INTERSPECIFIC VARIATION IN RESPIRATORY AND PHOTOSYNTHETIC PARAMETERS IN ANTARCTIC BRYOPHYTES

Rates of carbon flux in 14 species of Antarctic bryophytes were measur ed under controlled conditions using an infra-red gas analysis system. The results were used to produce estimates of model parameters for re spiration and photosynthesis. The relationships between respiration; p hotosynthesis, irradiance and temperature followed standard patterns. Temperature optima for gross and net photosynthesis were 10-20 and 0-2 0 degrees C respectively, suggesting that the plants were not truly ps ychrophilic. Photosynthesis was saturated at 30-270 mu mol m(-2) s(-1) , consistent with the view that bryophytes are, physiologically, shade plants, although there was no evidence of photoinhibition over the ra nge of irradiances tested (up to 700 mu mol m(-2) s(-1)). Comparison o f the results with environmental data suggests that photosynthesis is usually temperature-limited during daylight in the growing season. The refore, any change in the temperature of the habitat could affect the productivity of the bryophytes. Rates of photosynthesis varied widely between species, and these relationships were largely maintained over the range of temperatures and irradiances tested. Photosynthetic ranki ngs were correlated with the water availability in the plant habitats, supporting the hypothesis that water is the important factor in deter mining the distribution of populations in Antarctic habitats.