Introduction
Waterlogging is an abiotic stress and
characterized by the saturation of root zone soil by water, ultimately
resulting in anoxia or oxygen deprivation (Sairam et al. 2009; Xu et al.
2016). It
has increasingly become one of the major constraints to crop growth and
production, resulting in severe economic losses (Shabala 2011; Zeng et al. 2013). Waterlogging is often encountered over vast regions of the world
due to excessive rainfall, lack of soil drainage, and irregular topography (Xu et al. 2014, 2016). It has been estimated that nearly 10% of global
irrigated land has suffered from waterlogging, causing a yield loss between 40 and 80% for
grains (Zeng et al.
2013; Zheng et al. 2017). Therefore, it is necessary to identify suitable
agricultural management strategies to alleviate the negative impact of
waterlogging on crop growth, yield and ultimately total production.
The exploration of crop tolerance towards
waterlogging stress is a potential strategy, especially where the current
agricultural drainage infrastructure is poor, particularly in rural areas (Setter and Waters 2003; Shao et al. 2013). The
tolerance of crops towards waterlogging stress is related to the crop genotype
and the growth stage when waterlogging occurs, the duration of waterlogging,
and the depth of the groundwater (Xu et al.
2015; Pampana et al. 2016; Ghobadi et al. 2017). As
one of the most widely cultivated crops, winter wheat (Triticum aestivum
L.) is highly sensitive to waterlogging during the reproductive phase, especially
during booting, heading, flowering and filling stages (de San Celedonio
et al. 2014; Marti et al. 2015; de San Celedonio
et al. 2017).
However, studies about the duration of waterlogging stress for winter wheat
have shown different results in terms of the impact on grain yield. Some
studies have shown that short-term waterlogging, even for one or two days, can
reduce grain yield (Melhuish
et al. 1991; Malik et al. 2002),
while Meyer and Barrs (1988)
reported no adverse effects on yield after four days of waterlogging. In areas
of shallow groundwater tables, the impact of waterlogging can be severe due to
oxygen deprivation in the root zone (Malik et al.
2001). Multiple studies have identified the trend of
winter wheat growth and grain yield under waterlogging stress by examining
different duration or groundwater depth throughout the whole growth period (de San Celedonio et al. 2014; Pampana et
al. 2016; Ghobadi et al. 2017).
However, few studies have examined the individual and interactive effects of
duration and groundwater depth of waterlogging during one growth stage,
particularly during anthesis.
When plants are exposed to waterlogged
conditions, the stomatal resistance of leaves increases, which affects several
physiological and biochemical processes (Malik et al.
2001; Shao et al. 2013). Some
researchers have reported that waterlogging decreased the stomatal conductance,
resulting in a reduction in the transpiration and photosynthetic rates of
winter wheat (Zhang et al. 2008; de San Celedonio
et al. 2014).
However, waterlogged plants generally have shown a potential to recover from
waterlogging stress (Pang et al. 2004; de
San Celedonio et al. 2017). The
dynamics of these physiological traits during the waterlogging and subsequent
recovery period have rarely been studied. It is, therefore, essential to
understand the mechanisms of winter wheat waterlogging tolerance during
anthesis in order to maintain crop production.
The present study therefore explored appropriate
water management strategies to improve the waterlogging tolerance of
winter wheat during the anthesis phase. The
objectives of this study were to evaluate the impacts of waterlogging stress
during the anthesis phase on the growth and physiological traits of winter wheat
and establish their quantitative relationship under waterlogging stress.
