Does soil biodiversity depend upon metabiotic activity and in ̄uences?

A central tenet of biological science is that living organisms modify their environments. Metabiosis is a form of ecological dependence in which one organism or a functional group of organisms must modify the environment before another organism or functional group of organisms can live or thrive in it. Soil ecosystems are modi®ed by metabionts to create habitats or supply resources for which dependent organisms may adapt, evolve and hence diversify. Thus, the diversity of the soil biota and its functional capabilities may to a large extent be the result of and dependent upon metabiotic activity and in ̄uences. Examples of metabiotic activity in soil ecosystems are: plants are the main source of O2 for the soil biota; decomposers deplete soil O2 thus enabling the growth of microaerophiles or anaerobes; ammonium released by bacterial deamination supports the growth of autotrophic ammonium-oxidisers; burrowing earthworms improve soil drainage and create aeration channels for aerobic biota; detoxi®cation of plant residues by biodegraders permits proliferation of toxin-sensitive organisms; wood decay by microbes creates habitats for arthropods associated with rotting wood; arthropod comminution of litter liberates nutrients that facilitate microbial activity. Some metabionts, the panmetabionts, had a global in ̄uence by modifying the biosphere, its evolving biota and by maintaining its biogeochemistry. For example, during the development of the biosphere the cyanobacteria began the transformation of the atmosphere through the production of O2. The accumulation of atmospheric O2 had an overwhelming in ̄uence on the formation of soils, their physico-chemistry and biology, in particular the evolution of diverse major groups of aerobic terrestrial organisms (plants, fungi and animals). Many practices to improve soil fertility, e.g. agro-forestry, mulching, legume inoculation, minimum tillage are applications of metabiotic techniques, which maintain or improve soil biodiversity and its functional potentiality. Conversely, where ecosystems are degraded through human activity, e.g. forest destruction, irrigation with saline water, strip-mining, deep tillage, there is an inevitable reduction of species of animals and plants. It can also result in the loss of some components of the soil community, e.g. mycorrhizal fungi, macrobiota such as invertebrates, with a consequent reduction in or a loss of the metabiotic activities of functional groups of the soil biota. Types of metabiotic action include facilitation, ecological engineering, commensalism and keystone predation. Metabiosis must rank with biotic interrelationships and interactions, such as competition, predation or mutualism, in its effects upon soil communities and ecosystems. # 1999 Elsevier Science B.V. All rights reserved.