Geoscience Reference
In-Depth Information
The model of the leaf canopy photosynthesis derived by Collatz et al. (1990) for
vegetation species of classes C
3
and C
4
together with the bud model (Ball 1988)
have been used to derive the biospheric model SiB2. In this model, photosynthesis
and Greenhouse conductivity are closely connected (Sellers et al. 1996).
According to Collatz et al. (1991), there are three factors limiting the plant
photosynthesis intensity. These are an ef
ciency of the photosynthetic ferment
system w
c
(the so-called limitation after Rubisco), an amount of PAR absorbed by
cellulose chlorophyll w
e
, and an ability of a vegetation species to assimilate and
emit to the environment the products of photosynthesis w
s
. As a result, the value of
photosynthesis intensity A is a minimum of the three limitations enumerated above:
A
min w
c
;
w
e
;
w
s
ð
Þ
where A is the photosynthesis intensity (mol/m
2
s); w
c
is a Rubisco (ferment) lim-
itation of photosynthesis intensity (mol/m
2
s); w
e
is a limitation of assimilation by
illumination (mol/m
2
s); w
s
is a limitation of carbon content for a vegetation species
(mol/m
2
s).
The physiological limitation of assimilation w
c
is a function of the ferment
supplies of species, in other words, it is an ability of cellulose to realize the bio-
chemical reactions. The ferment reserve of the plant is described in the model with
the V
max
parameters, a maximum catalytic supply of ferments (Rubisco) taking part
in photosynthesis. The w
c
value also depends on the leaf canopy temperature and
soil moisture. Collatz et al. (1990) suggested the following expression for w
c
for
vegetation classes C
3
and C
4
:
c
i
C
w
c
¼ V
m
;
for C
3
;
c
i
þ
K
c
ð
1
þ
O
2
=
K
o
Þ
w
c
¼ V
m
;
for C
4
;
where V
m
is a maximum catalytic supply of ferments (Rubisco) (mol/m
2
/s); c
i
is the
partial pressure of CO
2
in the leaf (Pa); O
2
is the partial pressure of O
2
in the leaf
(Pa);
C
is the point of CO
2
compensation (Pa) = O
2
/S; S is a special interaction
between CO
2
and O
2
; K
c
is the Michaelis
—
Menten constant for CO
2
, (Pa); K
o
is
the constant of O
2
suppression (inhibition).
The V
m
parameter is expressed through V
max
, the function of dependence on the
soil temperature and moisture. The S, K
c
, K
o
parameters are functions of
temperature.
A limitation of assimilation intensity w
e
is described as follows:
c
i
C
w
e
¼
ð
F
p
n
Þe
3
ð
1
x
p
Þ
;
for C
3
;
C
c
i
þ
2
w
e
¼
ð
F
p
n
Þe
4
ð
1
x
p
Þ ;
for C
4
;
Search WWH ::
Custom Search