The Research Of North Subtropical Secondary Oak Forest Carbon Budget

In this study, eddy covariance method was used to monitor carbon flux in north subtropical secondary oak forest of Yangtze River Delta Urban Forest Ecosystem Research Station, which is located in Xiashu forest farm, Jiangsu Province. The carbon flux data and daily meteorological data was collected from December, 2007 to November, 2008 in this area. After meticulous processing and analysis, the results showed as bellow:(1)During the research, soil heat flux and soil water content showed significant negative correlation,the winter soil heat flux and soil water content showed the most relevant, spring and summer reprecented less, and the autumn showed the least. Daily average of soil heat flux and daily average net radiation showed significant positive correlation.Annual daily average latent heat flux in Secondary oak forest ecosystem was mostly positive, which reached the max on August, 2008. The annual max daily average sensible heat flux appeared on May, 2008, the min showed on September, 2008.(2)After careful study about the means of Sunny oak forest net ecosystem carbon exchange(NEE), we found its diurnal variation law showed that, from about 7:00 AM,oak forest ecosystem began to absorb CO2. And during the period bewteem 10:00 AM to 2:00 PM, it remained at a relatively large uptake until it changed into acting carbon emissions in the evening around 5:30 PM.While in December to next February, the overall carbon sink capacity of the ecosystem decreased to the lowest value of the year. However, during March to May, the ecosystem carbon uptake increased rapidly, and the ecosystem respiration was also obvious at night.During June to August in the summer, the ecosystem carbon sink capacity of the whole year reached the highest, and the max of carbon sequestration value in the whole year appeared. The entire ecosystem's respiration during the night was also slightly higher than all the months. During September to November in Autumn, significant carbon sinks also appeared, but the intensity was weaker than in June to August.(3)Duringthe growing season, NEE of North subtropical secondary oak forest ecosystem was increasing negative with the increase of PAR at a certain range. Response relationship between the two was consistent with Michaelis-Menten model And the response relationship between day temperature (soil temperature) in non-growing season and half-hour time carbon flux data ,removed the friction velocity U*<0.2m/s, conformed the Van't Hoff model; response relationship between night temperature(soil temperature)during the growing season and carbon flux data excluding the night of friction velocity U*<0.2m/s also meet the Van't Hoff model: NEE=-α?PAR/(β+PAR) -γ. Net ecosystem carbon exchange (NEE) and the saturation vapor pressure deficit (VPD) was negatively correlated in Oak forest ecosystem.In the growing season, the NEE and soil temperature was negatively correlated,and it also negatively related with the PAR, the impact of soil temperature on NEE is more obvious than the photosynthetic active radiation; During the non-growing season, NEE of oak forest ecosystem,that was the ecosystem respiration (Reco), was positively correlated with air temperature.(4)During December to next February,north subtropical secondary oak forest ecosystem performed as the carbon source, The max cumulative amount of NEE appeared in December, as 14.2785gCO2? m-2 ? d-1, Ecosystems of the total amount of carbon emissions into the atmosphere was 208.3732gC ? m-2 during this period. During March to early April, and time among the mid-November to the late November, the primary total productivity of the ecosystem(GPP) was less than the respiration value of the ecosystem(Reco), while the NEE still show positive, and the ecosystem represented as the carbon resource. During this period, the general carbon emission was up to 22.7584gC?m-2.However,during the mid-April to mid-November, the ecosystem's GPP absolute value was obviously more than the Reco, and the ecosystem showed as a carbon resource. The negative max of the NEE diurnal accumulation appeared in May, up to -25.5607 gCO2?m-2?d-1, and the ecosystem reached its absorption at 354.6169gC?m-2. The whole year among December 1,2007 to November 30, 2008, the general amount of NEE was -123.485gC·m-2·a-1, represented as a slightly carbon sink.