Pressure chambers

The pressure chamber (or Scholander bomb) is a piece of equipment that allows the precise measurement of the water potential of a plant, by extracting the sap. It is used, for example, in viticulture to assess the water status of the vine. At LEPSE, it is mainly used to assess the water status of grapevine, wheat and sometimes Arabidopsis thaliana.

Principle

A pressure chamber consists of a cylinder that encloses a member (leaf, rod, etc.) whose end protrudes from the cover. The cover of the chamber includes a seal (a plug between two brass washers). This seal, tightened around the end, allows the member to be sealed in the cylinder. The pressure chamber is connected to a source of compressed nitrogen. Two valves control the flow of gas into the closed chamber. The pressure gauge indicates the evolution of the pressure in the chamber. When the gas pressure in the chamber balances the sap pressure in the organ, a meniscus appears on the end of the organ protruding from the sap cover: equilibrium is said to have been reached. The pressure corresponds to the water potential.

Objective

Measuring the basic or minimum water potential. The leaf water potential (Y) reflects the state of water binding within the plant tissue.

Application

• Measurement of the basic leaf potential (late night)
• Measurement of minimum leaf potential (during the day, solar noon in the field)
• Measurement of stem potential (leaf wrapped in plastic and aluminium foil)
• Sap sampling (ABA determination)

The method is destructive and not automated.

Pressure chambers at LEPSE

Our fleet consists of pressure chambers and compressed nitrogen cylinders. The chambers are calibrated every year, and since March 2021, with a calibration bench designed by Stéphane Berthézène and installed in our unit by Stéphane Berthézène and Anthony Rosello (photos 1 and 2).

Equipment manager : Aurélien Ausset
Calibration bench metrology manager : Stéphane Berthézène