Department of Biology, University of Utah, Salt Lake City, UT 84112, USA.
Tree Physiol. 2010 Dec;30(12):1545-54. doi: 10.1093/treephys/tpq096.
Thermal dissipation probes (the Granier method) are routinely used in forest ecology and water balance studies to estimate whole-tree transpiration. This method utilizes an empirically derived equation to measure sap flux density, which has been reported as independent of wood characteristics. However, errors in calculated sap flux density may occur when large gradients in sap velocity occur along the sensor length or when sensors are inserted into non-conducting wood. These may be conditions routinely associated with ring-porous species, yet there are few cases in which the original calibration has been validated for ring-porous species. We report results from laboratory calibration measurements conducted on excised stems of four ring-porous species and two diffuse-porous species. Our calibration results for ring-porous species were considerably different compared with the original calibration equation. Calibration equation coefficients obtained in this study differed by as much as two to almost three orders of magnitude when compared with the original equation of Granier. Coefficients also differed between ring-porous species across all pressure gradient conditions considered; however, no differences between calibration slopes were observed for data collected within the range of expected in situ pressure gradients. In addition, dye perfusions showed that in three of the four ring-porous species considered, active sapwood was limited to the outermost growth ring. In contrast, our calibration results for diffuse-porous species showed generally good agreement with the empirically derived Granier calibration, and dye perfusions showed that active sapwood was associated with many annual growth rings. Our results suggest that the original calibration of Granier is not universally applicable to all species and xylem types and that previous estimates of absolute rates of water use for ring-porous species obtained using the original calibration coefficients may be associated with substantial error.
热耗散探针（Granier 方法）常用于森林生态学和水量平衡研究中，以估算整树蒸腾量。该方法利用经验推导的方程来测量 sap 流密度，据报道该方法与木材特性无关。然而，当 sap 速度在传感器长度上出现大梯度或传感器插入不导电木材时，计算得出的 sap 流密度可能会出现误差。这些可能是与环孔材物种通常相关的条件，但很少有案例对环孔材物种进行了原始校准验证。我们报告了对四个环孔材物种和两个散孔材物种的离体茎进行实验室校准测量的结果。与原始校准方程相比，我们对环孔材物种的校准结果有很大差异。与 Granier 的原始方程相比，本研究中获得的校准方程系数差异高达两个到三个数量级。在考虑的所有压力梯度条件下，环孔材物种之间的系数也存在差异；然而，在预期的原位压力梯度范围内收集的数据中，没有观察到校准斜率的差异。此外，示踪剂灌注表明，在所考虑的四个环孔材物种中的三个物种中，活跃的边材仅限于最外层的生长轮。相比之下，我们对散孔材物种的校准结果与经验推导的 Granier 校准通常吻合良好，示踪剂灌注表明活跃的边材与许多年生长轮有关。我们的结果表明，Granier 的原始校准不适用于所有物种和木质部类型，并且使用原始校准系数获得的环孔材物种的绝对耗水量的先前估计可能存在很大误差。
