EVALUATION OF CANOPY TRANSPIRATION RATE BY APPLYING
PLANT HORMONE ABSCISIC ACID
Daisuke YASUTAKE*, **, Masaharu KITANO**, Tetsuo KOBAYASHI***, Kota HIDAKA**,
Takahiro WAJIMA** and Wenjun HE***
* Research Fellow of the Japan Society for the Promotion of Science, d-yasu@bpes.kyushu-u.ac.jp
** Faculty of Agriculture, Kochi University, Nankoku, Kochi, 783-8502 Japan
*** Faculty of Agriculture, Kyushu University, Fukuoka, 812-8581 Japan
**** Institute of Agro-Environment and Sustainable Development, CAAS, Beijing, 100081 China
The canopy transpiration rate is an important biological factor affecting soil hydrology in crop fields.
However, it has been impossible to evaluate the canopy transpiration rate by the conventional methods
such as micrometeorological methods and chamber method etc.
In this study, a new method for
evaluating the transpiration rate and stomatal conductance in plant canopy was developed, which is
based on the rise in leaf temperature caused by applying a transpiration inhibiting plant hormone,
abscisic acid (ABA), to plants (Fig.1).
On the basis of the difference in heat balances between the
ABA applied and the non-ABA applied plants, the canopy transpiration rate (EL) can be estimated as
EL = CP ρΔTL (GR + GA ) / λn
(1)
where Cp ρ is the volumetric heat capacity of air, ΔTL is the rise in leaf temperature by the ABA
application, GR is the radiative transfer conductance, GA is the canopy boundary layer conductance, λ is
the latent heat for vaporization and n ( = 0~1) is the depression coefficient in transpiration by the ABA
application.
EL depends mainly on ΔTL, GA and n.
ΔTL and GA can be measured in the field, however,
n has to be determined experimentally by comparing the transpiration rates in the ABA applied and the
nonABA applied plants.
Canopy stomatal conductance (GS) can be also evaluated from EL obtained
by Eq.(1) and micrometeorological elements.
In the preliminary experiments, transpiration rates in a
single leaf and whole plants estimated by Eq.(1) agreed well with the measured ones.
The new method was applied to corn canopy at different growth stages in the upper Yellow River
basin, China.
Diurnal changes in EL and GS in the corn canopy can be evaluated at the initial stage
with a LAI (leaf area index) of 0.37 (9 June 2005) and the development stage with a LAI of 3.78 (1 July
2004) (Fig.2).
The ratios (EL/ET) of the accumulated EL during the daytime to the accumulated
evapotranspiration (ET) were 0.30 and 0.84 at the initial and development stages, respectively.
values of EL/ET corresponded to the report by Kang et al. (2003).
initial stage.
These
GS varied in parallel with EL in the
However, in the development stage, GS reached a maximum value at 11:00 and
thereafter decreased rapidly with increase in wind speed (U) under the condition of high solar radiation
(RS), high air temperature (TA) and low air humidity (RH).
This shows the daytime stomatal closure
caused by environmental stress in the development stage.
Thus, the new method with ABA
application is useful for evaluating transpiration rate and stomatal conductance in plant canopy, and
can detect the plant water stress.
Keywords : abscisic acid, leaf temperature, plant canopy, stomatal conductance, transpiration rate.
Reference : Kang et al. (2003) Agricultural Water Management 59, 239254.
micrometeorological
observation
evapotranspiration
ET
soil
evaporation
plant
transpiration
ES
EL
depressed transpiration
by ABA
E S E L'= (1－n) E L
increased
leaf temp.
leaf temp.
T L'
TL
ABA application
Fig.1
Schematic diagram of a concept of the new method for evaluating the canopy transpiration rate
by applying plant hormone abscisic acid (ABA).
ABA is applied to a few plants in the field, which
induces depression in transpiration and rise in leaf temperature.
Meteorological and cultivating
conditions at the part where ABA is applied are assumed to be same as those at the other part in the
The canopy transpiration rate is evaluated on the basis of the difference in heat balances
between the ABA applied and the non-ABA applied plants.
Symbols are explained in the text.
(b) development stage (LAI = 3.78)
R S (W m2)
500
TA
50
20
RH
4
2
ET
EL
4
2
3
6
9
12
15
Time of day
18
21
24
0
6
4
2
ET
0.1
EL
0.05
0
6
0
RH
10
0
0.15
0.1
0.05
50
20
GS (mm s 1) ET, EL (g m2 s1)
0
0.15
100
TA
30
0
6
GS (mm s 1) ET, EL (g m2 s1)
0
40
U (m s 1)
U (m s 1)
10
8
Fig.2
500
100
30
0
1000
TA (℃)
TA (℃)
0
40
RH (%)
R S (W m2)
(a) initial stage ( LAI = 0.37)
1000
RH (%)
field.
0
6
4
2
0
0
3
6
9
12
15
18
21
24
Time of day
Diurnal changes in solar radiation (RS), temperature (TA) and relative humidity (RH) in air, wind
speed (U), evapotranspiration rate (ET), canopy transpiration rate (EL) and stomatal conductance (GS)
in the cornfield at the initial stage (a; LAI = 0.37, 9 June 2005) and the development stage (b; LAI = 3.78,
1 July 2004).
EL and GS, and ET were evaluated by the new method and the Bowen ratio method, respectively.