干旱区生态环境知识资源中心

We studied the occurrence, elevation limit of the habitat, and structural-functional characteristics of C4 plants in the Western (1800-2300 m) and Eastern (3500-4100 m) Pamir mountains. All of the alpine species with cooperative photosynthesis dwelling above 3500 m were members of the goosefoot family (Chenopodiaceae) and belonged to two biochemical types, NAD-ME (species of the genus Atriplex) and NADP-ME (species of the genera Halogeton and Salsola). Examination of chlorenchyma cell ultrastructure with the aid of an electron microscope showed that structural characteristics of the cells are manifested in enlargement of plastids and increase of mitochondria size in NADP-ME species. Plants of the C4 type from extreme elevations were also characterized by high content and activity of RuBP carboxylase and depressed activity of enzymes of the dicarboxylic acid cycle (PEP carboxylase and NADP-ME) as compared with C4 species of the goosefoot family from hot deserts, but they accomplished primary CO2 fixation on the the C4 model. Alpine plants with the Kranz syndrome had a low temperature optimum of photosynthesis (about 20-degrees-C) and did not differ from C3 plants of this region in the temperature dependency of CO2 fixation.