Soils are complex ecosystems – three-dimensional and highly heterogeneous habitats that are simply teeming with living organisms. About 6.5% of the total organic substance of soil is alive. Up to 300 earthworms, 10,000 insect larvae and 10 million nematodes live in a square metre of grassland. And a single gram of dry soil contains about a billion bacteria and hundreds of thousands of single-cell organisms and fungi.
These microorganisms are responsible for all processes in the soil. They provide the plants with nutrients, stabilize the soil structure, improve the water storage and promote plant growth. Without this life in the soil no plant can grow and the soil is more or less dead. The character of the soil – its properties and how it functions – is determined by its microbiological ecosystem.
Bacteria and fungi do most of the work in the soil. Bacteria are responsible for the essential processes. They provide nitrogen and phosphate and are indispensable for carbon fixation. Without them plant remains in which carbon dioxide (CO2) is sequestered cannot be stored permanently in the soil.
Atmospheric CO2 is bound by plants or autotrophic micro–organisms and fed to the soil by processes such as root exudation and deposition of roots or leaves. In this way carbon is made bio-available for the microbial metabolism factory and then either returned to the atmosphere or it finds its way as extracellular compounds or as microbial necromass into the stable subterranean carbon store.
The latter process in particular is an important lever for using our soils as effective carbon stores – with the microorganisms doing the work.