树干自然温度梯度变化对热扩散法测算树干液流速率的影响

为了揭示树干自然温度梯度的变化规律及其对树干液流速率测算结果的影响,于2007年5月至10月利用改进的SF-L型热扩散式树液流测定装置,对北京低山区生长的油松和侧柏的树干自然温度梯度、加热温差和气象、土壤水分因子进行了连日同步监测。结果表明:(1)树干自然温度梯度对加热针温差的影响,侧柏大于油松。(2)树干自然温度梯度对液流速率计算结果的影响具有显著的统计意义(P0.01),平均误差大于30%,误差峰值出现在太阳高度角较小的时候。(3)影响树干自然温度梯度最重要的环境因子是光照强度,其次是空气温度。上述结果说明,树干自然温度梯度对热扩散法测定的液流速率的影响不可忽视,研究树木耗水机制时应予以充分考虑。光照强度和空气温度是影响树干自然温度梯度最重要的两个因子,但其影响机制仍需进一步研究。

Influence of trunk natural temperature gradient change on sap flow velocity measured with thermal dissipation method

To illustrate the impact of trunk natural temperature gradient on sap flow velocity measured with thermal dissipation method, the trunk natural temperature gradient and heated temperature difference of Pinus tabulaeformis and Platycladus orientalis growing in low mountain areas around Beijing, together with weather and soil water conditions, were monitored daily and synchronously by using improved SF-L type thermal dissipation sap flow velocity measuring device and associated equipments from May 2007 to October 2007. The results showed that trunk natural temperature gradient of P. orientalis had greater impact on heated temperature difference than that of P. tabulaeformis. There was notable statistical difference (P<0.01) between the measurement results of sap flow velocity considering trunk natural temperature gradient and not. The average error percentage of sap flow velocity measurements caused by trunk natural temperature gradient was over 30%.The peak appeared when the solar altitudinal angle is low. Among the environmental factors, light intensity exerted the most significant influence on trunk natural temperature gradient, followed by air temperature. So the influence of trunk natural temperature gradient on the measurement results of sap flow velocity should not be neglected but be fully considered during study on water consuming mechanism of trees. Light intensity and air temperature are the two most significant factors influencing trunk natural temperature gradient, but the mechanism behind needs further research.