Heterogeneity of chlorophyll fluorescence over thalli of several foliose macrolichens exposed to adverse environmental factors: Interspecific differences as related to thallus hydration and high irradiance

Spatial heterogeneity of chlorophyll (Chl) fluorescence over thalli of thre e foliose lichen species was studied using Chi fluorescence imaging (CFI) a nd slow Chl fluorescence kinetics supplemented with quenching analysis. CFI values indicated species-specific differences in location of the most phys iologically active zones within fully hydrated thalli: marginal thallus par ts (Hypogymnia physodes), central part and close-to-umbilicus spots (Lasall ia pustulata), and irregulary-distributed zones within thallus (Umbilicaria hirsuta). During gradual desiccation of lichen thalii, decrease in Chl flu orescence parameters (F-0 - minimum Chl fluorescence at point O, F-P - maxi mum Chi fluorescence at P point, Phi (2) - effective quantum yield of photo chemical energy conversion in photosystem 2) was observed. Under severe des iccation (> 85 % of water saturation deficit), substantial thalli parts los t their apparent physiological activity and the resting parts exhibited onl y a small Chi fluorescence. Distribution of these active patches was identi cal with the most active areas found under full hydration. Thus spatial het erogeneity of Chi fluorescence in foliose lichens may reflect location of g rowth zones (pseudomeristems) within thalli and adjacent newly produced bio mass. When exposed to high irradiance, fully-hydrated thalli of L. pustulat a and U. hirsuta showed either an increase or no change in F-0, and a decre ase in Fp. Distribution of Chi fluorescence after the high irradiance treat ment, however, remained the same as before the treatment. After 60 min of r ecovery in the dark, F-0 and F-P did not recover to initial values, which m ay indicate that the lichen used underwent a photoinhibition. The CFI metho d is an effective tool in assessing spatial heterogeneity of physiological activity over lichen thalli exposed to a variety of environmental factors. It may be also used to select a representative area at a lichen thallus bef ore application of single-spot fluorometric techniques in lichens.