| According to the heat balance principle, the stem flow of Yali pear were studied by Dynamax sap flow measuring system in Taigu country of Shanxi Province. In order to explore monthly variation of the sap flow and regular pattern by different stem diameter, weather condition, the diurnal variation of sap flow were measured from June to October in 2010. Furthermore, we still studied the relationship between the sap flow of pear tree and environmental factors. the results showed:(1) Obviously, the sap flow velocity of pear tree was low in morning, evening, and reached high value in midday, its daily variation curve exhibited in a parabolic distribution. Diurnal variation curve of sap flow belonged to unimodal curve usually, however, it could change into two-humped or multi-peaked curve because of distinct stem diameter of pear tree and varied meteorologic factor. Whether there have the stem flow or not in midnight, it was closely connected with quantity of water loss of pear tree in the daytime. Owing to self-physiology and adverse climate, sap flow velocity of pear tree fell down gradually from august.(2) The more biomass, leaf area of pear tree have, the more water consumption of transpiration will occur. The sap flow of various trunk of pear tree has similar activity period which conform to duration of sunshine practically. In addition, being differernt from single peak, the thick trunk (SGB-35) showed as two-humped shape on the sap flow velocity curve subject. This phenomenon could be attributed to that former held large-scale of growing and was intensely response to environmental factors.(3) The sequence about transpiration rate, and time span of stem flow respectively ranged as:sunny day>cloudy weather>rainy day, sunny day> rainy day>cloudy weather. The starting time of sap flow is later in cloudy weather than sunny day about 2 hours evidently, while the start-up time in rainy day is no regular on account of unequal quantity, lasting time of precipitation.(4)Among of 11 models, the cubic curve model was demonsrated to be optimal model which was be used to analyse the extent that environmental factors affected the stem flow of pear tree. the results indicated that the sap flow velocity had a very significant correlation with photosynthetically active radiation (PAR), and then has lower correlation with air temperature, air relative humidity, vapor pressure deficit (vpd). whereas it didn't insignificantly correlated with wind speed. With the multiple stepwise regression analysis, we also acquired the regression equation about relationship between the sap flow of pear tree and related environmental factors. the equation could be used to estimate the transpiration of the pear tree. |
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