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Solhaug, K.A./ Gauslaa, Y. 2012: Secondary Lichen Compounds as Protection Against Excess Solar Radiation and Herbivores. - In: Lüttge, U./ Beyschlag, W./ Büdel, B./ Francis, D.: Progress in Botany. 37. Springer pp. 283-304. [RLL List # 241 / Rec.# 36773]
Abstract: The functional roles of secondary lichen compounds are reviewed with focus on sun-screening and herbivore-deterring functions. Hypotheses on ecological functions can be tested because lichen compounds can nondestructively be extracted from air-dry lichens with 100% acetone. Substantial evidence supports a sun-screening function of cortical compounds. They screen solar radiation by absorptance (parietin, melanins) or by reflectance (atranorin). Their concentration correlates with light exposure and they protect the photobiont against excessive visible light. UV-B induces the formation of parietin, usnic acid, and melanins; the synthesis of the two first compounds has been shown to be boosted by photosynthates. The numerous extractable medullary lichen compounds hardly function as sun-screens. Some of these carbon-based compounds deter generalist herbivores, particularly in lichens in oligotrophic sites. Lichens in nitrogen-rich sites often deter grazing animals as efficient as those from oligotrophic sites despite low contents of lichen compounds. Acetone rinsing of nitrophytic lichens does not lead to increased grazing, meaning that their defense remains to be described. Thanks to grazing experiments using acetone rinsing, there is now solid support for the optimal defense theory in lichen–herbivore interactions. Recent studies have shown that lichen-feeding gastropods can shape epiphytic lichen communities.
URL: http://link.springer.com/chapter/10.1007/978-3-642-22746-2_11
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