Productivity Estimation Of The Poplar Plantations On The Beaches In Middle And Low Reaches Of Yangtze Rive Using Eddy Covariance Measurement

The continuously increasing concentrations of greenhouse gases and global climatic changing have resulted in the focus on global carbon cycle that has been one of hot topics towards the researches in the field of ecology. The net ecosystem productivity (NEP) is the balance between gross primary productivity (GPP) and ecosystem respiration (R_eco), the key factors revealing ecosystem carbon source/sink and an important study field of global carbon cycle. The paper estimated GPP, net primary productivity (NPP) and NEP in YueYang site and AnQing site in middle and low reaches of Yangtze River using eddy covariance and IRGA method, and analyzed the daily and seasonal dynamics of net ecosystem carbon exchange (NEE) and their environmental factors, and comparing results using eddy covariance measurement with sample plots inventories. The above research is critical for estimate of wetland ecosystem carbon storage especially constructed wetland, and provides supporting data for development and validation of wetland ecosystem carbon cycle model under the background of global climate change. Conclusions of this study are as following:Between 2005.7.15 and 2007.7.14, GPP, net primary productivity (NPP), NEP in YueYang site and AnQing site were 3949.6 gC·m^-2,2228.2 gC·m^-2,1031.3 gC·m^-2 and 3745.4gC·m^-2,2356.3gC·m^-2,1012.2 gC·m^-2; R_eco, soil respiration (Rsoil), root respiration (Rroot) at two sites were 2918.3 gC·m^-2,2297.4 gC·m^-2,1100.5 gC·m^-2 and 2733.2 gC·m^-2,2407 gC·m^-2,1062.9 gC·m^-2.The variations of NEE show obvious daily variability and seasonal variability, and PAR temperature and soil water content are the main factors determining NEE. Exponential equations such as Van't Hoff,Arrhenius and Lyold-Talor can be used to describe the relationship between R_eco and temperatures with similar statistical significance,while Lyold-Talor equation is the most sensitive for temperature index (Ql0);The multiplicative model driven by canopy air temperature and soil water content was more corresponsive to R_eco; R_eco with Michaelis-Menten models inversion is smaller than the multiplicative model, underestimating above 30%. The results using eddy covariance measurement and sample plots inventories were almost the same. At two research sites, condition of light and temperature is similar, and the water condition is different; the excessive soil water content inhibits the ecosystem carbon emissions, and inhibits the growth of poplar and reduces the ecosystem carbon storage of photosynthetic assimilation at the same time.