Abstract: The aim of this study was to explore leaf photosynthetic and biochemical characteristics and adaptive mechanisms of Rhododendron pulchrum Sweet under different light environments, including full light (FL, 100% natural sunlight), slight shading (LS, 82.01% full light), moderate shading (MS, 50.13% full light), and severe shading (SS, 15.80% full light). The results showed that leaf area and the contents of photosynthetic pigments and total nitrogen increased with decreasing light intensity, while specific leaf mass, total carbon content and carbon/nitrogen ratio decreased, and chlorophyll a/b decreased firstly and then increased. Maximum quantum photochemical efficiency and non-photochemical quenching coefficient were significantly higher under MS and FL treatments than that under the other treatments, respectively. The actual quantum photochemical efficiency, photochemical quenching coefficient, and quantum yield of quenching under SS treatment were significantly lower than that under the other three treatments. Dark respiration rate and light compensation point decreased with decreasing light intensity, while the maximum values in apparent quantum efficiency, maximum net photosynthetic rate and light saturation point) were detected under MS treatment, suggesting the strongest photosynthetic capacity. R. pulchrum under FL treatment had lower net photosynthetic rate (P_n) accompanied with lower stomatal conductance and higher stomatal limitation value. Such decrease in P_n under FL treatment was mainly due to stomatal limitation. In comparison, P_n under SS treatment was inhibited mainly due to the reduction in photochemical efficiency and imbalance in fraction of incident light in photosystem Ⅱ. Our results suggested that R. pulchrum had good performance in tolerance range of light intensities, and that moderate shading (i.e., 50% full light) was optimal for its growth. Consequently, proper shading or community configuration under deciduous forest with sparse canopy should be employed regarding its cultivation or application in gardens.

Key words: Rhododendron pulchrum Sweet, light environment, chlorophyll fluorescence, gas exchange, photosynthetic adaptability.