Modelling decomposition of standard plant material along an altitudinal gradient: A re-analysis of data of Couteaux et al. (2002)

We explored an alternative method to analyse data of Couteaux et al. [2002, Soil Biology and Biochemistry 34, 69-78] on the decomposition of a standard organic material in six soils along an altitudinal gradient in the Venezuelan Andes (65-3968ma.s.l.). Couteaux et al., fitted separate two-component decomposition models to data of the individual sites, allowing the initial size of the labile and the resistant component to differ between sites. This procedure led them to conclude that the initial size of the resistant component and its decomposition rate depend on temperature while decomposition rate of the labile component does not, which seems biologically unlikely and at variance with literature. As an alternative we fitted a single two-component model to the whole data set, using identical initial component sizes for all sites. We found no statistical ground for using variable initial component sizes. It appeared that the data does not allow a conclusion on the effect of temperature on the decomposition of the labile component. We also investigated alternatives for the values of Q(10) and T-opt that were used by Couteaux et al., and found that temperature explains a larger part of the differences in decomposition rate among sites when using a Q(10) value of 3.75 instead of 2.2 and a Top, value of 27 degrees C instead of 25 degrees C. We discuss the arguments used in model selection and the consequences for predictions of long-term accumulation of soil carbon. Our analysis suggests an even stronger positive feedback between global warming and soil carbon emission than the analysis by Couteaux et al. (c) 2006 Published by Elsevier Ltd.