以欧美杨107（Populus×euramericana cv.Neva）为研究对象，观测了不同冠层的光响应曲线及光合特性的日变化，并分析了影响不同冠层净光合速率的主要生理生态因子。结果表明：光响应新模型Pn=α(1-βI)(I-Icp)1+rI对欧美杨107不同冠层光响应曲线拟合效果较好；由光响应曲线得出冠层Ⅰ、Ⅱ、Ⅲ（造林后第1、2、3年所生的轮生枝）的最大净光合速率依次增大，分别为10076、10152、12318 μmol/(m2·s)，且净光合速率的日均值亦表现为冠层Ⅰ较小、冠层Ⅱ次之、冠层Ⅲ较大，表明冠层的光合能力由强到弱依次为冠层Ⅲ、冠层Ⅱ、冠层Ⅰ。通径分析表明，对冠层Ⅰ、Ⅱ而言，胞间CO2浓度、空气温度是影响净光合速率的主要因子；对冠层Ⅲ而言，气孔导度、胞间CO2浓度、光合有效辐射、空气温度是影响净光合速率的主要因子。

Light response curve and diurnal change of photosynthesis characteristics were measured in different canopy layers of poplar clone 107 (Populus×euramericana cv. Neva), and the main ecophysiological factors affecting net photosynthesis rate were analyzed. The results showed that light response curve of different canopy layers of poplar clone 107 was simulated better with a new model of Pn=α(1-βI)(I-Icp)1+rI. The maximum net photosynthetic rate of the canopy Ⅰ, Ⅱ and Ⅲ displayed in light response curve were 10.076, 10.152 and 12.318μmol/(m2·s) respectively. And the diurnal average of net photosynthetic rate of the canopy displayed in an ascending order as: canopy Ⅰ,Ⅱ and Ⅲ. These results showed that the StrongWeak order of canopy photosynthetic capacity was the canopy Ⅲ, Ⅱ, Ⅰ. The contributions of main ecophysiological factors to net photosynthetic rate in different canopy layers were determined using Path Analysis. For canopy Ⅰand Ⅱ, the consistency of CO2 among cells and air temperature were the main factors to impact net photosynthetic rate. For the canopy Ⅲ, stomatal conductance, consistency of CO2 among cells, photosynthetic active radiation and air temperature were the main factors.