Published online by Cambridge University Press: 11 May 2010
Soil respiration (RS, Fig. 8.1) is the sum of an autotrophic component (RA) produced by roots and the associated rhizosphere (mycorrhizae and rhizosphere bacteria) and a heterotrophic component (RH) originating from soil micro-organisms that decompose the organic materials from both above-ground and below-ground litter (Bowden et al., 1993; Boone et al., 1998; Epron et al., 1999). Autotrophic respiration involves root carbohydrates and root exudates that have very low residence time in soil, while the heterotrophic component involves carbon compounds with a longer residence time, ranging from months to years for fresh litter and from years to centuries for old soil organic matter. All components are thought to be differently influenced by climatic conditions and site characteristics (Boone et al., 1998; Epron et al., 2001; Lavigne et al., 2004; Dilustro et al., 2005) and are thought to respond differently to elevated atmospheric CO2 or soil warming (Rustad et al., 2001; King et al., 2004; Pendall et al., 2004; Soe et al., 2004; Eliasson et al., 2005). Thus, separate estimations of these components are required for analyzing and modelling soil respiration and its response to climate or perturbation, for providing a better knowledge of carbon budgets of ecosystems and for improving carbon sequestration in soil (Hanson et al., 2000; Ryan and Law, 2005; Subke et al., 2006).