LI-COR LI-600, Instruction Manual

Page: 91 / 131

LI-600 Porometer/Fluorometer Instruction Manual
9-4
where ( g
sw
) is the one-sided stomatal conductance to
water vapor, and ( g
bw
) is the one-sided boundary layer
conductance, both in (mol H
2
O m
-2
s
-1
).
Boundary layer conductance in the LI-600 cuvette is a
function of the flow rate (equation 9-10).
The actual measurements for water vapor being made in
the LI-600 are done using relative humidity sensors on
the inlet and outlets of the cuvette. In order to calculate
the mass balance as described above, the relative humid-
ities must be converted to molar fractions, requiring
additional measurements for the temperature of the
sensors (
T
ref
) and the atmospheric pressure ( Press ).
The vapor pressures are calculated from the relative
humidity measurement and a saturation vapor function
from Buck (1981):
9-7
where satvap(T) is the saturation vapor pressure (kPa) at
the given temperature T (°C)
9-8
where VP
x
is the calculated vapor pressure (kPa) with x
is 'cham','ref' or 'leaf', rh
x
is the relative humidity (%)
measured by the LI-600 sensors and T
ref
(°C) is the tem-
perature read by a thermistor in the block adjacent to
the RH sensors. For calculation of leaf vapor pressure, it
is assumed that the internal air-space is at saturation,
i.e., relative humidity within the leaf is 100%, which
reduces the equation to equation 9-7.