| dc.description.abstract | Lichens represent a mutualistic community of fungal partners (mycobiont) and photosynthetic partners (photobiont), furthermore an undetermined number of other microorganisms living in and on the surface layers contribute to this association. They are present in 8 % of terrestrial plant communities. Lichens are characterized not only by their slow growth, but also by their extreme tolerance to various environmental conditions. Under the given conditions, lichens can also be a source of feed (most often in case of emergency only) for certain groups of animals. After a brief, general characterization of the world of lichens, our literature review also presents some secondary metabolites of lichens, their number today is more than a thousand. Most of the secondary substances are produced by the mycobiont partner, but microcystins are synthetized by the cyanobacterial members of the lichen communities. The chemical composition of lichens is characterized by low protein and fat content, variable ash content and a very significant carbohydrate content, the latter group is characterized by special polysaccharides such as lichenin and isolichenin, that do not occur anywhere else beside cellulose and hemicellulose. All this can be supplemented by specific lichen metabolites (usnic acid, pulvinic acid, microcystins and others) and lead to rare but typical lichen poisonings. The biological effect of usnic acid is outstanding, as it causes liver damage in non-ruminants and in humans, and in ruminants, large herbivores (reindeer, usually cervids) the rumen bacterial flora largely neutralizes usnic acid. It has been proven that lichens are behind the classic poisonings that caused massive animal deaths (Wyoming, 2003-2004), although it is possible that not only usnic acid, but also other constituents are responsible for the symptoms. Lichens where the photobiont partner can produce liver-damaging microcystins can pose a potential danger. Changes in climatic conditions may increase the role of lichens as a forage source for certain animal groups. Further tests and data are necessary for an even more precise understanding of lichen poisoning. | en_US |
