Spores inoculating roots sounds like something out of a science fiction movie. Yet a healthy soil contains multitudes of fungal spores that establish relationships with the root systems of plants. These relationships are beneficial to plants and are called mycorrhizae (myco = fungus, rhizae = roots). You may have seen white mycorrhizal threads in the soil, often under mulch.
Spores might be thought of as the “seeds” of fungi. They develop hyphae that are similar in function to roots of plants. The hyphae follow the tracks through the soil left by rain and irrigation water towards growing plant root tips. Roots under slight nutritional or drought deficiency give out chemical signals that can stimulate mycorrhizal growth. When and if hyphae find a needy root, they penetrate through its cell walls and allow chemicals, including nutrients, to pass into the root itself. The hyphae can develop into a mass around a root and extend the root’s potential for nutrient or water absorption into the surrounding soil, even at a distance from the plant. The root’s hairs, which are the normal nutrient and water absorption mechanisms, are suddenly “root hairs on steroids” (2009, Chalker-Scott). Almost magic, but better. It’s science.
Why am I excited about mycorrhizae anyway? In Nevada, our soils are often water and nutrient deficient. Mycorrhizae allow a plant to access soil water and nutrients from pockets that otherwise might be inaccessible. These little magicians can also link roots of plants of different species giving the plant with the highest nutrient requirement nutrients passed along from a different plant. According to Dr. Chalker-Scott of Washington State University, “The resulting network is a virtual fungal freeway of nutrient and water acquisition and transfer.”
The hyphae masses in the soil improve soil stability, enhance organic matter decomposition and acidify the root zone, an important factor in our generally alkaline soils. An acid root zone improves phosphorus uptake, which can otherwise be problematic in Nevada soils. This can reduce the need for phosphorus fertilizers and limit environmental damage caused by phosphorus leaching into ground or surface water. Mycorrhizae also improve plant establishment and survival, leaf, root and shoot growth and fruit yield.
To encourage mycorrhizal colonization, reduce fungicide and other pesticide use. Avoid using soluble phosphorus fertilizers, compacting soil, too much rototilling or disrupting soil. Do add organic matter to soil with as little disturbance as possible. Avoid overwatering.
For information, read “Mycorrhizae, So, what the Heck are They, Anyway” by Dr. Linda Chalker-Scott, Washington State University (https://s3.wp.wsu.edu/uploads/sites/403/2015/03/mycorrhizae.pdf).
JoAnne Skelly is Associate Professor & Extension Educator, Emerita at University of Nevada Cooperative Extension. She can be reached at firstname.lastname@example.org.