Abstract: Haloxylon ammodendron, Calligonum caput-medusae and Alhagi sparsifolia Shap. are all the dominant species in extremely arid region in the south marginal zone of the Taklimakan Desert in northwest China. These species can be planted in wind break and sand-fixation forest at the desert-oasis ecotone. In this extremely arid region, the mean annual precipitation is 35.1 mm only, the mean annual evaporation is as high as 2 595.3 mm, and average wind speed is 1.9 m•s^-1. Growth of H. ammodendron, C. caput-medusae and A. sparsifolia depends highly on snowmelt from the Kunlun Mountains or/and groundwater. In order to explore the water consumption of these three plant species, the values of their sap flow were measured every 10 minutes during the period from June to November with a heat balance Dynamax packaged sap flow measuring system. Moreover, some meteorological factors including solar radiation (Rs), air temperature (Ta), air relative humidity (RH) and wind speed were synchronously measured by an automatic weather station. The correlations between sap flow rate and meteorological factors were analyzed. The result are as follows: (1) The data of sap flow under sunny weather were calculated every 30 minutes during July 13-18, the daily curve of sap flow of H. ammodendron was bimodal or multi-peaked, and there was a significant noon depression of sap flow; that of C. caput-medusae was unimodal or multi-peaked, that of A. sparsifolia Shap was unimodal, and there was no obvious noon depression of sap flow neither for C. caput-medusae nor for A. sparsifolia Shap. The starting time and peak value occurrence of sap flow of C. caput-medusae and A. sparsifolia Shap were delayed about 1 hour than that of H. ammodendron, and the time of sap flow rate reduction of the three plant species was similar; (2) In whole growing season, the average monthly values of sap flow flux during the period from June to November were calculated. The result are that the value of H. ammodendron was high all along, and it reached its peak in July, the values of C. caput-medusae and A. sparsifolia Shap reached their peak in August, and then the values of all the species began to decrease until to their minimums in November; (3) In order to research the response of sap flow of the three plant species under different weather conditions, the values of sap flow flux of different plant species were selected and compared, and the sap flow flux under different weather was in an order of sunshine>sandstorm>cloudy weather>rainfall; (4) There was a significant positive correlation between the sap flow rate of the three plant species and the Rs, Ta and VPD (P<0.01),but a significant negative one between it and RH(P<0.01).

Key words: heat balance, meteorological factor, stem sap flow, Qira, Taklimakan