Photosynthetic symbionts in Antarctic terrestrial ecosystems: the physiological response of lichen photobionts to drought and cold

Lichens form an important part of the biodiversity in terrestrial ecosystems of Antarctica where they represent the dominant vegetation. Previous studies on the genetic diversity of photobionts of lichens have indicated that clade S Trebouxia photobionts are the most widespread in continental Antarctica, predominantly in macrolichens. For the first time, a comparative study of the physiology of a variety of isolated Antarctic lichen photobionts (genus Trebouxia ) was performed. Photosynthetic activity was examined by chlorophyll a fluorescence and correlated with freezing and desiccation under laboratory conditions and photosynthetic pigments were quantified in response to desiccation. Data were obtained from photobionts collected from the Antarctic regions of North Victoria Land, Coal Nunatak and Rothera Point, as well as from a European site (Gotland, Sweden). While the isolated algae reacted individually to stress treatments, they were highly susceptible to desiccation stress but could rapidly recover from freezing. Photobiont-specific physiological adaptations are considered to explain the dominance of clade S Trebouxia photobionts.