PHOTOINHIBITION STUDIES IN LICHENS USING CHLOROPHYLL FLUORESCENCE ANALYSIS

Specimens of six lichen species (Evernia prunastri (L.) Ach., Hypogymn ia physodes (L.) Nyl., Parmelia saxatilis (L.) Ach., Platismatia glauc a (L.) W. Culb. & C Culb., Pseudevernia furfuracea (L.) Zopf., and Ram alina farinacea (L.) Ach.) were maintained at 5 mumol photons m-2 sec. -1 for 2 days. Then the fluorescence parameters F(o), F(p), F(v), and F(v)/F(m) were measured. Photoinhibition way studied at 300 and 1,000 mumol photons m-2 sec.-1 of light irradiance for 3 days, and then al 2 0 mumol photons m-2 sec.-1 for 5 hr. to achieve recovery. Different pa tterns of photoinhibition were observed among the considered species. Hypogymnia physodes, P. glauca, and P. furfuracea exhibited a signific ant decline in the F(v)/F(p) ratio (indicative of photoinhibition) at both photon flux densities. Platismatia glauca and P. furfuracea prese nted a significant increase of F(o) (photoinhibitory damage to Photosy stem II centers). Furthermore, P. glauca was not able to recover after a period of lower photon flux density (PFD). In contrast, E. prunastr i, P. saxatilis, and R. farinacea were only photoinhibited when expose d to the highest PFD, and always recovered. With the exception of P. s axatilis, there is a close correspondence between the species' sensiti vity to the light treatments and their water relations, measured in te rms of wet event duration, rate of water loss, and maximum thallus wat er content. A possible role of the previous light history at their nat ural habitats is also discussed.