was modified with temperature. Our findings thus suggest that the temperature dependence of organic matter decomposition cannot be fully described with the simple approaches usually employed but that there is a more complicated interplay between the temperature dependence of decomposition rates and temperature effects on the chemical recalcitrance of different organic matter fractions. (c) 2008 Elsevier Ltd. All rights reserved.