Unlike plants, fungi cannot make their own food. They absorb their
food from dead organic matter, or other living organisms. The source of
their food is called a substrate if it is dead, and a host if it is
The body (mycelium) of a fungus is made of threads called hyphae. Hyphae absorb nutrients from the substrate, spread, grow, and produce fruiting bodies. The fruiting body of the fungus is the part that we can see, and touch.
Black Truffle Cup Fungus Morel
Giant Puffball Mushroom Earth Star
Mycorrhizae result from the symbiosis (partnership) between a fungus' hyphae and a living plant root. Symbiotic partnerships occur only between living organisms. If a fungus obtains its carbohydrates from dead organic matter it is a "decomposer" and not symbiotic.
Symbiotic partnerships are formed in three ways. A parasitic relationship benefits the fungus but harms the host. In mutual symbiosis, both fungus and host benefit from their partnership. A neutral symbiosis benefits the fungus with no harm or benefit to the host.
Mycorrhizal symbioses are mutual and two types are recognized: ectomycorrhizae and endomycorrhizae.
In ectomycorrhizal symbiosis, the hyphal threads coat the tips of tree roots. Some threads spread from the root coating into the soil to capture minerals. Others spread inward between the root cells. These hyphae make a path from the soil into the tree for the minerals the tree needs, and allow the fungus to feed in turn upon the carbohydrates produced by the tree's photosynthesis.
The importance of the ectomycorrhizal partnership is shown in the close physical relationship between the fungus and its host tree. It is very difficult to separate hyphae from the host cells. Ectomycorrhizal hosts include many trees: oaks, pines, firs, hemlocks, beeches, birches, and more. Many large forest fungi form ectomycorrhizal partnerships, both truffles with underground fruiting bodies and fungi with the umbrella-shaped fruiting bodies known as mushrooms.
Endomycorrhizal partnerships are the most common type of mycorrhizal symbiosis. Endomycorrhizal fungi do not coat the root. Only a few hyphae spread across the root's surface and those that pierce the root enter into the root cells. The hosts for this symbiosis are green plants that are not ectomycorrhizal. This type of fungus usually produces single spores in the soil for reproduction, not large fruiting bodies.
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Last update: 25 Oct 96. © 1996, Robert Fogel, Ivins, UT 84738. Edited by Patricia Rogers.Ectomycorrhiza photographs courtesy of J. M. Trappe and U.S. Forest Service