Materials and Methods
Experimental
details
The
experiments were carried out in concrete lysimeters at the water saving park at
Hohai University in Nanjing, P.R. China (31°57′ N, 118°50′ E, 144 m
a.s.l) in 2008–2009
(2009 season) and 2009–2010
(2010 season) growing season of winter wheat. The long-term annual
precipitation in the area is 1,051 mm, and pan evaporation is 900 mm, based on
the climate data from 1951 to 2009. The rainfall, relative humidity
and average temperature during the winter wheat growing period, as measured by
an automated weather station, are presented in Fig. 1. There were 15 lysimeter
test-pits with 2.5 m lengths, 2.0 m widths, and 2.0 m depths with planting
areas of approximately 5 m2. The lysimeters were built of concrete
and sealed with waterproof material, and a mobile rainout shelter was installed
on the ground. The lysimeters contained loamy clay soil, with a mean dry density
of 1.46 g cm-3 and 1.45 g cm-3, field water capacity of
26.47 and 27.31%, and soil organic matter of 2.41 and 2.32% for 0–30 cm soil
layer in 2009 and 2010 seasons, respectively. The groundwater level of the
lysimeters was adjusted by using a float valve that controlled the solenoid
valve for each treatment. An irrigation system was equipped to supply
irrigation for each lysimeter through pipelines, and the water amount was
recorded using a flow gauge.
Winter wheat (Triticum
aestivum L. ‘Yangmai 14’) was hand sown evenly with a 240 seeds/m2
seeding rate on November 12, 2008 and November 20, 2009.
Ten days prior to sowing, a compound fertilizer (N:P2O5:K2O =
15:10:15) was broadcasted uniformly to all lysimeters as basal fertilizer at a
rate of 400 kg·ha−1. The winter wheat crops were irrigated
when the soil water content of each treatment reached 50% of field capacity.
Experimental design
The experiments were arranged in a complete
randomized block design with three replicates. Wheat plants not exposed to
waterlogging stress were considered as the control, waterlogged stress was
developed by keep groundwater depth to 600 mm below ground during the tillering
phase; at 800 mm below ground during the jointing–booting phase; and at 1,000
mm below ground during the heading, anthesis, and milky phase. Plants during the anthesis phase were
subjected to waterlogging stress with the groundwater depth of 200 and 400 mm
below ground level each for 3 days, respectively. Other treatments were exposed to 5 days of waterlogging
stress with the groundwater depth of 200 and 400 mm below ground level
respectively. All
waterlogging treatments were imposed on April 23, 2009 and April 29, 2010.
Within two days after the end of each treatment, the groundwater level was
adjusted to match the control treatment.
Observations
and measurement
Plant
height and leaf area of ten randomly tagged plants in each lysimeter were
monitored every ten days. The leaf area was measured with Li-3100C (Li-Cor, Lincoln, NE, USA). The rate of photosynthesis (PN), stomatal conductance (gs) and transpiration (E) of the second or third fully expanded
leaf of each individual plant were measured one day prior to waterlogging, one
day before beginning drainage, three and ten days after waterlogging withdrawal,
using a Li-6400XT (Li-Cor, Lincoln, NE, USA) during
full sun/daylight between 9:00 to 11:00 a.m.
One day before harvest, ten randomly selected
plants from each lysimeter were excavated using a flat shovel. The plants were
separated into four parts (root, stem, leaf and spike) and oven dried at 70°C
to a constant weight for the measurement of dry biomass. The root/shoot ratio
was calculated as total root dry biomass divided by above ground dry biomass,
which included the dry biomass of stem, leaf and spike.
At the end of growing seasons, wheat crop in each
lysimeter were harvested manually to determine yield and yield components. The
number of spikes and grains per spike were counted, and the fulfilled grains
ratio was calculated as the number of fulfilled grains divided by all grains
which included hollow and shrunken grains. The grains of wheat were air dried
for one week prior to grain yield and the thousand kernel weight was adjusted
to 13% moisture content.
Analysis
of waterlogging stress sensitivity
The plants that were waterlogged when the groundwater depth is less
than 500 mm below the soil surface. The
sum of excess water that accumulates each day in the primary root zone of the
top 500 mm soil layer (SEW) was
calculated with the following equation:
%20179-187_files/image002.png){kind=small}
(1)
where SEW is
the sum of excess water (mm); hi
is the groundwater depth of the ith day
(mm); i is the waterlogging day; m is the total number of days of
waterlogging stress.
