Lichen and moss bags as monitoring device in urban areas. Part I: influence of exposure on sample vitality

Abstract Samples of the lichen Pseudevernia furfuracea (L.) Zopf and the moss Hypnum cupressiforme Hedw. were exposed for 6 weeks in nylon bags in two air pollution monitoring stations in Trieste and Naples (Italy) with different climates and pollution loads to evaluate influence of environmental conditions on sample vitality. This was assessed before and after exposure by transmission electron microscopy observations, K cellular location, and measurements of C, N, S and photosynthetic pigments content, CO2 gas exchange, and chlorophyll fluorescence. Almost all data sets indicate that exposures caused some damage to the species, considerably heavier in the moss, especially in Naples. The two cryptogams differed significantly in accumulation and retention of C, N, and S, the lichen clearly reflecting NO2 availability. The difference in vitality loss was related to the different ecophysiology of the species, because concentrations of phytotoxic pollutants were low during exposure. Critical notes on the analytical techniques are also given. Almost all the techniques used showed that the short exposures were sufficient to cause some damage to both organisms. Under the environmental conditions of both cities the lichen revealed a stronger resilience than the moss, apparently because the two organisms have a different ecophysiology. In both cities the lichen maintained good vitality levels, although some light stress traits were evidenced by TEM analysis and chlorophyll fluorescence. On the contrary, at the end of the Naples exposure, all the moss samples were almost dead, and therefore it can be excluded that they were able to actively accumulate trace metals yielded in solution by rain. In this case, any enrichment in trace metals could solely be related to passive phenomena of superficial adsorption.