Transpiration and root pressure cause water to rise in plants by
Transpiration and root pressure cause water to rise in plants by pulling and pushing it, respectively.
The transpiration driven ascent of xylem sap depends mainly on the Cohesion, Adhesion and Surface Tension of water. These properties give water high tensile strength, i.e., an ability to resist a pulling force, and high capillarity, i.e., the ability to rise in thin tubes. This generates a negative hydrostatic pressure like suction through a straw that pulls the xylem sap and helps in bulk transport.
As various ions from the soil are actively transported into the vascular tissues of the roots, water follows (its potential gradient) and increases the pressure inside the xylem. This positive pressure is called root pressure and can be responsible for pushing up water to small heights in the stem.
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