The min–max normalization method was employed for
dimensionless elements to eliminate interannual variability in crop growth. The
calculation formula for the normalized value of a member of the set of observed
values of X{x1,x2,…,xn}
as given:
%20179-187_files/image004.png){kind=small}
(2)
where zj
and xj are the jth normalized and original values in {X}, respectively, and min {X} and max {X} are the minimum and maximum values of X given its range, respectively.
Statistical
analysis
ANOVA
was conducted to determine the effect of waterlogging on winter wheat. Differences
between means were distinguished through the least significant difference (LSD)
test at the 0.05 confidence level. The quantitative relationships for crop
growth, physiological traits, and grain yield with waterlogging stress were
calculated through linear regression. Relative values that are standardized for
each season were used to eliminate the influence of climate during different
growing seasons.
Results
Physiological
parameters
Waterlogging
stress drastically reduced the photosynthesis rate of winter wheat in both
seasons (Fig. 2). The photosynthesis rate of
groundwater depth of 200 mm and 400 mm for 3 days
treatments decreased by 11 and 5% in 2009 and by 13 and 11% in 2010,
respectively, after three days of waterlogging, compared to the control
treatment. For both seasons, the largest reduction of PN was measured for groundwater depth of
200 mm for 5 days, whereas the smallest
reduction was obtained for groundwater depth of 400 mm
for 3 days treatment. The PN of all waterlogging
treatments gradually increased with the relief of the waterlogging stress.
Seven days after the waterlogging was ended, the PN for groundwater depth of
400 mm for 3 days treatment reached 19.37 μmol m-2 s-1
in 2009, and 20.71 μmol m-2
s-1 in 2010, decreasing by 5% in 2009 and 4% in 2010 compared to the
control.
The transpiration rate (E)
for winter wheat sharply decreased with waterlogging stress three and five days
after the beginning of waterlogging, but no observable change of the E was realized for the control (Fig. 3).
Compared to the control, the E decreased by 24 and 11% for groundwater depth
of 200 mm and 400 mm for 5 days treatments in 2009 and by 43 and 24% in
2010, respectively. From the end of waterlogging, the E started to increase gradually, and was
higher for groundwater depth of 200 mm for 3 days, groundwater
depth of 400 mm for 3 days and groundwater depth of 400 mm for 5 days
treatments than the control after seven days of recovery for the 2009 season.
The fluctuation of stomatal conductance (gs) during the waterlogging
period was similar to PN and E
(Fig. 4). The gs decreased with the waterlogging stress and
increased after termination of stress. When
waterlogging stress was imposed for five days, the gs for groundwater depth of
200 mm for 5 days treatment was greatly
affected with a 44 and 40% reduction for the 2009 and 2010 seasons,
respectively, when compared to the control. The increase in the duration of
waterlogging stress was directly proportional to the decrease of gs. The gs for groundwater depth of 200 mm
and 400 mm for 5 days
treatments were similar and lower than groundwater depth of
200 mm and 400 mm for 3 days
treatments when waterlogging ended. After seven days of recovery, the gs for groundwater depth of
400 mm for 3 days treatment gradually increased
from 0.23 to 0.35 mmol m-2 s-1
in 2009 and from 0.23 to 0.40 mmol m-2 s-1 in 2010.
