| A vast amount of research in relation to air pollution has been conducted with very high concentrations of pollutants and/or relatively sensitive lichen species showing negative impacts of air pollution in lichen physiology and structure. Not only are these lichens subject to varying air quality, but they must also be able to cope with high light in collection areas, Pacific Northwest Forests, in summer while they remain in desiccated state for most part of the day with high irradiance. This research reports on relatively low-level air pollution impacts on net carbon uptake, pigmentation and structure using intermediate tolerant species, Parmelia sulcata and Platismatia glauca, from two different polluted field sites using air pollution data. To access light sensitivity, the same lichen species were used to measure Fv/Fm, photochemical efficiency of photosystem II, by exposing them to high light intensity in both dry and wet state. Lichens revealed higher net carbon uptake and higher pigment content at polluted sites in comparison to a clean site in summer although in winter no significant differences between clean and polluted samples were found in net carbon uptake. Using electron microscopy, lichens also revealed higher cytoplamic lipid content in polluted materials compared to clean ones. In these physiological and structural results, each lichen species responded to one of polluted sites showing positive responses which had different combinations of pollutants. In photoinhibition study, both species exhibited significantly lower rates of photoinhibition in the desiccated state by inactivating their photosynthetic apparatus compared to in hydrated state. P. sulcata which is in less shaded habitat is more tolerant to high irradaince by possessing higher content of carotenoids and higher volume density of upper cortex to protect their photobionts from high irradiance than P. glauca. The results represent the lichen responses in their natural habitat with respect to moderately elevated air pollution and increased light intensity giving an ecophysiological significance to adaptation of lichens to different environments. |
