TARGAS-1 Operation Manual V. 1.02 86 support@ppsystems.com
(
W + E
)
×
e
P
(A.4) However, the difference between the molar flows into and out of the cuvette must equal the
transpiration, so:
E =
(
W + E
)
×
e
P
‐ W ×
e
P
(A.5) Therefore:
E
(
mmol m
‐
s
‐
)
=
W ×
(
e
‐e
)
(
P‐e
)
× 10
mmol
e
is defined as the partial pressure of water vapor of reference air supplied to the cuvette, but not yet
inside the cuvette, and therefore uninfluenced by the cuvette stirring fans or the leaf itself. e
partial
pressure is determined by the H
2
O IRGA during Reference phase.
e
is defined as the partial pressure of water vapor in the air inside the cuvette, surrounding the leaf.
This air is both highly mixed by the stirring fans and influenced by transpiration water vapor from the leaf.
e
partial pressure is determined by the H
2
O IRGA during Analysis phase. As related to the calculated
values in the TARGAS-1 display:
e
= H2Or
e
= H2Oa
Leaf Temperature
Calculate leaf temperature (T
) from the energy balance
The Energy Balance technique estimates leaf temperature by equating energy flux into the leaf with
energy flux out of the leaf. The model includes incident solar radiation, leaf re-radiation, convective heat
transfer, and transpiration. (Note: the energy balance estimate for leaf temperature is one option on
TARGAS-1, the other option is to use chamber temperature.)
(A.6) From Parkinson, 1983, the energy balance technique gives the difference between air and leaf
temperature as:
t =
H‐× E
.×
×
+
[
× (
(
T
+ 273)
)
]
where:
H = incident radiation absorbed by the leaf
= latent heat of vaporization of water
E = transpiration rate
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