Physiological response of the epiphytic lichen Evernia prunastri (L.) Ach. to ecologically relevant nitrogen concentrations

This study investigated the physiological response of the epiphytic lichen Evernia prunastri to ecologically relevant concentrations of nitrogen compounds. Lichen samples were sprayed for 4 weeks either with water or 50, 150 and 500 μM NH4Cl. The integrity of cell membranes and chlorophyll a fluorescence emission (FV/FM and PIABS) were analyzed. No membrane damage occurred after the exposure period. FV/FM, a classical fluorescence indicator, decreased during the second week of treatment with 500 μM \{NH4Cl\} and the third week with 50 and 150 μM NH4Cl. PIABS, an overall index of the photosynthetic performance, was more sensitive and decreased already during the first week with 500 μM \{NH4Cl\} and the second week with 150 μM NH4Cl. Since E. prunastri has been exposed to ammonium loads corresponding to real environmental conditions, these findings open the way to an effective use of this species as early indicators of environmental nitrogen excess.