J.-C. Calvet Agricultural and Forest Meteorology 103 2000 229–247 231
with a =
T
2
− T
o
T
o
− T
1
4 In this study, the values of T
1
, T
o
, and T
2
were set to 0, 30, and 40
◦
C, respectively Shuttleworth, 1989. 2.2. A Jarvis parameterisation based on air
temperature inputs In divers SVAT models, the temperature dependence
of g
s
relies on air temperature, rather than on leaf tem- perature. Since, in most cases, T
a
may vary differently from T
s
, it is important to investigate the effect of using T
a
instead of T
s
on the description of soil water stress. For example, in Noilhan and Planton 1989, the value
of g
s
is derived from Eq. 2, where the value of D
s
is replaced by the air saturation deficit D
a
, defined as D
a
= q
sat
T
a
− q
a
5 Also, Eq. 3 is replaced by
g
s
T
a
= g
s
T
o
1 − T
o
− T
a 2
T
o
− T
1 2
6 with T
1
=
◦
C and T
o
= 25
◦
C Noilhan and Planton, 1989.
Since the leaf gas exchange studies considered here are based on the use of T
s
, the use of T
a
will be inves- tigated in the case of the micrometeorological datasets
only. 2.3. An A–g
s
parameterisation In the A–g
s
physiological module of the ISBA–A–g
s
model Jacobs et al., 1996; Calvet et al., 1998, the parameters governing the magnitude of g
s
and its sen- sitivity to leaf-to-air saturation deficit D
s
are, respec- tively, the unstressed mesophyll conductance g
∗ m
, and the maximum leaf-to-air saturation deficit D
∗ max
Ap- pendix A. The parameter g
∗ m
conditions the maximum attainable stomatal conductance, while D
∗ max
represent the sensitivity of stomatal aperture to air humidity.
Typical values of the parameters of the A–g
s
model, for either C
3
or C
4
plants, are displayed in Table 1. This table does not include values of unstressed g
∗ m
and D
∗ max
which are believed to display more variability
Table 1 Standard values of the parameters of the A–g
s
model according to the plant type C
3
or C
4
adapted from Jacobs et al. 1996
a
Plant type Parameter X X
25
Q
10
T
1 ◦
C T
2 ◦
C C
3
ε mg J
− 1
0.017 – –
– f
0.95 –
– –
Ŵ ppm 45
1.5 –
– g
m
mm s
− 1
– 2.0
5 36
A
m,max
mg m
− 2
s
− 1
2.2 2.0
8 38
C
4
ε mg J
− 1
0.014 – –
– f
0.60 –
– –
Ŵ ppm 2.8
1.5 –
– g
m
mm s
− 1
– 2.0
13 36
A
m,max
mg m
− 2
s
− 1
1.7 2.0
13 38
a
ε is the maximum quantum use efficiency, f
the maximum potential value of the ratio between internal and external leaf con-
centration of CO
2
, Ŵ the compensation point, g
m
the mesophyll conductance, and A
m,max
the maximum net assimilation of the leaf. The Q
10
, T
1
and T
2
values modulate the sensitivity of each pa- rameter to temperature through either XT
s
= X
25
Q
T
s
− 2510
10
or XT
s
= X
25
Q
T
s
− 2510
10
{[1 + exp{0.3T
1
− T
s
}][1 + exp{0.3T
s
− T
2
}]}, where XT
s
and X
25
are the values of the parameters cor- responding to the leaf temperatures T
s
and 25
◦
C, respectively.
between plant species. Also, the cuticular conduc- tance g
c
, allowing diffusion of water vapour and CO
2
through leaf cuticle, is accounted for Appendix A. In this study, the following average values of g
c
were employed: 0.25 mm s
− 1
for herbaceous C
3
plants, 0.17 mm s
− 1
for woody plants other than conifers, 0.05 mm s
− 1
for conifers, and 0.15 mm s
− 1
for C
4
plants. They were derived from the review study of Kerstiens 1996.
The leaf temperature dependence of g
s
is accounted for by Q
10
functions applied to the parameters of the photosynthesis model Table 1. This is different from
the Jarvis-type approaches presented before, in which the temperature response is applied to the value of g
s
.
