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INTRODUCTING A THERMAL DISSIPATION PROBE SYSTEM FOR MEASURING BI-DIRECTIONAL ROOT WATER FLUX
Citation:
Coulombe, R. A. AND J R. Brooks. INTRODUCTING A THERMAL DISSIPATION PROBE SYSTEM FOR MEASURING BI-DIRECTIONAL ROOT WATER FLUX. Presented at Linking the Complexity of Forest Canopies to Ecosystem and Landscape Function, IUFRO Canopy Processes, Corvallis, OR, July 16-17, 2001.
Description:
The interest in measuring the direction and magnitude of root sapflow has accelerated in the past few years because of interest in the redistribution of water in the soil by roots. Plant roots have been shown to redistribute water between areas of soil with differing water content. ?Hydraulic lift' and ?downward siphoning' are processes which move water up or down in the soil column depending on water potential gradients within the soil and roots. Horizontal water redistribution is also possible given a sufficient water potential gradient and a pathway of roots.
To measure sapflow in roots, researchers have employed methods based on stem sap flow systems that need only measure one direction of flow. However, root sap flow methods must be able to identify flow in two directions to be useful for measuring water redistribution. Burgess, et al., (2000) recently reviewed various sapflow systems for their useful in root sapflow measurements, and noted that the thermal dissipation probe was inadequate for measuring bi-directional flow. In this study we designed and tested a modified ?Thermal Dissipation Probe' (TDP) system which we feel addresses the shortcomings noted by Burgess. The TDP stem sap flow measurement system (Granier, 1987) is based on comparisons between the temperature of a constantly heated probe and that of an unheated probe inserted radially into the stem xylem and is incapable of indicating direction of flow. By adding an additional reference probe and two direction indicator probes we created a symmetrical TDP probe system which can indicate the direction of root sap flow and measure the relative magnitude of the bi-directional flow. The system was tested in the laboratory using an apparatus to create, and volumetrically measure, bi-directional flow through a root section. The root flow TDP system provided a very robust and sensitive measure of flow direction and relative magnitude. The root sap flow TDP system should provide a relatively user friendly and accurate measure of bi-directional root sap flow in the field.