Assessing freezing tolerance in Antarctic and Arctic plants, lichens and algae by using an innovative freeze-inducing and monitoring system

Assessing freezing tolerance in photosynthetic tissues is essential for understanding plant adaptation to extreme environments such as Antarctica and the Arctic. This study presents a new portable thermoelectric device capable of applying controlled thermal cycles and measuring photosynthetic efficiency (Fv/Fm) in situ using chlorophyll fluorescence. The device, designed for remote field studies, offers significant improvements in portability, precision, and analytical capacity compared to previous systems. It was tested in both Antarctic and Arctic environments, covering a wide taxonomic diversity including algae, lichens, bryophytes, and tracheophytes, and revealing differential patterns of freezing tolerance across groups. To explore these differences, the experimental approach included (1) nucleation temperature; (2) the maintainability of Fv/Fm after a freeze-thaw cycle at different temperatures, durations, and temperature vs. time change ramps; and (3) the time-course of Fv/Fm during a freeze-thaw cycle, i.e. allowing for impact vs. recovery assessment. The results show that many species tolerate subzero temperatures by maintaining photosystem II functionality even after ice formation, with tolerance varying among taxonomic groups. Antarctic lichens exhibited exceptional resistance, while vascular plants showed greater sensitivity. The device demonstrated high thermal homogeneity, reliability, and efficiency, making it a versatile tool for ecophysiological studies under extreme conditions.