Leaf pressure chamber

Scholandermanual pumping

The Pump-Up Pressure Chamber is different from the conventional gas chamber in that it does not require a source of compressed gas. The instrument produces pressure in the chamber required to take water potential readings by pumping it as shown below. The relatively small chamber allows the user to achieve about one half Bar (7.25 psi) pressure per stroke. The instrument is limited to 20 Bar and is designed primarily for irrigation scheduling/monitoring, particularly for managing deficit irrigation. How it works Simply put, the pressure chamber is just a device for applying air pressure to a leaf (or small shoot), where most of the leaf is inside the chamber but a small part of the leaf stem (the petiole) is exposed to the outside of the chamber through a seal. The amount of pressure that it takes to cause water to appear at the cut surface of the petiole tells you how much hard the plant is working to pull water up through the roots. A high value of pressure means a high value of tension and a high degree of water stress. The unit of pressure most commonly used is Bar. (1 Bar = 14.5 PSI)