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REGULAR ARTICLE
Physiological and morphological traits related
to water use by three rice (Oryza sativa L.) genotypesgrown under aerobic rice systems
Naoki Matsuo & Kiyoshi Ozawa &
Toshihiro Mochizuki
Received: 2 August 2009 /Accepted: 4 May 2010 /Published online: 4 June 2010# Springer Science+Business Media B.V. 2010
Abstract We compared the plant growth, stomatal
conductance (gs), leaf water content (LWC), and root
length density (RLD) ofOryza sativa L. ssp. japonica
cv. Sensho (traditional upland), ssp. indica cv.
Beodien (traditional upland), and ssp. japonica cv.
Koshihikari (improved lowland) under two aerobic
rice systems [well-irrigated (WI) and water-saving
(WS) treatments]. Irrigation water was applied every
2 days from 21 to 68 days after sowing (DAS) and
everyday thereafter in WI treatment and it was applied
when soil water potential at 15 cm depth reached
15 kPa from 21 to 68 DAS and every 2 days
thereafter in WS treatment to impose repetitive water
stress. WS treatment used 35% less water than WI.
Leaf area index (LAI) and shoot dry weight (SDW)
were the lowest for Koshihikari in both treatments
and the ratio of LAI and SDW in WS treatment to that
in WI treatment was the lowest in Koshihikari. This
indicates that aerobic cultivation was not suitable forKoshihikari even under well-irrigated conditions and
that the effect of repetitive water stress was the most
serious in Koshihikari. Midday gs of Sensho and
Beodien in WS treatment were affected by irrigation,
whereas that of Koshihikari was low and stable. LWC
of Koshihikari was smaller than those of upland
genotypes in both treatments. LWC of upland
genotypes in WI and WS reached maximum and
minimum values at predawn and evening, respective-
ly, and recovered at night, but LWC of Koshihikari in
WS treatment did not recover at night. RLD of uplandgenotypes was higher than that of Koshihikari, but no
significant differences were observed among treat-
ments. These results indicate that genotypic difference
of physiological traits under aerobic conditions (both
WI and WS) was caused by the genotypic difference
of water uptake capacity, which can be partly caused
by the RLD. In Koshihikari, however, the LWC
difference between treatments can not be explained
only by the RLD. Further studies will be needed to
Plant Soil (2010) 335:349361
DOI 10.1007/s11104-010-0423-1
Responsible Editor: Len Wade.
N. Matsuo (*)
Graduate School of Bioresource and Bioenvironmental
Sciences, Kyushu University,
111 Harumachi, Kasuya-cho, Kasuya-gun,
Fukuoka 811-2307, Japan
e-mail: [email protected]
K. Ozawa
Japan International Research Center for Agricultural
Sciences,
1091-1, Maezato-Kawarabaru,
Ishigaki, Okinawa 907-0002, Japan
T. Mochizuki
Faculty of Agriculture, Kyushu University,
111 Harumachi, Kasuya-cho, Kasuya-gun,
Fukuoka 811-2307, Japan
Present address:
N. Matsuo
Lowland Crop Rotation Research Team, National
Agricultural Research Center for Kyushu Okinawa Region,
496 Izumi, Chikugo,
Fukuoka 833-0041, Japan
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clarify physiological mechanism responsible for the
water uptake capacity of roots in aerobic rice systems.
Keywords Aerobic rice system . Lowland rice .
Root systems . Stomatal conductance . Upland rice .
Water-saving cultivation
Abbreviations
AWD alternate wetting and drying system
DAS days after sowing
gs stomatal conductance
L0 root hydraulic conductance
LA leaf area
LAI leaf area index
Lpr root hydraulic conductivity
LWC leaf water content
LWP leaf water potential
RLD root length densityRWD root weight density
SDW shoot dry weight
SMC volumetric soil moisture content
SWP soil water potential
WI well-irrigated
WS water-saving
WUE water-use efficiency
Introduction
Rice is one of the worlds main staple crops and
provides the necessary daily calories for millions of
people (Kush 1997). More than 90% of the worlds
rice is produced and consumed in Asia (FAO 1997),
and rice production must be increased by an estimated
56% over the next 30 years to keep up with
population growth and income-induced demand for
food in most Asian countries (Hossain 1997), where
about 75% of total rice production comes from
irrigated lowlands (Maclean et al. 2002). Irrigatedrice accounts for about 50% of the total amount of
water diverted for irrigation, which itself accounts for
80% of the fresh water diverted (Guerra et al. 1998).
