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From May to October of 2010, TDP （Thermal Dissipation Sapwood Flow Velocity Probe） was applied to explore the radial variation in sap flow at 10 mm, 20 mm, 30 mm of ligustrun lucidum trunk and the relationship with meteorological factors in this article, aimed to providing theoretical according to measure its sap flow accurately. Results showed that:（1） The average sap flow velocity of ligustrun lucidum showed the trend of“low-high-low”in the whole growing season on the south or north of the tree, Fs20（the sap flow velocity at 20 mm）>Fs30（the sap flow velocity at 30 mm）>Fs10（the sap flow velocity at 10mm）.（2） The trends of average sap flow velocity at three depth were basically the same on south and north in different months. On south, June>July>August>September>October>May. On north, July>June>August>September>October>May.（3） In three typical weather conditions of sunny, cloudy and rainy days, in spring, the sap flow velocity was Fs10>Fs20>Fs30 on south, Fs20>Fs10>Fs30 on north, Fs20>Fs30>Fs10 in summer and autumn on south or north of the tree. The starting time of sap flow was Fs10>Fs20>Fs30, the pausing time was Fs30>Fs20>Fs10 on south or north of the tree in the whole growing season. The closer the point was to cambium, the earlier the sap flow started and the later paused.（4） The trends of sap flow velocity in daily variability were all similar at different depths on south and north of the tree. In sunny days, the sap flow velocity at different depths respectively exhibited sharp-peak, wide-peak, double peaks curves in spring, summer and autumn; In cloudy days, the sap flow velocity at different depths all exhibited multi-peak curves in spring, summer and autumn; In rainy days, the daily variability was disorderly, it has no obvious pattern. The starting time of sap flow in summer was earlier than in spring and autumn. The pausing time of sap flow in summer was latter than in spring and autumn. Therefore, the peak duration of sap flow in summer was longer than spring and autumn, the curve in summer was wider than in spring and autumn.（5） On the differences of south and north of ligustrun lucidum trunk, in sunny and cloudy days, the trends of sap flow velocity at different depth were basically the same, they were all exhibited single peak curves. The daily average sap flow velocity at 30mm is S>N, roughly the same at 20 mm, N>S at 10 mm. The starting time, peak time, pausing time of sap flow on north were all earlier than south.In rainy days, the sap flow velocity at different depth on south and north of ligustrun lucidum trunk was all in a low level, the trend exhibited irregularly. The daily average sap flow velocity was roughly the same at 30 mm, N>S at 20 mm, S>N at 10 mm. The sap flow showed a significant correlation at 30 mm and 20 mm in two directions, but no significant at 10 mm,（6） Throughout the whole growing season, the sap flow at different depths on south or north of ligustrun lucidum trunk showed a significant positive correlation with air temperature, solar radiation and wind speed. Besides 20 mm on north showed no significant correlation with air relative humidity, the other depths all showed a significant negative correlation with air relative humidity. The sap flow at different depths on south and north had no significant correlation with rain. In the whole growing season, the influence by the environmental change at 10 mm to the cambium was bigger than 20 mm and 30 mm.
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