Soil Function and the Dynamics of Soil Change.

Soil is a dynamic and living entity with inherent capacity to resist and/or recover from disturbance (ie soil degradation) through restoration of soil attributes necessary for ecosystem function and long-term sustainability. Ecosystems perform fundamental services that function to recycle nutrients, regulate hydrological processes, control erosion, and detoxify wastes. Renewal processes are carried out by plant and animal communities that interact with the physical environment to elicit change. For example, an important service provided by belowground ecosystems is the heterotrophic decomposition of organic matter and the concomitant recycling of plant available nutrients. Energy, carbon and nutrients are cycled through soil organic matter, primarily through the activity of bacteria and fungi. Soil nematodes, protozoa and amoebae contribute to nutrient recycling and translocation subsequent to ingesting bacteria and fungi. Decomposition processes are controlled by soil microclimate variables, such as moisture, temperature, and oxygen content, by intrinsic soil properties, such as soil texture and pH, and by the quality of the organic substrate available to the decomposers. The ability of this ecosystem to continue to provide services depends on the maintenance of functional diversity. High-input, intensive management tends to produce ecologically simplified systems that favor bacterial-pathways of decomposition, dominated by labile substrates and opportunistic, bacterial-feeding fauna. Low-input management tends to produce a more heterogeneous, complex habitat and resource base and systems that favor fungal-pathways dominated by fungal-feeding soil microfauna. The enhancement of functional diversity is an important ecological strategy for recovery of degraded soils and the development of long-term sustainable management strategies.