The transpiration water consumption of Haloxylon ammodendron is an importantphysiological index, and its variation law is influenced by many environmental factorscomprehensively. The transpiration water consumption of individual trees could beaccurately measured by investigating the characteristics of sap flow andenvironmental factors, and the transpiration of single-tree also could be predicted withthe help of environmental indicators by building the modeling with the sap flow andenvironmental factors. Combined with automatic weather stations, thermal dissipationprobe (TDP) was continuously used to measure the sap flow dynamics andenvironmental factors of Haloxylon ammodendron in the southern marginal zone ofthe Gurbantunggut desert, the sap flow velocity response to the environmentalelements were analyzed and the stem sap flow of Haloxylon ammodendron weresimulated based on the potential evapotranspiration and transpiration requirementindex . The results showed that:(1) The change of sap flow velocity mainly presented single peak or occasionallyappeared double peak curve in summer. The amplitude of daily variation and sap flowpeak in summer were greater than in the spring and autumn and presented asignificant differences with the sap-flow velocity during different seasons. Thestarting and peak times of sap flow were earlier and had a weak sap flow at night insummer. (2) In the growing season, net radiation, air temperature and saturated vapor pressuredeficit were the key factors of leading to the instantaneous changes. The instantaneoussap-flow of Haloxylon ammodendron was positively correlated with wind speed, netradiation, saturated vapor pressure deficit and air temperature, and negativelycorrelated with the actual water vapor pressure and air humidity. The net radiation, saturated vapor pressure deficit and air temperature were the key factor affectting theseasonal change of sap flow velocity. The daily average flow rate was positivelycorrelated with the net radiation, air temperature,saturated vapor pressure (3) deficit,actual water vapor pressure, soil water content and soil temperature, and asignificant negatively correlated with the air humidity. (4) There were different degrees of correlation between environmental factors, Thefirst three axes of principal component analysis (PCA) explained 47%, 20%, 17.6% ofvariances in the environmental data sets, while the first principal component includingRH, Ta, VPD, ET0 and Rn could explain 47% of environmental information changes, the second principal component with Ts and ea could explain 20% of environmentinformation, the third principal component given priority to HS and u2 could explain17.6% of the environment change information. The first principal component reflectsthe needs of the atmosphere transpiration, and the second and third principalcomponents reflect the effect of soil environmental conditions on transpiration rate. (4) The accuracy of sigmoid based on potential evapotranspiration in spring andsummer was higher, and the polynomial model was better than the ET0 model inautumn. (5)The hysteresis between velocity of sap flow and environmental factors wererevealed, presented significant differences during different seasons. In spring andautumn, 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 thepotential evapotranspiration presented a counterclockwise trend. As in the spring andautumn seasons, the relationship between the sap flow velocity and VPD alsopresented a trend of clockwise during summer, however, the relationship between thesap flow velocity and the net radiation or potential evapotranspiration presented aclockwise as figure 8. (6)The daily transpiration of Haloxylon ammodendron forest was 0.35 mm/d, totaltranspiration was 53.35 mm during the whole study period, The daily transpirationwas increased from April to July, then began to decrease until the end of the growingperiod
