Mutualism and biodiversity in soils

Most soil invertebrates and roots have developed strong interactions with micro-organisms to exploit the organic and mineral resources of soil. Micro-fauna are mainly predators of microorganisms whereas larger organisms interact with micro-organisms through the “external rumen” or facultative endosymbiotic digestive systems. Mobilisation of nutrient and organic resources through mutualism with soil microflora seems to be all the more efficient as the organisms are large (like e.g., roots, termites or earthworms) and temperature is high. In the humid tropics, part of the existing species richness may have originated from an increased base of resources resulting from the development of mutualistic relationships. Evidence for this process is given for earthworm communities. Consequences for soil function and the species richness of plants and consumers are discussed.