Microtensiometers Accurately Measure Stem Water Potential in Woody Perennials.

Stem water potential (Ψ stem ) is considered to be the standard measure of plant water status. However, it is measured with the pressure chamber (PC), an equipment that can neither provide continuous information nor be automated, limiting its use. Recent developments of microtensiometers (MT; FloraPulse sensors), which can continuously measure water tension in woody tissue of the trunk of the tree, can potentially highlight the dynamic nature of plant water relations. Thus, this study aimed to validate and assess the usefulness of the MT by comparing the Ψ stem provided by MT with those same measurements from the PC. Here, two irrigation treatments (a control and a deficit treatment) were applied in a pear ( Pyrus communis L.) orchard in Washington State (USA) to capture the full range of water potentials in this environment. Discrete measurements of leaf gas exchange, canopy temperature and Ψ stem measured with PC and MT were made every two hours for four days from dawn to sunset. There were strong linear relationships between the Ψ stem -MT and Ψ stem -PC (R 2 > 0.8) and with vapor pressure deficit (R 2 > 0.7). However, Ψ stem -MT was more variable and lower than Ψ stem -PC when Ψ stem -MT was below -1.5 MPa, especially during the evening. Minimum Ψ stem -MT occurred later in the afternoon compared to Ψ stem -PC. Ψ stem showed similar sensitivity and coefficients of variation for both PC and MT acquired data. Overall, the promising results achieved indicated the potential for MT to be used to continuously assess tree water status.