CARBON ISOTOPE COMPOSITION OF PLANTS ALONG ALTITUDINAL GRADIENT AND ITS RELATIONSHIP TO ENVIRONMENTAL FACTORS ON THE QINGHAI-TIBET PLATEAU POLISH JOURNAL OF ECOLOGY

ABSTRACT: Distribution pattern of δ13C values of plateau plants and their responses to environment along altitudinal gradients were in-vestigated. In the growing season of 2003 (June– August), stable carbon isotope ratios (δ13C) of 174 plant samples belonging to 89 species of 20 families and 58 genera along the gradient 2800– 4400 m (above sea level) was studied in six sites on the east edge of Qinghai-Tibet Plateau. The results indicated that the range of δ13C values of plants is narrow from –30.2 ‰ to –25.2‰, which means that none of the species examined belonged to C4 photosynthetic pathway and all of these species performed C3 photosynthetic pathway. The average δ13C values of plants at 6 sites were positively correlated to altitude (r = 0.974, P <0.01). The results revealed that site-averaged δ13C values were negatively cor-related with temperature (r = 0.907, P <0.05) as well as CO2 partial pressure (r = 0.940, P <0.01). The combination of these two factors account for 80 % of the variation of δ13C val-ues (r2 = 0.859, P <0.01). Varying precipitation with increasing altitude does not affect the plant δ13C values (r = 0.469, P> 0.05) as well as the sunlight duration(r = 0.630, P> 0.05). KEY WORDS: δ13C value; plateau plants; en-vironmental factors; Qinghai-Tibet Platea