Growth traits
The
waterlogging stress duration, groundwater depth and their interactions had no
significant effect on the plant height in either season (P ≤ 0.05, Table 1). The highest plant height was obtained for
the control treatment, whereas the lowest plant height was noted for groundwater depth of 200 mm for 5 days
treatment. The leaf area index, root biomass and root/shoot ratio were
significantly influenced by groundwater depth for both seasons (P ≤ 0.05). Compare to
the control, waterlogging increased leaf area index by 22.0 and 34.5% for groundwater depth of 200 mm and 400 mm for 3
days in 2009 and by 18.5 and 27.8% in 2010, respectively. The largest
root biomass was
%20179-187_files/image006.jpg)
Fig. 1: Average daily air temperature, relative humidity
and rainfall during the 2009 and 2010 seasons
%20179-187_files/image008.jpg)
Fig. 2: Changes in the photosynthesis rate for the different
waterlogging treatments during the anthesis phase for
the 2009 and 2010 season. CK denotes no waterlogging; T2 and T3 denote
maintaining the groundwater depth at 200 mm and 400 mm below soil surface for
three days; T4 and T5 denote maintaining the groundwater depth at 200 mm and
400 mm below the soil surface for five days
recorded for the control for both seasons, whereas the
smallest root biomass was observed for groundwater
depth of 200 mm for 5 days treatment in 2009 and for groundwater depth of 200 mm for 3 days
treatment in 2010. For both seasons, the largest root/shoot ratio value was
obtained under the control treatment. The shoot biomass and total dry biomass
were not significantly affected by waterlogging duration, groundwater depth and
their interactions for the 2009 season (P
≤ 0.05).
Grain yield and yield components
The waterlogging duration
had no significant effect on the grain yield in either season, while the grain
yield decreased with groundwater depth (P ≤ 0.05, Table 2). For both seasons, the highest grain yield was recorded
in %20179-187_files/image010.jpg)
Fig. 3:
Changes in the transpiration rate for the
different waterlogging treatments during anthesis
phase for the 2009 and 2010 season. CK denotes no waterlogging; T2 and T3
denote maintaining the groundwater depth at 200 mm and 400 mm below soil
surface for three days; T4 and T5 denote maintaining the groundwater depth at
200 mm and 400 mm below the soil surface for five days
%20179-187_files/image012.jpg)
Fig. 4:
Changes in the stomatal
conductance for the different waterlogging treatments during anthesis phase for the 2009 and 2010 season. CK denotes no
waterlogging; T2 and T3 denote maintaining the groundwater depth at 200 mm and
400 mm below soil surface for three days; T4 and T5 denote maintaining the
groundwater depth at 200 mm and 400 mm below the soil
surface for five days
the control treatment, followed by the groundwater depth of 400 mm for 3 days and 5 days treatments, and the lowest yield was obtained for groundwater depth of 200 mm for 5 days treatment. The spike number significantly decreased with
the duration of waterlogging and groundwater depth in 2010 (P ≤ 0.05), while the interaction between the duration and
