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Fungi in the soil: mushrooms, mycelia and mycorrhiza

In the cool, damp and dark of the autumn forest, fungi are flourishing everywhere. Don't be fooled - there is far more to a fungus than the humble mushroom.

In the cool, damp and dark of the autumn forest, fungi are flourishing everywhere. Don't be fooled - there is far more to a fungus than the humble mushroom.

A mushroom is merely the reproductive body of a fungus, produced occasionally to release spores into the air. The majority of the fungus lives under the ground as an interconnected network of thread-like filaments called hyphae. A single network, called a mycelium, can cover vast areas under the soil. One mycelium in eastern Oregon was recorded at 2,400 acres in size - equivalent to 1,665 football fields.

Fungi appear to be closely related to plants. However, while plants are able to harness sunlight to create their own food, fungi are more like animals, needing to obtain carbon compounds for growth and energy from other sources.

Soil fungi have evolved several ways to obtain essential nutrients. Some fungi are parasites or pathogens - infecting plants or trees and living off their bodies (an example is the fungi that cause root rot). Others are decomposers, secreting enzymes to break down wood, leaf litter and other organic matter. This releases nutrients for the fungi, and helps recycle nutrients into usable forms for other life forms to use.

Another type of fungi - known as mycorrhizal fungi - has evolved a mutually beneficial partnership with plants and trees. Their hyphae form a sheath around their roots, in some cases penetrating plant cells. The fungus uses its network of hyphae to absorb minerals and water from the soil, delivering some to the plant. In exchange, the plant supplies the fungus with carbon and energy in the form of simple sugars. The fungi are also thought to protect trees against pathogens and extreme environmental temperatures, while contributing to soil structure and ecology.

This symbiotic relationship has evolved over a very long time - it is thought that fungi enabled plants to move from the water to the land half a billion years ago. In British Columbia, all major timber trees and many ornamentals are symbiotically dependant on a relationship with fungi (excepting some species in the families Cupressaceae and Aceraceae). Without fungi, the incredible diversity of plant life that surrounds Squamish may not exist at all.

Fungi can be negatively affected by a number of human practices or susceptible to human interventions including air pollution, use of fertilizers, clear-cut logging, fire management and non-sustainable harvesting of edible mushrooms. Unfortunately, as the majority of fungi are hidden under the ground, their contribution can be overlooked. Research into fungi in ecosystems and protection of endangered species is therefore an extremely important area of research.

The next time you go for a walk, keep an eye out for mushrooms. If you find one, consider the part of the fungus that you cannot see - the branching mycelium possibly intertwined with the roots of surrounding trees. The mushroom is a humble but essential piece of the complex soil story hidden beneath your feet.

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