PHOTOSYNTHETIC PIGMENTS AND CO2 EXCHANGE IN PLANTS OF HIGH ARCTIC TUNDRA

Maximum values of chlorophyll (Chl) (a + b) content, potential (P(P)) and net (P(N)) photosynthetic rate in the population of 25 species growing in the tundra of Wrangel Island are presented. Field measurements of response of P(P) and P(N) to irradiance were done. Maximum Chl content in arctic plants was typically low [0.5-2.9 g kg-1(f.m.)] and rather close to the range characterizing extreme biomes: i.e. deserts and high mountains. By contrast, the sum of carotenoids (Car) was high [1.1-2.3 g kg-1(d.m.)]. In most tundra plants the ratio Chl/Car varied from 4 to 5. Lower values of Chl/Car were observed only in the high mountain plants of the Pamirs. The peculiarity of pigment apparatus organization in arctic species was expressed in low values of the ratio of pigment-protein complexes LHC/CPI + CP2 that was mostly close to 1 or lower, as well as m the small size of photosynthetic unit which was 100-200 molecules. Irradiance response of photosynthesis, pigments and structure characteristics indicated features usually considered typical both of sun and shade tolerant plants. Their high ability to adapt both to low and high irradiance at low temperature is a substantial guarantee for 24-h photosynthesis during polar day.