Floristic composition, life forms for C4 species, and the pattern of altitude distribution were studied on Tibetan Plateau. 79 species, in 7 families and 46 genera, were identified with C4 photosynthesis. 95 % of these C4 species belong to Gramineae (51 species), Cyperaceae (14 species), and Chenopodiaceae (10 species), indicating that C4 plants mainly occur in very few families (7 of 204) on the Tibetan Plateau. High altitude distribution for all the Chenopodiaceae C4 species (> 3 000 m above sea level) suggests that plants of this kind have large tolerance to cold, dryness, and strong ultraviolet radiation. Most Gramineae and Cyperaceae C4 species occurrences are consistent with extensive distribution of steppes and meadows in the vast flat of the central Plateau (1 000-3 000 m a.s.l.). Relatively high amount of hemicryptophyte form plants (44 %) in the region indicates that the vegetation, especially grassland, meadows, and steppe, are in good condition. There is a strong relationship between numbers of C4 species and altitude in the Tibetan Plateau. Occurrence of C4 species is significantly less in both high and low altitude plateaux in Tibet. Altitude distribution pattern for C4 species in the region is not only consistent with the altitude and climate, but also with the vegetation types in altitude gradient.
Natural occurrence of C4 species, life form, altitude pattern, and infection by the Three Gorges Project (TGP) were studied in the TGP region. 76 species (about 2.5 % of the total 2 685 vascular plant species in the region), in 6 families and 42 genera, were identified with C4 photosynthesis. 91 % of these C4 species belong to Monocotyledoneae, e.g. Cyperaceae (14 species), Gramineae (54 species), and Commelinaceae (1 species). Of these C4 species, Gramineae was the leading C4 family: 54 C4 grass species (71 % of the total C4 species), about 36 % of the total grasses, were identified in the TGP region. 98 % C4 species was found in therophyte (55 %) and hemicryptophyte (43 %). This is consistent with high grass and sedge compositions in the region. Most habitats of more than a half of these C4 species (65 %) will be submerged permanently, but no species will be endangered or extinct, because 95 % C4 species can be found from 500 to 800 m above sea level. The abundance of some C4 species will be dropped due to the reduction of distribution scope. It will take a long-term to explore the effects of the TGP on plants, vegetation, and environment.