However, an increasing scarcity of fresh water threat-
ens the sustainability of irrigated rice ecosystems
(Guerra et al. 1998; Tuong and Bouman 2003): this
problem has been caused by population growth,
increasing urban and industrial development, and
decreasing availability of usable water due to pollu-
tion and resource depletion (Bouman and Tuong
2001). Therefore, the development of new rice
cultivation techniques and cultivars are required to
reduce water consumption in rice production systems.
Various field techniques to save irrigation water
have been explored. They include direct seeding,
keeping the soil saturated, and alternate wetting anddrying systems (AWD) in lowland fields. Bouman
and Tuong (2001) concluded that, compared with
continuously flooded conditions, small yield reduc-
tions (0 to 6%) occurred under saturated conditions,
but larger reductions (10 to 40%) occurred under
AWD, when soil water potential (SWP) during dry
phase reached values between 10 and 40 kPa.
A new water-saving technology is called aerobic
rice system (Bouman 2001; Bouman et al. 2005). In
aerobic rice systems, fields remain unsaturated
throughout the growing season, as in wheat or maizecultivation. Water can be supplied by surface irriga-
tion (e.g. flush or furrow irrigation) or by sprinklers,
but in both cases, the goal is to keep the soil wet but
not flooded or saturated. Aerobic rice systems could
reduce water inputs by 11.5 to 50.7% in the
Philippines (Belder et al. 2005; Bouman et al.
2005), by 29.2 to 65.3% in northern China (Bouman
et al. 2006; Yang et al. 2005), and by 62.5 to 70.8% in
Japan (Matsuo and Mochizuki 2009) compared with
flooded paddy conditions. Matsuo and Mochizuki
(2009) showed that aerobic rice systems could savemore than 47% of irrigation water in comparison with
AWD. Thus, aerobic rice systems have the potential
to reduce irrigation requirements more than other
techniques that have been developed.
In practice, irrigation is applied to bring the soil water
content up to field capacity after the water potential has
reached a certain lower threshold, such as 15 or
30 kPa at a depth of 15 cm (Bouman et al. 2005;
Matsuo and Mochizuki 2009). As a result, the soil in
aerobic rice systems undergoes repetitive cycles of wet
conditions and relatively mild drought stress. The mostimportant concern is to save as much water as possible
while maintaining yields at 70 to 80% of the yield for
high-input flooded rice (Belder et al. 2005). Numerous
reports have focused on drought resistance in rice
under temporary or long-term water deficits (Cooper
1999; Fukai and Cooper 1995; Jackson et al. 1996;
Lafitte et al. 2003; Ludlow and Muchow 1990; Turner
1986), and many traits that potentially contribute to
drought resistance have been reviewed (Cooper 1999;
350 Plant Soil (2010) 335:349361
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Fischer et al. 2003; Fukai and Cooper1995; Kamoshita
et al. 2008; Lafitte et al. 2003; Nguyen et al. 1997;
Price and Courtois 1999). However, the soil moisture
conditions under aerobic rice systems should differ
from those under temporary or long-term water deficits
(i.e. alternately wet conditions and mild water stress vs.
temporary mild or severe water stress).Despite this difference, many studies of aerobic rice
systems have focused mainly on comparing agro-
nomic traits such as shoot growth, yield, and yield
components of aerobic rice with those observed under
flooded paddy conditions (Bouman et al. 2005; Peng et
al. 2006; Yang et al. 2005). This may be because the
concept of aerobic rice is quite new and the difference
in soil water conditions between aerobic rice system
and temporary water stress conditions is not yet
appreciated. Furthermore, there are no studies which
have compared the agronomical, morphological and physiological traits between the two situations. This
confusion may delay the development of a unified
understanding of important traits for aerobic rice
systems. Bouman et al. (2006) investigated root traits
such as root length density (RLD), root weight density
(RWD), and rooting depth and pattern for two aerobic
rice genotypes and one lowland genotype under
aerobic rice systems. They found no significant differ-
ence in root traits among the three genotypes, although
the yields of the aerobic rice genotypes were higher
than that of the lowland genotype. Matsuo et al. (2009)reported that repetitive water stress reduced the root
hydraulic conductance (L0) more in a lowland rice
genotype than it did in two upland rice genotypes.
