Abstract:

By means of sap flow measurement technique with thermal diffusion probe and micro-meteorological station, daily meteorological factors and sap flow of Platycladus orientalis both at different trunk height, in different trunk direction and different diametric singletrees were measured in the Western Mountain of Beijing. Relations between sap flow velocity (SFV) and environmental factors, such as solar radiation intensity, air temperature, air humidity, wind speed and soil temperature, were also analyzed. Result showed that, SFV in upper trunk sapwood was much higher, with an early start_up and a fast ascendant, but descended steeply after got the peak in the late morning and 2 times higher than that in lower trunk sapwood. SFV both in eastern, northern and western orientation in trunk sapwood was similar and much higher than that in southern direction, and there was no certain relation between SFV and its corresponding sapwood width and crown dimension. Singletree sap flow verified according to trunk diameters that large trees sap flow was higher than that of small ones. Daily environmental factors under canopy verified regularly and had a correlation with sap flow significantly. SFV of all the diametric sample trees had a minus correlation with air humidity. And SFV of large trees had a positive relation with solar radiation intensity and air temperature, but small trees were inverse, significantly. Wind speed had an important effect on sap flow conductance. 20～40 cm layer soil temperature had a significant impact on trees water consumption that SFV of large trees was minus related to soil temperature but SFV of small trees was positive. Taking solar radiation intensity, air temperature, air humidity, wind speed, and soil temperature in 5～60 cm as independent variable and SFV as dependent, by stepwise regressing, multiple linear equation was established with a significant regression test.

Key words: Platycladus orientalis, sap flow velocity, spatial variation, environmental factor, correlative analysis