Abstract: To explore the effects of altitude on stable carbon isotope composition (δ¹³C_p) and intrinsic water use efficiency (iWUE) of different functional plants at different altitudes (i.e., 2200, 2500, 2700, 3000, 3200 and 4200 m) on the eastern slope of the Meili Snow Mountain, Southwest China, we examined the variations in δ¹³C_p and iWUE of plants with different photosynthetic pathways (C₃ and Crassulacean acid metabolism, CAM) and different life forms in C₃ plants (shrubs, broad-leaved trees, and coniferous trees) along the altitude gradient. Results showed that: (1) The δ¹³C_p values of C₃ plants ranged from -26.72‰ to -31.67‰, with an average value of -29.12‰. δ¹³C_p values of CAM plants ranged from -13.24‰ to -14.59‰, with an average value of -13.77‰. (2) The δ¹³C_p and iWUE values of CAM plants were significantly higher than those of C₃ plants, and the δ¹³C_p and iWUE values for different life forms in C₃ plants varied in the order of shrubs>broad-leaved trees>coniferous trees; (3) Below 3200 m, the δ¹³C_p and iWUE values of trees and shrubs decreased with increasing altitude, which was influenced by soil moisture. Above 3200 m, however, the δ¹³C_p and iWUE values of shrubs increased with increasing altitude, which was influenced by temperature. Overall, the response of water use efficiency of species from different functional groups in the Meili Snow Mountains to the variations of altitude may reflect the different adaptability of different plant species to alpine climate.

Key words: C₃ plant, CAM plant, soil moisture, temperature, plant functional type