Effects of the urban environmental conditions on the chlorophyll a fluorescence emission in transplants of three ecologically distinct lichens

The sensitivity of three foliose lichen species to urban environments with different air pollution loads and climatic conditions was tested using chlorophyll a fluorescence (ChlaF) PAM measurements. Transplants of Xanthoria parietina (L.) Th. Fr., Flavoparmelia caperata (L.) Hale and Parmotrema perlatum (Huds.) M. Choisy collected in a pristine site of the Classic Karst (Trieste, NE Italy) were exposed for 12 weeks (August–December 2008) at that site (control, A), and in two urban sites with heavy traffic in Trieste (B) and Udine (C). Concentrations of the main gaseous pollutants were monitored by passive samplers in A (NO2, O3), and by pollution monitoring stations in B and C (NOX, NO2, SO2, O3). In the laboratory, Kautsky curves were induced under standardized conditions at species-specific PPFD values before exposure, after 6 weeks and at the end of the exposure. Significant decrease in Fv/Fm was only observed in P. perlatum transplants exposed in B, possibly as a consequence of the dry conditions of that site. Non-photochemical quenching (NPQ) was negatively affected in all three species, although with different intensity, in both urban sites, but more intensively in C than in B. ChlaF data shows clearly that (i) the decrease of NPQ was modulated by time exposure to NOX as well as by NOX concentration, and (ii) the species response to pollutants was related to species ecology: X. parietina, which is more nitro- and xerophytic than the other two species, tolerated better the transplant environmental conditions, confirming recent floristic observations carried out in several urban areas of Central Europe.

Research highlights▶ Species ecology influences the lichen response to photo-oxidative pollutants. ▶ Drought tolerant lichens are more apt to survive to the hostile town mesoclimate.mesoclimate. ▶ NPQ is affected by time exposure to NOx as well as by NOx concentration.