CHLOROPHYLL A FLUORESCENCE AND PHOTOSYNTHETIC PIGMENT COMPOSITION OF THREE UMBILICARIA LICHEN SPECIES IN RELATION TO CLIFF LIGHT MICROENVIRONMENT

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  This work detected differing PS II photochemical efficiency within algal symbionts of the lithic lichens Umbilicaria americana, U. mammulata and U. muehlenbergii in relation to higher irradiances present among unmanipulated cliff microenvironments. Potential quantum yield of photosystem II, measured as F_V/F_M, decreased significantly with increased light intensities from shaded to full sun umbilicate populations. Observed lower recoveries within high - light microclimate samples, as compared to shaded microclimates, were consistent with permanent damage to photosystem II. Chlorophyll a, chlorophyll b and total carotenoid concentrations were less useful parameters for assessment of consistent differences among umbilicate thalli growing under different light regimes.