| The western areas of China is facing the serious problem of water shortage because of the unique natural and geographical conditions. And the situation is serious increasingly with the population growth and the long-term unreasonable development and utilization for the natural resource, and the uneven distribution of precipitation, which enlarged contradiction between water shortage and plant growth. Therefore, it is necessary to study the mechanism of water utilization to improve the survival rate of vegetation. In this paper, we took the Liupan Mountains in Ningxia Hui Autonomous Region for experiment area, and studied the variation of spatial and temporal of the water consumption by transpiration of Larix principis-rupprechtii plantation and the effect factors on it by using the technology of TDP during the growing season in 2008. The main results are as follows:(1) The studies on transpiration Change of Larix principis-rupprechtii plantations indicated that: the sap flow velocity is lowest in the early morning, and highest around noon, and lowest at night. The sap flow value between 8:00 and 18:00 accounted for more than 70% of the total sap flow value. The percentage of peak value sap flow velocity appearing at 10:00-16:00 is respectively 98.61%,84.49% and 55.82% at the three types of weather conditions. The sap flow velocity was "L" curve in the night, and it is smoother in sunny, and is the most steady in rainy day. It moved larger in cloudy day. The ratio of consumption accounted for 10.6% ~ 29.6% in Cloudy and rainy day of night, and the proportion was greater at sunny days. Further reach indicated that the day's average water consumption accounts for 12.81% of the night under water deficit, the ratio rose to 21.65% under sufficient water conditions. The sap flow value of every month was decreased in the order of June, May, July, Aug., Sept., and Oct.(2) The studies of the effects of soil moisture on transpiration showed that: soil moisture and rainfall are highly synchronized. The Range of soil water potential was decreased in the order of 20-40cm, 40-60cm, 0-20cm under the soil water deficit, and was decreased in the order of 20-40cm, 0-20cm, 40-60cm under adequate soil moisture. Under the soil water deficit conditions, the flow velocity varied with soil water potential, but the flow velocity and soil water potential has poor synchronization under the water adequate conditions.(3) The results of the analysis on meteorological factors: the sap flow velocity was highly degree of consistent on solar radiation and air temperature, but solar radiation had lagged effect, the effects of the air temperature and solar radiation on the sap flow velocity appeared at night, there was a negative correlation between the sap flow velocity and relative humidity, and the variation of soil temperature in 20cm was more regularly than 40cm. The change of smallest wind speed and the sap flow velocity was consistent. The results showed that: the differences of different factors were significantly, Correlation of the different meteorological factors was significantly lower. Under the two type water conditions, the effect of meteorological factors on the sap flow velocity was smaller than soil moisture. That is under water deficit conditions, the sap flow velocity was influenced by the soil moisture, but under the water sufficient conditions was influenced by the meteorological factors.(4) The study of other factors showed that: The variation of the sap flow velocity was significant with the radial expansion and contraction of the trunk , but the variation of former lagged in the latter. The value of the radial variation showing clear diurnal cycle was smallest before and after evening, and was largest around 8:00 in the morning.
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