Where do soil biota live?

Organisms are generally considered to be “soil” organisms if they live in soil and the layers of dead organic matter that overlie the soil. Thus, soil biota live in the soil, in the surface layers of dead plant leaves (or litter), in dead vertebrate and invertebrate animals (carrion), in dead trees and logs, dead roots and in dung pellets and pats.

There are some true soil dwelling biota that rarely see the light of day but many “soil” animals migrate up and down the soil/litter/dung/carrion profile as these layers are moistened and then dry out again. For example, springtails will migrate into the litter from the soil when the litter is moistened with rain or dew but retreat into the moister regions of the soil once the day warms up and dries the litter out again.

Earthworms also migrate from the soil below dung pats up into the pats and drag bits of dung down into their burrows. Migrations allow soil biota to exploit the rich food sources in the surface organic residues.

Even in the soil, biota are not uniformly distributed throughout. They aggregate at areas which are rich in organic matter such as around a small piece of dead leaf which has fallen into the soil, or in the faecal pellet of a springtail or around a dead root, or in the rhizosphere. The rhizosphere is that region which extends a few millimeters out from a root where root exudates and sloughed cells from roots provide an aggregation of organic materials which provide a rich food source for soil animals and microbes.

Ninety percent of soil organisms live in the top 10 cm soil. This is also the zone where most plant roots live, where most organic matter in soil occurs, and most nutrients are also found. It’s no wonder that soil organisms congregate in this region of highest nutrition.