| Cinnamomum burmannii is an evergreen broad-leaved tree species belonging to genus Connamomum of the Lauraceae. Cinnamomum burmannii usually grows in a non-calcium environment, but it is also found on the Karst hills of Guilin and usually grows in the environment that soil layer is thick. Cinnamomum burmannii can be grown as dominant or constructive species of tree community on the Karst hills of Guilin, and plays a very important roal in the community succession on the Karst hills and in the improval of Karst environment. Photosynthesis can be uesd to evaluate the first productivity of plant. The photosynthesis of plant is closely related with its environment. Based on the study of the photosynthetic physioecology of plant, the ecological adaptation mechanism of plant to the environment could be revealed.The photosynthetic characteristics of trees and saplings of Cinnamomum burmannii on the Karst hills in Guilin were studied in this paper, the purpose is to reveal the photosynthetic characteristics and water utilization of Cinnamomum burmannii on the Karst hills in Guilin, and to propose a measurement of the vegetative restoration. The diurnal and seasonal changes of photosynthesis of Cinnamomum burmannii, the measurement of leaves photosynthesis under artificial controlled conditions of light intensities and CO2 concentration were measured with Licor-6400 photosynthesis system. The main results obtained were as follows:The daily course of net photosynthetic rate(Pn)of Cinnamomum burmannii on the Karst hills showed a double-peak curve in spring, sunmmer and autumn, and a single-peak curve in winter. There were remarkably differences in the daily changes of net photosynthetic rate between the different weather condition in summer. The factors that influenced the net photosynthetic rate(Pn)were mainly photosynthetic active radiation(PAR), leaf water vapour deficit(VPDL) and relative humidity(RH)in spring, photosynthetic active radiation, air temperature(Ta)and transpiration rate(Tr)in summer, transpiration rate, photosynthetic active radiation and relative humidity in autumn, and photosynthetic active radiation, air temperature, and relative humidity in winter. Among them, photosynthetic active radiation, air temperature and relative humidity were the mainly factors that affected the net photosynthetic rate of Cinnamomum burmannii on the Karst hills during all the whole seasons. The seasonal changes of net photosynthetic rate of Cinnamomum burmannii had the order of summer>spring>autumn> winter, and water use efficiency had the order of winter>spring>summer>autumn.The light saturation poin(tLSP)and compensation poin(tLCP)of Cinnamomum burmannii on the Karst hills were rspectively 1164μmolphotons·m-2·s-1 and 28μmolphotons·m-2·s-1, the maximum net photosynthetic rate(Pmax)was 10.1μmol CO2·m-2·s-1, and the apparent quantum yields(AQY)was 0.053, the dark respiration rate(Rd)was 0.500μmolCO2·m-2·s-1, the CO2 saturation poin(tCSP)and compensation poin(tCCP)were 1000μmol·mol-1 and 45.1μmol·mol-1, carboxylation efficiency(CE)was 0.0446.The daily course of net photosynthetic rate(Pn)of Cinnamomum burmannii sapling in spring, sunmmer and autumn were single peaked, which during winter was double peaked. In spring the net photosynthetic rate was mainly affected by photosynthetic active radiation, air temperature, leaf water vapour deficit, and the main factors of the net photosynthetic rate in summer were intercellular CO2 concentration, stomatal conductance, photosynthetic active radiation, in autumn were air temperature, relative humidity, leaf water vapour deficit, and in winter were air temperature, leaf water vapour deficit, air CO2 concentration.The seasonal changes of net photosynthetic rate of Cinnamomum burmannii sapling had the order of summer>autumn>spring>winter, and water use efficiency had the order of autumn>spring> summer>winter.The light saturation point and compensation point of Cinnamomum burmannii sapling were 702μmolphotons·m-2·s-1 and 2.8μmolphotons·m-2·s-1, the maximum net photosynthetic rate was 5.72μmol CO2·m-2·s-1, apparent quantum yields was 0.047, dark respiration rate was 0.199μmolCO2·m-2·s-1, CO2 saturation point and compensation point of Cinnamomum burmannii sapling were 1200μmol·mol-1 and 64.5μmol·mol-1, carboxylation efficiency was 0.0171.This paper is for the first time to study the photosynthetic characteristics of Cinnamomum burmannii, the results indicate that Cinnamomum burmannii belongs to a C3 type plant, it has a definite tolerance of shade, and it is suitable to amultiple light condition. The use efficiency of low light quantum is high, light use efficiency and water use efficiency are different during different seasons. Cinnamomum burmannii can adjust its water use activity to adapt the environment of Karst hills, it can be used for the restoration of vegetation on Karst hills, the Cinnamomum burmannii sapling has some tolerance with low light quantum, and when cultivate the Cinnamomum burmannii saplings, we ought to offer a light that with a appropriate intensity.
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