Ecology of Fungi

Asexual spores come in many forms. There are conidiospores that can be multicellular or unicellular and that are directly released from the tip or side of the hyphae. Others will bud off from the vegetative part of the organism. Those spores that are released from a sporangium are called sporangiospores.

ECOLOGY OF FUNGI

Fungi have an important role to play in ecology as they are the major decomposers in nature. Organic matter is broken down that would otherwise be unable to be recycled because no other organism type can recycle these nutrients.

Fungi prefer dark and moist conditions and live in hostile environments that other organisms can’t. The forest floor is a common place for them, where there is a lot of decaying debris. As mentioned, they send out exoenzymes that decompose many structures to make nutrients that other organisms can use. Two main elements, nitrogen and phosphorus are necessary for life and yet are not readily available to many organisms without the action of fungal organisms.

The way that fungi participate most in the cycle of nutrients is through the action of their exoenzymes. These are released into the environment to break down cell walls and other nutrients of decaying matter. This requires water so the presence of water and damp environments is crucial to their digestive process.

The mutualistic relationship to other organisms includes relationships between plants, animals, and cyanobacteria. Mutualistic relationships are also called symbiotic relationships when both members in the relationship receive benefit from the others.

As mentioned, mycorrhizae are extremely common, affecting 90 percent of terrestrial plants. In this association, the hyphae branch out and come in contact with the soil in order to channel minerals and water toward the plant, increasing the ability of plants to take up nutrients. The tradeoff is that the fungi benefit from the products of photosynthesis coming from the plants.

Mycorrhizae do not diversify much as they do not participate in sexual reproduction. In many ways, they are quite primitive and cannot live outside of the mycorrhizae. There

are several types of mycorrhizae. One is called ectomycorrhizae, in which the fungal hyphae form a sheath around the roots called a mantle with a net of hyphae that extend outward from the roots.

Another type of mycorrhiza is called the glomeromycete fungi or endomycorrhizae. In such cases, the fungi form arbuscules (vesicles) that penetrate the root cells, resulting in metabolic exchange between the fungus and plant. A third type involves those seen in orchids. The orchid plant forms seeds that need a mycorrhizal exchange between the fungal organism and the seed. The fungus provides nutrients to the seed until it can germinate.

Lichens have the ability to survive in very hostile environments and are basically everywhere. Lichens are not single organism but, as mentioned, are the combined efforts of fungi and cyanobacteria or algae. These are hardy relationships, surviving cold and desiccation in order to come alive in more prosperous situations. They are important in ecology because they are highly sensitive to air pollution. The fungi responsible can be Basidiomycota or Ascomycota species—with no member of the lichen able to survive outside of the symbiotic relationship.

The body of the lichen is referred to as a thallus, which involves hyphae that are wrapped around a photosynthetic partner species. Sometimes, when cyanobacteria are involved, the cyanobacteria will take nitrogen from the air and fix it for the hyphal partner. The fungus will protect the photosynthetic partner from desiccation and excessive light and will provide minerals to the cyanobacterial organism. The fungus can also form the attachment of the lichen to the underlying substrate. These lichens will form soredia, which are clusters of the algae or cyanobacteria surrounded by mycelia that are dispersed by wind and water in order to make new lichens.

Fungi have mutualistic relationships with animals as well—particularly insects. The fungus provides protection from pathogens and predators, while the fungus gets a way to disseminate spores and gets nutrients from the insect. The fungus will cover the insect colonies and, in some cases, the fungi will digest the cellulose that cannot be broken down by the insects. When this happens, the insect eats the fungus that has the

broken-down nutrients in it. The insects, in return, will protect the area from invading and competing fungal organisms.