Life

Symbiont fungi

Many fungi are involved in close and long associations known as symbiotic associations, which are mutually beneficial to both organisms. Two of these associations, lichens and mycorrhizas, have enabled some photosynthetic organisms to colonise deserted environments. Lichens are the combination of a fungus with a green alga or cyanobacteria; they are the first colonisers of bare rocky areas, they survive even when dry, they need light, air and mineral salts. The fungus makes it easier to absorb mineral salts and water as well as to maintain suitable conditions for the photosynthetic process, while the alga or bacterium supplies food in the form of by-products of the photosynthetic process. Lichens are not only economically important, but they are also used as bio-indicators or to date geological events (such as landslides or the withdrawal of glaciers). They are winter food for reindeers in the Arctic regions, are used in perfumery and to produce some colours. Mycorrhizas are associations between fungi and plant roots. The fungus uses the organic substances produced by the plant, supplies the plant with the minerals contained in the soil and makes it easier for the roots to absorb water. Sometimes, these associations become vital for both organisms, as is the case for some orchids, whose seeds do not sprout without a specific symbiont fungus. In its turn, the fungus cannot grow without a plant. A surprising association is the one that occurs between some species of fungi and some species of ants, such as, for instance, the Atta cephalotes. The ants collect and break up leaves and petals of flowers, on which grow special fungi that can only be found in ant nests, where they find the perfect conditions to spread.