Water,Carbon And Light Use Efficiency Of A Typical Agro-ecosystem In Semi-arid Area

Water use efficiency?WUE?,light use efficiency?LUE?,carbon use efficiency?CUE?can quantify photosynthesis and respiration efficiency of ecosystem,while is the important parameters to measure carbon sequestration amount and efficiency.Based on eddy covariance data and meteorological data of field observation stations in semi-arid area of Huining County,Gansu Province during the two growing seasons from 2015 to 2016,this paper analyzed the change of carbon,water flux and WUE,LUE,CUE at different time scales of agroecosystem and the influence of environmental factors on WUE,LUE,CUE,while explored the response of WUE,LUE,CUE under different meteorological conditions and soil moisture conditions.The main results are as follows:1.Van't Hoff model,Arrhenius model,Lloyd&Taylor model and Ts-SWC model were used to fit the relationship between ecosystem respiration,air temperature?soil temperature?and soil water content at half-hour scale.According to the daily and seasonal dynamic simulation of the model,it was found that Van't Hoff model which used soil temperature was better than the other three models through statistical results and the simulation results at different time scales.Van't Hoff model was chosen to count the daytime ecosystem respiration,and then calculate the total ecosystem productivity.2.The daily average values of WUE,LUE,CUE were 4.71 g C kg^-1 H₂O,0.33 g C mol^-1 and 0.53 in the growing season of 2015,which were 4.69 g C kg^-1 H₂O,0.35g C mol^-1 and 0.53 in the growing season of 2016.The WUE,LUE,CUE showed a single peak curve during the growing season.WUE and LUE showed a"U"curve during the day,while CUE showed a single peak dynamic change during the day.3.In the study of the factors which affecting WUE,LUE,CUE,we found that the factors affecting WUE were air temperature,photosynthetically active radiation,canopy conductance and vapor pressure deficit depending on the strength of correlation.The factors affecting LUE were vapor pressure deficit,photosynthetically active radiation,air temperature and canopy conductance according to the correlation intensity,while CUE has a good correlation with air temperature in the growing season.WUE,LUE,CUE are interrelated and interacted,which have good correlations between them.4.WUE in cloudy days is bigger than that in sunny days,the difference of LUE in cloudy days is not obvious,and CUE in sunny days is bigger than that in cloudy days.Vapour pressure deficit and flow rate were negatively linear correlated with WUE and LUE in both cloudy and sunny days,while were negatively logarithmic correlated with CUE.The study area has been under the condition of drought stress for a long time,but the WUE,LUE,CUE under water stress was higher than that under non-stress.The relationship between canopy conductance and WUE,LUE,CUE under different soil moisture conditions indicates that soil moisture is an important factor restricting carbon sequestration in the study area.