Mycorrhizae

What are mycorrhizae?

The word "mycorrhizae" literally means "fungus-roots" and defines the close mutually beneficial relationship between specialized soil fungi (mycorrhizal fungi) and plant roots.

About 95% of the world’s land plants form the mycorrhizal relationship in their native habitats. It is estimated that mycorrhizal fungal filaments explore hundreds to thousands more soil volume compared to roots alone.

There is a lot of confusion about mycorrhizae, a word that describes the common relationship between plants and beneficial fungi. While the modern gardener is just beginning to learn about mycorrhizae, it has actually been around for millions of years. In fact, the fossil record shows that mycorrhiza appeared at about the same time as plants appeared on land.

The roots of almost all higher plants are known to form "mutualistic symbioses" with fungi. This is termed "mycorrhizae" which means fungus-root. This term is derived from the Greek, "mykes" which means mushroom or fungus and "rhiza" which mean root. The relationship is mutually beneficial. It forms colonies on the roots of a host plant. The fungus spreads threadlike feeding structures called hyphae into the soil. This type of colonization allows the host plant to develop a much larger root system, sometimes 100 times in length with up to 2000 times more surface area. The increased root surface area provides more room for water and nutrients to be taken in. The fungus serves as a bridge between the host plant and available nutrients. The hyphae help to break down organic material thus helping to release nutrients to the plant. Some fungi release chemicals to inhibit other organisms that might otherwise harm the plant. They develop a soil community that supports friendly bacteria, nematodes, springtails, earthworms, etc., but inhibits herbivores and pathogens. The fungus is considered a plant, but it has no chlorophyll so can not produce its own food. In return for their hard work, the fungi obtain a steady source of food (sugar) from the host plant.

This relationship developed because of need. Under conditions which are optimum, when the plant gets appropriate water and regular fertilizer, the plant had no need for the fungus and it will often disappear. For this reason, where there is adequate nutrition and moisture, non-mycorrhizal plants occur. These include most cultivated garden annuals and perennials. But in nature, conditions are not always optimum. Over past 400 million years or more, many plants have developed such that they depend upon this relationship.