442
J.D. Tenhunen et al.
Table 21.2. Estimates of leaf gas exchange model parameters utilized in simulation of
tundra ecosystem carbon dioxide exchange for three community types distributed along
the topographic and water availability gradient occurring within the Imnavait Creek
watershed. Parameters were derived by fitting the model to observed data obtained from
the species described in the text. Parameters indicated were assumed to be valid during
the mid-season or mature stage of leaves from approximately July 15 to July 31. For
parameter definitions, see Harley and Tenhunen (1991) or Appendix of Tenhunen et al.
(1990)
Parameter
Value
Units
Deciduous
Graminoid Evergreen Moss
shrub
Shrub
C (Pm])
10.9
11.5
10.4
f (H2O)
(1O.0)a
(11.0)
(9.8)b
AHa (Pm])
33559
*
*
36206
J mol- 1
AHd (Pm])
250000
*
100000
J mol- 1
AS (Pm])
805
*
333
J K- 1 mol- 1
a
0.06
*
0.00012
mol CO2/mol photons
f (Rd)
20.4
*
26.5
Ea (Rd)
51178
*
*
67145
J mol- 1
f (Ke)
31.95
*
*
Ea (Ke)
63500
*
*
J mol- 1
f (Ko)
19.61
*
*
Ea (Ko)
35000
*
*
*
J mol- 1
f (t)
-3.9489
*
Ea (t)
-28990
*
*
J mol- 1
C (Vemax)
34.3
35.0
32.3
f(H2O)
(29.8)
(30.3)
(29.5)
AHa (Vemax) 65000
*
*
*
J mol- 1
AHd (Vemax) 250000
*
*
J mol- 1
AS (Vema.)
600
*
*
J K- 1 mol- 1
Gfac
30
*
Not
applicable
* Indicates that parameter value is the same as indicated for deciduous shrubs.
a Value in parentheses is that applied to young and senescing leaves.
bValue for young leaves of Salix, not for evergreen shrubs - see explanation in text.
and evergreen elements in dry shrub and tussock tundra simulations. Average harvested leaf area for each species was distributed into four layers and
these were then considered to be alternately interspersed. For simulations in
wet meadow locations, the physiology established for Salix = Ledum was
used together with that for graminoids, i.e., for Eriophorum.
Rapid phenological development during the Arctic summer influences not
only the amount of leaf area exposed in the vascular plant canopy for carbon
dioxide fixation (Sect. 21.3), but also photosynthetic capacity. Physiological
effects are included in GAS-FLUX via temporal change in the parameters
C(P m1 ) and C(V cmax ). For the simulation on July 1 and August 15, these
parameters were set at the values given in parentheses in Table 21.2 to
describe the response of both young and senescent leaves. The values
J.D. Tenhunen et al.
Table 21.2. Estimates of leaf gas exchange model parameters utilized in simulation of
tundra ecosystem carbon dioxide exchange for three community types distributed along
the topographic and water availability gradient occurring within the Imnavait Creek
watershed. Parameters were derived by fitting the model to observed data obtained from
the species described in the text. Parameters indicated were assumed to be valid during
the mid-season or mature stage of leaves from approximately July 15 to July 31. For
parameter definitions, see Harley and Tenhunen (1991) or Appendix of Tenhunen et al.
(1990)
Parameter
Value
Units
Deciduous
Graminoid Evergreen Moss
shrub
Shrub
C (Pm])
10.9
11.5
10.4
f (H2O)
(1O.0)a
(11.0)
(9.8)b
AHa (Pm])
33559
*
*
36206
J mol- 1
AHd (Pm])
250000
*
100000
J mol- 1
AS (Pm])
805
*
333
J K- 1 mol- 1
a
0.06
*
0.00012
mol CO2/mol photons
f (Rd)
20.4
*
26.5
Ea (Rd)
51178
*
*
67145
J mol- 1
f (Ke)
31.95
*
*
Ea (Ke)
63500
*
*
J mol- 1
f (Ko)
19.61
*
*
Ea (Ko)
35000
*
*
*
J mol- 1
f (t)
-3.9489
*
Ea (t)
-28990
*
*
J mol- 1
C (Vemax)
34.3
35.0
32.3
f(H2O)
(29.8)
(30.3)
(29.5)
AHa (Vemax) 65000
*
*
*
J mol- 1
AHd (Vemax) 250000
*
*
J mol- 1
AS (Vema.)
600
*
*
J K- 1 mol- 1
Gfac
30
*
Not
applicable
* Indicates that parameter value is the same as indicated for deciduous shrubs.
a Value in parentheses is that applied to young and senescing leaves.
bValue for young leaves of Salix, not for evergreen shrubs - see explanation in text.
and evergreen elements in dry shrub and tussock tundra simulations. Average harvested leaf area for each species was distributed into four layers and
these were then considered to be alternately interspersed. For simulations in
wet meadow locations, the physiology established for Salix = Ledum was
used together with that for graminoids, i.e., for Eriophorum.
Rapid phenological development during the Arctic summer influences not
only the amount of leaf area exposed in the vascular plant canopy for carbon
dioxide fixation (Sect. 21.3), but also photosynthetic capacity. Physiological
effects are included in GAS-FLUX via temporal change in the parameters
C(P m1 ) and C(V cmax ). For the simulation on July 1 and August 15, these
parameters were set at the values given in parentheses in Table 21.2 to
describe the response of both young and senescent leaves. The values