PSY1 Psychrometer (Stem & Leaf) for plant water potential
Continuous plant water potential measurement in megapascals (MPa)
Measuring plant water potential (or plant water stress), the ICT International Psychrometer is a unique, non-destructive, standalone, and in-situ logging device. Applying the research of Dixon and Tyree (1984), the PSY1 Psychrometer is a scientifically validated and widely accepted method for the continuous measurement of plant water potential.
The measurement of water potential in the Soil-Plant-Atmosphere Continuum requires accurate measurements of plant water potential. Traditionally, this has been undertaken using pressure chambers, such as the Scholander Pressure Chamber; however, these require manual measurements to be made at discrete times of the day in a destructive manner. In contrast, the PSY1 Psychrometer continuous (every 10 minutes) measurements of plant water potential in megapascals (MPa). The PSY1 Psychrometer time series data can be combined with other data collected to measure the Soil-Plant-Atmosphere Continuum, such as the SFM1x and SFM1 Sap Flow Meter, or to better understand the water potential gradients that drive ecosystem water flows and govern many plant functions.
The continuous measurement of plant water potential is frequently used to select drought tolerant species in plant breeding.
Using the Psychrometer
A comprehensive series of videos detailing the use, installation, calibration, and thermocouple adjustment of the Psychrometer is available here on YouTube.
The Psychrometer logger is available with either a:
- Stem chamber (PSY1-Stem)
- Leaf Chamber (PSY1-Leaf)
Accessories are available to provide consistent installations:
- The PSY-IK Psychrometer Installation Kit ensures a correct and successful installation of ICT International Psychrometers.
- Different stem clamps sizes are available for the PSY1-Stem, to accommodate smaller to larger plant stems or branches
- A dedicated leaf clamp is available for the PSY1-Leaf.
- To measure osmotic potential of plant material there is a dedicated Osmotic Potential Insulator (PSY-OPI).
Chamber Design
The Psychrometer head consists of two welded chromel-constantan thermocouples connected in series within a chromium plated brass chamber that forms a large insulating thermal mass.
Inside the chamber, one thermocouple is in contact with the stem sample and the other simultaneously measures the chamber air temperature. A third soldered copper-constantan thermocouple is located within the sample chamber body to measure the instrument temperature for the purpose of temperature compensation.
Comparison between Leaf Chamber (left) and Stem chamber (right)
Within the chamber, the thermocouples are set so one is slightly above the surface of the sample chamber such that upon installation it is placed in contact with an exposed section of sapwood, while a second thermocouple remains within the sample chamber measuring the chamber air temperature. A Peltier cooling current is then applied to the junction, the differential output of the two junctions is a measure of the temperature gradient between the sample and the dew point measuring junction. By measuring the psychrometric (wet bulb) depression and applying automatic temperature correction of the error induced by temperature gradients within the chamber, precise and repeatable measurements of plant water potential are accurately obtained.
1. PSY1-STEM Psychrometer
The PSY1 Stem Psychrometer is attached to the stem using a clamp to hold it in position using moderate pressure, and it is then protected against external temperature influences with additional dedicated insulation.
The minimum stem dimensions required is of at least 10mm.
2. PSY1-LEAF Psychrometer
The leaf psychrometer follows the same principle of measurement as the stem psychrometer, however, the body of the chamber is reduced to accommodate smaller and thinner leaf areas in several plant species. The technique used to prepare and install this instrument has also changed as it requires additional care to prepare the installation site. The leaf psychrometer measures the water potential (water status) on a leaf of a plant. The leaf water potential is a quantified indicator of how water stressed a particular plant is based on the measurement taken from the leaf.
Poplar tree instrumented with psychrometers (stem and leaf) and a sap flow meter on the main stem.
In terms of data logging capabilities of the PSY1, they all remain the same regardless of the application (Leaf or Stem psychrometer chambers). The difference between a leaf and stem psychrometer chamber is the size and plant preparation.
Psychrometer Technical Details
Measurement Details
| Units | MPa |
| Range | -0.1 MPa To -10 MPa (1 To 100 Bars) |
| Resolution | 0.01 MPa (0.1 Bar) |
| Accuracy | ±0.1 MPa (1 Bar) |
| Response Time | Measurement Mode: 51 Seconds |
| Live Mode: | 1 Second |
| Sampling Rate | 10 Hz |
Data Access and Storage
| Computer Interface | USB |
| Data Storage | MicroSD Card |
| Memory Capacity | Up To 16GB |
Operating Conditions
| Temperature Range | -10 To 50°C |
| R/H Range | 0-99% |
Dimensions:
| Logger | |
| Width: | 80 mm |
| Depth: | 35 mm |
| Psychrometer Chamber for Stem applications | |
| Diameter: | 25.5 mm |
| Depth: | 20 mm |
| Depth With Calibration Chamber: | 30 mm |
| Psychrometer Chamber for Leaf applications | |
| Diameter: | 19mm |
| Depth: | 19mm |
| Depth With Calibration Chamber: | 27mm |
Logging Specifications
| Analogue Channels |
|
| Minimum Logging Interval | 1 Second |
| Delayed Start | Suspend Logging, Customised Intervals |
| Sampling Frequency | 10hz |
| Upgradable | User upgradeable firmware using USB boot strap loader function |
Power
| Internal Power | |
| Internal Battery Specifications | 950mah Lithium Polymer, 4.20 Volts Fully Charged |
| Fully Charged Battery | 4.20 Volts |
| Low Power Mode | 3.60 Volts – instrument ceases to take measurements |
| Discharged Battery | 2.90 Volts – instrument automatically switches off at and below this voltage when no external power connected. |
| External Power Requirements | |
| Bus Power | 8-30 volts DC, non-polarised, current draw is 200Ma active when the external voltage rises above 16 volts DC |
| USB Power | 5 Volts DC, 100ma Fixed Charge Rate |
| Internal Charge Rate: Bus Power | 60ma – 200Ma variable internal charge rate |
Clamps available:
- PSYS-C37: Small Clamp, 0 – 37mm stem diameter
- PSYS-C77: Medium Clamp, 30 – 77mm stem diameter
- PSYS-C125: Large Clamp, 79-125mm stem diameter
- PSYS-LC: Leaf Clamp for Stem Psychrometer
- PSYL-LLC: Leaf Clamp for Leaf Psychrometer
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