Effects of high temperature on epiphytic lichens: issues for consideration in a changing climate scenario

The effect of high temperatures on the lichen Evernia prunastri was investigated by analysing the content of photosynthetic pigments, chlorophyll degradation, and the integrity of cell membranes. Results indicate that E. prunastri can tolerate a temperature of 40 degrees C for 24 h, but for longer periods a reduction in chlorophyll b is apparent, suggesting that chlorophyll b could be used as a valuable parameter to detect changes caused by prolonged exposure to such temperatures. Exposure of E. prunastri to a temperature of 80 degrees C had strongly negative effects on the content of photosynthetic pigments, causing both inhibition of chlorophyll synthesis and chlorophyll degradation to phaeophytin; slow acclimation was not capable of preventing such damage. Damage to cell membranes, as indicated by changes in electrical conductivity of the medium, proved to be a useful and simple tool for measuring damage caused by high temperatures. Besides the effects of temperature, results also indicate that exposure to a prolonged dark period has an important negative influence on the chlorophyll alb ratio, suggesting that lichens could be profitably used not only to monitor climate changes, but also to monitor the effects of global dimming.