Rice Science, 2012, 19(1): 44−48
Copyright © 2012, China National Rice Research Institute
Published by Elsevier BV. All rights reserved
Effects of Aerated Irrigation on Leaf Senescence at Late Growth Stage
and Grain Yield of Rice
ZHU Lian-feng, YU Sheng-miao, JIN Qian-yu
(State Key Laboratory of Rice Biology, China National Rice Research Institute, Hangzhou 310006, China)
Abstract: With the japonica inbred cultivar Xiushui 09, indica hybrid combinations Guodao 6 and Liangyoupeijiu as materials,
field experiments were conducted in 2007 and 2008 to study the effects of aerated irrigation on leaf senescence at late
growth stage and grain yield of rice. The dissolved oxygen concentration of aerated water evidently increased and decreased
at a slow rate. The soil oxidation-reduction potential under aerated irrigation treatment was significantly higher than that of the
CK, contributing to significant increases in effective panicles, seed setting rate and grain yield. In addition, the aerated
irrigation improved root function, increased superoxide dismutase activity and decreased malondialdehyde content in flag
leaves at post-flowering, which delayed leaf senescence process, prolonged leaf functional activity and led to enhanced grain
filling.
Key words: rice; aerated irrigation; physiological characteristics; leaf senescence; yield
Plant roots consume oxygen during growth and
development, and sufficient oxygen should be available
for root consumption. Rice is one of the wetland
plants which has well-developed aerenchyma, a
continuous system of air spaces in the plant that
allows diffusion of O2 from the shoot or the air to the
roots. Although the aerenchyma system avoids
inhibition of respiration due to lack of O2, which is
inevitable for the plants non-adapted to wet soils, soil
aeration is still a key factor that affects the growth and
development of rice (Zhang et al, 2000; Stefano et al,
2002; Fu et al, 2007; Ding et al, 2008; Dai et al, 2008).
Our predecessors understood the relation between
oxygen and rice growth mostly through the study of
rice irrigation patterns. Aerobic irrigation measurements,
such as intermittent irrigation, wetting irrigation and
dry-wet alternate irrigation, increased soil oxygen
content, improved soil environment, and enhanced
rice growth and grain yield by appropriate adjustments
of the time, duration and quantity of irrigation
(Cannell et al, 1985; Zhang et al, 2002; Pan et al, 2009;
Liu et al, 2009). However, these irrigation methods
seldom yielded satisfactory results when applied in
large-scale rice production, because of the difficulty in
practical operation, varied weather conditions and other
factors. Air pump aeration and some other measurements
were widely used in drip irrigation system and
horticulture to increase the oxygen content of the water.
These aerated irrigations increased crop rhizosphere
oxygen content and promoted root growth, leading to
Received: 25 July 2011; Accepted: 12 October 2011
Corresponding author: JIN Qian-yu ([email protected])
improved water and fertilizer use efficiency and
enhanced rice production (Zhang et al, 2002; Song et al,
2005). Super-micro bubble (SMB) technology was a
new invention that produced numerous air bubbles
with an average diameter of less than 3 μm in treated
water, and the dissolved oxygen concentration
exceeded the oxygen saturation value in non-treated
water. At present, the studies of super-micro bubble
technology mainly referred to contaminated water
purification or wastewater treatment, while its
application on rice irrigation had not been reported
(Masayuki et al, 2003; Chen et al, 2008). This study
treated irrigation water applying super-micro bubble
technology and assessed the effects of the aerated
irrigation on leaf senescence and grain yield of rice.
We also explored the relationship of oxygen with rice
growth and development for the purpose of enriching
the cultivation theory and providing reference for
super high yield production of rice.
MATERIALS AND METHODS
Design of experiment
The treatments consisted of two kinds of irrigation,
i.e. conventional irrigation with river water (CK) and
aerated irrigation with river water treated by supermicro bubble generating system (Aeration). Aerating
steps: Dig a pit of 3 m × 2 m × 2 m at the irrigation
water inlet to the experiment field, and place in the
super-micro bubble generating system (model MBO75ZS); treat the water over 30 minutes before irrigation,
and then let the river water flow into the top layer of
ZHU Lian-feng, et al. Effects of Aerated Irrigation on Yield and Leaf Senescence at Late Growth Stage of Rice
Measurement and analysis
The effects of super-micro bubble generating system
on the dissolved oxygen concentration were investigated.
