Desiccation tolerance of the epilithic lichen Lecanora muralis (Schreb.) Rabenh. in the temperate climate

Lecanora muralis (Schreb.) Rabenh. is a ubiquitous epilithic crustose lichen of the temperate climate. It is well studied in terms of diel and annual carbon budget and productivity with continuous long-term observations in the field in 1995/96 by Otto L. Lange, Würzburg, and collaborators. However, these earlier studies left open the question to which extent the lichen is desiccation tolerant and if desiccation tolerance might possibly limit photosynthetic activity. In present study measurements of chlorophyll fluorescence parameters were performed to assess photosynthetic activity under various daily weather conditions throughout the year and recovery from desiccation after various periods of dryness in ambient air. Under any weather conditions, including strong frost for several days with night-temperatures around −15 °C and strong heat of several days with day-temperatures around 35 °C, the lichen was fully photosynthetically competent after wetting the samples for 15 min by submersion in water when they were dry in the field in the absence of actual incident precipitation. Chlorophyll fluorescence parameters were identical under all weather conditions sampled. A sample kept dry in ambient air for 37 days showed full recovery of chlorophyll fluorescence parameters after wetting for 30 min. Samples desiccated for longer periods up to 155 days took longer wetting times of about 300 min and recovered only partially but nevertheless showed active photosynthetic electron transport. Of 17 samples desiccated for 177–178 days only three recovered after rewetting for several days. It is concluded that the desiccation tolerance of L. muralis is sufficient to overcome dry spells of duration as it normally occurs in its natural environment. Desiccation tolerance is not likely to limit carbon budget and productivity.