groundwater depth was significant only in 2009 (P ≤ 0.05). The highest and lowest number of spikes was obtained
for the control and groundwater depth of
200 mm for 3 days treatments in 2009,
respectively, and groundwater depth of
400 mm for 3 days and 200 mm for 5 days treatments in 2010. The number of spikelets decreased
significantly by groundwater depth for the 2010 season (P ≤ 0.05). Compared to the
control, Table 1: Plant height, leaf area index (LAI), root biomass
(RM), shoot biomass (SM), total dry biomass (TDM) and root/shoot ratio (RSR) of
winter wheat at final harvest as affected by waterlogging stress during the
2009 and 2010 growing seasons
|
Treatment |
Height (cm) |
LAI (cm2 cm-2) |
RM (g per plant) |
SM (g per plant) |
TDM (g per plant) |
RSR (g·g-1) |
|
|
2009 |
No waterlogging stress |
82.70 ± 1.72 a |
3.13 ± 0.16 c |
0.49 ± 0.03 a |
6.17 ± 0.08 a |
6.65 ± 0.09 a |
0.079 ± 0.005 a |
|
Groundwater depth of 200 mm for 3 days |
74.43 ± 2.49 a |
3.82 ± 0.10 ab |
0.34 ± 0.02 bc |
5.55 ± 0.20 b |
5.89 ± 0.22 b |
0.061 ± 0.003 cd |
|
|
Groundwater depth of 400 mm for 3 days |
75.54 ± 1.65 a |
3.63 ± 0.18 b |
0.42 ± 0.03 ab |
5.76 ± 0.24 ab |
6.18 ± 0.28 ab |
0.073 ± 0.003 ab |
|
|
Groundwater depth of 200 mm for 5 days |
73.90 ± 1.42 a |
4.21 ± 0.12 a |
0.30 ± 0.02 c |
5.64 ± 0.15 b |
5.94 ± 0.15 b |
0.053 ± 0.004 d |
|
|
Groundwater depth of 400 mm for 5 days |
78.11 ± 0.90 a |
3.39 ± 0.24 bc |
0.39 ± 0.02 b |
5.87 ± 0.07 ab |
6.26 ± 0.08 ab |
0.066 ± 0.003 bc |
|
|
Depth |
ns |
* |
* |
ns |
ns |
** |
|
|
Duration |
ns |
ns |
ns |
ns |
ns |
ns |
|
|
Interaction |
ns |
ns |
ns |
ns |
ns |
ns |
|
|
2010 |
No waterlogging stress |
81.17 ± 2.28 a |
3.35 ± 0.24 c |
0.47 ± 0.03 a |
6.27 ± 0.19 a |
6.75 ± 0.18 a |
0.076 ± 0.006 a |
|
Groundwater depth of 200 mm for 3 days |
74.99 ± 2.68 ab |
3.97 ± 0.09 ab |
0.30 ± 0.02 c |
5.79 ± 0.13 a |
6.08 ± 0.12 bc |
0.052 ± 0.005 b |
|
|
Groundwater depth of 400 mm for 3 days |
75.81 ± 1.08 ab |
3.65 ± 0.14 bc |
0.41 ± 0.03 a |
5.86 ± 0.15 a |
6.27 ± 0.18 ab |
0.069 ± 0.004 a |
|
|
Groundwater depth of 200 mm for 5 days |
72.76 ± 2.34 b |
4.28 ± 0.11 a |
0.32 ± 0.03 bc |
5.27 ± 0.18 b |
5.59 ± 0.16 c |
0.061 ± 0.007 ab |
|
|
Groundwater depth of 400 mm for 5 days |
75.94 ± 1.98 ab |
3.86 ± 0.16 ab |
0.40 ± 0.01 ab |
5.83 ± 0.13 a |
6.23 ± 0.13 b |
0.068 ± 0.003 a |
|
|
Depth |
ns |
* |
** |
ns |
* |
* |
|
|
Duration |
ns |
ns |
ns |
ns |
ns |
ns |
|
|
Interaction |
ns |
ns |
ns |
ns |
ns |
ns |
|
Note: In
the same column and in the same year, values followed by different letters are
significantly different among treatment at the 0.05 level by LSD. ns, non-significant at 0.05 level, *, **, and ***
significant at 0.05, 0.01 and 0.001 levels, respectively. Each value is the
mean of three replications
Table 2:
Grain yield and components of winter wheat for
different waterlogging stress in 2009 and 2010 season
|
Season |
Treatment |
Spikes
(# of ears m-2) |
Spikelets (#
of grains per ear) |
Thousand
kernel weight (g) |
Filled
grains (%) |
Grain
yield (kg·ha-1) |
|
2009 |
No waterlogging stress |
508.0 ± 2.7 a |
32.0 ± 0.1 a |
40.9 ± 0.3 a |
91.7 ± 0.2 a |
6093 ± 84 a |
