How Nature Feeds Plants: The Relationship Between Soil, Roots and Microorganisms

At The Glen Road we’re soil people. If you want to grow great plants you have to begin with the soil. Here’s is a short answer to the big WHY?…

Soil is the loose outer layer of the earth’s surface. It is made up of five major components: mineral matter, organic matter, air, water and microorganisms. It is one of the most dynamic sites of biological interactions in nature.

Soil is the largest terrestrial ecosystem. Here there are many different relationships between soil microbes and roots. They can be symbiotic or antagonistic in nature. Organisms live in close proximity to the root systems of plants. They interact with not only the roots but amongst themselves. These interactions can be beneficial, detrimental or neutral to plant roots.

Soil microorganisms are the most important agents in the transportation of various elements: such as nitrogen, phosphorus, potassium, sulfur, etc., from the biosphere to the soil. These essential elements undergo changes from their inorganic state as free elements in nature into their combined state in living microorganisms. In a process known as mineralization, microbes convert complex organic compounds into simple inorganic compounds and then into usable nutrients.

Microorganisms that help root systems take up nutrients are bacteria, fungi and algae. In the upper layers of the soil horizons O and A the microbe population is very high. It decreases in deeper horizons. This area in the soil close to the roots is called the rhizosphere; the thin layer of soil around the roots. This is a favourite place for microbes to live. The roots give off exudates; foods, like sugars and amino acids, to attract microorganisms. In return the organisms bring minerals, nitrogen, vitamins and other amino acids to the root zone. Here in the rhizosphere there could be 100 times more microbes than in other soil horizon.

Actinomycetes, or thread bacteria, are important decomposers in the soil. They help decompose resistant, organic compounds. They are responsible for the production of antibiotics, primarily Streptomycin and Aureomycin. These natural antibiotics can protect plant roots from disease.

Some microbes, such as mycorrhizae, have a very close or symbiotic relationship with roots. Some fungi grow inside root cells. These are called endotrophic mycorrihizae that grow branch-like threads inside the root cells. Ectotrophic mycorrihizae have thread like filaments that grow between the cells creating networks. They also form a cover or a mesh around the host root. They can look like short, swollen, multi-branched rootlets or long, root-like nets. Both types of fungi extend out from the host roots into the surrounding soil, transporting water and nutrients.

Algae, or cyanobacteria, are a photosynthetic, nitrogen-fixing group of bacteria that survive in different habitats: soil or water. They fix atmospheric nitrogen in aerobic or anaerobic conditions. Some species are specialized to convert nitrogen into NH3, NO2 and NO3. These nutrients can be absorbed by roots and converted by the plant into proteins and acids.

A balanced soil food web is a best management approach to maintaining a healthy rhizosphere; where soil, roots and organisms interact. Feed your plants by feeding your soil. Add clean organic material on a regular basis.

For more information refer to the following:

Dr. Elaine Ingham talking about the Soil Food Web.

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