3. Datasets
A number of authors have shown the interest of analysing physiological leaf gas exchange measure-
ments to improve the parameterisation of vegetation transpiration e.g. Choudhury and Monteith, 1986;
Monteith, 1995. In this study, a literature survey of ex- isting leaf-air exchange measurements was conducted
and very complete micrometeorological datasets were used in order to investigate the response of g
s
to
232 J.-C. Calvet Agricultural and Forest Meteorology 103 2000 229–247
Table 2 The studied herbaceous C
3
plants and the obtained unstressed: 1 mesophyll conductance at 25
◦
C g
∗ m25
, and maximum leaf-to-air saturation deficit D
∗ max
, as defined in Appendix A for the A–g
s
approach; 2 minimum stomatal resistance r
∗ smin
and the sensitivity to air humidity α
∗ H
, in the case of the Jarvis model Section 2.1 Plant species
Reference D
∗ max
g kg
− 1
g
∗ m25
mm s
− 1
α
∗ H
kg g
− 1
r
∗ smin
s m
− 1
Elaeis guineensis oil palm Dufrene and Saugier 1993
31.7 2.05
0.03818 71.1
Phalaris aquatica phalaris Morison and Gifford 1983
32.3 3.82
0.55296 20.5
Manihot esculenta cassava El-Sharkawy et al. 1984
41.0 0.80
0.03591 117.1
Oryza sativa rice Morison and Gifford 1983
42.4 1.00
0.36068 47.9
Nicotiana glauca tobacco Dai et al. 1992
42.7 1.11
0.04393 56.7
Ipomoea vagans convolvulus Maroco et al. 1997
48.1 0.40
0.04370 121.1
Ipomoea pes-tigridis convolvulus Maroco et al. 1997
48.6 1.05
0.05711 53.9
MUREX fallow Calvet et al. 1998
53.5 0.55
0.03801 117.7
Oryza sativa rice Kawamitsu et al. 1993
59.8 0.58
0.04207 56.2
Oryza sativa rice Kawamitsu et al. 1993
60.8 0.99
0.04051 88.4
Datura stramonium datura Bunce 1985
67.9 1.36
0.23392 23.5
Manihot esculenta cassava El-Sharkawy et al. 1984
67.9 0.58
0.02963 103.6
Lycopersicon esculentum tomato Jolliet and Bailey 1992
81.7 0.10
0.03902 240.8
Ricinus communis castor bean Dai et al. 1992
81.9 1.51
0.03873 31.0
Abutilon theophrasti abutilon Bunce 1985
82.0 1.00
0.18410 30.2
Vigna unguiculata cowpea Turner et al. 1984
83.8 0.31
0.11147 114.3
Lycopersicon esculentum tomato Bakker 1991
95.9 0.42
0.06150 76.5
Capsicum annuum sweet pepper Bakker 1991
102.2 0.42
0.05928 76.8
Vigna unguiculata cowpea Hall and Schulze 1980
103.0 0.51
0.03331 71.1
Nicotiana glauca tobacco Farquhar et al. 1980
105.0 0.07
0.01785 311.6
Vicia faba broad bean Mott and Parkhurst 1991
105.9 0.78
0.17529 50.7
Cucumis sativus cucumber Bakker 1991
115.9 0.82
0.06203 42.0
Solanum melongena eggplant Bakker 1991
121.7 0.84
0.06059 41.1
Helianthus annuus sunflower Hall et al. 1976
123.9 1.29
0.03404 32.6
Glycine max soybean Bunce 1985
131.6 0.46
0.09648 69.8
Macroptilium atropurpureum siratro El-Sharkawy et al. 1984
159.4 0.33
0.02712 90.9
Phaseolus vulgaris common bean El-Sharkawy et al. 1984
178.2 0.25
0.02222 120.4
Phaseolus vulgaris common bean Comstock and Ehleringer 1993
217.4 0.92
0.02716 34.4
Vigna luteola Hall et al. 1976
220.2 1.00
0.02963 30.9
Helianthus nuttalii Turner et al. 1984
230.7 0.29
0.05457 95.9
Helianthus annuus sunflower Turner et al. 1984
273.0 0.29
0.01635 107.5
Oryza sativa rice El-Sharkawy et al. 1984
334.5 0.20
0.01600 129.1
Helianthus annuus sunflower Turner et al. 1985
560.3 0.26
0.04042 95.6
saturation deficit in stressed and unstressed condi- tions, over C
3
or C
4
plants, woody or herbaceous. In unstressed conditions, a total of 63 case studies
could be gathered, corresponding to different plant species or growing conditions: 33 herbaceous C
3
plants Table 2, 19 woody C
3
plants Table 3, and 11 C
4
plants Table 4. These studies were extracted from 28 published articles listed in Tables 2–4, and
concern 52 different species, most of which are culti- vated ones.
