Freezing of air-dried samples of the lichen Evernia prunastri (L.) Ach. ensures that thalli remain healthy for later physiological measurements

We tested whether freezing of air-dried lichen thalli alter physiological parameters commonly used as valuable stress markers in laboratory and field ecophysiological studies, namely integrity of cell membranes (measured as electrolyte leakage), assimilation pigments (chlorophyll a, chlorophyll b, chlorophyll a+b, total carotenoids content), chlorophyll integrity (OD435/OD415) and chlorophyll a fluorescence emission (expressed as FV/FM, the potential quantum yield of primary photochemistry and PIABS, a global indicator of the photosynthetic performance). Thalli of the lichen Evernia prunastri (L.) Ach. were air-dried, stored in the freezer at ca. -18°C under dark conditions and analysed after short-term storage (15, 30 and 90 days). These periods are compatible with the needs of a relatively rapid data evaluation in biomonitoring studies. After freezing, the investigated parameters showed that lichens remained healthy and suitable for later physiological measurements without biasing data quality.