Based on findings in vascular plants showing that the capacity to provide enough carbon skeletons for rapid ammonium assimilation into amino acids is a prerequisite for tolerance to eutrophication, we tested the hypothesis that lichens from shady habitats are particularly sensitive to nitrogen pollution. We tested this hypothesis using published ecological indicator values (estimates of eutrophication tolerance and light preferences on an ordinal scale) for more than 500 central European lichen species. Our results show that shade-adapted lichens are indeed at the same time intolerant to eutrophication. However, not all eutrophication-sensitive lichens inhabit shady environments, suggesting the existence of several independent mechanisms causing intolerance of high nitrogen levels in lichens. The correlation of shade adaptation with nitrogen intolerance is limited to epiphytic and saxicolous species, since terricolous lichens are out-competed by vascular plants in dense vegetation. Our results suggest that lichen communities of shady bark, wood and rock are particularly sensitive to eutrophication.