|
Groundwater depth of 200 mm for
3 days |
478.0 ± 2.1 c |
31.0 ± 0.3 ab |
39.9 ± 0.1 bc |
91.0 ± 0.1 b |
5378 ± 75 c |
|
|
Groundwater depth of 400 mm for
3 days |
500.7 ± 2.7 ab |
31.5 ± 0.2 ab |
40.2 ± 0.2 ab |
91.1 ± 0.3 ab |
5785 ± 70 ab |
|
|
Groundwater depth of 200 mm for
5 days |
483.0 ± 2.5 c |
30.8 ± 0.2 b |
39.2 ± 0.2 c |
90.4 ± 0.2 b |
5277 ± 94 c |
|
|
Groundwater depth of 400 mm for
5 days |
493.3 ± 3.2 b |
31.2 ± 0.5 ab |
39.9 ± 0.2 b |
90.9 ± 0.2 b |
5590 ± 157 bc |
|
|
Depth |
*** |
ns |
* |
ns |
** |
|
|
Duration |
ns |
ns |
ns |
ns |
ns |
|
|
Interaction |
* |
ns |
ns |
ns |
ns |
|
|
2010 |
No waterlogging stress |
431.0 ± 3.6 a |
36.6 ± 0.2 a |
41.7 ± 0.4 a |
90.9 ± 0.1 a |
5981 ± 144 a |
|
Groundwater depth of 200 mm for
3 days |
419.3 ± 2.4 bc |
34.9 ± 0.3 b |
41.2 ± 0.2 a |
90.5 ± 0.1 a |
5462 ± 104 bc |
|
|
Groundwater depth of 400 mm for
3 days |
432.3 ± 4.3 a |
36.0 ± 0.2 a |
41.3 ± 0.1 a |
90.7 ± 0.2 a |
5831 ± 115 a |
|
|
Groundwater depth of 200 mm for
5 days |
410.7 ± 3.3 c |
34.1 ± 0.2 c |
41.1 ± 0.3 a |
90.5 ± 0.1 a |
5216 ± 104 c |
|
|
Groundwater depth of 400 mm for
5 days |
426.3 ± 1.9 ab |
35.9 ± 0.2 a |
41.4 ± 0.1 a |
90.9 ± 0.2 a |
5753 ± 71 ab |
|
|
Depth |
** |
*** |
ns |
ns |
** |
|
|
Duration |
* |
ns |
ns |
ns |
ns |
|
|
Interaction |
ns |
ns |
ns |
ns |
ns |
|
Note: In
the same column and in the same year, values followed by different letters are
significantly different among treatment at the 0.05 level by LSD. ns, non-significant at 0.05 level, *, **, and ***
significant at 0.05, 0.01 and 0.001 levels, respectively. Each value is the
mean of three replications
the number of spikelets decreased by 5 and 7% for groundwater depth of 200 mm for 3 days and for 5 days in 2010, respectively. The thousand kernel weight and
filled grains of winter wheat decreased with waterlogging duration, groundwater
depth and their interactions, but the differences were not significant for the
2010 season (P ≤ 0.05).
Relationship
between wheat physiological parameters, growth traits, yield and waterlogging
stress
The
correlation analysis showed that PN, E and gs were significantly correlated
with waterlogging stress (P ≤ 0.01; Table 3). The relationships were well fitted
using a linear regression with regression coefficients of -0.92, -0.90 and
-0.92, respectively. Plant height showed a significant negative linear
correlation with waterlogging stress (P
≤ 0.01). The relationship of leaf area index with waterlogging stress was
best fitted with a positive linear correlation with the slope value and
determination coefficient (R2) of 0.93 and 0.90, respectively (P ≤ 0.01). The root biomass and
biomass, total dry biomass and root/shoot ratio of winter wheat had a significant
negative correlation with waterlogging stress (P ≤ 0.01). The relationship between grain yield and
waterlogging stress was well fitted using a linear regression with the
regression coefficients of -0.99. Negative correlations were also found for the
grain yield components, including number of panicles, number of spikelets,
thousand kernel weight and the number of filled
grains, with waterlogging stress (P
≤ 0.01).