Few experiments concerned with the response to soil water deficit present all the measurements
required to perform a g
s
–D
s
analysis and characterise the effect of soil water stress on models’ parameters.
Only five were available to the author: 1 three gas exchange studies at leaf scale, over sunflower, cow-
pea, and hazel tree, 2 two micrometeorological field experiments, at the canopy scale, comprising flux
and surface temperature measurements, over a soy- bean crop Olioso et al., 1996; Calvet et al., 1998,
and over the fallow site of the 3-year MUREX ex- periment Calvet et al., 1998, 1999. The vegetation
of the MUREX fallow consisted of many C
3
herba- ceous plant species: Brachypodium sp. 45 of the
J.-C. Calvet Agricultural and Forest Meteorology 103 2000 229–247 233
Table 3 The studied woody C
3
plants and the obtained unstressed: 1 mesophyll conductance at 25
◦
C g
∗ m25
, and maximum leaf-to-air saturation deficit D
∗ max
, as defined in Appendix A for the A–g
s
approach; 2 minimum stomatal conductance r
∗ smin
and the sensitivity to air humidity α
∗ H
, in the case of the Jarvis model Section 2.1 Plant species
Reference D
∗ max
g kg
− 1
g
∗ m25
mm s
− 1
α
∗ H
kg g
− 1
r
∗ smin
s m
− 1
Arbutus unedo strawberry tree Turner et al. 1984
29.4 0.10
0.04966 460.5
Pinus radiata pine Attiwill et al. 1982
33.6 0.19
0.03478 809.9
Pseudotsuga menziesii douglas fir Meinzer 1982
37.3 0.05
0.05714 809.9
Vitis vinifera grape vine Jacobs et al. 1996
58.2 2.00
– –
Actinidia deliciosa kiwifruit vine Gucci et al. 1996
63.0 0.98
0.04602 67.5
Corylus avellana hazel tree Farquhar et al. 1980
65.9 0.09
0.03600 321.5
Corylus avellana hazel tree Turner et al. 1984
68.7 0.13
0.03950 247.6
Malus pumila apple tree Thorpe et al. 1980
83.3 0.25
0.05333 127.3
Populus hybrid poplar Will and Teskey 1997
113.2 4.70
0.04285 19.4
Citrus sinensis lemon tree Cohen and Cohen 1983
138.5 0.09
0.02286 318.2
Eucalyptus deglupta eucalyptus El-Sharkawy et al. 1984
156.4 0.19
0.02353 171.3
Pinus taeda loblolly pine Will and Teskey 1997
174.4 0.39
0.03047 110.0
Hedera helix ivy Aphalo and Jarvis 1991
185.7 0.21
0.05814 130.3
Gossypium hirsutum cotton Turner et al. 1984
189.9 0.08
0.03298 514.1
Cercis canadensis Will and Teskey 1997
197.3 0.23
0.02449 152.3
Nerium oleander oleander Turner et al. 1984
232.4 0.13
0.02185 184.7
Prunus dulcis plum tree Turner et al. 1984
284.9 0.18
0.06524 164.8
Pistacia vera pistachio tree Turner et al. 1984
294.8 0.10
0.02884 270.5
Quercus rubra oak Will and Teskey 1997
518.3 0.15
0.01127 194.3
plants and Potentilla reptans 22 were the main dominant species, together with Erigeron canadensis,
Epilobium tetragonum, and Rumex acetosa. In the case of the micrometeorological datasets,
estimates of g
s
and D
s
were obtained at the canopy level from observations of LAI, flux, air humidity and
temperature, and surface temperature. The microm- eteorological measurements employed in this study
Table 4 The studied C
4
plants and the obtained unstressed: 1 mesophyll conductance at 25
◦
C g
∗ m25
, and maximum leaf-to-air saturation deficit D
∗ max
, as defined in Appendix A for the A–g
s
approach; 2 minimum stomatal conductance r
∗ smin
and the sensitivity to air humidity α
∗ H
, in the case of the Jarvis model Section 2.1
Plant species Reference
D
∗ max
g kg
− 1
g
∗ m25
mm s
− 1
α
∗ H
kg g
− 1
r
∗ smin
s m
− 1
Saccharum spp. Hybrid sugarcane Grantz and Meinzer 1990
15.9 25.49
0.05785 67.5
Zea mays maize Dai et al. 1992
