THE PARTITIONING OF HYDRAULIC CONDUCTANCES WITHIN MATURE ORANGE TREES

Sap flow (F) and leaf water potential (LWP) were followed diurnally in mature Valencia and Shamouti orange trees in an orchard. The hydraulic conductance of these trees was computed from the diurnal relationship between the LWP and F. The driving force for water movement was estimated from a weighted average of sunlit and shaded LWP, assuming that leaves in the shade transpire to some extent. LWP of covered, non-transpiring leaves was also measured hourly. It was assumed to represent the xylem water potential within the axial conduit of the trunk. Relating covered LWP to F on an hourly basis enables the computation of the hydraulic conductance of the root system, including axial conductances. The hydraulic conductance of the transpiring crown was computed. Its magnitude was comparable to the root system hydraulic conductance. © 1990 Oxford University Press.