Abstract: In order to explore the effects of light intensity on the growth and photosynthesis of species distributed in the karst area, the morphology, biomass allocation and photosynthesis physiological characteristics of Ardisia corymbifera, Illicicum difengpi and Pittosporum pulchrum two-year-old seedlings were compared under 100%, 50% and 25% light levels. The results showed that shading environment facilitated the height, total leaf area and crown area of the three plant seedlings. Overall, the root mass fraction and root mass/crown mass ratio of the three species increased significantly, and leaf mass fraction, leaf area ratio and specific leaf area decreased significantly with the increase of light intensity. The net photosynthetic rate (P_n) of A. corymbifera and I. difengpi was significantly lower under full light than under shading environment, implying that stomatal restriction was the main factor leading to the decline of P_n. The P_n of P. pulchrum increased significantly with the increase of light intensity. With the increase of light, chlorophyll content per unit area of I. difengpi and P. pulchrum decreased significantly, while the carotenoid content per unit area, chlorophyll a/b and carotenoid/chlorophyll ratios of A. corymbifera increased significantly. The total biomass of A. corymbifera and I. difengpi seedlings reached the maxima under 50% shading, and the total biomass of P. pulchrum significantly increased with the increase of light intensity. These three karst plant seedlings adapted to different light conditions by different plant morphology and characteristics of photosynthesis. P. pulchrum preferred to strong light, while the seedlings of A. corymbifera and I. difengpi inclined to the shading environment.

Key words: photosynthetic characteristics, diurnal photosynthetic variation, root excision, moisture content, water use efficiency