Monitoring Carbon Stock Changes in European Soils: Process Understanding and Sampling Strategies

Abstract

Soils are the main reservoir for carbon (C) in terrestrial ecosystems. On a global average, they contain about 2–3 times as much organic carbon (OC) as the atmosphere or standing biomass, namely about 1500–2000Gt (Janzen 2005). It is well established that this reservoir is not inert, but in a dynamic stage of accumulation or decomposition. These processes are influenced by human activities. A major anthropogenic disturbance of soils is a land-use change from forest or natural grassland to agricultural soils (Johnson and Curtis 2001; Guo and Gifford 2002), and the permanent mechanical disturbance by ploughing. Prairie soils, for instance, lost 50% of their original soil C after 50 years of cultivation, and at a rate of about 70 g m−2 y−2 (Matson et al. 1997). The remaining 50% are temporary stabilized against decomposition by various mechanisms (Gleixner et al. 2001), but also this C can be mobilized under changing conditions, although at a much slower rate. Apparently, there is no organic matter in soils which is totally protected against microbial attack. But accumulation or degradation of soil C are influenced by environmental conditions and management. Thus, the following section will discuss (1) the processes that lead to C stabilization or mobilization, (2) approaches of soil C assessment, (3) existing approaches for the determination of soil C changes and (4) optimization strategies for soil sampling at the European scale.