C4 Plants in the Vegetation of Tibet,China: Their Natural Occurrence and Altitude Distribution Pattern

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.