Effects of sample conservation on assessments of the photosynthetic efficiency of phytoplankton using PAM fluorometry

► Delayed PAM fluorescence measurements are sometimes unavoidable. ► Storage's impacts on photosynthetic parameters of phytoplankton have been tested. ► Long term storage (12 h) should be definitively avoided. ► Storage at room temperature (25 °C) is valuable only at very short term. ► Cooling (15 °C) is the unique valid solution when delays exceed a few hours.