If you were to go out into your backyard and scoop up a single cup of soil, that cup would contain billions of different types of microorganisms. These would include many different species of bacteria, fungi, and nematodes. I'll be taking you through the three major groups in this three-part article. While all microorganisms are essential to the breakdown and enrichment of soil, the most important are bacteria, fungi, and nematodes. They breakdown a variety of organic materials in soil, in turn producing the building blocks that eventually become humus. This process is important to the makeup of soil. Humus consists of three major fractions: humic substances, polysaccharides and other non-humic substances, and humin. Each of these materials has an impact on the physical, chemical and bio-chemical properties of soil in many important ways.
Fungi are small, microscopic cells that usually appear as long threads, called hyphae. These threads slowly push their way between soil particles, roots, and rocks. Hyphae can be as small as a few cells or as long as a few yards, and are extremely small in diameter.
They also have the ability to group into masses, which are called mycelium and look like roots. These fungi perform important tasks that are related to water dynamics, by physically binding soil particles together. This creates stable aggregates that help increase the water infiltration and the capacity of the soil to hold water. They also perform tasks that are essential to nutrient cycling, and disease suppression in the soil. Additionally, they are important to the decomposition cycle of the soil-food-web, because they convert hard-to-digest organic material into forms that other organisms can use. There are three general groups that fungi can be placed into that are based on how they get their energy.
Saprophytic fungi; these fungi convert dead organic materials into fungal biomass, carbon dioxide and small molecules. Fungi are important for immobilizing nutrients in the soil. Many of the secondary metabolites of fungi are organic acids, so they help increase the accumulation of humic-acid in organic rich matter that is unwilling to decompose and may stay in the soil for hundreds of years.
Let's talk about mycorrhizal fungi. These fungi colonize plant roots, and in exchange for carbon from the plant the fungi help solubilize phosphorus and bring the soil nutrients.
These fungi cause reduced production or death when they colonize the roots and other organisms of plants. These fungi can cause major economic loss to farmers each year. Though these fungi can be negative, many can help control diseases, and they also feed on insects that may be useful as bio-control agents. Fungi can be essential to many plants, because they help the plant extract nutrients from the soil.