Leaf Porometer Operator’s Manual
2. About the Leaf Porometer
10
Mode has several advantages over Manual Mode and other
porometers. First, the 30 second Auto Mode measurement
duration ensures that stomatal conductance doesn’t change
due to the presence of the sensor head. Second, Auto Mode
takes only 30 seconds per measurement, ensuring that your
measurements are completed in a timely manner. Finally,
Auto Mode sets a definite endpoint for the measurement,
meaning that the user doesn’t have to pick an arbitrary end-
point, as is common with other diffusion porometers and
with Manual Mode measurements.
For the porometer to “detect” the presence of a transpiring
leaf and begin the Auto Mode measurement, the measured
stomatal conductance must reach 5 mmol m
-2
s
-1
.
So, if you
are making measurements on leaves with extremely low
conductances, it may be necessary to make the measure-
ments in Manual Mode.
Precautions
Before using or calibrating the porometer, remember:
• Avoid leaves that are wet or heavy with dew; never
take readings in the rain.
• Do not touch the Teflon disk, or get your fingers near
it, during a reading. This will cause inaccurate readings.
• If you blow into the sensor, it will take a few minutes
for the stomatal conductance reading to return to nor-
mal.
• Clean the sensor periodically to keep it free of dirt and
pollen that can build up during use and affect readings.
(See “Cleaning the Sensor Block,” in Chapter 7.)
• Avoid chemical fumes. Fumes can be extremely harm-
ful to the sensor (i.e. alcohol, gasoline, foam).
