Effects of ultraviolet on polyphenolics of Umbilicaria americana

Abstract

The foliose lichen Umbilicaria americana Poelt & Nash was exposed to spectrally altered radiation in three growth chamber experiments and one field experiment. After 1 week in growth chambers the phenolic content (% w/w) increased significantly under a spectral band including visible light and UV-A, and the increase was greater when intensity was higher. Under exposure to both UV-A and UV-B the concentration of phenolics was lower than with UV-A alone and, depending on dosage, approached or achieved control levels. In a population of U. americana on a vertical rock face, the interaction between filter treatments and collection dates had a highly significant effect on phenolic levels (P = 0.01). In thalli protected from UV-B, phenolic levels were higher than in those exposed to natural sunlight in June and October, but the same response was not observed in July and August. Thallus groupings covered by filters that admitted both UV-B and UV-A accumulated less phenolics than controls in August, but on other sampling dates contained the same concentrations. Key words: Umbilicaria americana, UV-A, UV-B, depsides, tridepsides.