SEASONAL-VARIATION IN RESPIRATORY AND PHOTOSYNTHETIC PARAMETERS IN 3 MOSSES FROM THE MARITIME ANTARCTIC

Carbon fixation under controlled conditions was measured in three moss es from the maritime Antarctic using an infra-red gas analysis system. Gas exchange parameters were determined during each season in 1993 an d 1994 using the Arrhenius equation and a hyperbolic tangent function applied to respiration and photosynthesis, respectively. Environmental data was collected in 1994 for comparison. All seasonal variations we re greater in Brachythecium than in the species from less hydric habit ats. Respiration rates were highest in summer and lowest in winter at all temperatures in Brachythecium, but there was little change in Chor isodontium or Andreaea. There was some seasonal variation in the initi al slope (K-p) of the photosynthesis-irradiance curve in all species, although,the environmental data suggested that this was of little ecol ogical importance. In all species seasonal changes in the maximum rate s of photosynthesis (GP(max), NPmax) were observed, generally with a p attern of summer maxima, although there were some interannual differen ces. These changes are considered to be the most important in affectin g the overall annual productivity of the mosses. There were no seasona l variations in the optimum temperatures for either gross or net photo synthesis, or for the irradiance at the onset of light saturation (I-k ). The results have important implications for the use of models to es timate the productivity of the Antarctic flora based upon present or p redicted climate data. (C) 1996 Annals of Botany Company