Leaf Porometer Operator’s Manual
2. About the Leaf Porometer
9
Manual Mode vs. Auto Mode
When the porometer is in Manual Mode (see pg 15 for
instructions on how to configure the porometer to Manual
Mode), the stomatal conductance is measured directly from
the theory presented in Chapter 6 and displayed continu-
ously. The real time conductance measurement can be saved
at any time during a Manual Mode measurement. Manual
mode should only be used at low conductances (i.e. < 20
mmol m
-2
s
-1
). At higher conductances, the readings
become inaccurate and can take an exceptionally long time
to complete. For the theory in Chapter 6 to accurately pre-
dict the stomatal conductance using the steady state diffu-
sion technique, true steady state conditions must exist in the
diffusion path. The amount of time necessary to reach
steady state conditions is proportional to the conductance.
At conductances less than 20 mmol m
-2
s
-1
, steady state con-
ditions are generally reached in less than 5 minutes. At
higher conductances, steady state conditions can take up to
30 minutes. Please note that leaving the sensor head on the
leaf surface for more than a few minutes can cause the sto-
matal conductance to change in response to the presence of
the sensor head clip. Some common uses for manual mode
are measuring dark conductance in plants and measuring
conductance of static conductance materials (e.g. fruit peels,
waterproof fabric).
Auto Mode makes an accurate stomatal conductance mea-
surement in 30 seconds. To do this, the porometer takes the
first 30 seconds of stomatal conductance data and applies a
“look ahead” algorithm to predict the final stomatal con-
ductance reading that would be achieved if unlimited time
were allowed for true steady state conditions to occur. Auto
