Sensitivity of Lichens to Diesel Exhaust under Laboratory Conditions

Abstract

Lichen vegetation reacts very sensitively to a variety of air pollutants including increased nitrogen concentrations as well as to traffic exhaust in general, which makes lichens reliable monitoring organisms for atmospheric pollution. Recent environmental studies have shown that decreasing abundance of acidophytic lichen species and the increase of nitrophytic lichens can be explained by elevated levels of atmospheric nitric-compounds adsorbed onto nanoparticles. One major source of these atmospheric compounds amongst a wider pollution inventory is diesel exhaust—a mixture of gases and particle matter. This study aimed to shed light on the impact of diesel exhaust on the viability of six differently sensitive lichen species. Diesel exhaust particle concentrations in the laboratory experiments resembled those at a local highway during rush hour. By incubation in a closed stainless steel chamber we could exclude influences from other pollutants than diesel exhaust providing explicit data about the effects of diesel exhaust on lichens. The investigations revealed effects on the photosynthesis of the lichen photobionts and hence the lichen vitality. The conclusions of this study are that 1) the photobiont is affected stronger as the mycobiont and 2) older parts of the lichen are damaged first. Another remarkable result of this study is that 3) these lichens are regenerating to some extent during incubation-free periods — unless the organism is not damaged too much to restore photosynthetic activity. To our knowledge this is the first study evaluating the impact of diesel exhaust on lichens under laboratory conditions separate from other interfering pollutants.