Dynamic measurements of roots hydraulic conductance using a high-pressure flowmeter in the laboratory and field

A new high-pressure flowmeter(HPFM)is described which is capableof rapid water-flow measurements. The HPFM permits dynamic determinationof hydraulic conductance of roots, K_r, and can be used in tehlaboratory or field. The base of a root is connected to theHPFM and water is perfused into the root system opposite tothe normal direction of flow during trnaspiration. The perfusionpressure is changed at a constant rate of 3–7 kPa s^–1while measuring the flow into the root every 2–4 s. Theslope of the plot of flow versus applied pressure is K_r. This paper describes the HPFM, presnents the theory of dynamicflow measurements, discusses sources of error, presnets evidencethat dynamic measurements of K_r in Ficus maclellandi (and sixother tropical species from Panama) yield the correct result,and demonstrates the use of the method under field conditionsin Panama on Cecropia obtusifolia and Palicourea guianensis. Key words: High-pressure flowmeter, root and shoot hydraulic conductance, Ficus maclellandi, Cecropia obtusifolia, Palicourea guianensis