written by: Rip Winkel – Horticulture Agent, Cottonwood Extension District
Sometimes we think that bacteria, fungi, nematodes, and other soil microbes are pests to be illuminated, like the fungus infecting your tomatoes for example. But these microorganisms are not all bad, and they all have their own role in the soil food web. In fact, beneficial bacteria and fungi help to decompose many nutrients that would otherwise be unavailable for plants to use. Some bacteria and fungi even have specialized interactions with certain plant roots, where they exchange nutrients to help one another grow. For example, mycorrhizae (pronounced My-cor-rye-zay) refers to a group of fungi which form a symbiotic relationship with many plants. These fungi grow either inside of a plant’s roots or attach to the surface of a root. The fungi benefits from the plant’s food and nutrients and in turn grow out into the surrounding soil to absorb nutrients and water. So, mycorrhizae actually enhance a plant’s ability to take up nutrients and water.
Soil is mostly made up of non-plant parasites, although some fungi, bacteria, and nematodes infect plant roots. These plant parasitic organisms can cause damage to plants, but the soil ecosystem is highly diverse and complex where plant parasites are not the only parasites living in the soil. Nematodes are an example of this. They are a non-segmented worm typically 1/500 of an inch (50 µm) in diameter and 1/20 of an inch (1 mm) in length. Though a few nematode species are responsible for plant diseases, the majority of them are fungal and bacterial feeders.
Microorganisms decompose organic matter in the soil and nutrients are also released as ions. This decomposed organic matter is where much of the nutrients plants need come from. We need microorganisms in our soil and without them plant life would not be able to exist.