Journal Article

Novel, cyclic heat dissipation method for the correction of natural temperature gradients in sap flow measurements. Part 2. Laboratory validation

J. Leonardo Reyes-Acosta, Maurits W. Vandegehuchte, Kathy Steppe and Maciek W. Lubczynski

Edited by Nathan Phillips

in Tree Physiology

Volume 32, issue 7, pages 913-929
Published in print July 2012 | ISSN: 0829-318X
Published online June 2012 | e-ISSN: 1758-4469 | DOI: http://dx.doi.org/10.1093/treephys/tps042
Novel, cyclic heat dissipation method for the correction of natural temperature gradients in sap flow measurements. Part 2. Laboratory validation

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Sap flow measurements conducted with thermal dissipation probes (TDPs) are vulnerable to natural temperature gradient (NTG) bias. Few studies, however, attempted to explain the dynamics underlying the NTG formation and its influence on the sensors' signal. This study focused on understanding how the TDP signals are affected by negative and positive temperature influences from NTG and tested the novel cyclic heat dissipation (CHD) method to filter out the NTG bias. A series of three experiments were performed in which gravity-driven water flow was enforced on freshly cut stem segments of Fagus sylvatica L., while an artificial temperature gradient (ATG) was induced. The first experiment sought to confirm the incidence of the ATG on sensors. The second experiment established the mis-estimations caused by the biasing effect of the ATG on standard TDP measurements. The third experiment tested the accuracy of the CHD method to account for the ATG biasing effect, as compared with other cyclic correction methods. During experiments, sap flow measured by TDP was assessed against gravimetric measurements. The results show that negative and positive ATGs were comparable in pattern but substantially larger than field NTGs. Second, the ATG bias caused an overestimation of the standard TDP sap flux density of ∼17 cm3 cm−2 h−1 by 76%, and the sap flux density of ∼2 cm3 cm−2 h−1 by over 800%. Finally, the proposed CHD method successfully reduced the max. ATG bias to 25% at ∼11 cm3 cm−2 h−1 and to 40% at ∼1 cm3 cm−2 h−1. We concluded that: (i) the TDP method is susceptible to NTG especially at low flows; (ii) the CHD method successfully corrected the TDP signal and resulted in generally more accurate sap flux density estimates (mean absolute percentage error ranging between 11 and 21%) than standard constant power TDP method and other cyclic power methods; and (iii) the ATG enforcing system is a suitable way of re-creating NTG for future tests.

Keywords: cyclic heat dissipation; Mariotte water-flow verification system; sap flow; temperature gradient; thermal dissipation probe

Journal Article.  10564 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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