A continuous flow porometer.
The equipment described makes use of a continuous measured flow (v) of dry N2O into a porometer cup attached to a known leaf area (a). The gas within the cup is well stirred and the humidity of the outgoing gas is measured with an Al2O3 sensor. The relationship between stomatal resistance (rs), aerodynamic resistance (ra), outgoing gas vapour pressure (e2) and saturated vapour pressure at leaf temperature (e3) was ra+rs = a(e3/e2-1)/v. The porometer gave continuous readings, had a short response time and was easy to calibrate.