Photoinhibition studies in lichens using chlorophyll fluorescence analysis

Specimens of six lichen species (Evernia prunastri (L.) Ach., Hypogymnia physodes (L.) Nyl., Parmelia saxatilis (L.) Ach., Platismatia glauca (L.) W. Culb. & C. Culb., Pseudevernia furfuracea (L.) Zopf., and Ramalina farinacea (L.) Ach.) were maintained at 5 μmol photons m-2sec.-1for 2 days. Then the fluorescence parameters Fo, Fp, Fv, and Fv/Fmwere measured. Photoinhibition was studied at 300 and 1,000 μmol photons m-2sec.-1of light irradiance for 3 days, and then at 20 μmmol photons m-2sec.-1for 5 hr. to achieve recovery. Different patterns of photoinhibition were observed among the considered species. Hypogymnia physodes, P. glauca, and P. furfuracea exhibited a significant decline in the Fv/Fpratio (indicative of photoinhibition) at both photon flux densities. Platismatia glauca and P. furfuracea presented a significant increase of Fo(photoinhibitory damage to Photosystem II centers). Furthermore, P. glauca was not able to recover after a period of lower photon flux density (PFD). In contrast, E. prunastri, P. saxatilis, and R. farinacea were only photoinhibited when exposed to the highest PFD, and always recovered. With the exception of P. saxatilis, there is a close correspondence between the species' sensitivity to the light treatments and their water relations, measured in terms of wet event duration, rate of water loss, and maximum thallus water content. A possible role of the previous light history at their natural habitats is also discussed.