A Study On Carbon Flux Between Chinese Fir Planations And Atmosphere In Subtropical Belts

Observation of CO2 flux was conducted over 2-years in Chinese fir plantation ecosystem, a typical forested plantation in subtropical region of China, with open eddy correlation system and eddy covariance measurement technologies, with the aid of Huitong Chinese fir plantation ecosystem station, one of key national field stations for scientific observation & experiment. Field data was recorded for CO2 flux exchange between the Chinese fir plantation ecosystem and atmosphere through download and calculation of original data. Data-base was established with the means of data quality control and data quality evaluation, for further exploration of relationship between CO2 flux and environmental factors. Variation in CO2 flux was discussed at daily level and seasonal level. The main results were as the followings.a) Four general data correction methods were analyzed for eddy flux data, including coordinate transform, WPL correction, correction of spectral loss, and correction of storage. The rectangular coordinate transform was selected from the three coordinate transform methods, including double coordinate rotation (DR), triple coordinate rotation (TR), and planar fit method (PF), in terms of the degree of influence on the flux data. The NEE (Net Ecosystem Exchange) was induced with TR method, by 16.7% to a total of increasing carbon sink, with an average of the two years'observation flux data, including induction in day time by 1.4% and increase in night time by 23.7% of NEE. And the NEE was increased by 33.5% including increasing in day time by 30.4% and inducing in night time by 12.6% with WPL method, and induced no more than 1% with FC method, respectively. NEE was increased by 0.4% with correction of storage, including inducing in day time by 24.0% and increasing in night time by 64.2%.b) Analysis and evaluation of carbon oxide flux data was conducted with multiple means of steady state test, analysis of covariance, power spectrum density and co-spectrum analysis, detection of sink-source of CO2 flux, and closure of energy balance. And results indicated that data quality was not very high due to heterogeneity in underlying surface where the flux tower was established. c) Response feature analysis indicated that NEE response to environmental factors varied with different time-scales. There was significant relationship between NEE and temperature fitted by exponential function, and photosynthetic active radiation (PAR) fitted by Michaelis-Menten equation at the level of half-hour scale. And there was significant relationship between NEE and temperature, vapor pressure, and soil moisture content fitted by quadratic polynomial function, and PAR fitted by cubic polynomial function at the level of daily scale. There was significant relationship between NEE and temperature, PAR fitted by reciprocal function at the level of monthly scale.d) Response of ecosystem respiration (RE) to environmental factors varied with different time-scales. The significant relationship was fitted by exponential function between RE and temperature, and fitted by linear relation between RE and PAR, and fitted by power function with vapor pressure, and fitted by quadratic polynomial function with vapor pressure deficit, at the level of daily scale. And the significant relationship was fitted by exponential function between RE and temperature, and fitted by quadratic polynomial function with vapor pressure, and fitted by linear relation with PAR, at the level of monthly scale.e) The relationship between gross ecosystem exchange (GEE) and environmental factors was relatively simple at the daily and monthly scale. The significant relationship for GEE was fitted by logarithmic function with PAR, and fitted by linear relation with temperature and vapor pressure, and fitted by quadratic polynomial function with vapor pressure deficit, respectively, at the level of daily scale. And the relationship for GEE was significantly fitted by linear relation with temperature, PAR, vapor pressure and vapor pressure deficit at the monthly scale.f) There was obvious dynamics in CO2 flux at daily and monthly scale. It was positive for CO2 flux with little amplitude of variation at night time, and negative for CO2 flux varied within wide limits at daytime. Duration of negative for CO2 flux prolonged gradually and occurrence time for the minimum CO2 flux shifted to an earlier time with Winter shifting to Spring, and Summer. Whileas the converse response for both of above was found with Summer shifting to Autumn, and Winter. The maximum in daily range in CO2 flux occurred in August, and the minimum in January. The daily range increased from January to August, and induced from August to December. The change in NEE varied with seasons, with a peak in Winter (February,2008 and January,2009, respectively.), whileas the minimum occurred with environmental factors without obvious trend (March,2008 and June,2009, respectively).g) There was solitary wave variation in RE at the yearly scale, with peak occurred in August, and wave hollow in Winter (February,2008 and January,2009, respectively.). And the variation in GEE was depicted similar with RE, whileas with peak occurred in Winter (February,2008 and January,2009), and wave hollow in Summer (July,2008 and August,2009, respectively.).