Study On Water Coupled Carbon Of Typical Forest Vegetation Canopy In Beijing Mountainous Area

The switching of CO2and water between forest ecosystem and environment mainly occurred in vegetation-atmospheric interface. The water and carbon flux from the atmospheric interface was the precondition of the maintenance and development of the forest ecosystems. The study of canopy carbon and water fluxes can provide theoretical guidance and scientific basis for forest management. Both the water and CO2is exchanged with the environment through the stoma, and with the restriction of the canopy stomatal conductance, so water carbon flux research can take the canopy stomatal conductance as one main node. Focus on the typical forests in the Beijing mountain area, the thesis has done some continuous monitoring and researching on environmental factors, the sap flow, Platycladus orientalis leaf carbon assimilation rate, leaf stable carbon isotope and water use efficiency of different canopy height during Year2011and Year2012. This thesis has further investigated Platycladus orientalis forest canopy water and carbon coupling mechanism from the perspective the sap flow and leaf stable carbon isotope. The main conclusions are as follows:(1) The sap flow rate of Platycladus orientalis, Chinese pine, Robinia pseudoacacia and Quercus are typical single-peak changing trend, the correlation of solar radiation is high. Solar radiation, air temperature and the VDP are positively correlation with the sap flow rate, while relative humidity has a negative correlation with the sap flow rate. According to the scale expansion, the typical forest transpiration are as follows:Platycladus orientalis is428.71mm, Chinese pine is329.30mm, Robinia pseudoacacia is311.82mm and Quercus is263.05mm.(2) The range of water use efficiency among the typical forests in the Beijing mountain area are3.432～4.653mmolCO2·mor-1H2O. The water use efficiency of the Chinese pine is the lowest, while the water use efficiency of the Quercus is the highest. Sun leaves’stable carbon isotope composition and water use efficiency are greater than shade leaves’; Stable carbon isotope composition and water use efficiency have an upward trend with the increasing of the canopy’s height. It is similar that the instantaneous water use efficiency and the long-term water use efficiency about the different canopy of blade on the Platycladus orientalis.(3)The daily variation of carbon assimilation on orientalis is single-peak changing trend, Sun leaves’carbon assimilation rate is higher than the shade leaves, and upper leaves’carbon assimilation rate is higher than the lower leaves. Stomatal conductance increases with the rise of canopy height, leaf intercellular CO2concentration decreases with the increasing canopy’s height. Sun leaves’stomatal conductance is greater than the shade leaves’and sun leaves’intercellular CO2concentration is less than the shade leaves’on the same canopy.Through the correlation analysis, this study found that carbon assimilation rate is significantly associated with stomatal conductance, intercellular CO2concentration, photosynthetic effective radiation, VDP, temperature and humidity of the air.δ13C values has positively correlation with water use efficiency, carbon assimilation rate and stomatal conductance, while has negatively related with the intercellular CO2concentration.(4)This thesis established the arborvitae forest vegetation----atmospheric interface water carbon flux coupling model. The simulation result of the model is better than others. Canopy transpiration and canopy stomatal conductance of the orientalis, pinus tabulaeformis, robinia have reached0.01level and significantly correlated with the radiation from the sun and VDP.The average carbon assimilation rate of orientalis’canopy is between1.168～16.797μmol·m-2·s-1and is single-peak changing trend. Carbon assimilation rate have a polynomial related with photosynthetic effective radiation, deficient vapor pressure and temperature. It proves the relativity is obvious. Canopy average carbon assimilation rate increases along with the increase of photosynthetic active radiation, but when the photosynthetic active radiation continues to increase to5500μmol·m-2·s-1, carbon assimilation rate will no longer increase. When the VDP is less than1.2, the average carbon assimilation rate of orientalis’canopy will increases along with the increase of VDP. When the VDP is greater than1.2, the average carbon assimilation rate will decreases along with the increase of VDP.