Study On Agro-ecosystem NEE Using Eddy Covariance And Static Chamber/Gas Chromatogram Methods In North China Plain

To be able to compare the results of flux data by two different flux measurements,as eddy covariance technique and static chamber/gas chromatogram. We analyzed theflux measurements using the two techniques at agro-ecosystem from Oct-2005 toOct-2006 in Yucheng station Shandong province, CAS. The character about NEE ofdiurnal and seasonal was compared by eddy covariance and chamber measurements,but similar seasonal trend of ecosystem respiration was observed from these twodifferent measurements. The main results are as follows:1) A linear regression method and an exponential regression method werecompared in chamber-based measurements. CO₂ fluxes calculated by the linearregression method were lower than that by the exponential regression method. Theshorter time for chamber-based measurement was, the higher the CO₂ flux wasobserved. However, CO₂ concentration changed linearly with the time after closingchambers at night. No significant difference was found between the CO₂ flux calculatedusing both methods. It is suitable to use ER10 method (exponential regression, 10min'sobservation) in the daytime and LR15 method (Linear regression, 15min's observation)in the nighttime in our experiment. After transfer CO₂ flux inside chamber to the oneoutside chamber using light respond curve, chamber-based CO₂ fluxes were used tocompare with one's observed by eddy covariance technique;2) It was similar for diurnal trends of CO₂ fluxes measured using eddy covariancetechnique and chamber method, obviously the trend is single-peak. CO₂ fluxesmeasured by the chamber method were 23.9% lower than those measured by the eddycovariance technique in the daytime and 42.5% lower than by the chamber method inthe nighttime under low wind speed in winter wheat field; CO₂ fluxes measured bychamber method were 35.5% higher than those measured by eddy covariance techniquein the daytime and 4.3% higher than by the chamber method in the nighttime insummer maize field;3) Similar seasonal trend of NEE was observed from these two differentmeasurements. The highest assimilation of CO₂ appeared in 191d after breeding date inwinter wheat field (-1428.9 mg·m^-2·h^-1). At growing stage of winter wheat field theaverage daily net ecosystem exchange from eddy covariance(-783.3mg·m^-2·h^-1) waslower than that from chamber method(-308.5 mg·m^-2·h^-1) by 60%; The highestassimilation of CO₂ appeared in 64d after breeding date in summer maize field(-1037.7mg·m^-2·h^-1) measured by eddy covariance technique. At same stage of summer maize field the average daily net ecosystem exchange from chamber method(-931.6mg·m^-2·h^-1) was higher than that from eddy covariance technique(-584.5mg·m^-2·h^-1) by 37.3%;4) Environmental factor has carried out analysis affecting agro-ecosystem NEEmeasured by two methods. Such as PAR, wind speed, areas and height of sensor wereconsidered. Observation discovers that while wind speed is lower at night, results ofmeasurement by eddy covariance is lower in winter wheat field, we can use the valuemeasured by chamber methods to measure it. In small piece area only carry outexperiments by chamber method can use eddy covariance technique to exchange toright value in the daytime.