Abstract
The interactions among water content, chlorophyll a fluorescence emission, and potassium leakage were analyzed during dehydration in desiccation-tolerant bryophytes from xeric habitats (Hedwigia ciliata (Hedw.) P. Beauv., Hypnum cupressiforme Hedw., Leucodon sciuroides (Hedw.) Schwaegr., Orthotrichum cupulatum Brid., Pleurochaete squarrosa (Brid.) Lindb., Porella platyphylla (L.) Pfeiff., and Tortula ruralis (Hedw.) Gaertn., Meyer & Scherb.) and desiccation-intolerant bryophytes from mesic and hydric environments (Barbula ehrenbergii (Lor.) Fleisch., Cinclidotus aquaticus (Hedw.) B. & S., Conocephalum conicum (L.) Underw., Lunularia cruciata (L.) Dum. ex Lindb., Palustriella commutata (Hedw.) Ochyra, Philonotis calcarea (B. & S.) Schimp., and Rhynchostegium riparioides (Hedw.) Card.). Their fluorescence characteristics at low water content were low efficiency of photosynthetic quantum conversion, closed photosystem II reaction centers, and strong nonphotochemical quenching only in desiccation-tolerant species. Full restoration of fluorescence parameters upon rewatering in species from xeric environments indicated that the photosynthetic apparatus was fully functional after desiccation. Species from hydric and mesic habitats were unable to restore photochemical activity. This might be a consequence of photoinhibition but also of membrane damage, as indicated by the large leakage of potassium. It is suggested that the capacity to enhance thermal energy dissipation during dehydration might have evolved in species from xeric environments as an adaptation to the utilization of an erratic supply of water. This protective strategy would lower the probability of photodamage during water loss and thus maintain the photosynthetic apparatus in a quickly recuperable state.Key words: bryophytes, chlorophyll fluorescence, dehydration, desiccation tolerance, thermal energy dissipation.
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