The effective quantum yield of photochemical energy conversion in photosystem II (Φ2) was shown to be reduced in the terricolous lichens Cetraria aculeata and Cetraria islandica by short-term exposure to aqueous SO2 at pH values occurring in the precipitation of areas with high SO2 pollution. Significant reduction of Φ2 was found at pH <= 3.3. At pH 2.8, Φ2 was close to zero and did not recover within 24 h. This suggests that sensitivity to SO2 (primarily associated with epiphytic lichens in the past) has contributed to the decline of both species in central Europe. In C. islandica, but not in C. aculeata, thalli with the natural content of lichen substances were more tolerant to SO2 than thalli where the extracellular lichen substances were extracted before the experiment. This supports published results that the depsidone fumarprotocetraric acid, a major lichen substance of C. islandica, increases the pollution tolerance in lichens. Artificial acidic precipitation with aqueous sulphur dioxide at pH 2.8-3.5 affects terricolous Cetraria species.

The study aimed to explore if changes in crown defoliation and stem growth of Scots pines (Pinus sylvestris L.) could be related to changes in ambient ozone (O(3)) concentration in central Europe. To meet this objective the study was performed in 3 Lithuanian national parks, close to the ICP integrated monitoring stations from which data on meteorology and pollution were provided. Contribution of peak O(3) concentrations to the integrated impact of acidifying compounds and meteorological parameters on pine stem growth was found to be more significant than its contribution to the integrated impact of acidifying compounds and meteorological parameters on pine defoliation. Findings of the study provide statistical evidence that peak concentrations of ambient O(3) can have a negative impact on pine tree crown defoliation and stem growth reduction under field conditions in central and northeastern Europe where the AOT40 values for forests are commonly below their phytotoxic levels.