Chin J Plant Ecol ›› 2023, Vol. 47 ›› Issue (3): 404-417.DOI: 10.17521/cjpe.2022.0321

• Research Articles • Previous Articles     Next Articles

Analysis of applicability of Granier’s original equation for calculating the stem sap flux density—Take Populus tomentosa as an example

ZHAO Xiao-Ning1, TIAN Xiao-Nan1, LI Xin2, LI Guang-De3, GUO You-Zheng1, JIA Li-Ming1, DUAN Jie1, XI Ben-Ye1,**()   

  1. 1Ministry of Education Key Laboratory of Silviculture and Conservation, Beijing Forestry University, Laboratory for Silviculture and Forest Ecosystem in Arid- and Semi-Arid Region of State Forestry and Grassland Administration, Beijing 100083, China
    2Beijing Sinton Technology Company, Beijing 100193, China
    3Faculty of Agriculture, Forestry and Medicine, the Open University of China, Beijing 100039, China
  • Received:2022-07-29 Accepted:2022-09-12 Online:2023-03-20 Published:2023-02-28
  • Contact: XI Ben-Ye
  • About author:First author contact:

    *Contributed equally to this work

  • Supported by:
    Key R&D Plan of Ningxia Huizu Autonomous Region(2019BFG02024);National Key R&D Program of China(2021YFD2201203);National Natural Science Foundation of China(32171763)


Aims Thermal dissipation probes (TDP) have been extensively applied in studying forest transpiration. The calculation accuracy of TDP data directly affects the precise quantification of water consumption of trees and stands. Granier’s original equation (Fd = 0.0119K1.231, Fd is the sap flux density (cm·s-1), K is the temperature difference coefficient) is a standard method for calculating the data measured by TDP, but its accuracy is questioned. The objective of this study is to systematically understand the applicability of Granier’s original equation to Populus tomentosa and clarify the need for calibration.

Methods With P. tomentosa as the experimental material, this study used the stem-weighing and the whole-tree potometer methods to evaluate the accuracy of Granier’s original equation for different types of TDP probes, and compared the applicability of equations calibrated by various methods.

Important findings Compared with the values measured by the stem-weighing method, the sap flux density calculated by Granier’s original equation was underestimated by 52.3%-61.4% on average. The calibrated equations by the stem-weighing method and the whole-tree potometer method were Fd= 0.0362K1.870 and Fd = 0.0105K0.976, respectively. The calibrated equation by one method produced a large deviation when applied to calculate the sap flux density measured by other methods. Relative to the values estimated by Granier’s original equation, the average sap flux density of seven field-grown trees calculated using the whole-tree potometer calibrated equation did not change significantly, but that calculated using the equations calibrated by the stem-weighing method or in other studies became significantly larger. Compared with the sap flux density measured by the whole-tree potometer method, the calculation precision of Granier’s original equation is considerably higher than that of other calibrated equations, and its relative average absolute error and root mean square error were 10% and 0.000 5 cm·s-1, respectively. In addition, the coefficients of the calibrated equation differed greatly across different trees, but their values were negatively correlated with the length ratio of the probe inserted into the water conducting sapwood. To sum up, it may be necessary to calibrate original Granier’s equation when applying TDP to measure sap flux density. However, the application effects of calibrated equations by different methods varied considerably, indicating that the calibrated equations derived in previous studies have great limitations. Meanwhile, this study did not find sufficient evidence to support the viewpoint that it is necessary to use a calibrated equation for accurately estimate the sap flux density of P. tomentosa, especially considering that no significant difference was observed when using the calibrated equation by the whole-tree potometer method and Granier’s original equation to estimate the sap flux density of field-grown P. tomentosa. Therefore, continued application of Granier’s original equation is recommended for this tree species.

Key words: transpiration, water use, water relation, heat dissipation, poplar