UTILITY OF MODULATED FLUORESCENCE IN MEASURING PHOTOSYNTHETIC ACTIVITY OF ANTARCTIC PLANTS - FIELD AND LABORATORY STUDIES

Antarctic terrestrial plants face severe physiological stress conditio ns daily. In winter there is extreme cold and darkness. During summer there is continuous light for some months and plant surface temperatur es may fluctuate through more than 50 degrees C diurnally. Conditions are almost uniformly desiccative, except during spring when snow melt saturates thalli and plants may be completely inundated. The study of photosynthesis in these conditions is fundamental to a proper understa nding of plant persistence, productivity and growth in polar regions. Lichens dominate the terrestrial vegetation of Antarctica and are ther efore of great interest. Lichen photosynthesis has been shown to be de pendent upon thallus water content and temperature as well as the irra diance incident on the thallus. Conventional infrared gas analysis (IR GA) techniques have been used most widely to study lichen photosynthes is in both the field and laboratory. Recent progress in the developmen t of pulse amplitude modulated fluorescence systems has allowed the in vestigation of chlorophyll fluorescence in the field under naturally i lluminated conditions. This paper highlights the utility of modulated fluorescence systems for the study of antarctic lichen photosynthesis, relates fluorescence results to those obtained by IRGA techniques, id entifies problems inherent in fluorescence analysis of lichens and dis cusses possible areas of future research.