Engineering

Biology

Statistics

Repeatability

Materials science

Cabin pressurization

Relative humidity

Agricultural engineering

Range (aeronautics)

Biochemistry

Computer science

Botany

Humidity

Thermodynamics

Physics

Mathematics

Accuracy and precision

Environmental science

Operations management

Horticulture

Composite material

Photosynthesis

Specific leaf area

Metric (unit)

Meteorology

Biological system

Dehydration

Volume (thermodynamics)

Plant Cell & Environment

Leaf water potential (ψleaf ), typically measured using the pressure chamber, is the most important metric of plant water status, providing high theoretical value and information content for multiple applications in quantifying critical physiological processes including drought responses. Pressure chamber measurements of ψleaf (ψleafPC ) are most typical, yet, the practical complexity of the technique and of the underlying theory has led to ambiguous understanding of the conditions to optimize measurements. Consequently, specific techniques and precautions diversified across the global research community, raising questions of reliability and repeatability. Here, we surveyed specific methods of ψleafPC from multiple laboratories, and synthesized experiments testing common assumptions and practices in ψleafPC for diverse species: (i) the need for equilibration of previously transpiring leaves; (ii) leaf storage before measurement; (iii) the equilibration of ψleaf for leaves on bagged branches of a range of dehydration; (iv) the equilibration of ψleaf across the lamina for bagged leaves, and the accuracy of measuring leaves with artificially 'elongated petioles'; (v) the need in ψleaf measurements for bagging leaves and high humidity within the chamber; (vi) the need to avoid liquid water on leaf surfaces; (vii) the use of 'pulse' pressurization versus gradual pressurization; and (viii) variation among experimenters in ψleafPC determination. Based on our findings we provide a best practice protocol to maximise accuracy, and provide recommendations for ongoing species-specific tests of important assumptions in future studies.

Leaf water potential measurements using the pressure chamber: Synthetic testing of assumptions towards best practices for precision and accuracy