Interactions among soil biota in coniferous ecosystems

Abstract

The dominance of ectomycorrhizae in most coniferous forest ecosystems profoundly alters the classical concept of the role of exudation and rhizodeposition of cell fragments in the formation of the rhizosphere. In the unaltered, non-ectomycorrhizal rhizosphere the soluble exudates and sloughed cells supporting higher populations of bacteria and other soil biota in the rhizosphere result from the root. The loss of root hairs and the presence of a sheath of fungal hyphae around roots in ectomycorrhizae, suggests that the exudates and sloughed cells will be mainly fungal in origin, creating a mycorrhizosphere. Unfortunately, very little quantitative data exist to test this hypothesis.Recent work has shown that much of the rhizodeposition is in fact whole roots and mycorrhizae; soluble exudates and root cap plus mucigel account for only 3-15% of the organic matter produced in pot experiments. In forests, 3-5 times more organic matter in the form of roots and mycorrhizae is returned to the soil than is returned by decomposition of litter.Data on biomass of bacteria, fungi and other mycorrhizosphere biota obtained by direct measurement or observation are very limited. Much of the research on interactions among biota has focused on host-pathogen interactions rather than quantification of the impact of biota on ecosystem processes.