To understand the water use character of main tree species in soft sand-rock area

three main tree species (Caragana korshinskii Kom、Hippophae rhamnoides Linn. Pinus tabuliformis) in Geqiugou

Ordos

Inner Mongolia was examined using stem heart balance method to explore sap flow of these three tree species under different weather conditions and the daily change. The results showed: (1) The sap flow rates of the three tree species showed a unimodal curve

and nearly reached the peak at the same time during growing. (2) In the sunny day

the sapflow rate of Hippophae rhamnoides Linn was the highest

about 0.11772cm/s

the sap flow rate of Caragana korshinskii Kom and Pinus tabuliformis were similar; the daily average rates of the three species were 0.02901cm/s

0.01815cm/s

and 0.02203cm/s

respectively. (3) In different weather conditions

the sapflow rates of the three species showed sunny day＞cloudy day＞rainy day

and the time when they reached the peak showed sunny day＞cloudy day＞rainy day. The results of the study are to provide theoretical basis for studying the water supply-demand relationship of plants in soft sand-rock area and environmental management.