The dissolved oxygen concentrations (mg/L) of the
aerated water and non-aerated water were measured
every 12 h using a portable dissolved oxygen meter
(YSI 550A, YSI Environmental, USA).
At the heading stage, select three representative
plants of each treatment. Cut the stems at 10 cm from
the ground with scissors, cover the cutting edge with
pre-weighted cotton, and then wrap with plastic film.
Collect the exudates from18:00 pm to 6:00 am, weigh
the cotton with root exudates, then separate the exudates
into centrifuge tube for analysis. The contents of total
soluble sugar and free amino acids in the root
exudates were determined according to the methods of
Kong et al (2008).
Fresh flag leaf samples were collected every 7 d
after flowering. Superoxide dismutase (SOD) activity
and malondialdehyde (MDA) content were determined
according to the methods of Zhao et al (2002).
Plants in each plot were harvested at maturity for
the determination of grain yield. Yield components
including number of panicles per m2, number of
spikelets per panicle, spikelet filling percentage and
grain weight were determined from the plants of 5
hills. Spikelet filling rate was calculated as the number
of grains that sank to the bottom of a beaker filled
with salt solution with specific gravity of 1.06 as
percentage of total spikelets.
The results were analyzed for variance by ANOVA,
and statistical differences among means of the three
replicates were tested by least significant difference at
the 0.05 probability level with the SPSS13.0 for
Windows. Only the 2008 data were analyzed because
the two separate experiments in 2007 and 2008 gave
very similar results.
RESULTS
Oxygenation effects of super-micro bubble technology
Fig. 1 showed the dynamics of dissolved oxygen
concentration in 2000 L non-treated water (CK) and
aerated water (water aerated for 30 min). After
aeration, the concentration of dissolved oxygen in
irrigated water was 7.93 mg/L, while that of CK was
3.16 mg/L. In natural conditions, the oxygen in the air
will dissolve into water, which finally comes to an
equilibrium. Because the concentration of dissolved
oxygen for CK was lower initially, with the dissolving
of oxygen from air, the oxygen content increased in
CK. The dissolved oxygen concentration reached
super-saturation by aeration, and the super-micro
bubbles collapsed as time passed. The concentration
Dissolved oxygen concentration (mg/L)
the pit water for aeration treatment while the aerated
water outflow from the bottom of the pit through
plastic pipe into the experimental plots. Besides the
two treatments, a standing water layer was maintained
during plant recovery stage, and intermittent irrigation
was applied during the other stages.
Field trials were conducted at the China National
Rice Research Institute, Hangzhou, Zhejiang Province,
China, during the rice growing season (May to
November) of two successive years 2007 and 2008.
The materials used in 2007 were indica hybrid rice
Guodao 6 and japonica inbred rice Xiushui 09, and
indica hybrid rice Liangyoupeijiu and japonica inbred
rice Xiushui 09 were used in 2008. The three rice
materials were chosen because they were planted to a
large extent in Zhejiang Province. Seedlings were
raised in the field with sowing date on 24 May (hybrid
rice) or 30 May (inbred rice) and transplanted on 24
June at a hill spacing of 0.3 m × 0.2 m with one
seedling per hill (hybrid rice) or at a hill spacing of
0.2 m × 0.2 m with four seedlings per hill (inbred rice).
The plot dimensions were 8.0 m × 5.2 m. A completely
randomized block design with three replications was
used in the study. The soil of the field was loam clay
with 36.8 g/kg organic matter and available N-P-K at
142.0, 17.0 and 14.1 mg/kg, respectively. A sum of
63.0 kg N, 72.0 kg P2O5 and 67.5 kg K2O as
compound fertilizer with N:P:K = 14:16:15, and 27.0
kg of nitrogen per hectare were applied in the form of
urea and incorporated before transplanting. Nitrogen
as urea was applied at mid-tillering (45.0 kg/hm2) and
panicle initiation stage (15.0 kg/hm2), and potassium
as potassium chloride (60% K2O) was also applied at
panicle initiation stage (52.5 kg/hm2).
