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Concurrent measurements of change in the bark and xylem diameters of trees reveal a phloem-generated turgor signal

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Original languageEnglish
Pages (from-to)1-12
Number of pages12
JournalNew Phytologist
Issue number4
Publication statusPublished - Jun 2013


Phloem transport in plants under field conditions is currently not well understood. This is largely the result of the lack of techniques suitable for measuring phloem physiological properties.
We present a model that interprets the changes in xylem diameter and live bark thickness and separates the components responsible for such changes. We test the predictions from this model on data from three mature Scots pine trees in Finland. The model separates the live bark thickness variations caused by bark water capacitance from a residual signal interpreted to indicate the turgor changes in the bark.
The predictions from the model are consistent with processes related with phloem transport. At the diurnal scale, this signal related to patterns of photosynthetic activity and phloem loading. At the seasonal scale, bark turgor showed rapid changes during two droughts and after two rainfall events consistent with physiological predictions. Daily cumulative totals of this turgor term were related to daily cumulative totals of canopy photosynthesis. Finally, the model parameter representing radial hydraulic conductance between phloem and xylem showed a temperature dependency consistent with the temperature-driven changes in water viscosity.
We propose that this model has potential for continuous field monitoring of tree phloem function.

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