Plant Physiology Methods: Whole Plants

| HCS Home | Index | Calendar | Resources | Assignments | Group rotation

Psychrometer

Decagon thermocouple psychrometer

The psychrometer can be used to measure total plant water potential (MPa) on fresh leaf tissue, or plant osmotic potential (MPa) using frozen/thawed tissue.

Solutes lower the water potential which also results in a decrease in the equilibrium vapor pressure above the solution. This effect can be measured with the thermocouple psychrometer.

The plant shoot is harvested and put in a plastic bag or wrapped on saranwrap to prevent desiccation.

Samples for the psychrometer are put in steel cups that are lined with strips of filter paper to promote equilibration between liquid and vapor phases.

For total leaf water potential, fresh leaf tissue is used

For osmotic potential, a fully-expanded leaf is taken from each plant, folded and put in a garlic press. In the press cells are crushed and broken; bean tends to be extruded as a puree, but corn will produce a clean sap sample.

It is important to wipe away debris and sap from the rim and outside of the sample cup before it is put in the sample changer.

It is also important to put samples into the apparatus as soon as possible so that they do not dry out on the bench. A push rod under the changer allows you to lower the sample cups gently so that the contents do not splash out.

A sample cup containing a solution of known water potential is included with every batch of 8 leaf samples. (the changer takes 9 samples)

A special plastic cup containing a drop of water is also included.

The water blank is put in the 0 position of the changer.

The access hole is plugged and the water blank (0) is brought to the read position.

The changer is covered is covered with an insulated container.

The apparatus is left for at least 30 minutes for temperatures to stabilize.

To begin reading the lever is used to raise the blank cup so that the thermocouple sensor is moistened. The lever is lowered and the samples are rotated so that 1 is in the read position. The lever is raised so that sample 1 is locked in position under the thermocouple.

Replace the cooler

The meter is turned on with the switch in the temperature position. When the temperature reading stabilizes the central switch is changed to read microvolts.

Readings typically rise for a few seconds, reach a maximum value and then start to decline. You should aim to record the maximum value, which is proportional to the water potential of the sample in the cup.

| HCS Home | Index | Calendar | Resources | Assignments | Group rotation

Copyright © The Ohio State University
All rights reserved.

\| HCS Home \| Index \| Calendar \| Resources \| Assignments \| Group rotation Psychrometer
Decagon thermocouple psychrometer The psychrometer can be used to measure total plant water potential (MPa) on fresh leaf tissue, or plant osmotic potential (MPa) using frozen/thawed tissue. Solutes lower the water potential which also results in a decrease in the equilibrium vapor pressure above the solution. This effect can be measured with the thermocouple psychrometer.
	The plant shoot is harvested and put in a plastic bag or wrapped on saranwrap to prevent desiccation.
Samples for the psychrometer are put in steel cups that are lined with strips of filter paper to promote equilibration between liquid and vapor phases.
	For total leaf water potential, fresh leaf tissue is used For osmotic potential, a fully-expanded leaf is taken from each plant, folded and put in a garlic press. In the press cells are crushed and broken; bean tends to be extruded as a puree, but corn will produce a clean sap sample. It is important to wipe away debris and sap from the rim and outside of the sample cup before it is put in the sample changer.
		It is also important to put samples into the apparatus as soon as possible so that they do not dry out on the bench. A push rod under the changer allows you to lower the sample cups gently so that the contents do not splash out.
A sample cup containing a solution of known water potential is included with every batch of 8 leaf samples. (the changer takes 9 samples)
	A special plastic cup containing a drop of water is also included. The water blank is put in the 0 position of the changer.
The access hole is plugged and the water blank (0) is brought to the read position.
		The changer is covered is covered with an insulated container. The apparatus is left for at least 30 minutes for temperatures to stabilize.
To begin reading the lever is used to raise the blank cup so that the thermocouple sensor is moistened. The lever is lowered and the samples are rotated so that 1 is in the read position. The lever is raised so that sample 1 is locked in position under the thermocouple. Replace the cooler
	The meter is turned on with the switch in the temperature position. When the temperature reading stabilizes the central switch is changed to read microvolts. Readings typically rise for a few seconds, reach a maximum value and then start to decline. You should aim to record the maximum value, which is proportional to the water potential of the sample in the cup.