Long-term fluorometric measurements of photosynthetic processes in Antarctic moss Bryum sp. during austral summer season

Photosynthetic activity pattern of Bryum sp. was monitored for 28days using a chlorophyll a fluorescence measuring system installed in the field. For the study, long-term research plot, a moss-dominated vegetaiton oasis at seashore located close to the J.G. Mendel station (James Ross Island, Antarctica) was selected. In this study, two measuring sites were used: (1) control plot with moss cover and (2) moss located inside open top chamber (OTC). At both sites, effective quantum yield of photosynthetic processes in photosyntem II (FPSII) was measured and relative photosynthetic electron transport rate (ETRrel) evaluated each 15 min. Simultaneously, microclimate of the sites was measured including air and moss surface temperature, relative air humidity and photosynthetically active radiation. The length of photosyntetically active period depended mainly on hydration of moss cushion. Water availability, however, was not limiting in the measuring period (Jan 8 - Feb 18, 2009), because the sites were well suplied by melt water from neighbouring snowfield. Thus, daily courses of ETRrel were dependent on incident PAR. On sunny days, ETRrel reached values over 400. Inhibition of primary photosynthetic processes due to below-zero temperature and resulting freezing of moss cushions appeared two times within the measuring periods thanks to rapid decreases in air temperature. The effect of low air temperature on ETRrel was less apparent in OTC site since moss cushion freezing period was shorter and less pronounced than in control site thanks to OTC-induced shift in air temperature. For future photosynthetic studies in Antarctic mosses, simultaneous measurements of gas exchange- and chlorophyll fluorescence-related parameters is recommended so that the effects of particular limiting factors for photosynthesis and photosynthetic productivity can be distinguished and evaluated