DYNAMICS OF WATER AND ION TRANSPORT DRIVEN BY CORN CANOPY
IN THE YELLOW RIVER BASIN
Masaharu KITANO*, Daisuke YASUTAKE*, **, Tetsuo KOBAYASHI***, Kota HIDAKA*, Takahiro
WAJIMA*, Weizhen WANG**** and Wenjun HE*****
* Faculty of Agriculture, Kochi University, Nankoku, Kochi, 783-8502 Japan, kitano@cc.kochi-u.ac.jp
** Research Fellow of the Japan Society for the Promotion of Science
*** Faculty of Agriculture, Kyushu University, Fukuoka, 812-8581 Japan
**** Cold and Arid Regions Environmental and Engineering Institute, CAS, Lanzhou, 730000 China
***** Institute of Agro-Environment and Sustainable Development, CAAS, Beijing, 100081 China
Water deficit and salt accumulation in rhizosphere are the serious problems in crop fields in
semi-arid regions, which are affected by dynamics of transport processes of water and ions in the
plant-environment system. Transpiration stream and selective nutrients uptake driven by crop canopy
can be considered to largely depend on plant active functions, and therefore water balance and ion
balance in the rhizosphere should be analyzed with special reference to these plant functions.
In this
study, dynamics of water and ion transport driven by crop canopy were analyzed in a cornfield at
Togtoh in the upper Yellow River basin (Inner Mongolia, China).
Xylem sap exuded from the stem stumps of corn plants at the development stage was collected
during the nighttime in July 2005 in the experimental cornfield, and concentrations of nutrient ions (NO 3-,
PO43-, K+, Na+, Ca2+ and Cl-) were analyzed by using an ion chromatograph.
Those ion concentrations
of the Yellow River water, the irrigation water, the ground water, the rhizosphere and the respective
plant organs were also analyzed.
Furthermore, diurnal change of canopy transpiration was evaluated
by using the newly developed method in which transpiration inhibiting plant hormone abscisic acid
(ABA) was applied to roots, and the integrated canopy transpiration during the corn development stage
for 39 days was evaluated by the dual crop coefficient approach (Allen et al. 1998).
From accumulation
of the respective ions to the corn shoots and the integrated canopy transpiration during the
development stage, the average concentrations of ions in transpiration stream in xylem were estimated.
Ions except for Na+ were highly concentrated in the nighttime xylem sap by the selective and active
nutrients uptake by roots, and in particular, extremely high concentrations of the macronutrients such as
NO3-, PO43- and K+ were found, while these concentrations in the river water, the irrigation water and
the ground water were remarkably lower (Fig.1).
On the other hand, Na+, which is not the essential
element for crop growth, was scarcely absorbed by roots and resultantly accumulated in the ground
water and the rhizosphere with remarkably higher concentrations.
transpiration during the development stage was evaluated as 18.5 L
plant -1,
The integrated canopy
and ions except for Na+
were highly concentrated into transpiration stream in xylem and distributed to shoots (Table 1).
These
results suggest that salinization in crop filed is closely related to the selective and active nutrients
uptake by crop roots.
Keywords : active uptake, transpiration stream, water and ion transport
Reference : Allen et al. (1998) Crop evapotranspiration. FAO IRRIGATION AND DRAINAGE PAPER 56.
Na+ Concentration (mg L 1)
300

[NO3 ]
200
100
0
300
[PO43]
200
100
Fig.1
200
100
[Ca2+]
200
100
0
800
Cl Concentration (mg L 1)
K+ Concentration (mg L 1)
0
300
[K+]
200
100
0
[Na+]
0
300
Ca2+ Concentration (mg L 1)
PO43 Concentration (mg L 1)
NO3 Concentration (mg L 1)
300
[Cl]
600
400
200
0
Yellow Irrigation Ground Exudate
River
water
water
Yellow Irrigation Ground Exudate
River
water
water
Concentrations of NO3-, PO43-, K+, Na+, Ca2+ and Cl- ( [NO3-], [PO43-], [K+], [Na+], [Ca2+] and
[Cl-] ) in the Yellow River, the irrigation water, the ground water and the nighttime exudate from the stem
stump.
Table 1
Ion contents in corn shoot on 7 June and 15 July, ion accumulation between 7 June and 15
July, and average ion concentrations in transpiration stream in xylem sap.
PO43
K+
Na+
Ca2+
Cl
11.6
99.2
6.7
17.2
28.1
271.0
1389.7
84.2
329.1
573.2
(mg shoot1)
259.4
1290.5
77.5
311.9
545.1
(mg L1)
14.0
69.8
4.2
16.9
29.5
Units
Ion contents in shoot
7 June
(mg shoot1)
15 July
Ion accumulations
in shoot (7 Jun.15Jul.)
Ion concentrations
in transpiration stream