Appendix 3. Photosynthesis Equations Used in CIRAS-2
CIRAS-2 Operator's Manual Version 2.04
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Appendix 3. Photosynthesis Equations Used in CIRAS-2
Calculations
Step 1.0
Calculate the mass flow of air (
W
) per unit leaf area entering the cuvette
The CIRAS-2 mass flowmeter is calibrated to read the volume flow at 20 °C and 1013.25 mb (V
20
). Molar
volume is 22.414 at 0 °C and 1 standard atmosphere (STP). Therefore:
Where:
a
is projected leaf area (cm
2
). The V
20
term is calculated above using cm
3
sec
-1
, but displayed by
CIRAS-2 as ml min
-1
.
Step 2.0
Calculate transpiration rate (
E
) from the partial pressures of water vapor of the air entering (e
in
)
and leaving (e
out
) the cuvette
(2.1)
The molar flow of
water vapor
(mol m
2
s
-1
) into the cuvette is:
(2.2)
The molar flow of
air
out of the cuvette (due to the addition of transpired water) is (
W+E
). Therefore,
the molar flow of
water
vapor
out of the cuvette is:
(2.3)
However, the difference between the molar flows into and out of the cuvette must equal the
transpiration, so: