Beyond ozone-tolerance: effects of ozone fumigation on trace element and PAH enriched thalli of the lichen biomonitor Pseudevernia furfuracea

In this study, the effects of ozone (O3) on the physiology of the lichen Pseudevernia furfuracea var. furfuracea previously subjected to field stressing conditions were assessed. Samples collected in a pristine site were exposed for 6 weeks at 3 sites characterized by different pollution, e.g. elemental and PAH depositions (site RU, close to wood-burning house chimneys; site UI, close to cast-ironworks; site CK, in a semi-natural context). Afterwards, samples were transferred to controlled fumigation chambers, where they were either O3-treated for 2 weeks (250 ppb O3 for 5 h day−1, O3+ samples) or not (0 ppb O3, O3− samples). Three physiological markers (Fv/Fm, maximum quantum yield of primary photochemistry; MDA, malondialdehyde content; potassium leakage) as well as elemental and PAH concentrations were measured in matched sets of sample replicates at each experimental step. Data were explored by multivariate techniques and the effects of field exposure and fumigation were tested by generalized linear models (GLM). Detrimental effects on MDA and Fv/Fm were observed limited to samples exposed in RU and UI sites. Physiological parameters in O3-treated samples showed heterogeneous variation patterns with respect to field-exposed ones. A recovery of Fv/Fm was observed in RU- and UI-exposed samples, whereas a significant increase of MDA was highlighted limited to CK O3+ and CK O3− samples, possibly related to a “chamber effect”. Overall, the impairment caused by ozonation was limited, proving the strong O3-tolerance of our test species. Interestingly, the content of the most abundant 4-ring PAHs in RU O3+ samples, which underwent the highest field enrichment of PAHs, was significantly lower than that of matched RU O3−samples. This suggested a possible role of ozone in degrading PAHs at thallus level, with interesting interpretative repercussions in the context of transplant-based surveys aimed at evaluating PAH depositions when O3 ground levels are high