Mutualism between Fungi & Plant Roots

We tend to see the life of a plant as a simple, solitary effort of converting sunshine to energy and gathering nutrients and water from the soil. However, just below ground there is often the support of hidden allies.

Most plants are masters of photosynthesis (autotrophic). They are able to take sunlight and convert it into carbohydrates, which the plants store and use as food when needed, to perform activities such as growth and reproduction. Plants also have roots to get nutrients and moisture from the soil. But many plants have difficulty obtaining enough water and nutrients such as nitrogen and phosphorus to properly support their growth.

Fungi are heterorophic which means they are incapable of photosynthesis and are only able to absorb what they need from their surroundings in order to survive.

So plants and fungi often join forces to provide for each other in a way that is advantageous to both. Plants produce excess carbohydrates and other metabolites for the fungi to use as fuel, while the fungi allow the plants to get water as well as nutrients including nitrogen and phosphorus in larger quantities than the roots would be able to on their own. In addition, the fungi protect the plant roots from pathogens in the soil and provide soil stabilization. In many cases the network of fungi that colonized the roots act as extensions of the plants own root systems, using branching filaments called hyphae to collect and distribute what it gathers.

Mycorrhizal FungiThis mutualistic association between fungal entities and the roots of plants is known as Mycorrhizal. Some scientists speculate that up to 90% of land plants rely, in varying degrees, upon some form of mycorrhizal fungi. Some plant varieties are so dependent on this relationship, that they would not survive without it.

The Douglas fir alone is estimated to have associations with 2,000 species of mycorrhizal fungi. One such fungi is the Pacific golden chanterelle (Cantharellus formosus).

The complete story of the relationships between fungi and plant roots is a bit more complicated than can be described here. In some instances, the relationship might be seen as bordering on parasitism rather than mutualism. In the article entitled, “Functioning of mycorrhizal associations along the mutualism-parasitism continuum”, the authors state that, “Mycorrhizal fungi might be considered to be parasitic on plants when net cost of the symbiosis exceeds net benefits.” There are many species specific mycorrhizal relationships that exist, and each has its own unique relationship between the plant (macrosymbiont) and the fungi (microsymbiont) that colonize its roots.