Abstract: The transpiration water consumption of Haloxylon ammodendron is an important physiological index, and its variation law is influenced by many environmental factors. The transpiration water consumption of individual trees could be accurately measured by investigating the characteristics of sap flow and environmental factors,and the transpiration of single-tree also could be predicted with the help of environmental indicators by building the model of the sap flow with environmental factors. Combined with automatic weather stations,a thermal dissipation probe(TDP)was continuously used to measure the sap-flow dynamics and environmental factors of Haloxylon ammodendron in the southern marginal zone of the Gurbantünggüt Desert,Xinjiang,China,the sap-flow velocity response to the environmental elements were analyzed and the stem sap flow of Haloxylon ammodendron were simulated based on the potential evapotranspiration and transpiration requirement index. Results show as follows:(1)The change of sap-flow velocity mainly presented single-peak curve,the time of the velocity rising stage was shorter than that of the descending stage,which was inconsistent with the diurnal variation of meteorological factors. There were differences with the amplitude of daily variation during different seasons,in summer,the sap-flow started earlier and stopped later,the peak value was higher and presented earlier compared with spring and autumn.(2)There were different degrees of correlation between environmental factors. The first three axes of principal component analysis(PCA)explained 47%,20%,17.6% of variances in the environmental data sets,while the first principal component including RH,T_a,VPD,ET₀ and R_n could explain 47% of environmental information changes;the second principal component with T_s and e_a could explain 20% of environment information;the third principal component given priority to H_S and u₂ could explain 17.6% of the environment change information. The first principal component reflects the needs of the atmosphere transpiration,and the second and third principal components reflect the effect of soil environmental conditions on transpiration rate. (3)The accuracy of sigmoid based on potential evapotranspiration in spring and summer was higher,and the polynomial model was better than the ET₀ model in autumn.(4)The hysteresis between velocity of sap flow and environmental factors was revealed in Haloxylon ammodendron,and presented significant differences in different seasons. In spring and autumn,the relationship between the velocity of sap flow and VPD was clockwise,while the relationship between the velocity of sap flow and the net radiation or the potential evapotranspiration presented a counterclockwise trend. During summer,however,the relationship between the sap flow velocity and the net radiation or potential evapotranspiration presented a clockwise of the figure 8. The water consumption of Haloxylon ammodendron and its response to environmental factors had significant differences in different seasons, which also provided the theoretical support for the study on the water consumption of desert plants and the management of artificial irrigated plants.

Key words: Gurbantünggüt Desert, hysteresis, principle component analysis, stem sap flow, simulation