Abstract: In order to study the growth process of Quercus mongolica seedlings under different light conditions, a controlled experiment was conducted under four light intensity treatments, including full sun light (FS), light shade (LS), medium shade (MS) and severe shade (SS). The morphological characteristics, photosynthetic traits and biomass allocation of Q. mongolica seedlings were measured. The results show that: (1) Specific leaf area under medium shade and severe shade was significantly greater than that under full sun light and light shade. No significant differences in seedling height were found among the different light conditions. The basal diameter under full sun light was significantly greater than that under medium shade and severe shade. The main root length was similar to the root diameter; both were bigger under full sun light than under the other three shade conditions, and were bigger under light shade and medium shade than under severe shade. (2) The maximum net photosynthetic rate under four light conditions showed a pattern of light shade > full sun light > medium shade > severe shade. The apparent quantum efficiency under full sun light and light shade were significantly higher than that under medium shade and severe shade. There was no significant difference in the dark respiratory rate among different light conditions. (3) Both total biomass and root biomass were the highest under full sun light, followed by under light shade and medium shade, and lowest under severe shade. There were little differences in leaf biomass and stem biomass; the biomass of different organs was in order of root > leaf > stem, and the proportions of root biomass ranged 68%-76%. The rootshoot ratio under full sun light, light shade and medium shade were bigger than that under severe shade.

Key words: municipal pollution discharge model, permissible pollution bearing capacity, Jinghe River., permissible pollution discharge