Lichens as Indicators of Air Pollution

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Summary

Lichens are well known as sensitive indicators of air pollution, particularly for sulfur dioxide. In part, this is related to their unique biology. Evidence supporting this assertion goes back well over 100 years and is based on extensive field and laboratory studies. In general, these studies reinforce each other, but for oxidants the data are not entirely consistent, and consequently require further work. At the least, lichens appear to be less sensitive to oxidants than vascular plants. Acid precipitation effects are closely related to SO2 effects. The mechanistic basis for SO2 effects is briefly reviewed. The extreme sensitivity of lichens to SO2 is partially related to their ability to absorb more SO2 for a given concentration than typical vascular plants. The use of lichens as long-term integrators of elemental deposition patterns is well established, but their use for monitoring dry deposition has only recently been recognized. Air pollutants adversely impact not only growth, reproductive potential, and morphology, but also a wide variety of physiological processes, which also becomes reflected in ultrastructural changes. The impact of organic pollutants on lichens is largely undocumented and is a prime area for future work, even though much work remains to be accomplished with the traditionally recognized air pollutants.