Diagram (top): © Bryce Kendrick

facts about ectomycorrhizae and mushrooms

Unlike plants that are capable of producing their own carbon through photosynthesis, fungi must obtain their carbon from an external source. Mycorrhizal fungi form a mutualistic association with plant and trees roots. Mycorrhizal fungi produce hyphae that explore the soil, absorb soil nutrients such as phosphorus, nitrogen and other minerals and water, move them to the roots, where they are exchanged for simple carbohydrates. Trees in British Columbia predominently form either an ectomycorrhizal or an arbuscular mycorrhizal association, or both, depending on the type of tree. Ectomycorrhizal trees can form mycorrhizae with a broad range of fungi that are in turn capable of forming mycorrhizae with a broad range of host trees. However, there are suites of fungi that are associated with specific host trees.

Ectomycorrhizal associations are characterized by a fungal mantle produced around the fine root. As well, hyphae penetrate the root and surround the cortical cells, without penetrating these cells. This net of hyphae surrounding the cells is known as the Hartig net. Exchanges of nutrients and sugars between fungus and plant occur in the Hartig net. Once the fungus has adequate nutrient reserves, hyphae in the soil develop fruiting bodies either above or below the ground.

Fruiting body production is a complex procedure dependent on the soil temperature and moisture status, the time of year, the biology of the fungus and the interactions of other fungi and other microbes. Fruiting bodies come in a variety of different shapes, sizes, colours, smells and tastes. Mushrooms, boletes, coral fungi, truffles, conks, cup fungi are examples of above ground fruiting bodies. These fungi can be poisonous, edible and choice, hallucinogenic (magic mushrooms), used for medicinal, pharmaceutical or industrial purposes.

Mushrooms and their allies are the most common of the large types of fruiting bodies found in forests. All mushrooms are composed of a pileus, lamellae, and a stipe. Sometimes, rather than having lamellae, a fruiting body will have tubes, pores, spines or veins. Basidia and spores are the microscopic sexual structures found on the lamellae, tubes, spines or veins and are referred to as the hymenial layer. Sometimes sterile cells known as cystidia are also found on the hymenial layer. Some spores and cystidia change colour when chemical reagents are applied to them. Spore colour, size and colour change in chemical reagents are important in identifying mushrooms. Sometimes a protective layer of tissue known as the annulus on the stipe and the volva at the base of the stipe are present and are important for identification.