Abstract
A new high-pressure flowmeter (HPFM) is described which is capable of rapid water-flow measurements. The HPFM permits dynamic determination of hydraulic conductance of roots, K r , and can be used in the laboratory 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 flow versus applied pressure is K r . This paper describes the HPFM, presents the theory of dynamic flow measurements, discusses sources of error, presents evidence that dynamic measurements of K r in Ficus maclellandi (and six other tropical species from Panama) yield the correct result, and demonstrates the use of the method under field conditions in Panama on Cecropia obtusifolia and Palicourea guianensis
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