A synthesis of bias and uncertainty in sap flow methods
A synthesis of bias and uncertainty in sap flow methods
复制标题
DOI：
10.1016/j.agrformet.2019.03.012
复制
发表时间：
2019-06-15
影响因子：
6.2
通讯作者：
Poyatos, Rafael
中科院分区：
文献类型：
--
作者：
Flo, Victor;Martinez-Vilalta, Jordi;Poyatos, Rafael
摘要植物蒸腾作用的测定广泛采用测温法。不同的方法系列取决于它们如何施加热量和跟踪边材温度（热脉冲，散热，热场变形或热平衡）。这些方法已针对许多物种进行了校准，但尚未对其不确定性和可靠性进行全球评估。在这里，我们对从文献中收集的290个单独的校准实验进行了荟萃分析，以评估校准性能以及方法，实验条件和木材特性（密度和孔隙率类型）之间的差异。我们使用不同的指标来表征平均准确度（测量值与真实参考值的接近程度）、比例偏倚（由测量流量对误差幅度的影响引起）、测量值与参考值之间关系的线性以及精密度（再现性和重复性）。我们发现校准性能存在较大的方法内和方法间变异性，其中物种解释的变异性比例较低。当使用茎段时，校准性能最好。我们没有发现证据表明木材密度或孔隙度类型对校准性能有很强的影响。耗散法的准确度较低，比例偏倚较大，但线性和精密度相对较高。脉冲方法也显示出显著的比例偏差，这是由于它们高估了低流量。这些结果表明，耗散方法可能更适合于评估相对液流（例如，研究中的治疗效果）和脉冲方法可能更适合于量化绝对流量。尽管如此，所有的树干液流方法显示出高精度，允许潜在的校正测量时，进行研究特定的校准。如果实验条件和木材性质，包括木材水分的变化，更好地报告，我们的理解如何液流方法进行跨物种将大大提高。
Sap flow measurements with thermometric methods are widely used to measure transpiration in plants. Different method families exist depending on how they apply heat and track sapwood temperature (heat pulse, heat dissipation, heat field deformation or heat balance). These methods have been calibrated for many species, but a global assessment of their uncertainty and reliability has not yet been conducted. Here we perform a meta-analysis of 290 individual calibration experiments assembled from the literature to assess calibration performance and how this varies across methods, experimental conditions and wood properties (density and porosity types). We used different metrics to characterize mean accuracy (closeness of the measurements to the true, reference value), proportional bias (resulting from an effect of measured flow on the magnitude of the error), linearity in the relationship between measurements and reference values, and precision (reproducibility and repeatability). We found a large intra- and inter-method variability in calibration performance, with a low proportion of this variability explained by species. Calibration performance was best when using stem segments. We did not find evidence of strong effects of wood density or porosity type in calibration performance. Dissipation methods showed lower accuracy and higher proportional bias than the other methods but they showed relatively high linearity and precision. Pulse methods also showed significant proportional bias, driven by their overestimation of low flows. These results suggest that Dissipation methods may be more appropriate to assess relative sap flow (e.g., treatment effects within a study) and Pulse methods may be more suitable to quantify absolute flows. Nevertheless, all sap flow methods showed high precision, allowing potential correction of the measurements when a study-specific calibration is performed. Our understanding of how sap flow methods perform across species would be greatly improved if experimental conditions and wood properties, including changes in wood moisture, were better reported.