Mycorrhizae And Lichens

A mycorrhiza (MIE-koh-RIE-zuh) is a symbiotic structure formed by a fungus and plant roots. More than 80 percent of vascular plants contain such fungi on their roots. The fungus absorbs and concentrates nitrogen, phosphate, and other ions for delivery to the plant root and increases surface area of the plant's root system. In turn, the fungus receives sugars that the plant makes during photosynthesis. All three fungal phyla form mycorrhizae. These mycorrhizal relationships appear to have coevolved with plants.

Lichens (LIE-kuhnz) represent symbiotic relationships between a fungus and a photosynthetic partner (usually a cyanobacterium or green alga). Most fungi in lichens are ascomycetes. The photosynthesizer makes sugars for the fungus, and the fungus provides moisture, shelter, and anchorage for the photosynthesizer. The fungus produces acids that decompose rocks, making minerals available to the lichen. The chemical decomposition of rocks by lichens contributes to the production of soil.

Lichens are identified according to their distribution and structure. Crustose lichens grow as a layer on the surface of rocks and trees. Fruticose lichens are shrublike, and some grow up to 1.5 m (5 ft) in length. Foliose lichens live on flat surfaces, where they form matlike growths with tangled bodies. One example of a lichen is shown in Figure 26-8.

figure 26-8

Lichens are grouped according to their type of body. For example, this red lichen is a crustose lichen that grows on rocks.

figure 26-8

Lichens are grouped according to their type of body. For example, this red lichen is a crustose lichen that grows on rocks.

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