The Soil Foodweb is the interaction of all the organisms who make their home in the soil. The lives & deaths of bacteria, fungi, protozoa and nematodes, among others, go largely unnoticed by most gardeners. But they form the bottom of a very large foodweb in the soil, a web where even one missing organism puts the entire system out of balance.
Bacteria are among the chief decomposers in the web, second only to fungi. They break down “green”, easy to digest organic matter, ingesting nitrogen, carbon & other nutrients. These nutrients become immobilized in the bodies of the bacteria, which keeps them from leaching out of the soil. These nutrients are later released when the bacteria are consumed by higher order organisms or die and their bodies decay.
Fungi are the premier decomposers in the foodweb. They are Mother Nature’s #1 recyclers and break down much of the organic matter in the soil, immobilizing the nutrients and holding them in their bodies until they can be mineralized (released) by the higher organisms in the web. Fungi secrete an acidic enzyme and so are able to break down complex molecules that other organisms can’t. Fungi also create a subway system in the soil which can shuttle nutrients and water back to the plant. Some fungi even build barriers around the rhizosphere of a plant and protect it from disease & predators.
Protozoa are the premier nutrient cyclers of the foodweb. They feast on bacteria and fungi (and each other), releasing (mineralizing) the nutrients which are held in their bodies. Any nutrients they don’t use for their survival are released into the soil in a plant-useable form. There are 3 types in the soil: ciliates, flagellates and amoeba.
Nematodes are non-segmented, blind roundworms that mineralize nutrients contained in bacteria and fungi. These little guys are everywhere, but most gardeners only know the bad guys. There are fungal-feeding, bacterial-feeding and predatory nematodes which are all beneficial organisms in the soil foodweb. Besides mineralizing the nutrients, they help to keep populations of other members of the web in check.
All the Rest
Arthropods & Earthworms are the shredders of the foodweb, tearing the organic matter into smaller bits which can be consumed by bacteria & fungi, and pulling it down into the soil. They also aerate the soil as they move through, leaving behind burrows and tunnels.