Soil organism influence on ecosystem-level processes bypassing the ecological hierarchy?

We discuss the paradox of the apparent simplicity of ecosystem process cont rol and the high diversity of (soil) organisms. Simple process models usual ly can predict, e.g., decomposition and nitrogen mineralization, without ex plicitly including organism biomass, species diversity or abundance dynamic s. Based on these and other observations, we discuss a way of describing ecosy stems that is consistent with observations at only two organizational level s (the ecosystem and the organism level). The usefulness of intermediate or ganizational level is questioned and the ecosystem is compared with a gas c ontainer, acting as an 'averaging engine'. We also discuss under which cond itions this simple approach may not be sufficient for a valid description o f an ecosystem process. (C) 1999 Elsevier Science B.V.