热脉冲技术3种方法组合在测量树干液流中的应用

Application of three heat pulse technique-based methods to determine the stem sap flow

利用树干液流方法获取树木蒸腾特征对理解树木水分生理、森林生态和森林系统水分交换具有重要意义.利用广泛应用于土壤热参数和土壤蒸发测量的三针热脉冲探头,基于热比率法（HRM）、最大温度法（T-Max）和单针热脉冲法（SHPP）同时实现了旱柳液流密度的测定,并与热扩散探针（TDP）测量结果进行对比分析.结果表明：三针热脉冲探头安装约5周后进入稳定测量阶段,3种方法初期测量结果比稳定测量阶段高135%-220%,HRM、T-Max和SHPP法与TDP测量结果具有显著的线性相关性,R2分别为0.93、0.73和0.91,SHPP与HRM法测定结果的R2达到0.94.HRM在低速和逆向液流时测量具有较高的精度;SHPP探头配置简单、测量精度高,但无法甄别液流方向,是测定液流非常有前途的方法;T-Max测量液流误差较大,无法测量〈5 cm^3·cm^-2·h^-1的液流,不建议单独用于液流测量,但其能够准确测定树干热扩散系数,并可用于其他方法液流计算.建议根据试验目的,选取不同方法或者几种方法组合进行树干液流测量.

It is of critical importance to acquire tree transpiration characters through sap flow methodology to understand tree water physiology,forest ecology and ecosystem water exchange. Tri-probe heat pulse sensors,which are widely utilized in soil thermal parameters and soil evaporation measurement,were applied to implement Salix matsudana sap flow density（ Vs） measurements via heatratio method（ HRM）,T-Max method（ T-Max） and single-probe heat pulse probe（ SHPP） method,and comparative analysis was conducted with additional Grainer ＇s thermal diffusion probes（ TDP） measured results. The results showed that,it took about five weeks to reach a stable measurement stage after TPHP installation,Vsmeasured with three methods in the early stage after installation was 135%- 220% higher than Vsin the stable measurement stage,and Vsestimated via HRM,T-Max and SHPP methods were significantly linearly correlated with Vsestimated via TDP method,with R2 of 0. 93,0. 73 and 0. 91,respectively,and R2 for Vsmeasured by SHPP and HRM reached 0. 94. HRM had relatively higher precision in measuring low rates and reverse sap flow.SHPP method seemed to be very promising to measure sap flow for configuration simplicity and high measuring accuracy,whereas it couldn＇t distinguish directions of flow. T-Max method had relatively higher error in sap flow measurement,and it couldn＇t measure sap flow below 5 cm^3·cm^- 2·h^- 1,thus this method could not be used alone,however it could measure thermal diffusivity for calcula-ting sap flow when other methods were imposed. It was recommended to choose a proper method or a combination of several methods to measure stem sap flow,based on specific research purpose.