Seasonal Variation in Respiratory and Photosynthetic Parameters in Three Mosses from the Maritime Antarctic

Carbon fixation under controlled conditions was measured inthree mosses from the maritime Antarctic using an infra-redgas analysis system. Gas exchange parameters were determinedduring each season in 1993 and 1994 using the Arrhenius equationand a hyperbolic tangent function applied to respiration andphotosynthesis, respectively. Environmental data was collectedin 1994 for comparison. All seasonal variations were greaterinBrachythecium than in the species from less hydric habitats.Respiration rates were highest in summer and lowest in winterat all temperatures inBrachythecium, but there was little changeinChorisodontium orAndreaea . There was some seasonal variationin the initial slope (K_p) of the photosynthesis-irradiance curvein all species, although the environmental data suggested thatthis was of little ecological importance. In all species seasonalchanges in the maximum rates of photosynthesis (GP_max, NP_max)were observed, generally with a pattern of summer maxima, althoughthere were some interannual differences. These changes are consideredto be the most important in affecting the overall annual productivityof the mosses. There were no seasonal variations in the optimumtemperatures for either gross or net photosynthesis, or forthe irradiance at the onset of light saturation (I_k). The resultshave important implications for the use of models to estimatethe productivity of the Antarctic flora based upon present orpredicted climate data. Antarctica; bryophytes; mosses; carbon exchange; irradiance; photosynthesis; productivity models; respiration; seasonal variation; temperature