DYNAMIC MEASUREMENTS OF ROOT HYDRAULIC CONDUCTANCE USING A HIGH-PRESSURE FLOWMETER IN THE LABORATORY AND FIELD

A new high-pressure flowmeter (HPFM) is described which is capable of rapid water-Row measurements. The HPFM permits dynamic determination o f hydraulic conductance of roots, K-r, and can be used in the laborato ry or field. The base of a root is connected to the HPFM and water is perfused into the root system opposite to the normal direction of flow during transpiration. The perfusion pressure is changed at a constant rate of 3-7 kPa s-(1) while measuring the flow into the root every 2- 4 s. The slope of the plot of Row versus applied pressure is K-r. This paper describes the HPFM, presents the theory of dynamic flow measure ments, discusses sources of error, presents evidence that dynamic meas urements of K-r in Ficus maclellandi (and six other tropical species f rom Panama) yield the correct result, and demonstrates the use of the method under field conditions in Panama on Cecropia obtusifolia and Pa licourea guianensis.