Studies On The Carbon Flux Of Typical Farmland Ecosystem Of Winter Wheet Double Cropped With Summer Maize In The North Henan Plain

This experiment was carried on in the north area typical farmland ecosystem of henan province in 2004²006. Used the combination method of continuous measuring and periodic measuring to study on the carbon flux law of winter wheet-summer maize two crops a year farm ecosystem. The research shows the results as follows:1. The analysis of the relationship between carbon flux,latent heat flux and sensible heat flux in farmland ecosystemThrough the application of the ecosystem on the principle of energy balance closure of the data shows that a very good degree of closure; The latent heat flux data comparison between Eddy covariance method and Bowen ratio method, the results showed that the two methods was very significant correlation (r=0.86), The analysis shows that differences of no difference (P=0.0723). The 3D map of carbon flux, sensible heat flux and latent heat flux show that: the maize season have more peak-surfaces, and Fc with the increasing of latent heat and sensible heat flux in a corresponding increase; the differents is the peak-surfaces appeared mainly in the latent heat flux value range of 4¹6MJ·m^-2·S^-1 in maize season, and 4¹2MJ·m^-2·S^-1 in wheet season, meanwhile the sensible heat flux are positive value that is the heat flow to the atmosphere.2. The relationship between diferent scale photosynthesis and carbon flux in farmland ecosystemAnalysing the wind direction influence factors to the carbon flux, found that the main contributing area to carbon flux is in the direction of northeast– southwest in the maize and wheet season, the southwest contributeing plots are scattered in the south left and right 30°. In the Maize agri-ecosystem,we have different-scale measurement of single-leaf net photosynthesis (Pn),canopy apparent photosynthesis(CAP) and carbon flux(Fc). Findings that: there have a close trend between CAP and Fc, the average correlation-coefficient is 0.91; To analyse the diurnal accumulation of CAP and Fc from 7:00 to 18:00, the integral value is maximum in heading stage, reach 38.60g·m^-2. Later, the trend begin decline; We get a curve-equation with the regression analyzing to Pn·LAI and Fc, the trendline of equation and real value have a perfect superposition and the correlation-coefficient is 0.79 significantly.The Path Analyse of different factors to Fc reveal that: the direct Path-effects of the H2O concentration of atmosphere,Pn·LAI,PAR,CO₂ concentration are significant . So, the moisture content,light and plant grow-vigor have significant influence on Fc.3. The relationship between soil respiration,soil temperature and soil volumetric water content in farmland ecosystemThe farmland measurement results of soil respiration,soil temperature and volumetric water content in different period showed that: 30% volumetric content volume is a critical line; more than 30% value ,the trend of soil respiration was contrary to the water content; less than 30% value,the same trend. Because of the deeper measurement depth to soil temperature in winter wheet season, when the soil temperature is low(10℃below), the trend of two indexes are on the contrary; when the soil temperature increases to up 17℃, the same trend; The values of soil temperature and soil respiration have a good mutual response in maize season, and the Q10 value is about 3, the main reason is that the soil volumetric water content is around 30% all maize growing stage. Summary, The combined effect of soil volumetric water content and soil temperature influence the soil respiration.4. The relationship between CO₂ flux and soil respirationFrom the diurnal variety of CO₂ flux and soil respiration flux, CO₂ flux to achieve the greatest negative value around 12:00 in general, that means the largest rate of carbon sequestration., The two indexs'showing a "wave" symmetry between 9:00 to 12:00 in wheat season, consistent trend in maize season. The low soil respiration value region are appeare ante meridiem, but the big ups and downs than the wheat season. From different growth stages, the soil respiration highest value in maize season higher about 3μmol·s^-1·m^-2 than wheat season, CO₂ flux highest value higher about -0.2μmol·s^-1·m^-2, and CO₂ Flux and soil respiration along with the growing of crops changing, lower in the seedling stage, increased with crop growing gradually, then after the fall; Specifically,the trend of wheat season begin fallback in early April, maize fallback between August 10th to the beginning of September.5. The farmland ecosystem evaluation of carbon source/sink and the variety of the CO₂ flux accumulationFrom the view of data results, the accumulation of CO₂ flux of wheat season reached the highest ^-22.2g·m^-2·d^-1 in March 28th, then decline gradually; In maize season, to the highest accumulation value reached -19.5g·m^-2·d^-1 in September 2nd . The accumulation of CO₂ flux and the dry matter achieve a close relationship and mutual good proof, the two indexs accumulation reaches the maximum in the number of days 221 to 226 days of wheat growing days, correspondingly the maize season accumulation is increasing all alone. We have a comparison of annal CO₂ flux with the three and a half years'data. The results shows that: In the plant growing stage, there have a large amount of fixed CO₂, the total fixed carbon amount reached 1318.1 g·m^-2 averagely in the wheat growing long-period; the less fixed amount reached 756.9g·m^-2 averagely in maize season; there have a direct proportion between carbon sequestration,the total amount of PAR and yield to the same crop in different year; there have a main period for CO₂ releasing in the interval of two crops. Integrated whole, farmland mainly as carbon sequestration of carbon sinks exist, the average net fixed CO₂ amount which to offset the releasing CO₂ in interval period is about in the range of 1600²100g·m^-2.