Simulation And Partition Evapotranspiration For Different Landform-Soil-Vegetation Formations In Horqin Sandy Land

Evapotranspiration is the core process for water and energy exchange in the ecosystem.Accurate estimation of evapotranspiration and its components is of great significance for profoundly revealing the cco-hydrological processes in arid and semi-arid regions.In this paper,four representative landform-soil-vegetation formations(i.e.mobile sand dune A4,semi-fixed sand dune G4,fixed sand dune F4,and transition zone Populus spp forest A1)were selected for study.This study applied Shuttleworth-Wallace(S-W)model to simulate and partition evapotranspiration(ET)at the four landform-soil-vegetation formations based on in situ sampled by the meteorological monitoring system and the experiment of vegetation ecological indicators survey during 2017 and 2018 growing seasons.Eddy covariance technology was used to validate the performance of model.Furthermore,this paper analyzed the effects of persistent drought and continuous precipitation on vegetation ecology in desertification area from the evapotranspiration of vegetation community scale and the photosynthetic characteristics of leaf-scale plants.The main results are as follows:(1)ET showed as:A1>F4>G4>A4,which was consistent with canopy coverage.The ET rate at the vigorous growth stage was larger than those at the late and early growth stages,which was closely related to the variation of precipitation and the season of the year,and precipitation is the main source of ET in sand dunes.Evaporation(E)and E/ET showed as:A4>G4>F4>A1,which were consistent with canopy coverage.Although soil evaporation and evapotranspiration in desertification areas are greatly affected by hydrometeorological factors,E/ET of different landform-soil-vegetation combination units is maintained at a relatively stable level.In desertification areas,under different landforms and vegetation conditions,the evapotranspiration of vegetation varies greatly,but the vegetation transpiration of sandy vegetation is proportional to the precipitation.The precipitation and its distribution characteristics determine the strength of transpiration water consumption of sandy vegetation.(2)The simulation accuracy of the S-W model is greatly affected by the meteorological environment factors.In clear day,the accuracy of S-W model is best,and simulate value is close to observed value.The simulation performance of S-W model for clear days are better than cloudy and rainy days.In addition,the simulated value in rainy days are almost lower than observed value.During eddy covariance observation,the simulated ET generally equal to observed ET.The variety trend of simulated E is consistent with observed E.(3)The characteristics of ET varied obviously under the drought stress and after sustain precipitation events,sand evapotranspiration maintained lower level,and increased after precipitation.The lower the vegetation coverage,the more the response to precipitation,and compare to T from plants,E from soil was more sensitive to precipitation.During drought period,the role of dry sand layer greatly slowed down the evaporation,and semi-shrub and shrub growing on mobile and semi-mobile dune minimizing the impact of drought by reducing water consumption,and showing obvious "midday break".Different life-type vegetations have different response mechanisms to drought and precipitation.To adapt drought environment,Caragana microphylla maintained lower transpiration rate and higher water use efficiency,while Populus spp avoided drought by higher photosynthetic rate,transpiration rate and lower water use efficiency.After precipitation,the changes of photosynthetic characteristics and the sensing to precipitation of Caragana microphylla were more significant than Populus spp.After precipitation,Caragana microphylla rapidly absorbed soil moisture,restored healthy growth by strong photosynthesis,and showed strong adaptability to environmental changes.Compare to drought period,the photosynthetic characteristics of Populus spp after precipitation were similar,indicated less sensitive to precipitation and less sensitive to environment changes.