Abstract: The photosynthetic saturation and compensation points of American ginseng at 21.6% of natural light intensity(NLI)are higher than those at 11% of NLI,28 is the optimum temperature for photosynthesis of American ginseng..its photosynthetic products are mainly distributed in roots at ZI,6% of NLI and in fruits at 11% of NLI.The photosynthetic rate increases with increasing light intensity,reaches the maximum at 30N of NLI,and appeares to be a double peak curves during a day.The chlorophyll content of leaf reduces with increasing light intensity when NLI is higher than 20%,and the same for chlorophyll b content.In addition I the stoma number on lower surface of leaf,cuticle figure on upper surface of leaf,chloroplasts number and thylakoid structure are significantly different under higher and lower light intensities.The contents of saponin and amino acid in root of American ginseng and its yield are increased with increasing light intensity,being the highest at 30% of NLI and decreases at 40% of.NLI.

Key words: American ginseng, Penetrating light intensity, Total saponin content, Amino acid, Yield, Platycladus orientalis, photosynthetically active radiation, vapor pressure deficit., sap flow density, canopy stomatal conductance