lichens1
Description
Lichens, as organisms vulnerable to air pollution, are often used as bioindicators. Their functional variability enables inhabiting different climate regions and determines high water storage capacity. This parameter was examined for two lichen species – Platismatia glauca and Pseudevernia furfuracea. Samples were collected from an area of low air pollution (NE Poland) and exposed to contaminated environment (S Poland). The process of water interception was examined with the use of simulated rainfall under laboratory conditions. Water storage capacity was determined on an interception function as the value above which the volume of water retained in lichen thalli did not increase. PAHs concentration differed among the species and among the samples from clean and polluted environment. After exposure to polluted air, the concentration of PAHs was higher in Platismatia glauca, while in the case of samples from clean environment, there were no differences between the two species. The results of the experiment clearly indicate that air pollution reduces water storage capacity in both lichen species. Samples with higher concentration of aromatic hydrocarbons had lower water storage capacity. In the case of Platismatia glauca the value decreased from 35.84% in samples from clean environment to 8.29% after six months of exposure in the city centre. The respective values for Pseudevernia furfuracea were 25.44% and 12.39%. The species with higher water storage capacity accumulated more PAHs and, consequently, the decrease in water retention was greater. The results provide new insight into ecohydrological research, as lichens differ from plants in their reaction to prolonged exposure to air pollution. Changes in lichen water storage capacity caused by contaminants may affect the microclimate of their habitats. Therefore, there is a causal relation between air pollution and water retention by lichens. Keywords: water storage capacity; simulated precipitation, PAH, interception, retention