Geoscience Reference
In-Depth Information
Z
A
0
x
S
¼
x
S
ð
z
Þ
ds
ð
z
Þ
0
where s(z) is the function of distribution of the root system along the vertical cross-
section of the soil layer; A
0
is a maximum capacity of the root layer of the soil.
For conifers, r
a
r
st
;
and along the height of the tree the value of photosyn-
thesis per unit mass of pine-needles changes negligibly, and therefore we shall
consider some point, averaged over the tree height, for which the intensity of the
photosynthetically active radiation (PAR) is determined by the Beer-Lambert law:
5K
e
hS
L
H
1
E ¼
j
E
E
e
exp 0
:
where E
e
is the intensity of the incoming solar radiation over the forest,
ʺ
E
is the
share of PAR in the total solar radiation; K
e
is the coef
cient of extinction.
Assuming that the temperature of pine-needles coincides with that of the
atmosphere (T
L
=T), we use the following approximation for the
˃
(T) function:
(
"
#
)
l
T
T
1
l
1
T
T
1
T
0
T
1
T
0
T
1
exp l
1
rð
T
Þ
¼max 0
;
;
where the parameter l = 1.8; T
1
is a minimum temperature at which the photo-
synthesis still takes place; T
0
is a temperature optimal for photosynthesis.
The
function characterizes the dependence of photosynthesis on soil moisture.
With a short-term over-moistening of soil the photosynthesis does not decrease, and
therefore
ʩ
Xðx
S
Þ
¼1
8x
S
2
½0
;
1
:
In a general case, we use the dependence:
1
;
x
S
2ð
0
; x
HB
Þ;
Xðx
S
Þ
¼
ð
1
x
S
Þ=ð
1
x
HB
Þ;
x
S
2
½
x
HB
;
1
˄
B
) is introduced in order to describe the strategy of distribution
of assimilates, where
ʸ
i
(
The function
˄
B
is the biological time and to determine the ratio of the sum
of ef
cient temperatures T
l
to the mean multi-year sum of ef
cient temperatures T
ʣ
accumulated during the vegetation period:
s
B
ð
j
Þ
¼
X
j
T
l
=
T
R
;
l¼1
where j is the day number.
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