Do short term sap flow measurements scale with leaf transpiration? A case study on cucumis sativus plants

  • G. Egea /
  • A. Baille /
  • B. Martín /
  • P. A. Nortes /
  • M. M. González-Real
Book Series ar
Acta Horticulturae
  • Volumen: 846
  • Fecha: 01 December 2009
  • Páginas: 127-134
  • ISSN: 05677572
  • ISBN: 9789066056824
  • Source Type: Book Series
  • Document Type: Article
The application of the stem heat balance (HB) method is particularly suited for horticultural species with small stems. However, it is not clear to what extent sap flow dynamics really follow and mimic rapid changes in the actual transpiration rate due to changes in environmental factors such as solar radiation (Rs) and vapour pressure deficit (VPD). In this study, we compared short-term measurements (10 min average) of cucumber leaf transpiration, obtained by means of a non-invasive technique (leaf energy balance, LEB), and whole plant transpiration measured by the stem heat balance method (sap flow gauge Dynamax/USA-SHB). The dynamics of transpiration response to environmental factors (Rs and VPD) obtained with the two methods were compared and analyzed under spring greenhouse conditions. It was shown that both methods had similar time response to sudden changes in atmospheric demand, but sap flow was less sensitive than transpiration to those changes. This was because plant internal water storage contributed up to 7-12% of daily plant water use in this species. We concluded therefore that caution should be taken when using sap flow measurements to estimate transpiration rate at shorttime scale (hourly or even shorter), especially in highly fluctuating environmental conditions and when precise estimates of transpiration are required (e.g., soilless culture irrigation management, calibration of transpiration models, etc.).

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