Matsuo and Mochizuki (2009) investigated the pre-
dawn leaf water potential (LWP) and bleeding rate of
these three genotypes under aerobic rice systems and
reported that these two parameters of a lowland
genotype under aerobic rice systems were significantly
lower than those under a flooded paddy cultivation,
while no significant difference were observed among
cultivation methods in two upland genotypes. Numer-ous studies proposed the importance of water-related
traits, such as root traits (e.g. deep root and RLD),
LWP and plant water conductivity in upland rice
cultivations with or without drought (reviewed by
Kamoshita et al. 2008). Because aerobic rice systems
are partly similar cultivation methods with upland rice
cultivation, these traits may also play important roles in
aerobic rice systems. However, few studies verifies the
importance of those traits under aerobic rice systems.
The aim of the present study was to analyze
genotypic differences in morphological and physio-
logical traits related to plant water status, such as leaf
water content (LWC), stomatal conductance (gs), and
RLD, by comparing two upland rice genotypes and
one lowland rice genotype whose growth and yield
responses to aerobic rice systems were previouslyshown to differ (Matsuo and Mochizuki 2009),
under two aerobic rice systems.
Materials and methods
Plant materials
We used three rice (Oryza sativa L.) genotypes in this
study: a traditional japonica upland genotype, Sensho;
a traditional indica upland genotype, Beodien; and animproved lowland japonica genotype, Koshihikari.
Sensho and Beodien can grow equally well under
aerobic rice systems and flooded paddy conditions and
their yields under aerobic rice systems are almost same
as those under flooded paddy conditions. In contrast,
Koshihikari cannot grow well under aerobic rice
systems and its grain yield under aerobic rice systems
decreases by 80% compared with that under flooded
paddy conditions (Matsuo and Mochizuki 2009).
Experimental design
The lysimeter experiment was carried out in 2007 in a
plastic greenhouse at the Japan International Research
Center for Agricultural Sciences (JIRCAS), Tropical
Agriculture Research Front, Okinawa, Japan. The soil
contained 15.9% clay, 10.4% silt and 73.7% sand (i.e. it
was a sandy clay loam). Its bulk density was
1.46 g cm3, its volumetric water content at field
capacity (moisture remaining 24 h after irrigation) was
36.0%, and the permanent wilting point (1.5 MPa)
occurred at 7.0% moisture content. We applied twowater regimes [the well-irrigated (WI) and water-saving
(WS) treatments] in a randomized complete block
design with two replications under aerobic soil con-
ditions. About 1 year before sowing the seeds, we
installed cellulose acetate butyrate minirhizotron
observation tubes (180 cm long by 5 cm in diameter;
Bartz Technol. Co., Santa Barbara, CA, USA) in the
central row of each replication in WS treatment at an
angle of 45 from the vertical. A 90-cm section of
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the tube projected above the soil surface, and we
wrapped it with aluminum foil and capped it with a
rubber stopper.
Culture details
On 24 April, we sowed groups of three to four pre-germinated seeds at a spacing of 3015 cm in a
bottomless soil-filled container (180-cm length, 90-cm
width, and 90-cm depth) buried in the soil. Seedlings
were thinned to one plant per hill at 21 days after sowing
(DAS). We supplied 13 mm of irrigation daily in both
treatments until 21 DAS using line-source sprinklers.
