Comparative study of dehydration-response curves ofphotosynthesis in Antarctic lichen and Nostoc communae

Lichens (Xanthoria sp.) and Nostoc communae were collected in February 2009, during the Chech expedition to the James Ross Island in a close vicinity of J.G. Mendel station. Some specimen (Umbilicaria antarctica, Stereocaulon) were collected in February 2005 during the expedition to the Galindez Island, Woozle Hill, close to Vernadsky station. After transport to the Czech Republic, the thalli were kept in dry state in dark. Before measurements, thalli were rehydrated by spraying and kept in fully hydrated state under the dim light conditions for 24 hours at room temperature. In order to determine the relation between the water potential and the quantum yield of PSII, an OPTISCI fluorometer (Optiscience, USA) was used. For water potential measurements, a WP4T dewpoint water potential meter (Decagon Devices, US) was used. Simultaneous measurements of PhiII nad WP were done on gradually desiccating samples exposed to actinic light of PFD 60 micromol and at constant air temperature (18 oC) monitored by sensor/data logger (HOBO, Onset Computers, US). For each species, at least six replicates were measured.