Research On Carbon And Water Fluxes Of Typical Winter Wheat Agroecosystem In The Lower Reaches Of The Yellow River Plain

Under the background of global climate change,quantitative research on the exchange process and mechanism of material and energy between the land and atmosphere is an important approach for solving global climate warming,water resource exhaustion and ecosystem function degradation.The lower reaches of the Yellow River Plain is located in the warm temperature and semihumid zone,which has abundant light and heat resources,and is one of the most important zone of food and cotton production.The study for evapotranspiration,productivity and water use efficiency in the lower beaches of the Yellow River Plain has an important meaning of theorical and practical.The Fengqiu Ecology Experimental Station,Chinese Academy of Sciences was choosed as a typical zone.The eddy covariance system,total factors meteorological observation system,large aperture scintillometer were used to conducted ecological and hydrological processing experiment in the winter wheat ecosystem,including seasonal variation of carbon flux,productivity assessing,characteristic variation of evapotranspiration and its environmental factors,and characteristic variation and modeling of the water use efficiency.The major inclusions of this study were as follows:The net ecosystem exchange in the whole growing season of winter wheat was-360.15gC·m^-2.The gross primary productivity in the whole growing season of winter wheat was1920.01 gC·m^-2.The winter wheat agroecosystem had strong carbon sequestration ability.The carbon dioxide fluxes showed an obvious diurnal and seasonal variation characteristics in winter wheat agroecosystem.The winter wheat agroecosystem was a carbon source in tillering stage,while it was a carbon sink in overwintering stage,jointing stage and filling stage.The average value of apparent initial light energy utilization was 0.03 mg CO₂·μmol^-1.The average value of ecosystem production was 1.53 mg CO₂·m^-2·s^-1 when light saturation.The monthly average value of ecosystem respiration was 193.92 gC·m^-2·month^-1.The net ecosystem exchange and photosynthetically active radiation had a significant correlation in four growing seasons of winter wheat.The correlations between net ecosystem exchange and vapor pressure deficit were highly significant in tillering stage,jointing stage and watery stage,while it was significant in overwintering stage.The fitting results had shown positive correlation between daily total net ecosystem exchange and soil temperature in tillering stage,overwintering stage and filling stage,while it shown negative correlation between daily total net ecosystem exchange and soil temperature in jointing stage.The footprint of EC was smaller than LAS in initial growth stage and late growth stage of winter wheat.The majority of flux information of EC and LAS were from irrigable land and orchard,while little part of flux information were from residential area and road.At the site scale,the evapotranspiration derived from eddy covariance had a significant diurnal and seasonal variation.The total evapotranspiration in the growing season of winter wheat was722 mm,and the daily average of evapotranspiration was 2.64 mm/d.At the regional scale,the evapotranspiration of winter wheat derived from the LAS was 748.19 mm,and the daily average of evapotranspiration was 2.74 mm/d.The eddy covariance was choosed as the standard method,and four potential evapotranspiration models were synthetic analyzed for its application in the lower beaches of the Yellow River Plain.The results indicated that,the evapotranspiration derived from the FAO-PM model was similar with the evapotranspiration derived from the eddy covariance system.While the values derived from the PM model,R-K model and P-T model were smaller than them derived from the eddy covariance.In the initial growing season,the LE had significant positive correlation with R_n,u and u*.While the LE had a negative correlation with ST,SM and RH.In the late growing season,the LE had significant positive correlation with VPD,SM and T.The LE had negative correlation with ST and RH.The LE had significant correlation with R_n and u*.The mean diurnal variation of WUE of winter wheat showed intervers“U”type in four typical growing seasons.The seasonal variations of WUE,WUEⁱ and WUE^*were obvious.In the scale of seasonal variation,the tendency of WUE and WUE^*were showed increasing,while WUEi showed increasing first and decreasing then.The relationships between WUE and ET,VPD and T were shown significant positive relationship,with the correlation coefficients were 0.65、0.48 and 0.74.The relationships between WUE^*and ET,VPD and T were shown significant positive relationship,with the correlation coefficients were 0.67、0.77and 0.69.The relationships between WUE_i and ET,VPD and T were shown negative relationship,with the correlation coefficients were-0.05、-0.04 and-0.14.In the RCP2.6future scenario,the WUE of the winter wheat was the minimum value with 1.42.While in the RCP8.5 future scenarios,the WUE was the maximumvalue with 3.66.When the temperature increase by 3℃and the precipitation decrease by 30%,the WUE of winter wheat will decrease by 35.1%.When the temperature decrease by 3℃and the precipitation increase by30%,the WUE of winter wheat will increase by 13.8%.