We then implemented the two water treatments. In WI
treatment, we supplied 10 mm of irrigation water every
2 days from 22 to 67 DAS and everyday after 68 DAS
not to impose water stress on plants. In WS treatment,
we supplied 10 mm of irrigation water wheneverthe soil water potential (SWP) at a 15-cm depth
reached 15 kPa from 22 to 67 DAS and every
2 days after 68 DAS to impose repetitive water
stress on plants, which was often observed in
aerobic rice systems (e.g. Yang et al. 2005). In this
treatment, SWP was measured using tensiometers (as
described in the next section). The decision to re-
initiate irrigation in WS treatment therefore varied
among the plots. We supplied chemical fertilizers at
a rate of 4 g N m2, 12 g P m2, and 12 g K m2 as
basal dressings 1 day before sowing, and thenapplied N fertilizer at a rate of 4 g m2 at 28 and
53 DAS as top dressings.
Measurements and calculations
The JIRCAS weather station recorded daily mean,
maximum, and minimum temperatures and solar
radiation. The soil temperature was monitored from
69 to 76 DAS at a depth of 15 cm from the soil
surface. SWP was monitored from 28 DAS using
tensiometers (DIK-3126, Daiki Rika Kogyo Co., Ltd,Saitama, Japan) installed at depths of 15, 22.5, 30,
and 50 cm below the soil surface in WS treatment. It
was only monitored at a depth of 15 cm in WI
treatment. SWP was measured around 17:00 h every
day and then irrigation water was applied whenever
SWP at a depth of 15 cm decreased below 15 kPa.
Before beginning our experiment, we determined the
relationship between SWP and volumetric soil mois-
ture content (SMC) (data not shown) and the results
of calculated SMC were shown. Because the tensi-
ometers could not read the correct SWP values for
Sensho in WS treatment at 65 DAS, we determined
SMC gravimetrically thereafter.
We measured the leaf area (LA) and leaf length of
each genotype at 40 and 78 DAS. LA was measured
with an AAM-8 leaf area meter (Hayashi Denko Co.Ltd., Tokyo, Japan). We performed simple curve
linear regression to determine the relationship be-
tween leaf length and LA for each genotype. The
correlation coefficients of the equations was signifi-
cant (P
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relationship between LWC and leaf water potential
(LWP) that is often used as plant water status under
water stress conditions. The sampling procedure was
the same as in the LWC measurements, except that
the length of the leaf sample was 10 cm (at a distance
of 515 cm from the leaf tip). Excised leaves were
subdivided into 2-cm pieces and placed into samplecups, then LWP was measured with a WP4 dewpoint
psychrometer (Decagon Devices Inc.). LWC was then
determined as described above. We performed simple
linear regression to determine the relationship be-
tween LWC and LWP within each water treatment
(WI vs. WS) and genotype. We used one leaf section
from each replication at each sampling time. The
correlation coefficients of the equations were signif-
icant (P
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and every 2 days in WS treatment during this period.
SMC was highest in Koshihikari at all depths,
followed by Beodien. SMC at a depth of 15 cm in
WI treatment averaged 28.1 2.5% (meanSE) and
32.81.6% before and after 69 DAS, respectively
(data not shown). Figure 3 shows soil temperature of
Sensho at a depth of 15 cm in both water treatments
from 69 to 76 DAS. The soil temperature in WI
treatment fluctuated between the same ranges of
temperatures during this period. Although the soil
temperature in WS treatment was the same as that in
WI 1 day after irrigation, it increased to a higher
daytime value 2 days after irrigation. The cumulativedifference in soil temperature between WI and WS
treatment totaled 34.7C on hourly basis 2 days after
irrigation. The same trend was observed in the other
genotypes (data not shown).
Leaf and shoot growth
Figure 4 shows LAI growth for the three genotypes in
the two water treatments. Sensho showed faster LAI
development than the other genotypes in both water
treatments. The LAI of Beodien was the highest at 79DAS, but did not differ significantly from that of
Sensho. The LAI of Koshihikari was significantly
lower than those of the other two genotypes at all
0
10
20
30
40
50
SMC(%v
/v)
15 cm 22.5 cm
30 cm 50 cm
0
10
20
30
40
50
SMC(%v
/v)
010
20
30
40
50
28 36 44 52 60 68
DAS (day)
SMC
(%v
/v)
(a)
(b)
(c)
Fig. 1 Soil moisture content (SMC) of the three genotypes in
the water-saving treatment at depths of 15, 22.5, 30, and 50 cm
from 28 to 68 DAS. (a) Sensho; (b) Beodien; (c) Koshihikari.