Table 3:
Relationship between photosynthesis rate,
transpiration rate, stomatal conductance, plant
height, leaf area index, root biomass, shoot biomass, total dry biomass,
root/shoot ratio, spikes, spikelets, thousand kernel
weight, filled grains, grain yield and waterlogging stress
|
Dependent variable |
Linear regression equation |
R2 value |
P value |
|
Photosynthesis rate |
y=-0.92 x+0.84 |
0.85 |
<0.01 |
|
Transpiration rate |
y=-0.90 x+0.88 |
0.91 |
<0.01 |
|
Stomatal conductance |
y=-0.92 x+0.87 |
0.70 |
<0.01 |
|
Plant height |
y=-0.83 x+0.73 |
0.64 |
<0.01 |
|
Leaf area index |
y=0.93 x+0.08 |
0.90 |
<0.01 |
|
Root biomass |
y=-0.93 x+0.86 |
0.82 |
<0.01 |
|
Shoot biomass |
y=-0.82 x+0.81 |
0.67 |
<0.01 |
|
Total dry biomass |
y=-0.88 x+0.82 |
0.75 |
<0.01 |
|
Root/shoot ratio |
y=-0.85 x+0.89 |
0.70 |
<0.01 |
|
Spikes |
y=-0.97 x+0.96 |
0.80 |
<0.01 |
|
Spikelets |
y=-0.97 x+0.91 |
0.87 |
<0.01 |
|
Thousand kernel weight |
y=-0.86 x+0.80 |
0.75 |
<0.01 |
|
Filled grains |
y=-0.93 x+0.88 |
0.67 |
<0.01 |
|
Grain yield |
y=-0.99 x+0.92 |
0.89 |
<0.01 |
Discussion
Waterlogging stress is a limiting factor for winter wheat production (Saqib et al. 2004; Herzog et al.
2016; Li et al. 2016). It has been widely reported that waterlogging
that occurs during the reproductive phase has more adverse effects on the
growth and yield of winter wheat than during any other phase (Setter
et al. 2009; de San Celedonio et al.
2014; Wu et al. 2015). However, the extent of the reduction in yield
depends not only on the growth stage during which waterlogging occurs, but also
on the severity of the waterlogging stress, especially the duration of
waterlogging and groundwater depth (Herzog et al. 2016; de San Celedonio et al. 2017; Wu et al.
2018). This
is also evident from this study, whereby the growth index and grain yield were significantly reduced for the groundwater depth of 200 mm for 3 and 5 days treatments when waterlogging
stress occurred during the anthesis phase (P
≤ 0.05).
When waterlogging occurs, oxygen will rapidly deplete surrounding the roots, resulting in the
reduction of root hydraulic conductivity and an increase in stomatal resistance
(Shao et al.
2013; Wang et al. 2016). Generally, the restriction in leaf photosynthetic
performance has been attributed to stomatal closure
and the reduction of chlorophyll content in leaves (Bradford 1983; Yordanova et al. 2005). In this study, the reduction in stomatal
conductance, the rate of photosynthesis and transpiration were measured during
waterlogging stress period had been reported by Yordanova et al. (2005). It also has been reported that waterlogging
stress could cause senescence and leaf yellowing, which reflects the reduction
in photosynthetic activity (Shao et al.
2013; Wu et al. 2015).
Several studies have shown that it is difficult
for plants to recover from stress when waterlogging occurs during the later
growth phases (de San Celedonio
et al. 2014; Wu et al. 2018). However, in this study, there was no
significant difference in photosynthesis and transpiration rates between
waterlogging treatments and the control after seven days of recovery (P ≤ 0.05). The reason might be related to the
duration of waterlogging and the groundwater depth. The waterlogging period in
some studies were more than one week (Malik et al. 2002; Hossain et al. 2011; de San Celedonio et al. 2017), which may be beyond the tolerance capacity of wheat plants. In
addition, Wu et al. (2018) reported
that the root system of winter wheat is mainly distributed in 0–20 cm soil layer, which indicated
that plants suffered from serious stress when groundwater was in a shallow
condition.
Generally, plants have different mechanisms to recover
from slight waterlogging stress (Setter and Waters 2003; de San Celedonio et al. 2014). However, short periods of waterlogging, even as
little as three days, have been found to have considerable long-term impact on
the growth of winter wheat (Malik et
al. 2002). In
this study, the plant height and total dry biomass of winter wheat were reduced
by waterlogging during the anthesis phase (Malik et al. 2002; Wu et al.
