Temporal changes in accumulation of trace metals in vegetative and generative parts of Xanthoria parietina lichen thalli and their implications for biomonitoring studies

Certain lichens are widely used in air pollution biomonitoring because the contents of various elements in their thalli accurately reflect the chemical composition of the air. Temporal changes in selected concentrations of trace metals in vegetative and generative parts of Xanthoria parietina thalli exposed to urban-related pollution were analysed and the relationship between anatomical organisation and element accumulation identified. The lichen material included thalli relocated to an urban area of Cracow (southern Poland) along with their host trees, which had previously been cultivated at a site characterised by a lower level of air pollution. The thalli were sampled immediately and 1, 3, 6, and 12 months after planting trees. Concentrations of Zn, Pb, Cd, Cu, Ni, and Cr, as measured by means of flame atomic absorption spectrometry (FAAS), and various anatomical characteristics were determined in vegetative thalli and the corresponding apothecia. Accumulation of Pb over time demonstrated a pronounced upward trend; calculated exposed-to-control (EC) ratios indicate 'severe accumulation' of this element. Diverse levels of accumulation in different parts of thalli - higher, in the cases of Pb, Cd, Cu, Ni, Cr, and lower, in the case of Zn, in vegetative parts compared to apothecia - were observed. Thus sampling uniformity is highly desirable in air biomonitoring studies, along with a determination of which part of the thallus is to be designated for elemental analysis. The results also showed that certain anatomical characteristics are correlated with concentrations of metal elements in the thallus.