Physical mechanism of sap circulation in trees

Determine the physical mechanisms governing sap circulation within the xylem and phloem channels of trees, specifying the driving forces and flow dynamics responsible for transporting sap from roots to leaves along the full height of the tree.

Background

The paper revisits continuous electrical measurements on a poplar tree and, using Singular Spectrum Analysis, identifies that over 70–80% of signal variance corresponds to major luni-solar tides, suggesting an electrokinetic link between sap flow and gravitational forcing.

Classical hypotheses for sap movement include capillarity, osmotic pressure, and evapotranspiration. Despite extensive paper, the authors note that the detailed mechanics of sap circulation within the plant’s vascular channels remain insufficiently understood.