Abstract: The correlation between canopy light interception (LI) and leaf photosynthetic physiological characteristics reflects the response and adaptation of plant functional traits to the changes of light conditions, which is the result of integrative effects of canopy structure and environmental conditions. A total of 10 plots were randomly selected from the floodplain wetlands on the edge of the Heihe River in Zhangye City, Gansu Province, China. According to the principle of equal division, the canopy of Salix matsudana in those plots was divided into the upper, middle, and lower levels. The relationship between LI, transpiration rate (T_r), and net photosynthetic rate (P_n) of each canopy level was examined. The results showed that, with the decreases of canopy level of S. matsudana, leaf area index (LAI), mean leaf angle (MLA), leaf thickness, photosynthetically active radiation (PAR),LI, T_r, andP_n showed a decreasing trend, while leaf area was gradually increasing. Leaf moisture content first increased and then decreased. The type of leaf aggregation changed from aggregation to dispersion. In the upper and lower canopy, the relationships between LI and T_r and P_n showed significant positive correlations (P<0.05). In the middle layer, they showed significant positive correlations (P<0.01). Inside the canopy, theupper leaves used conservative survival strategy that reduced LI,T_r and P_n, while the middle and lower leaves showed the exploitative strategy that increased LI,T_r and P_n, reflecting the optimal allocation of resources between wetland plant’s traits according to functional requirements in heterogeneous habitats.

Key words: canopy, broadleaf plant, leaf dry mass., leaf length and width ratio, empirical model, leaf area