TARGAS-1 Operation Manual V. 1.02 153 support@ppsystems.com
(A.13) IRGA CO
2
readings are corrected for water vapor, temperature, and atmospheric pressure. The
addition of transpirational water vapor dilutes the air leaving the cuvette (
), and this is compensated
for in the calculation:
=
(
×
)
[
×
(
+
)
]
(A.14) To calculate net CO
2
assimilation we rearrange equation (A.13) to:
=
(
)
×
+
(
×
)
TARGAS-1 calculates and displays the CO
2
difference (
). As related to the calculated values
in the TARGAS-1 display:
=
=
Intercellular CO
2
Concentration
Calculate CO
2
concentration in the sub-stomatal cavity (
) using the equation derived by von
Caemmerer & Farquhar, 1981
(A.15) The sub-stomatal CO2 concentration,
, is given by:
=
×
+
(A.16) Where
is the total conductance to CO
2
transfer:
=
(
. ×
)
+
(
. ×
)
×
(1.585 is the diffusion ratio of CO
2
and water in air, and 1.37 is the diffusion ratio of CO
2
and water in the
boundary layer).
Note: These calculations are based on the following assumptions:
• the leaf is exposed on both upper and lower leaf surfaces
• the upper and lower boundary layer resistances are similar
• stomata are evenly distributed on both upper and lower leaf surfaces.
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