Data for one replication are shown, because the timing of
irrigation differed among the plots. SMC at a depth of 15 cm in
the well-irrigated treatment during this period averaged 28.1
2.5% (meanSE)
Table 1 Monthly mean air temperature, maximum air temperature, minimum air temperature, and solar radiation
Mean temp.
(C)
Mean maximum temp.
(C)
Mean minimum temp.
(C)
Solar rad.
(MJ m2 day1)
April 22.0 24.3 19.7 12.0
May 24.9 27.7 22.0 17.6
June 28.0 30.5 26.0 18.8July 29.6 32.2 27.3 22.4
0
10
20
30
40
50
69 70 71 72 73 74 75 76
DAS (day)
SMC(%v
/v)
Sensho
Beodien
Koshihikari
Fig. 2 Soil moisture content (SMC) of the three genotypes
in the water-saving treatment at a depth of 15 cm from 69 to
76 DAS. Because similar trends were observed at the other
depths, SMC at a depth of only 15 cm is shown. Data are
meansSE. SMC in the well-irrigated treatment at a depth of
15 cm during this period averaged 32.81.6% (meanSE)
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times in both water treatments. LAI tended to be higher
in WI treatment than in WS treatment until 65 DAS in
Sensho and 72 DAS in Beodien, but thereafter thevalues did not differ between treatments. The LAI of
Koshihikari was the same in both treatments until 65
DAS, but thereafter LAI was significantly higher in WI
treatment, reaching nearly twice that in WS treatment
by the end of the experiment.
Table 2 shows the SDW and WUE values for the
three genotypes at the end of the experiment. Sensho
had the highest SDW and WUE in both water
treatments, followed by Beodien. The SDW values
for Sensho and Beodien in WS treatment were
approximately 80% of those in WI treatment, whereasthat of Koshihikari in WS treatment was only 54% of
that in WI treatment. A two-way ANOVA detected
the significant effects of genotype and water treat-
ments on SDW, but their interaction was not detected.
WUE of Sensho was the highest, followed by
Beodien in both water treatments. WUE of Sensho
and Beodien were 20% or more higher in WS
treatment than in WI treatment, whereas that of
Koshihikari in WS treatment was only 86% of that
in WI treatment. A two-way ANOVA revealed a
significant genotypic effect on WUE.
Stomatal conductance and leaf water content
Figure 5 shows the midday gs values for the three
genotypes from 69 to 76 DAS. The gs values of
Sensho and Beodien were similar in WI treatment
(about from 500 to 700 mmol m2 s1) and both
were higher than those of Koshihikari (about from
400 to 550 mmol m2 s1). The gs values for Sensho
and Beodien were strongly affected by irrigation
in WS treatment: they were between 260 and400 mmol m2 s1 1 day after irrigation and
decreased to less than 170 mmol m2 s1 2 days
after irrigation. The gs values for Koshihikari were
relatively stable at 200300 mmol m2 s1 in WS
treatment, regardless of irrigation.
Figure 6 shows the daily changes in gs and LWC at
75 DAS. The gs values did not differ (less than
100 mmol m2 s1) among the water treatments and
genotypes at night (from 0:00 to 6:00 h and from
21:00 to 24:00 h). The daytime (from 9:00 to 18:00 h)
gs values of Sensho in WI treatment tended to behigher, followed by Beodien, and Koshihikari in this
order. The daytime gs values of Sensho and Beodien
averaged about 50% lower in WS treatment than in WI
treatment. In Koshihikari, however, the daytime gsvalues in WS treatment was on average 21% lower
than those in WI treatment. The LWC values were
slightly lower (though almost insignificant) in WS
treatment than in WI treatment throughout the day in
all three genotypes and the LWC values in WS
treatment were 1.5 to 6.9% lower than those in WI
treatment. The LWC values of Sensho and Beodienwere similar, and tended to be higher than those of
Koshihikari in both water treatments. LWC reached its
maximum and minimum values at 3:00 to 6:00 h and
15:00 to 18:00 h, respectively, in each water treatment
and genotype, with one exception: LWC of Koshihikari
in WS treatment reached its maximum at 3:00 h, but
did not recover at night (after 18:00 h), and the LWC
value at 24:00 h in WS treatment was significantly (P
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