Soil Biology Soil Biota

There are three levels of participation by soil biota in natural soil processes/functions:

Ecosystem engineers (e.g. earthworms, termites & ants),
Litter transformers (e.g. microarthropods)
Micro-food webs (e.g. microbes and microfaunal predators).

Ecosystem engineers

Ecosystem engineers such as ants and earthworms primarily alter the physical structure of soil but also have an influence on the overall rates of nutrient cycling and energy flows. These organisms initiate fragmentation of organic residues and take organic matter deeper into soil profiles. They also create pores that allow water and plant roots (as well as other soil biota) access to deeper parts of the profile.

Centipede

Litter transformers

Litter transformers such as the microarthropod collembolas are involved in fragmenting plant residues and other organic substances making this material more available to microbes by increasing residue surface area for further chemical degradation and nutrient cycling.

Collembola 'grazing' on decomposing plant material

Micro-food web processors

Soil biota play a major role at all levels in micro-food webs whereby energy is transferred from one organism to another and as a consequence nutrients are recycled through the soil environment. For example, bacteria, archaea and fungi decompose plant litter through enzyme degradation to sequester nutrients and these organisms are in turn eaten by predatory protozoa, nematodes and arthropods. This predation helps maintain specific populations and keeps the predator prey balance in check. At the same time, however, litter transformers are breaking down dead organic matter, including remains of biota from all levels of the food web.

Bacterial colony

Fungal hyphal network

Fungal spores forming at the terminus of hyphae

Soil biology is not evenly distributed in soil and occurs in 'hot-spots' associated with soil organic matter. Decomposing residues, (obvious sites for both physical and enzymatic attack by a range of soil biota), the rhizosphere, (the soil zone that surrounds and is influenced by the roots of plants) and macroaggregates are all examples of such hot spots.

This photograph shows fungal hyphae enmeshing decomposing straw residue where the fungi will secrete a suite of enzymes to break down the structure of the straw.

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