Evaluation of photosynthetic processes in Antarctic mosses and lichens exposed to controlled rate cooling: Species-specific responses

Abstract

Antarctic regions involve a great variety of habitats characterized by environmental stressors and life forms of autotrophic organisms with unique survival and functioning mechanisms. Lichens and mosses from these regions, similarly to high altitude alpine locations, have evolved physiological adaptations to perform photosynthesis at subzero temperatures. In this study we applied linear cooling technique in order to analyze interspecific differences in primary photosynthetic processes in Antarctic species affected by low and subzero temperature stress. We exposed Sanionia uncinata, Rhizoplaca aspidophora, Ochrolechia frigida, Cladonia sp., Himantormia lugubris and Umbilicaria decussata to the cooling from 20 to -35°C at a constant rate of 2°C min-1. Fluorometric parameters were measured during the cooling experiments: FV/FM - potential yield of photosynthetic processes in photosystem II, and F0 - minimal chlorophyll fluorescence. All the species showed S-curves for FV/FM in response to decreasing temperature and interspecific differences in the parameters of S-curve equation. Critical temperature for FV/FM was found -35°C for U. decussata, while the other species ranged between -16 to -20°C. The changes of F0 with thallus temperature decrease were species-specific. F0 decrease followed by an increase was found with cooling from 20 to -20°C, and from -20 to -35°C, respectively, in the majority of cases. These results suggest that the experimental moss and lichen species from Antarctica have a high resistance to freezing temperatures. The underlying physiological mechanisms are constitutive features of Antarctic lichens and mosses. They are a crucial part of the adaptation and short-term acclimatory changes in ecophysiological performance of the organisms in harsh polar environments.