Evaluation of granier's sap flux sensor in young mango trees

Abstract

Granier's technique of measuring sap flux density using a continuous heating system was tested on young mango trees. On containerized trees, sap flow underestimated transpiration measured gravimetrically by less than 10 %. In a 4-year-old field-grown tree, there was only a 5 % difference between cumulative summed sap flow in the branches and sap flow in the trunk over a 24-h period. Positioning of the sap flux sensor on the trunk was found to be non-critical for sap flow measurement in trees of diameter of less than 10 cm. Granier's sap flux sensor was sensitive to both slow and abrupt changes in canopy transpiration induced by successive branch girdling, defoliation and excision. A comparison of sap flow in the branches and water uptake by the tree measured using the 'cut-tree method' showed that sap flow method underestimated the actual water uptake by less than 6 %. The results of this study indicate that Granier's sap flux sensor is suitable for measuring whole-tree transpiration in young mango trees.