Mycelium (plural mycelia) is the vegetative part of a fungus, consisting of a mass of branching, thread-like hyphae. The mass of hyphae is sometimes called shiro, especially within the fairy ring fungi. Fungal colonies composed of mycelia are found in soil and on or within many other substrates. A typical single spore germinates into a homokaryotic mycelium, which cannot reproduce sexually; when two compatible homokaryotic mycelia join and form a dikaryotic mycelium, that mycelium may form fruiting bodies such as mushrooms. A mycelium may be minute, forming a colony that is too small to see, or it may be extensive:
It is through the mycelium that a fungus absorbs nutrients from its environment. It does this in a two-stage process. First, the hyphae secrete enzymes onto or into the food source, which break down biological polymers into smaller units such as monomers. These monomers are then absorbed into the mycelium by facilitated diffusion and active transport.
Mycelium is vital in terrestrial and aquatic ecosystems for its role in the decomposition of plant material. It contributes to the organic fraction of soil, and its growth releases carbon dioxide back into the atmosphere. The mycelium of mycorrhizal fungi increases the efficiency of water and nutrient absorption of most plants and confers resistance to some plant pathogens. Mycelium is an important food source for many soil invertebrates.
Sclerotia are compact or hard masses of mycelium.
One of the primary roles of fungi in an ecosystem is to decompose organic compounds. Petroleum products and pesticides that can be contaminants of soil are organic molecules. Therefore, fungi should have potential to remove such pollutants from the soil environment, a process known as bioremediation.
Mycelial mats have been suggested (see Paul Stamets) as having potential as biological filters, removing chemicals and microorganisms from soil and water. The use of fungal mycelia to accomplish this has been termed "mycofiltration".
Knowledge of the relationship between mycorrhizal fungi and plants suggests new ways to improve crop yields.
When spread on logging roads, mycelium can act as a binder, holding new soil in place and preventing washouts until woody plants can be established.
Mycelium has been used to bind agricultural by-products to form products dubbed Greensulate and Ecocradle, which are alternatives to plastic styrofoam for packaging and insulation. Two inventors, Eben Bayer and Gavin McIntyre, and their company Ecovative Design, developed the method to manipulate a network of mycelia into desirable shapes, with properties comparable to its plastic counterpart. The invention has won two awards and is now in use commercially by Steelcase as packaging for furniture. This use of mycelium has been discussed in Time Magazine, Popular Science and other media, as well as being the subject of a TED Talk "Are Mushrooms the New Plastic?" by Eben Bayer.
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