Carbon isotope composition of plants along altitudinal gradient and its relationship to environmental factors on the Qinghai-Tibet Plateau

Distribution pattern of delta C-13 values of plateau plants and their responses to environment along attitudinal gradients were investigated. In the growing season of 2003 (June-August), stable carbon isotope ratios (delta C-13) of 174 plant samples belonging to 89 species of 20 families and 58 genera along the gradient 28004400 m (above sea level) was studied in six sites on the east edge of Qinghai-Tibet Plateau. The results indicated that the range of delta C-13 values of plants is narrow from -30.2 parts per thousand to -25.2 parts per thousand, which means that none of the species examined belonged to C-4 photosynthetic pathway and all of these species performed C-3 photosynthetic pathway. The average delta C-13 values of plants at 6 sites were positively correlated to altitude (r = 0.974, P < 0.01). The results revealed that site-averaged delta C-13 values were negatively correlated 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 delta C-13 values (r(2) = 0.859, P < 0.01). Varying precipitation with increasing altitude does not affect the plant delta C-13 values (r = 0.469, P > 0.05) as well as the sunlight duration (r = 0.630, P > 0.05).