Geoscience Reference
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conductivities gi
i
and g
s
, pure CO
2
fl
ux, and water vapor
fl
ux E
it
as a result of the
process of photosynthesis.
This relationship is expressed as
;
Þ
q
c
p
kc
Þ
q
c
p
kc
;
e
s
e
i
E
lt
¼ g
l
e
s
e
a
ð
¼ g
s
e
i
e
s
ð
h
s
¼
ð
c
a
c
s
Þ
g
l
1
ð
c
s
c
i
Þ
g
s
1
A
n
¼
4
¼
6
;
p
:
p
:
where e
a
, e
s
, and e
i
are the partial pressures of water vapor in the open air, on the
surface, and in the stem, respectively (Pa); c
p
is the speci
c heat capacity of air (J/
kg K);
is a psychometric constant (Pa/K); gl
l
is the water vapor conductivity on
one side of the leaf (mol/m
2
is or m/s, = 1/(2rl); E
lt
is respiration intensity (kg/m
2
/s);
c
a
and c
s
are partial pressures of carbon dioxide outside and inside the stem,
respectively (Pa); e
i
¼ e
T
ðÞ
(Pa).
Equations of the photosynthesis-conductivity model describe the processes
taking place in a vegetation bud, and the next step is to integrate the relationships
with respect to a leaf canopy to obtain total values of A
c
and g
c
. This was made in
Sellers et al. (1996) with a supposition that the vertical distribution of vegetation
ferments in the canopy is connected with the time-averaged distribution of PAR:
c
V
max
L
¼ V
max
0
e
kL
;
where V
max
L
;
V
max
0
are the V
max
values on the level LAI = L and at the top of the
canopy (LAI = 0), respectively (mol/m
2
s);
k is a time-averaged value of the
coef
cient of PAR attenuation.
An amount of PAR assimilated by the leaf canopy is:
e
kL
G
ðÞ
l
F
p
n
F
p
0
flux caught by the leaf canopy (W/m
2
); G
where F
ˀ
0
is the value of the PAR
ðÞ
is a
projection of the orientation of the canopy leaves towards the direction of the
incoming radiation
fl
). Sellers et al. (1996) established that the use of the time-
averaged k value instead of the instant k value leads to only negligible uncertainties
in calculations.
Since now the wc, we, and ws parameters are connected (depending on the
vertical coordinate) with LAI of the leaf canopy through an exponent, it is possible
to use them to obtain an integral estimate of A
c
. We have already discussed the
difference of bushy and separately growing species (V < 1) and the notion of the
photic share (N < 1). Therefore bearing in mind that in the case of dense thickets the
photosynthesis intensity is reduced due to the lack of
fl
ux (
ʼ
“
”
, rich-in-ferment
vegetation material, and the integration is realized from 0 to L
T
/V:
green
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