Low temperature inhibition of photosystems I, and II in Antarctic lichens of different morphotypes

Chlorophyll fluorescence techniques represent an effective tool for photosynthetic performance of extremophilic poikilohydric autotrophs from cold Earth regions. Many parameteres of these techniques can detect the response of photosystem II (PS II) to a great variety of stressors. Chlorophyll fluorescence parametrs related to PS II funcioning are used quite often. For Antarctic lichens, that evolved several physiological mechanisms to cope with close to 0°C or even at sub-zero temperatures. The data gained from both field- and laboratory based studies helps predict ecophysiological consequeces of episodic drops in in situ temperature as well as resistence of Antarctic terrestial autotrophs to low temperature. However, the effect of low and sub-zero temperature on photosystem I (PS I) funcitioning is studied much less frequently than PS II. Therefore, the aim of our study was to evaluate PS II and PS I activities under low temperature and enlarge the knowledge on the low temperature effects on lichen photosynthesis. The focus of our laboratory experiments was to quantify the effect of a short-term treatment by 0°C on chlorophyll fluorescence parameters related to PS II and PS I functioning in two species of chlorolichens from Antarctica (Usnea antarctica, Himantormia lugubris). Our results suggest low temperature-induced decline in physiological processes in chloroplast (Performance index decrease) and activation of protective mechanisms (non-photochemical quenching increase).