Influence of polycyclic aromatic hydrocarbons on water storage capacity of two lichens species

The wide variability in functional traits that enable the cosmopolitan distribution of lichens often includes the water storage capacity, S, of their thallus. Lichen S in forest canopies can be large enough to intercept and evaporate significant amounts of rainwater, contributing to the runoff-reduction ecosystem services provided by urban forests; however, S is likely influenced by the presence of air pollutants (polycyclic aromatic hydrocarbons, PAHs) in urban areas. PAHs, being both chemically hydrophobic and damaging to lichen thalli, are expected to reduce lichens' S and, thereby, limit their contribution to hydrologic ecoservices of urban forests. Hence, the relationship between PAH accumulation and rainwater uptake was examined for two lichen species, common in urban forests around the world - Platismatia glauca and Pseudevernia furfuracea. Samples were collected from an area of low air pollution and another area in a highly urbanized city centre with high air pollution exposure (Krakow, Poland). Lichen S was determined using laboratory-simulated rainfall. PAH bioaccumulation differed between species and among the samples from clean and polluted environments. After exposure to polluted air, the concentration of PAHs was higher in P. glauca than P. furfuracea. Samples from the non-urban setting, however, showed no differences between the two species. In the case of P. glauca, S decreased from 35.8% in samples from clean environment to 8.3% after six months of exposure in the urban setting. The respective S values for P. furfuracea were 25.4% and 12.4%. Results strongly suggest that PAH exposure reduces S in both lichen species.The obtained results are important both in ecohydrology and microclimatology and are part of the research on the condition of urban forests.