Distribution patterns of usnic acid-producing lichens along local radiation gradients in West Greenland
Bjerke, Jarle; Werner Dahl, Tina
Lichens produce a wide variety of phenolics with high absorption levels in the ultraviolet range of the electromagnetic spectrum, and at least some of the phenolics are produced as protection against harmful UV radiation (UVR). A group of phenolics that has high photoprotector capacity is the widely occurring usnic acids. In arctic ecosystems, usnic acid-producing species are prominent and constitute a large part of the biomass. Distribution patterns and variations in abundance among usnic acid-producing lichens were studied along horizontal and vertical radiation gradients between Sisimiut and the ice cap in Central West Greenland, to see if degree of photoprotection reflect radiation regimes.Among the 24 recorded species, nine show oceanic preferences, six show continental preferences, five are ubiquitous, three are cryophilic, and one does not show any distinct pattern. Abundance, measured by an index (AA), and the number of species are highest near the coast where UVR is lowest. The distribution of species with low usnic acid levels is restricted by other factors than UVR. The species occupying the most light-exposed habitats and areas (ridges, high altitude and/or continental areas) all possess high levels of usnic acid, in addition to several other UV protective strategies, such as production of melanins and other phenolics, and thick upper cortex. It has been suggested that usnic acid-producing species can be used as bioindicators or biomonitors of near-ground UV-B radiation, and for this purpose some of the light-tolerant species may be suitable. Several controlled tests are needed, e.g. to determine response times to changes in UV-B radiation and whether the biosynthesis is doserelated, before lichens can be used as UV-B biomonitors.