Trophic interactions, the consumption of one organism, or a part of it, by another, are a fundamental component of all ecosystems. The vast majority of net primary productivity is eventually consumed, either by herbivores if the tissue is still alive, or by decomposers if the tissue has died (e.g. Cebrian, 2004). Similarly, these primary consumers are themselves consumed either by predators, parasites or decomposers (secondary consumers). Thus, trophic interactions form the pathways through which carbon flows through an ecosystem and, to a large extent, these interactions control ecosystem carbon dynamics, either directly (via consumption of another organism) or indirectly (e.g. altering competition between the prey individual/population and other organisms).
In this chapter we consider the principal ways by which trophic interactions influence soil carbon fluxes (Fig. 10.1). Firstly, we discuss the impacts of both above- and below-ground herbivores on carbon flux into, and out of, the soil and the interactions between herbivores, plants and soil organisms (dashed box in Fig. 10.1). Secondly, we investigate the role of soil fauna in organic matter decomposition, either directly via the consumption of litter, or indirectly via feeding on saprotrophs or the movement of organic matter (dotted box in Fig. 10.1). Thirdly, we examine the role of resource availability versus predation in structuring soil food webs, followed by the linkages between soil biodiversity and a range of ecosystem processes, including plant growth, litter decomposition and carbon mineralization (solid box in Fig. 10.1).