| This study used the eddy convariance（EC）system to observe the underlying surface energy flux and evapotranspiration（ET）of the vegetated land and the bare land on the Haloxylon ammodendron plantation in Minqin oasis-desert ecosystem.Using the data from December 2017 to December 2019,we analyzed the energy balance characteristics under different atmospheric turbulent conditions.The energy partitioning during soil dry and wet conditions,and the characteristics of ET in the growing season and non-growning season.The boosted regression tree method（BRT）was used to analysed the main environment factors controlling on energy partitioning and ET.The main results and conclusions were as follows:（1）The energy closure ratio（EBR）and data quality control（QC）of the vegetated land and the bare land were significantly affected by the atmospheric turbulent conditions of the near-surface atmospheric boundary layer.The annual EBR between the vegetated land and the bare land were 0.70 and 0.62,respectively.The EBR of the vegetated land and bare land during the growing season were 0.56 and 0.60,respectively.The EBR of the vegetated land was higher than that at the bare land during the non-growing season.The EBR of the vegetated land and bare land during the non-growing season were 0.82 and 0.62,respectively;The EBR and QC varied with atmospheric stability（ζ）.Changing from unstable atmosphere conditions（ζ<-0.04）to stable atmosphere conditions（ζ>0.04）,the EBR decreased（EBR>0.7 atζ<-0.04,EBR<0.4 atζ≥-0.04）,and the QC increased（QC<5 atζ<-0.04,QC>5 atζ≥-0.04）,with data quality bad;When friction speed（*）>0.3 m·s-1or turbulence thermal conditions（w’T’）>0.07℃·m·s-1,the EBR of the vegetated land and the bare land were high,and the quality of EC data were good（QC<5）.（2）The sensible heat（H）was the main energy partitioning at the vegetated land and the bare land,The surface（10 cm）soil water volumetric content（SWC）of the vegetated land was lower than that at the bare land.The net radiation（Rn）at the vegetated land was lower than that at the bare land,While The H at the vegetated land accounted higher than that at the bare land.The latent heat（LE）and evaporative fraction（EF）at the vegetated land accounted lower than that of the bare land.During the growing season,the energy ratio of surface soil heat flux（G）of two areas were 8.77%（the vagetated land）and 0.63%（the bare land）,respectively,and G was a positive value,indicating that the energy was transmitted from the surface to the underground.During the non-growing season,the G at two areas was negative,and the direction of energy transmission changed;According to the BRT results,SWC was the main factor controlling on the EF at the vegetated land and the bare land.VPD had a greater impact on the EF at the bare land than that at the vegetated land;The effect of SWC on EF at the two areas was a positive effect,while EF decreased with the increase of Rn and vapor pressure deficit（VPD）;The effect of VPD on EF was not obvious during soil dry condition,while the decrease of EF with Rn increased significantly.LE increased during the soil wet condition,and the effect of VPD on EF was greater,while the effect of Rn on EF was reduced.（3）The ET at the vegetated land and bare land was 0.38 mm·day-1and 0.44 mm·day-1respectively.And the ratios of ET to precipitation at the vegetated land and bare land was 1.14and 1.31 respectively.The main factor controlling on ET at the vegetated land was SWC,and the main factor controlling on ET at the bare land was Rn;Turbulent conditions also had an effect on the ET at the two areas.w’T’had a greater impact on ET during the growing season,while*had a greater impact on ET during the non-growing season.The difference in ET between the two areas was mainly associated with SWC at the two areas.The thicker dry sand layer at the vegetated land inhibiting ET was beneficial to the maintain deep soil moisture,which supplied for the growth of Haloxylon ammodendron vegetation.This study helps us to further understand the energy partitioning and evapotranspiration characteristics of sparse vegetation in the oasis-desert ecosystem,and provides a theoretical basis for the formulation of policies related to climate change in ecologically vulnerable areas. |
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