Abstract: In 2010,measurements were conducted on the foliar δ¹³C, photosynthesis,CO₂ diffusive conductivity, nitrogen content, photosynthetic nitrogen use efficiency (PNUE), and special leaf area (SLA) of Salix atopantha at different altitudes (2350 m, 2700 m, 3150 m, and 3530 m) in Wolong Natural Reserve. With the increase of altitude, the foliar nitrogen content (especially the nitrogen content per unit leaf area, N_area) and the PNUE increased, and the foliar δ¹³C had a significant increase, with an increment of 1.4‰ per 1000 m altitude. The stomatal and mesophyll CO₂ diffusion conductance also increased with increasing altitude, which had definite negative effect on the increase of foliar δ¹³C, but the effect was not strong enough. Comparing with CO₂ diffusion conductance, carboxylation capacity was a more important factor limiting the P_c/P_a, and even, the foliar δ¹³C. At altitude 2350-2700 m, air temperature was the main factor affecting the allocation of nitrogen in S. atopantha photosynthetic system, whereas at altitude 2700-3530 m, light could be the main affecting factor. No significant difference was observed in the SLA at different altitudes.

Key words: Salix atopantha, foliar δ¹³C, altitude, Wolong Natural Reserve