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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,


Present address:

N. Matsuo

Lowland Crop Rotation Research Team, National

Agricultural Research Center for Kyushu Okinawa Region,

496 Izumi, Chikugo,



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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

Plant Soil (2010) 335:349361 351


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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)

354 Plant Soil (2010) 335:349361


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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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