The importance of fungal activity in relation to tree growth is largely overlooked. People are sometimes disturbed when they see the fruiting bodies of such fungi, because there are often negative implications to seeing mushrooms in the landscape. Mushrooms may be a sign of overly acid soils or rot in tree roots. However, the mycorrhiza fungus performs essential functions in the soils, and they form symbiotic relationships with trees through the tree's root system. Some mycorrhizae penetrate the roots and some simply surround the root tissue. It's estimated that more than 80 percent of higher plant species develop symbiotic relationships with mycorrhizal fungi.
Benefits to the Tree
Because the relationship between trees and mycorrhizae is symbiotic, both the tree and the fungi extract some benefit. Mycorrhizae are more effective than tree roots at accumulating water and nutrients, and can store excess nutrients, releasing them to the tree as needed. The fungi also inhibit invasion by damaging fungi, and extend the life to root tips. Mycorrhizae release acids that break down substances that the plant cannot use without this help, and fix nitrogen from both the soils and atmosphere so that it is more available to the tree. Mycorrhizal fungi produce hormones that encourage the production of new root tips, which aids both the tree and the fungi.
Benefits to the Mycorrhiza
The symbiotic relationship between mycorrhizae and trees benefits the fungi as well. Fungi cannot manufacture their own food due to lack of chlorophyll, a process that converts sunlight to energy used for producing sugars. Therefore, fungi must get this food from chlorophyll-producing plants. They do so by either penetrating the plant roots or forming a sheath around the root tips. This energy allows the fungi to reproduce and form large networks within the soils.
Mycorrhiza and Intertree Interaction
Because the network of mycorrhizal fungi is often vast, trees may often form a network of interlocking root/fungi pathways that connect trees to each other. Professor Suzanne Simard of the University of British Columbia identified the "mother tree" concept, which suggests that the largest trees of the forest, or the mother trees, infect the new seedlings with mycorrhizae, providing a highway by which the mother tree can provide the seedling the nutrients it needs to survive. Trees under stress may receive carbon through underground pathways from nearby trees not experiencing stress.
Arbuscular vs. Ectomycorrhizas
There are essentially two ways in which mycorrhizae function. One type penetrates the root and the other type surrounds the root. The type that penetrates the root is called arbuscular mycorrhizae or endomycorrhizae, and it can be found in roots of crop plants and tropical plants. On the other hand, ectomycorrhizae commonly attach to trees in cooler parts of the world. Ectomycorrhizae modify the root tips by covering them with a sheath and take on the role normally occupied by the tiny root hairs. Some trees use both types.
- Oregon State University: Mycorrhizae, A Hidden Benefactor to Forest Trees
- Pearson College: The Role of Mycorrhizae in Forestry
- Trees for Life: Mycorrhizas
- University of Edinburgh: The Microbial World: Mycorrhizas
- Canadian Geographic: How Avatar Got it Right
- University of British Columbia: At the Root of the Problem
- University of Wisconsin: The Kingdom Fungi
- Photos.com/Photos.com/Getty Images