45
Fig. 1. Dissolved oxygen concentrations in the aerated water and
non-treated water.
Rice Science, Vol. 19, No. 1, 2012
46
of dissolved oxygen declined slowly and decreased to
6.87 mg/L after 104 h, which equals to that of CK.
Using the aeration technology, the dissolved oxygen
concentration is enhanced, exceeding that of CK
within 100 h after the treatment, and its decline is
delayed.
Soil oxidation-reduction potential increased from
panicle initiation stage of rice plants (Fig. 2), which
may be attributed to the water regime adopted in this
experiment. Comparison between the two treatments
showed that the soil oxidation-reduction potential of
aeration treatment was higher than that of CK during
the entire measurement periods, especially for heading
stage. The effects of aeration on the two conventional
cultivars were identical, but more obvious on the
hybrid Liangyoupeijiu. Under the same conditions, the
aeration can increase the oxygen content in soil
significantly, and improve the oxidation-reduction
potential in the root zone.
Effects of aerated irrigation on rice grain yield and
its components
In the two years’ experiment, the grain yields of the
three materials by aerated irrigation were significantly
higher than those of CK (Table 1), and the increasing
rates were 8.45% (2007) and 6.23% (2008) for Xiushui
09, 9.13% for Guodao 6 (2008), and 7.49% for
Liangyoupeijiu (2008), respectively. For yield
components, the panicle numbers per hectare by
aeration were all higher than those of CK. The tiller
dynamics showed that aerated irrigation mainly
increased the tiller emergence at early tillering stage,
but slightly influenced the maximum tiller number,
indicating that the early tillers at the lower nodes
contributed to the increase of the panicle number.
Compared with CK, the panicle number of aerated
irrigation treatment was increased at 4.8%–7.4%. In
addition, the number of spikelets per hectare and seedsetting rate of aerated irrigation were significantly
higher than those of CK, and the 1000-grain weight of
aerated irrigation also increased but at non-significant
level. The number of spikelets per panicle of aeration
treatment was equal to or a little below the number of
CK, with the lowest for Xiushui 09. Furthermore,
aerated irrigation increased the seed-setting rate,
completely-filled grain number and 1000-grain weight,
which led to significantly increased grain yield.
Effects of aerated irrigation on contents of soluble
sugar and free amino acids in the root exudates
Rice has maximum exudate quantity at heading
Fig. 2. Effects of aerated irrigation on soil oxidation-reduction potential.
T, Tillering stage; PI, Panicle initiation stage; H, Heading stage; M, Milky ripening stage. * and ** indicate significant differences at the 0.05 and
0.01 levels, respectively, compared with conventional irrigation (CK).
Table 1. Effects of aerated irrigation on rice grain yield and its components.
Year
Rice material
Xiushui 09
Treatment
No. of panicles
per hectare (×104)
Aerated irrigation
334.9*
CK
302.8
2007
Guodao 6
Aerated irrigation
188.7*
CK
178.1
Xiushui 09
Aerated irrigation
307.1*
CK
270.3
2008
Liangyoupeijiu Aerated irrigation
253.8*
CK
237.9
* indicates significant difference at the 0.05 level.
No. of spikelets
per panicle
131.0
136.7
194.7
196.5
115.5
122.0
155.9
154.7
No. of spikelets Seed-setting
per hectare (×104)
rate (%)
49343.9*
48036.7
48804.1*
47713.5
39262.8*
37289.9
52907.8*
51068.3
91.13*
86.15
75.30*
71.26
90.36*
85.28
74.79*
70.38
1000-grain
weight (g)
Grain yield
(t/hm2)
25.54
24.90
29.24
28.74
25.28
24.67
25.42
24.94
7.83*
7.22
6.93*
6.35
7.50*
7.06
8.32*
7.74
ZHU Lian-feng, et al. Effects of Aerated Irrigation on Yield and Leaf Senescence at Late Growth Stage of Rice
Table 2. Influence of aerated irrigation on exudate quantity and its
soluble sugar and free amino acid contents.
