Biodiversity, ecosystem functioning and above-ground-below-ground linkages

All terrestrial ecosystems consist of an explicit producer subsystem and a decomposer subsystem. While traditionally these components have usually been considered in isolation from one another, they are obligatory dependent upon each other. Producers provide the organic carbon sources that drive the decomposer community and decomposer activity is in turn responsible for mineralizing nutrients required for maintaining growth of the producers. Mutualists, herbivores, pathogens and parasites affect producer-decomposer interactions both by directing changes in the flow of energy and resources, and by imposing selective forces that lead to evolutionary changes in individual producer and decomposer populations. The direct and indirect interactions between above-ground and below ground communities therefore have the potential to operate as major drivers of population-, community- and ecosystem-level processes (Hooper et al. 2000; Van der Putten et al. 2001; Wardle 2002).