Soil organisms represent a large fraction of global terrestrial biodiversity. They carry out a range of processes important for soil health and fertility in soils of both natural ecosystems and agricultural systems.
Soil biodiversity is comprised of the organisms that spend all or a portion of their life cycles within the soil or on its immediate surface including surface litter and decaying logs.
The community of organisms living all or part of their lives in the soil constitutes the soil food web. The activities of soil organisms interact in a complex food web with some subsisting on living plants and animals (herbivores and predators), others on dead plant debris (detritivores), on fungi or on bacteria, and others living off but not consuming their hosts (parasites).
Plants, mosses, and some algae are autotrophs; they play the role of primary producers by using solar energy, water, and carbon (C) from atmospheric carbon dioxide (CO2) to make organic compounds and living tissues.
Read Also: Components of Soil Organic Matter
Other autotrophs obtain energy from the breakdown of soil minerals, through the oxidation of nitrogen (N), sulphur (S), iron (Fe), and C from carbonate minerals.
Soil fauna and most fungi, bacteria, and actinomycetes are heterotrophs, they rely on organic materials either directly (primary consumers) or through intermediaries (secondary or tertiary consumers) for C and energy needs.
A food web is a series of conversions of energy and nutrients as one organism eats another. In healthy soil, there are a large number of bacteria and bacterial feeding organisms.
Where the soil has received heavy treatments of pesticides, chemical fertilizers, soil fungicides, or fumigants that kill these organisms, the beneficial soil organisms may die (impeding the performance of their activities), or the balance between the pathogens and beneficial organisms may be upset, allowing those called opportunists (disease-causing organisms) to become problems.
Read Also: Constraints to the Maintenance of Organic Matter in Soils