|  |

| |

Enabling better global research outcomes in soil, plant & environmental monitoring.

PSY1 Leaf Psychrometer

Water Movement in Plants

Natural systems move matter across gradients:

  • Solutes (Concentration)
  • Height
  • Pressure

Plants move water across a water potential gradient (Ψ)

Water Movement

What is Water Potential (Ψ)?

Water potential is an integrated measurement of plant response to the environment.
Consider it to be equivalent to the blood pressure of a plant.

water potential

Total plant water potential is defined as:

Ψ = Ψp+ Ψs+ Ψm+ Ψg

Ψp=Turgor Pressure
Ψs= Osmotic Potential
Ψm= Matric Potential
Ψg= Gravity Potential

To Measure Plant Water Potential…

Pressure Chamber (Bomb)


In situ Psychrometers


In Situ Psychrometer vs. Pressure Chamber?

PSY vs PressureBomb

Strong relationship between the two instruments:


Leaf Psychrometer Applications

Leaf Psychrometers have been tested on:

Capsicum Poplar Wheat Corn
Capsicum Poplar Wheat Corn

Leaf Psychrometer Installation

Install Step 1

1. Select flat leaf surface for leaf psychrometer

Install Step 2

2. Position leaf into the slot of the clamp

Install Step 3

3. Select sandpaper grit based on thickness of leaf cuticle

Install Step 4

4. Apply water on cuticle remover for lubrication

Install Step 5

5. Abrade surface of leaf in a circular motion

Install Step 6

6. Apply silicon grease around psychrometer surface

Install Step 7

7. Spread silicon evenly on psychrometer surface perimeter (Approx. 0.5mm deep)

Install Step 8

8. Insert psychrometer chamber into clamp, secure by twisting the chamber on the leaf

Why do you need to abrade leaf surface?

  • Water vapour on the leaf diffuses through the substomatal cavity
  • The cuticle layer varies across different plant species:
    • Cuticle resistance effects the water potential measurement
  • Leaf abrasion reduces cuticle resistance and improves water vapour diffusion in leaf
  • Leaf abrasion reduces equilibration time of leaf and psychrometer chamber

Abrade Leaf

Grit Selection:
Grit Selection

Level of Abrasion:


Wheat Application

  • Wheat plants (4-weeks old) were grown in soil media
  • Leaf psychrometers were installed on five leaves:
    • Wheat leaf 1/leaf 2 were adjacent leaves
    • Wheat leaf 3/leaf 4 were adjacent leaves
    • Control leaf had no abrasion treatment
  • All wheat plants were irrigated together
Wheat Application

Wheat Data

Wheat Data

Uninstallation of Leaf Psychrometer

Leaf Psy Uninstall

  • Leaf 1 – Installation showed signs of failure after 4.5 days
  • Leaf 2 – Measurements continued to show reliable leaf water status after a week
  • Leaf 3 – Installation showed signs of failure after 4.5 days
  • Leaf 4 – Measurements continued to show reliable leaf water status after a week

Wheat Data

Wheat Data 2

Wheat Data 3

Corn Application

  • Three potted corn plants grown in a growth chamber for 4-weeks
  • Each leaf used 600-grit sandpaper to abrade the cuticle layer
  • Two leaf psychrometers were installed per plant at different leaf heights (Top and Bottom)

Corn Side

Corn Data

Corn data 1

corn before corn after
Before Irrigation After Irrigation

Corn data 2

  • Reliable Measurements from leaf psychrometer installations varied between species of plant:
    1. Wheat leaves provided up to a week.
    2. Corn leaves may provide up to two weeks.
  • Abrasion of leaf is required to provide reliable leaf water status measurements
  • Installation duration is dependent on a systematic abrasion technique
  • Reliable measurements are determined based on response to night time recovery and/or irrigation


Rice Genotyping with Leaf Water Potential (LWP)

Study conducted by Sibounheuang et al. (2006) demonstrated variations in LWP in 6 different rice genotypes using pressure chambers.

Objectives of experiment:
A. Determine genotype variations by measuring LWP at different leaf positions and plant sizes.
B. Examine whether genotype variations of different canopy size and water conductance are associated with LWP.


Experiment A

  • Glasshouse experiment with automated temperature control system
  • Six rice lines were tested and have known differences in LWP, osmotic potential, and osmotic adjustment from Jongdee (1998)
  • Midday water potential was measured with pressure chamber at 4 positions: Tip, Sheath, Base and Stem during a 10 day stress period
  • Plant sizes were determined by xylem anatomy (vascular bundles and stem cross section area)

Experiment A Results

  • Genotype differences in midday LWP could be based on hydraulic conductance
  • Leaf water potential was different among the 6 genotypes and demonstrated the same trend
  • Leaf water potential and xylem area relationship showed genotypes with higher LWP showed larger xylem area
rice graph

B. Canopy Size of Genotypes Associated with LWP

  • Field experiment with rainout shelters to induce stress period of four rice lines
  • Midday LWP was measured under 3 irrigation treatments (Irrigated, 14 and 18 days of stress) and 4 canopy sizes (control, 1/3 and 2/3 leaf removal and six tillers remaining)
  • Midday water potential was measured at 4, 10 and 14 days after imposed stress
  • Canopy size was measured by the number of vascular bundles
rice field

Experiment B Results

  • Genotype variations of reduced canopy sizes (removing leaves/tillers) were not significantly reflected in LWP
  • Differences in LWP among genotype variations were were not due to canopy size
  • Leaf water potential expressed in different genotypes maintained the same trends, however differences were not due to canopy size or leaf area
rice graph 2

Sibounheuang et al. (2006) Conclusions

Genotype variation expressed in LWP and change in water stress were largely seen at leaf tip.

Larger xylem size were associated with high LWP demonstrating a higher internal water conductance.

Hydraulic conductance of vascular bundles could have caused the genotype variation seen in rice.


Leaf Psychrometer Conclusions

  • PSY1 data logging systems provide wireless, continuous and automated measurements with a wide range of applications
  • Leaf psychrometers demonstrated reliable plant water status for wheat and corn crops up to a week of continuous measurements
  • Plant water status of rice crops have previously been monitored by the pressure chamber technique for genotyping. Leaf psychrometers provide the opportunity to continuously monitor leaf water status of rice in real time