Total exudates Soluble sugar Free amino
Variety
Treatment
acids content
content
per tiller
(µg/mL)
(µg/mL)
(mg/h)
Aeration
51.46**
25.54**
106.18**
Xiushui 09
CK
38.59
15.96
75.97
Aeration
60.90**
14.46**
59.66**
Liangyoupeijiu
CK
49.55
12.75
50.80
** indicates significant difference at the 0.01 level.
stage. Shown as the Table 2, the exudate quantity,
contents of total soluble sugar and free amino acid in
the root exudates of Xiushui 09 and Liangyoupeijiu by
aerated irrigation were significantly increased in
comparison with those of CK (P < 0.01).
Effects of aerated irrigation on SOD activity and MDA
content in flag leaf at the late growth stage of rice
From Fig. 3, we can see that the flag leaf SOD
activity of Xiushui 09 and Liangyoupeijiu by aerated
irrigation was significantly higher than that of CK
from flowering to 21 d after flowering. The SOD
activity of the two varieties under both treatments
decreased from flowering, and the decreasing speed
was slow during the first 14 d after flowering.
However the SOD actitiviy decreased faster after 14
days from flowering. Compared with CK, the
decreasing speed of flag leaf SOD activity of aerated
irrigation was smaller. The dynamics of leaf MDA
content showed that the MDA content of aerated
irrigation was lower than that of CK from flowering to
21 days after flowering and that the content difference
was small at the first 7 days, then became large from 7
to 21 d after flowering. Compared with CK, the MDA
content of aerated irrigation was lower from flowering,
and the difference became greater from 7 d after
flowering.
47
DISCUSSION
Root activity is a key requirement for the
improvement of fertilizer and water use efficiency,
prevention of leaf premature senescence and
maintenance of high photosynthetic capacity at the
late growth stage of rice. Oxygen-rich environment is
very conducive to the emergence and growth of roots
and to the maintenance of high root activity. Lin et al
(2005) reported that aerobic irrigation improved the
growth environment of rice root, leading to
significantly increased root exudates, root metabolism
and nutrient use efficiency. Root activity has
immediate and direct effects on leaf photosynthesis
(Zhao et al, 2007). Our experiment showed the
exudate quantity of rice roots under aerated irrigation
was obviously higher than that of CK, namely higher
root activity at heading stage. Moreover, the contents
of free amino acids and soluble sugar in the root
exudates of rice by aerated irrigation were also higher
than those of CK, and this was indicative of increased
nitrogen absorption and assimilation, which would
satisfy the nitrogen requirement of the plants and in
return, translocate adequate photosynthates to root
system. Higher free amino acids content was
favorable to the synthesis of chlorophyll and proteins
in leaves, and conducive to the prevention of protein
decomposition, which may result from the lack of free
amino acid. Stronger root activity ensured adequate
water supply for shoots, which enhanced the stomatal
conductance and transpiration rate. Therefore, the
photosynthetic capacity of leaves increased with the
improvement of root function, and this is in agreement
with the result of Zhang et al (2008).
Leaf senescence at the late growth stage of rice will
lead to loss of photosynthetic capacity and serious
Fig. 3. Influence of aerated irrigation on SOD activity and MDA content in rice flag leaf.
Rice Science, Vol. 19, No. 1, 2012
48
impact on grain filling. Wang et al (2008) reported
that the increase of relative content of reactive oxygen
species was the main reason for impaired photosystem
of plants. The integrity of the membrane system is
essential for normal photosynthetic growth of green
plants, while the SOD plays a major role in the
protection of the integrity of the membrane system.
This experiment showed that aerated irrigation
obviously increased the SOD activity of flag leaves at
post-flowering, and compared with CK, the flag leaf
SOD activity of aerated irrigation decreased slowly.
The MDA content of aerated irrigation was lower than
that of CK, and increased slowly as the growth
progressed. This indicates that aerated irrigation
enhanced the activity of antioxidant enzymes of rice
leaves. As a result, the production and scavenging of
reactive oxygen species comes to equilibrium, and the
damage by reactive oxygen species decreases.
Consequently, leaf senescence process is delayed, leaf
functional activity prolonged and grain filling
promoted, which contribute to the increase of grain
yield.
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