Abstract:Four different shading treatments, including L0 (100% radiation intensity), L1 (45% radiation intensity), L2 (25% radiation intensity) and L3 (18% radiation intensity), were treated , photosynthesis parameters, leaf morphology and leaf anatomical structure characteristics of U. szechuanica seedlings under different light regimes were studied. Results showed that Pn showed asymmetric convex linear changes under different shading. The variation of Pn under L0 treatment was strong, the maximum value of Pn appeared at 12:00, it began to decline sharply over it. However, the photosynthetic effective radiation under shading treatment was insufficient, the Pn of each time decreased significantly, and the peak value decreased. Correspondingly, the Gs basically showed the change of firstly rise and late decline, and Ci showed convex shape. The daily average sequence of Pn under different light environments was L0>L1>L2>L3. Shading had a significant effect on photosynthetic response parameters of U. szechuanica seedlings, which caused a significant decrease of LCP, LSP, and changes of Pnmax and Rd was so. Shading affected the leaf morphology. With the increase of shading intensity, single leaf area (SLA) increased, single leaf dry weight (SLWd) and lamina mass per unit area (LMA) decreased, and lamina area per unit mass (LAM) increased, there was significant difference between these indexes of seedlings under shading compared with the control. Under shading, leaves of U. szechuanica became thinner, thickness of epidermal cells (EP) decreased significantly, thickness of both palisade tissue (PT) and sponge tissue (ST) reduced. U. szechuanica seedlings likes light, which has certain physiological regulation ability to weak light, but strong shading will lead to poor malnutrition. Light conditions might be an important external factor affecting the living and population renewal of seedlings, so it was suggested to carry out moderate thinning of natural forest, reduce canopy density in forest, increase ventilation and light transmission, and create a favorable condition for propagating of wild population.