PHOTOSYNTHESIS, PIGMENTS, AND CHLOROPLAST ULTRASTRUCTURE OF AN ANTARCTIC LIVERWORT FROM SUN-EXPOSED AND SHADED SITES

Adaptations to severe environmental conditions were studied in the only recorded continental Antarctic hepatic, Cephaloziella exiliflora (Tayl.) Steph. During the summer growing season Antarctic plants melt out and many are exposed fully to the sun. C. exiliflora plants collected from sun-exposed and shaded sites were compared. Most plants were sun exposed, with dark purple leaves containing an anthocyanin-like pigment bound within the thick cell walls of the leaves. The purple plants grew in a dense turf, were larger with more closely spaced leaves, and had a higher carotenoid to chlorophyll ratio than the green plants. Shaded green plants contained more chlorophyll per unit weight. The chlorophyll a to chlorophyll b ratio did not vary. At low irradiances the green plants had higher photosynthetic oxygen evolution rates. Comparing leaves in similar positions along the stems showed that the chloroplasts in green leaves contained more appressed thylakoids than the chloroplasts in purple leaves. These differences are consistent with responses to varying light exposure. An understanding of these effects of changing irradiance on bryophytes is needed for monitoring the impact of increased ultraviolet light owing to the seasonal depletion of stratospheric ozone.