Transplants of Flavoparmelia caperata (L.) Hale were used to test possible relationships between chlorophyll a fluorescence (CaF) and ambient atmospheric conditions (temperature, precipitation, SO2 and NOx levels). Portions of the same thalli collected in a pristine site (A) of the Trieste Karst were exposed at that site, as the control, and in four other sites (B-E) in NE Italy, near to pollution monitoring stations. These sites had been selected in order to provide similar two by two climatic conditions (sites B,C: more humid; D,E: drier) and air pollution load (sites B,D: low; C,E: high). Before exposure and after 43 and 90 days of exposure, CaF measurements were carried out in the laboratory under controlled conditions. A classification of meteorological and pollution parameters recorded during exposure substantially confirmed the differences between site couplets. After 90 days, samples from sites A (control) and B (with very low pollution load) showed only slightly reduced NPQ, qN, Fo, and Fm values. Samples from site D, with medium air pollution load, and sites C,E, with high air pollution loads, showed proportionally greater variation for most of the CaF parameters. A highly significant correlation was found between NPQ, qN, Fm, and NOx pollution but not with SO2 or O3. Effects of NOx on lichens and possible action mechanisms are discussed. The results strongly suggest that CaF measurements of lichen transplants can be a valid tool in biomonitoring studies.

The hypothesis that CO(2) gas exchange and chlorophyll a fluorescence (ChlaF) of lichens vary according to the light regimes of their original habitat, as observed in vascular plants, was tested by analysing the photosynthetic performance of 12 populations of seven dorsoventral, foliose lichens collected from open, south-exposed rocks to densely shaded forests. Light response curves were induced at optimum thallus water content and ChlaF emission curves at the species-specific photon flux at which the quantum yield of CO(2) assimilation is the highest and is saturating the photosynthetic process. Photosynthetic pigments were quantified in crude extracts. The results confirm that the maximum rate of gross photosynthesis is correlated with the chlorophyll content of lichens, which is influenced by light as well as by nitrogen availability. Like leaves, shade tolerant lichens emit more ChlaF than sun-loving ones, whereas the photosynthetic quantum conversion is higher in the latter.

No abstract

The hypothesis that a daily water supply allows a lichen to endure the negative effects of environmental concentrations of NO(x) and O(3) was tested with a transplant experiment. Five groups (0, A-D) of Flavoparmelia caperata samples derived from the same thalli were used for destructive, pre-exposure measurements (0), or exposed for 5 weeks in the rural collection site (A), and in a urban site with high levels of NO(x) and O(3) (B-D). Two groups (C, D) were daily watered half an hour before the daily peak of NO(x) (C), and O(3) (D). The comparison between pre- and post-exposure measurements of stress biomarkers revealed that the different thallus hydration regime modified the pollution tolerance as well as the physiology of the exposed samples. The non-watered group B suffered an evident decrease in F(v)/F(m) and reduced glutathione, but increased ion leakage, whereas the watered groups C and D showed only decreased non-photosynthetic-quenching, possibly derived from NO(x) exposure. Ozone, which was higher in the rural than in the urban site, did not significantly affect the lichen metabolism. Our results re-open the discussion on the so-called "drought hypothesis", which suggests that the lichen desert observed in urban areas of central and eastern Europe is more a matter of dry microclimate than of air pollution.

No abstract