Vandegehuchte Maurits W, Burgess Stephen S O, Downey Alec, Steppe Kathy
Laboratory of Plant Ecology, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, 9000 Gent, Belgium
School of Plant Biology, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia.
Tree Physiol. 2015 Apr;35(4):346-53. doi: 10.1093/treephys/tpu068. Epub 2014 Aug 21.
While natural spatial temperature gradients between measurement needles have been thoroughly investigated for continuous heat-based sap flow methods, little attention has been given to how natural changes in stem temperature impact heat pulse-based methods through temporal rather than spatial effects. By modelling the theoretical equation for both an ideal instantaneous pulse and a step pulse and applying a finite element model which included actual needle dimensions and wound effects, the influence of a varying stem temperature on heat pulse-based methods was investigated. It was shown that the heat ratio (HR) method was influenced, while for the compensation heat pulse and Tmax methods changes in stem temperatures of up to 0.002 °C s(-1) did not lead to significantly different results. For the HR method, rising stem temperatures during measurements led to lower heat pulse velocity values, while decreasing stem temperatures led to both higher and lower heat pulse velocities, and to imaginary results for high flows. These errors of up to 40% can easily be prevented by including a temperature correction in the data analysis procedure, calculating the slope of the natural temperature change based on the measured temperatures before application of the heat pulse. Results of a greenhouse and outdoor experiment on Pinus pinea L. show the influence of this correction on low and average sap flux densities.
虽然对于基于热量的连续液流方法，测量针之间的自然空间温度梯度已得到充分研究，但对于茎干温度的自然变化如何通过时间而非空间效应影响基于热脉冲的方法，却很少有人关注。通过对理想瞬时脉冲和阶跃脉冲的理论方程进行建模，并应用包含实际针尺寸和伤口效应的有限元模型，研究了变化的茎干温度对基于热脉冲方法的影响。结果表明，热比（HR）方法受到影响，而对于补偿热脉冲法和Tmax方法，茎干温度变化高达0.002 °C s(-1) 时，不会导致显著不同的结果。对于HR方法，测量期间茎干温度上升会导致热脉冲速度值降低，而茎干温度下降则会导致热脉冲速度升高和降低，并导致高流量时出现虚数结果。通过在数据分析过程中纳入温度校正，基于热脉冲应用前测量的温度计算自然温度变化的斜率，可轻松防止高达40% 的这些误差。对欧洲赤松进行的温室和室外实验结果表明了这种校正对低和平均液流通量密度的影响。
