Purpose

Transpiration dominates hydrologic fluxes from terrestrial ecosystems to the atmosphere. Sap flow is the most widely used method to quantify transpiration, and calibrations can improve the accuracy of these estimates. Despite numerous suggestions to perform and apply sap flow calibrations, seemingly few reports apply these recommendations. Here, we sought to determine the prevalence of calibration across sap flow methodology.

Recent Findings

We reviewed tree sap flow literature over the past 9 years and determined that only 5.3% of these publications documented the performance of calibrations, the application of coefficients from previous calibrations, or the application of correction factors using calibration data to ensure or improve accuracy of transpiration estimates. These data indicate that calibration has not been adopted as a best practice. However, these data may also reflect challenges to the performance and application of calibration indicating fundamental limitations of sap flow methods.

Summary

We highlight the need for testing critical assumptions regarding calibration; specifically, that coefficients derived from calibrations on small stems are suitable for application to large stems and that different calibration approaches yield similar transpiration estimates. We encourage researchers to adopt calibration as a best practice for sap flow data and to explain how calibration was performed, how calibration data were applied, and to acknowledge and justify circumstances that preclude or do not necessitate calibration. Without the adoption of calibration and an improved understanding of its limitations, our understanding of transpiration and ability to quantify it using this technology will remain inadequate.

中文翻译：

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重新校准通过树液流估算树木蒸腾的最佳实践，挑战和局限性

目的

蒸腾作用主导着从陆地生态系统到大气的水文通量。汁液流动是最常用的量化蒸腾作用的方法，而标定可以提高这些估算的准确性。尽管执行和应用液流校准的建议很多，但似乎很少有报告采用这些建议。在这里，我们试图确定整个树液流动方法中校准的普遍性。

最近的发现

我们回顾了过去9年中的树液流动文献，并确定只有5.3％的出版物记录了校准的性能，先前校准的系数的应用或使用校准数据的校正因子的应用，以确保或改善蒸腾的准确性估计。这些数据表明未将校准作为最佳实践。但是，这些数据也可能反映对标定性能和应用的挑战，表明液流法的基本局限性。

概括

我们强调需要测试有关校准的关键假设；具体来说，从小茎上的标定得出的系数适用于大茎，并且不同的标定方法可得出相似的蒸腾估算值。我们鼓励研究人员将校准作为液流数据的最佳实践，并解释如何执行校准，如何应用校准数据，并承认和证明排除或不需要进行校准的情况。如果不采用校准方法，也不能更好地了解其局限性，那么我们对蒸腾作用的理解以及使用该技术对其进行量化的能力将仍然不足。