Evaluation of the pressure chamber technique for measurement of leaf water potential in cassava (<i>Manihot</i> species)

Abstract

The pressure chamber technique was evaluated as a method for estimating leaf water potential in cassava (Manihot esculenta Crantz). Xylem pressure potentials (ψ P ) measured with the pressure chamber were compared with leaf water potential (ψ L ) obtained for the same leaf with the in situ dew-point hygrometer.In both cassava varieties studied, ψ L and ψ P were linearly related (r 2 = 0.87 and 0.98 for CMC9 and CMC40 respectively). The length of petiole exposed outside the chamber affects the relation between ψ L and ψ P and should be kept at between 1 and 3 cm for better agreement. In CMC40, ψ P was consistently lower (drier) than ψ L by about 1.0 bar (1 bar = 100 kPa) in the entire range of water potential studied, but was not the case in CMC9. The reason for this difference is unclear but may be due to a filling of tissues other than xylem tissues (Boyer 1967) during the measurement of ψ P in CMC40. Average xylem osmotic potentials (ψ S ) were low (−1.0 ± 0.2 bars and −1.0 ± 0.4 bars for CMC9 and CMC40 respectively). It is, therefore, unnecessary to correct for ψ S when using the pressure chamber to estimate leaf water potentials in cassava.