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CIRAS-3 Operation Manual V. 1.09
161
The following approximation is made:
𝟒𝟒
×
�
(
𝑻
𝒄
+
𝟐𝟐𝟑
)
𝟑
� ≅ �𝟒
.
𝟔𝟑𝟗
+ (
𝟎
.
𝟓𝟓𝟑𝟒
×
𝑻
𝒄
)
�
(3.2)
From this we derive:
𝑻
𝒎𝒆𝒂𝒍
= (
𝑻
𝒄
+
∆𝒐
)
Saturation Vapor Pressure
Derive saturation vapor pressure at leaf temperature (e
leaf
) from T
leaf
(4.1)
From Buck, 1981 (using e
w1
and f
w1
)
we calculate
:
𝒆
𝒎𝒆𝒂𝒍
=
𝟔
.
𝟏𝟑𝟔𝟓
×
𝒆𝒆𝒑 �
𝑻
𝒎𝒆𝒂𝒍
× (
𝟏𝟐
.
𝟓𝟎𝟐
)
𝑻
𝒎𝒆𝒂𝒍
+
𝟐𝟒𝟎
.
𝟗𝟐 �
Stomatal Conductance
Calculate stomatal conductance (g
s
)
(4.2)
From
Caemmerer & Farquhar, 1981
(Eq B14), total leaf conductance is calculated as:
𝒈
𝒐𝒐𝒐𝒂𝒎
=
𝑬
×
�𝑷 −
(
𝒆
𝒎𝒆𝒂𝒍
+
𝒆
𝒐𝒐𝒐
)/
𝟐�
�𝒆
𝒎𝒆𝒂𝒍
− 𝒆
𝒐𝒐𝒐
�
(4.3)
Since
1/
𝒈
𝒐𝒐𝒐𝒂𝒎
=
𝒓
𝒔
+
𝒓
𝒃
,
(4.4)
stomatal resistance can be calculated as:
𝒓
𝒔
�𝒎
𝟐
𝒔 𝒎𝒐𝒎
−𝟏
�
=
�
�𝒆
𝒎𝒆𝒂𝒍
− 𝒆
𝒐𝒐𝒐
�
�𝑬
× (
𝑷 −
(
𝒆
𝒎𝒆𝒂𝒍
+
𝒆
𝒐𝒐𝒐
)/
𝟐
)
�
� − 𝒓
𝒃
(4.5)
Stomatal conductance is the inverse of stomatal resistance:
𝒈
𝒔
�𝒎𝒎𝒐𝒎 𝒎
−𝟐
𝒔
−𝟏
�
=
𝟏
𝒓
𝒔
×
𝟏𝟎
𝟑
Net Photosynthesis
Determine the rate of net photosynthesis (A) from the difference between CO
2
concentrations entering
(C
in
) and exiting (C
out
) the cuvette