Mushrooms are a familiar sight in woodlands and pastures, although most of us are only familiar with the cap and stalk of the fruiting body. There are over 80,000 known species of mushrooms found around the world, and scientists estimate that there are as many as 1 million more species yet to be discovered and identified. Mushrooms are found all over the world and range in size from microscopic to giant mushrooms, which spread out for miles underground. Different species of mushrooms grow in different habitats, and where they grow depends on how they obtain their nutrients.
Many mushrooms are mycorrhizal, which means that they form a mutually beneficial relationship with another plant, usually a tree. The mushrooms collect sugars from the tree and, in turn, provide the tree with water and nutrients. The fruiting bodies of mycorrhizal mushrooms do not grow directly on the tree but instead emerge from the soil surrounding the tree; underground, the mycelia of the mushrooms are intertwined with the roots of the tree. Because certain species of mushrooms prefer certain species of tree, identifying the nearby trees can help you identify the mushrooms. Amanita mushrooms, for example, like spruce trees, whereas many species of bolete mushrooms prefer deciduous trees, like oak or beech. Mycorrhizal mushrooms may also form symbiotic relationships with moss and other plants or with microflora in the soil. Science is still working to understand the complexities of mycorrhizal mushrooms.
Saprotrophic and Necrotrophic Mushrooms
Other mushrooms grow on dead or dying organic matter and may even work to kill the host plant. Saprotrophic mushrooms colonize plant or animal matter that is already dead, such as fallen trees or dung, whereas necrotrophic fungi live as parasites. They attach themselves to a living tree, for example, and divert water and nutrients away from the plant and into the mushrooms until the host plant dies, at which point, the mushrooms may continue to break down the dead plant matter. Saprotrophic and necrotrophic mushrooms are essential parts of the ecosystem, because they cull weak or diseased plants and create habitats for birds and other animals by hollowing out dead trees. And, in their work as decayers, they help add vital nutrients back into the soil, creating a bed for future trees and other plants. Many bracket or shelf mushrooms are saprotrophic or necrotrophic.
Biotrophs are different in that they depend on a living host, but they do not benefit the host like mycorrhizal mushrooms nor do they kill the host like necrotrophic mushrooms. Familiar biotrophic mushrooms include various molds, smuts and other fungal infections, and they often weaken or degrade the host on which they grow.