29.0 16.12
0.03312 73.8
Schoenefeldia gracilis C
4
grass Maroco et al. 1997
42.1 4.96
0.02869 111.7
Amaranthus retroflexus amaranth weed El-Sharkawy et al. 1984
60.9 3.38
0.02192 129.1
Sorghum bicolor grain sorghum El-Sharkawy et al. 1984
94.3 2.86
0.01633 137.1
Panicum maximum green panic Kawamitsu et al. 1993
99.0 1.49
0.01611 237.1
Zea mays maize Graham and Thurtell 1989
129.0 1.23
0.01306 251.0
Eragrostis tremula C
4
grass Maroco et al. 1997
146.7 3.05
0.01044 127.7
Zea mays maize Farquhar et al. 1989
166.4 9.14
– –
Dactyloctenium aegyptium C
4
grass Maroco et al. 1997
285.7 1.44
0.00646 232.5
Andropogon gayanus andropogon El-Sharkawy et al. 1984
397.6 0.97
0.00457 318.2
comprise of meteorological variables air temperature T
a
, and specific humidity q
a
at screen level, together with emissivity-corrected infrared temperature T
s
, and water vapour and heat fluxes, E and H, respectively.
The effective saturation deficit of the canopy is D
′ s
= { q
sat
T
s
− q
a
} − c
p
E H
{T
s
− T
a
} 7
234 J.-C. Calvet Agricultural and Forest Meteorology 103 2000 229–247
Fig. 1. Canopy leaf conductance, g
′ s
, vs. canopy leaf to air saturation deficit, D
′ s
, as obtained from micrometeorological measurements over the MUREX fallow site Calvet et al., 1999. Dry, intermediate, and wet soil moisture conditions correspond to solid circles, pluses and
open circles, respectively. The values of extractable soil moisture content, θ , are 0–0.1, 0.2–0.3 and 0.8–1.0, respectively.
and the equivalent stomatal conductance at the canopy scale is
g
′ s
= E
ρ
a
L D
′ s
8 where c
p
= 1.005×10
3
J kg
− 1
K
− 1
, q
sat
and ρ
a
are specific humidity at saturation and air density, respec-
tively, and L represents LAI. The values of D
′ s
and g
′ s
Fig. 2. Canopy leaf conductance, g
′ s
, vs. canopy leaf to air saturation deficit, D
′ s
, as obtained from micrometeorological measurements over the Soybean field Olioso et al., 1996. Dry, intermediate, and wet soil moisture conditions correspond to solid circles, pluses and open
circles, respectively. The values of extractable soil moisture content, θ , are 0.2–0.3, 0.4–0.5, and 0.6–0.7, respectively.
were calculated from Eqs. 7 and 8, respectively, for various soil moisture situations, in conditions
which were favourable to a significant physiological response of the canopy to soil and air water stress:
LAI values greater than 1 m
2
m
− 2
, no rain, and val- ues of the incoming solar radiation R
g
higher than 400 W m
− 2
. The obtained values of g
′ s
versus D
′ s
are presented in Figs. 1 and 2 for the MUREX and
J.-C. Calvet Agricultural and Forest Meteorology 103 2000 229–247 235
Soybean datasets, respectively. For the sake of clarity, only three classes of root-zone soil moisture were rep-
resented in Figs. 1 and 2: dry, intermediate, and wet. As the distribution of soil moisture conditions differed
from one experiment to the other, the classes’ bound- aries are not the same. While the classical decrease of
g
′ s
in response to increasing D
′ s
is observed for both datasets, marked differences appear in the relative
position of dry, intermediate, and wet points. In partic- ular, there is a clear dependence of g
′ s
on the soil mois- ture class in Fig. 2 Soybean, while the results from
MUREX show a more complex behaviour Fig. 1. These features are analysed in this paper in terms of
stomatal response to soil water stress Section 5.
4. Model calibration in unstressed conditions
