Effects of physical factors on photosynthesis by the Antarctic liverwort Marchantia berteroana

Effects of irradiance, temperature and water availability on respiration and photosynthesis in a maritime Antarctic liverwort, Marchantia berteroana, were investigated. Carbon dioxide exchange was measured using an infra-red gas analysis system under controlled conditions. The relationships between respiration, photosynthesis, irradiance and temperature were modelled. Application of these models to year-round micro-climate data provided an estimate of yearly net productivity of 823 (SE=75) mg C⋅g-1 ash-free dry weight. year-1; this is somewhat higher than figures obtained for other Antarctic cryptogams. Desiccation had a highly adverse affect on Marchantia. Photosynthetic capacity was reduced below a water content of 12 g⋅g-1 afdw, and there was only a limited recovery (ca. 10%) after dehydration. Freezing also caused a great reduction in photosynthesis, although the model suggested that photosynthesis at sub-zero temperatures is likely. It is suggested that seasonality in the photosynthetic capacity and the survival of sub-zero temperatures might be important. It is concluded that Marchantia is a relatively productive Antarctic cryptogam that may dominate favourable areas, but that its low tolerance of environmental stress, particularly desiccation, limits its distribution to relatively mild habitats.