Appendix 3. Photosynthesis Equations Used in CIRAS-2
CIRAS-2 Operator's Manual Version 2.04
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(2.4) Therefore:
Clarification of nomenclature:
i) e
in
is defined as the partial pressure of water vapor of dry reference air supplied to the cuvette, but
not yet inside the cuvette, and therefore uninfluenced by the cuvette stirring fans or the leaf itself.
Its partial pressure is determined by the Reference H
2
O IRGA.
ii) e
out
is defined as the partial pressure of water vapor of air inside the cuvette, surrounding the leaf.
This air is both highly mixed by the stirring fans and influenced by transpirational water vapor. Its
partial pressure is determined by the Analysis H
2
O IRGA. As relates to the calculated values in
the CIRAS-2 display:
Step 3.0
Calculate leaf temperature (T
leaf
) from the energy balance (optional to IR sensor method)
(3.1) From Reference 1 the difference between air and leaf temperature is:
Where:
H = incident radiation absorbed by the leaf
= latent heat of vaporization of water
E = transpiration rate
M
a
= molecular weight of air
C
p
= specific heat at constant pressure
r
b
= boundary layer resistance to water vapor transfer, empirically determined for each
cuvette by the pseudo-leaf (filter paper) method. 0.93 converts it to that for heat transfer.
σ = Stefan Boltzmann constant
T
c
= cuvette air temperature
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