Lichen substances prevent lichens from nutrient deficiency

Abstract

The dibenzofuran usnic acid, a widespread cortical secondary metabolite produced by lichen-forming fungi, was shown to promote the intracellular uptake of Cu2+ in two epiphytic lichens, Evernia mesomorpha and Ramalina menziesii, from acidic, nutrient-poor bark. Higher Cu2+ uptake in the former, which produces the depside divaricatic acid in addition to usnic acid, suggests that this depside promotes Cu2+ uptake. Since Cu 2+ is one of the rarest micronutrients, promotion of Cu2+ uptake by lichen substances may be crucial for the studied lichens to survive in their nutrient-poor habitats. In contrast, study of the uptake of other metals in E. mesomorpha revealed that the intracellular uptake of Mn2+, which regularly exceeds potentially toxic concentrations in leachates of acidic tree bark, was partially inhibited by the lichen substances produced by this species. Inhibition of Mn2+ uptake by lichen substances previously has been demonstrated in lichens. The uptake of Fe2+, Fe 3+, Mg2+, and Zn2+, which fail to reach toxic concentrations in acidic bark at unpolluted sites, although they are more common than Cu2+, was not affected by lichen substances of E. mesomorpha. © 2009 The Author(s).