what is the pressure developed in root xylem vessels due to accumulation of water
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Root Pressure
Root pressure is not common among trees of the Temperate Zone and occurs chiefly in the spring before leaves develop and transpiration is rapid. However, Parker (1964) reported copious exudation from black birch in New England in October and November, after leaf fall. There was no exudation following a dry summer. Hales (1727) made the first published measurements of root pressure and reported a pressure of 0.1 MPa in grape. Clark (1874) tested over 60 species of woody plants in Massachusetts and found exudation from only a few species, including maple, birch, walnut, hop hornbeam, and grape. Sap flow ceases as leaves develop and increasing transpiration produces negative pressure or tension in the xylem sap. The sugar content of birch sap often is about 1.5%, lower than that of maple sap (Chapter 7), and consists chiefly of reducing sugars. Detopped conifer seedlings can be induced to exude sap if intact seedlings are kept well moistened while being subjected to a preconditioning period of cold storage (Lopushinsky, 1980). However, reports of sap exudation in conifers under natural conditions are rare (Milburn and Kallackaral, 1991). Oleoresin flow is discussed in Chapter 8.
Root pressure is not common among trees of the Temperate Zone and occurs chiefly in the spring before leaves develop and transpiration is rapid. However, Parker (1964) reported copious exudation from black birch in New England in October and November, after leaf fall. There was no exudation following a dry summer. Hales (1727) made the first published measurements of root pressure and reported a pressure of 0.1 MPa in grape. Clark (1874) tested over 60 species of woody plants in Massachusetts and found exudation from only a few species, including maple, birch, walnut, hop hornbeam, and grape. Sap flow ceases as leaves develop and increasing transpiration produces negative pressure or tension in the xylem sap. The sugar content of birch sap often is about 1.5%, lower than that of maple sap (Chapter 7), and consists chiefly of reducing sugars. Detopped conifer seedlings can be induced to exude sap if intact seedlings are kept well moistened while being subjected to a preconditioning period of cold storage (Lopushinsky, 1980). However, reports of sap exudation in conifers under natural conditions are rare (Milburn and Kallackaral, 1991). Oleoresin flow is discussed in Chapter 8.
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