2015). The
higher leaf area index at harvest were found for groundwater depth of 200 mm and 400 mm for 3 days treatments compared to the control, which might
be due to slow growth rate after waterlogging (Shao et al. 2013). It also has been reported that waterlogging could injure root
metabolism and delay the time of maturity (Wu et al. 2015). In this study, the root biomass was significantly decreased for groundwater depth of 200 mm for 3 days
and 5 days treatments. In fact,
the root was the first organ to be affected by waterlogging, resulting in the
drastic reduction of root length and root biomass (Herzog et al. 2016). The abiotic stresses, such as waterlogging or drought, impede plant
dry matter accumulation and force redistribution in different organs and affect
the root to shoot ratio (Shao et al.
2013; Xu et al. 2015; Wu et al. 2018). Higher root to shoot ratios are more beneficial
to plants to adapt to adverse conditions (Wu et al. 2018). In this study, the shoot biomass was decreased for groundwater depth of 200 mm for 3 days
and for 5 days treatments, but
no enhanced effect on the root to shoot ratio by waterlogging was observed,
perhaps because roots were not completed excavated when were dug them manually
with a root shove.
Restricted plant growth might have a negative
effect on final yield and yield quality (Hassan et al. 2007; Chen and Weil 2010). The results of present study suggest that grain
yield of winter wheat was reduced for the groundwater depth of 200 mm for 3 days and 5 days, and that the shallower groundwater depth aggravated this
reduction. The reduction of grain yield of winter wheat was mainly attributed
to a decrease in the number of spikes and spikelets under waterlogging stress (Shao et al. 2013; Wu et al.
2015). In
this study, both the thousand kernel weight and filled grains were not found to
decrease with the degrees of waterlogging. This result may be attributed to the
reduction in the spikes and spikelet under waterlogging stress, which in turn
may increase the grains weight (Wu et al. 2018).
Information about the relationship between winter
wheat grain yield and waterlogging stress is helpful for efficient agricultural
management and crop production. In the present study, a negative linear
relationship was found between yield and yield components with the value for
SEW, have been reported (Shao et al.
2010).
Linear relationships were also found between the growth traits and
physiological activities with SEW. These findings indicated that the critical
500 mm depth of groundwater for SEW could be considered as a reasonable
assessment of waterlogging. However, there was a reduction in yield at
groundwater depths of 100–300 mm
rather than 500 mm (Gales et al.
1984; Malik et al. 2002; Wu et al. 2018). Williamson and Kriz (1970) reported that wheat yield was reduced at
groundwater depths between 500 and 1200 mm. Therefore, in order to obtain a
better correlation between yield and SEW, further research is needed to
evaluate the critical depth of groundwater for crops in a specific region
according to the cultivar, soil type, local weather conditions and other
factors.
In the present study, a satisfactory grain yield
was obtained for winter wheat under waterlogging stress for the groundwater depth of 200 mm and 400 mm for 5 days treatments. These
management strategies will provide farmers with a beneficial option for
efficient agricultural water management in grain production, especially when
water and labor force are inadequate and costly. This study was limited to the
effect of waterlogging stress during anthesis on growth, physiological
parameters and yield of winter wheat. In this study, the effect of waterlogging
was not investigated during other growth phases or the compound growth phases.
Therefore, further research is needed on the effect of
waterlogging stress during various growth phases to determine potential
tolerance for waterlogging.
Conclusion
Waterlogging stress during the anthesis affects the physiological
activities and growth of winter wheat. The transpiration and photosynthesis
rates decreased with waterlogging stress and increased gradually from the end
of waterlogging. The physiological activities and growth traits had negative correlations
with the sum of excess water, whereas LAI has a positive correlation with
waterlogging stress. Grain yield decreased linearly with the sum of excess
water, mainly due to the reduction of spikes and spikelets caused by
waterlogging stress.
Acknowledgment
This research was supported by the National Nature & Science
Foundation of China (No.51879072), the Fundamental Research Funds for the
Central Universities (2017B688X14), the Supporting Program of the Postgraduate
Research & Practice Innovation Program of Jiangsu Province (KYCX17_0432),
Jiang Su Qing Lan and the project of the Priority Academic Program Development
of Jiangsu Higher Education Institutions.
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