Environmental Engineering Reference
In-Depth Information
Fig. 20.1
Absorption coefficients for water from 700- to 2,500-nm wavelength. The y-axis scales
are different for panels (
a
) near-infrared, (
b
) shortwave-infrared 1, and (
c
) shortwave-infrared 2.
The coefficients are from the PROSPECT model (Jacquemoud and Baret
1990
;F´ret et al.
2008
)
Table 20.1
Quantities to express vegetation biophysical parameters
Abbreviation or
symbol
Term
Formula
Units
Weight: fresh, dry, and
at full turgor
a
W
f
,
W
d
, and
W
t
,
respectively
Measured
kg
m
2
Area: ground and leaf
A
g
&
A
lf
, respectively Measured
Leaf Area Index
LAI
A
lf
/
A
g
Dimensionless
Leaf dry matter content
b
kg m
2
C
m
W
d
/
A
lf
Leaf water potential
a
MJ m
3
Ψ
Measured
¼
MPa
Relative water content
a
RWC
(
W
f
W
d
)/
(
W
t
Dimensionless
W
d
)
Leaf water content
c
kg m
2
LWC (or
C
w
)
(
W
f
W
d
)/
A
lf
Canopy water content
c
kg m
2
CWC
LWC
LAI
kg m
2
Vegetation water content
VWC
CWC+ stem water
content
Fuel moisture content
FMC
LWC/
C
m
Dimensionless
a
By definition, leaves at full turgor have
Ψ ¼
0 MPa and RWC
¼
100%
b
C
m
is also known as the leaf mass to area ratio (LMA) and 1/
C
m
is known as the specific leaf area
(SLA)
c
LWC and CWC are also known as the leaf and canopy equivalent water thickness (EWT),
respectively (volume/area, 1 mm
1kgm
2
)
¼
potential (i.e., full turgor), which offsets the cellular osmotic potential so that
is
0 MPa (Nobel
2009
). Leaf wilting is a visible sign of water stress, which occurs
when the turgor pressure is 0 MPa and
Ψ
Ψ
is equal to the osmotic potential. RWC and
Ψ
of the leaf mesophyll cells and are
unrelated to leaf area (
A
lf
), fresh weight (
W
f
), or dry weight (
W
d
). For a given leaf,
there is a one-to-one relationship between RWC and
for leaves are approximately the RWC and
Ψ
known as a “pressure-
volume curve,” which is determined by measurement (Lenz et al.
2006
; Nobel
2009
).
Ψ
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