Tree Roots Part III: Mycorrhizae

How Tree Roots Work Part 1  |  How Tree Roots Work Part II: Digging Deeper

Soil Ecosystem

Did you know trees communicate with each other through a network like our World Wide Web? Tree roots live underground, but they are not alone. They are part of a vibrant ecosystem. Of course, soil contains large organisms like insects, worms, moles, and spiders, but the smallest lifeforms are very important to tree health. There are more bacteria in a teaspoon of soil than people on the planet. Other tiny soil organisms include fungi, algae, and protozoa. All of these species create pathways through the soil for air and water to soak in and become available to roots. The soil ecosystem also helps break down organic material into its basic elements. These elements become the nutrients that the tree uses to produce its food.

Fungal Communication Network

Among the inhabitants of soil are a special class of fungi called mycorrhizae. These fungi colonize the tips of fine, feeder roots and extend out into the soil. The fungus gets some protection and help from the tree, but provides a much greater service by helping to absorb nutrients and bring them into the tree’s cells. They also help the tree defend against other fungi that might colonize the roots and cause damage. There is even evidence that, when one tree is attacked by a disease or pest, the defensive signals are transmitted through mycorrhizae to other trees, which then begin producing defensive compounds before the attack arrives ( So, even though we typically preserve a “critical” root zone based on the tree’s diameter, there is actually often one continuous network of trees, roots, and fungi. It’s important to remember that what we do to our soil might affect several of our neighbors.

A magnified photo of brown tree roots colonized by white mycorrhizal fungi.

Brown tree roots living together with white mycorrhizal fungi. In nature, these fungi would spread outward and join up with other roots on other trees. Image courtesy New York Botanical Garden.


How Tree Roots Work Part 1  |  How Tree Roots Work Part II: Digging Deeper

Article contributed by Keith Babberney, Forester with the Community Tree Preservation Division in the Development Services Department. Questions? Email Keith.

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This information is sponsored by the City of Austin. Learn more about trees and resources at the Tree Information Center!