Leaf Porometer Operator’s Manual
6. Leaf Porometer Theory
59
The variable of interest is
g
s
or the stomatal conductance.
First the vapor flux along the diffusion path will be
determined using the relative humidity difference between
nodes 1 and 2 as follows:
(1)
Where the
C
's are related to relative humidity by
(2)
where
h
r
is the relative humidity,
e
s
(T
a
)
is the saturated vapor
pressure at air temperature, and
P
atm
is atmospheric
pressure. Saturated vapor pressure is calculated by the
Tetens formula with appropriate coefficients for water
vapor:
(3)
NOTE: T must be in degrees Celsius.
Next we must determine the value of
gd
2
by the equation
(4)
)
(
2
1
2
C
C
g
F
d
vapor
−
=
atm
a
s
r
i
p
T
e
h
C
)
(
=
+
=
97
.
240
502
.
17
exp
611
.
0
)
(
T
T
T
e
a
s
