Field Crops Research 115 (2010) 158–164
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Field Crops Research
journal homepage: www.elsevier.com/locate/fcr
Effect of lowering the root/shoot ratio by pruning roots on water use
efficiency and grain yield of winter wheat
Shou-Chen Ma a,b,c, Feng-Min Li a,*, Bing-Cheng Xu c, Zhan-Bin Huang d
a
Key Laboratory of Arid and Grassland Ecology, Ministry of Education, Lanzhou University, Lanzhou 730000, China
School of Surveying and Land Information Engineering, Henan Polytechnic University, Jiaozuo 454000, China
c
State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation,
Chinese Academy of Sciences and Ministry of Water Resources, Yangling 712100, China
d
School of Chemical and Environmental Engineering, China University of Mining & Technology, Beijing 100083, China
b
A R T I C L E I N F O
A B S T R A C T
Article history:
Received 29 July 2009
Received in revised form 19 October 2009
Accepted 22 October 2009
A pot and a field experiment were conducted to assess the effects of root/shoot ratio (R/S) on the water
use efficiency (WUE) and grain yield of winter wheat. The R/S was regulated by pruning the roots during
the stem elongation stage, resulting in reduced root systems of the plants. At the heading stage, the root
dry weight of root-pruned plants was less than that of intact-root plants, but their R/S was similar to that
of intact-root plants under both experimental conditions. After tiller pruning, the R/S of root-pruned
plants was significantly lower than that of intact-root plants (p < 0.05). Root pruning reduced the rate of
leaf transpiration and lowered the number of tillers per plant (p < 0.05) during the vegetative stage. As a
result, root-pruned wheat showed reduced water use when compared to intact-root plants before
heading (p < 0.05). At anthesis, there was no significant difference in transpiration between plants with
intact roots and those with pruned roots in the pots. However, under field conditions, transpiration of
root-pruned plants was significantly higher than that of intact-root plants at anthesis. Additionally, at
anthesis root-pruned plants had a higher rate of leaf photosynthesis and lower rate of root respiration,
which resulted in a significantly higher grain yield at maturity when compared to plants with intact
roots. Under both experimental conditions, there were no significant differences in shoot dry weight per
plant between root-pruned and intact-root plants grown in monoculture. When root-pruned plants
were grown with intact-root plants, the root-pruned wheat was less productive and had a lower relative
shoot dry weight (0.78 and 0.86, respectively) than the intact-root plants (1.24 and 1.16, respectively).
These results suggest that plants with pruned roots had a lower ability to compete and to acquire and use
the same resources in the mixture when compared with intact-root plants. Root pruning improved the
WUE of winter wheat under both experimental conditions. This suggests that appropriate management
for the root system/tillers in wheat crops can be used to increase grain yield and water use efficiency.
Specifically, lowering the R/S improved the grain yield and WUE of winter wheat significantly by
lowering its competitive ability and improving root efficiency. Therefore, drought-resistance breeding to
improve the grain yield and WUE, at least for wheat, should be made by targeted selection of less
competitive progeny with a small R/S for cultivation in arid and semiarid areas.
ß 2009 Elsevier B.V. All rights reserved.
Keywords:
Winter wheat
Root pruning
Tiller pruning
Competitive ability
Water use efficiency (WUE)
1. Introduction
In arid or semiarid areas, crops often experience unpredictable
water deficits during their life cycle. Lack of available water is the
primary factor limiting wheat yields in semiarid regions of China
(Deng et al., 2006). Generally, a large root system is more
advantageous to the plant than a small root system for acquiring
water (Kramer, 1969). Therefore, drought-resistance breeding
strategies have included selection of progeny with large root
* Corresponding author.
E-mail address: [email protected] (F.-M. Li).
0378-4290/$ – see front matter ß 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.fcr.2009.10.017
systems (Hurd, 1974). However, although the most competitive
individuals in water-limited environments are likely to gain a
disproportionate share of the water in the soil, partitioning of
limited resources to the roots to improve water capture requires a
reduction in reproductive partitioning to grain. This competitive
asymmetry may lead to excessive growth of some resourceforaging organs to such an extent that grain production and total
crop production are lowered (Zhang et al., 1999a). Recent studies
of wheat varieties of different ages have shown that modern
varieties with small root systems are less competitive, but more
productive than older varieties with large root systems. These
findings suggest that drought-resistance breeding has unknowingly led to lower competitive ability and increased grain yield via
S.-C. Ma et al. / Field Crops Research 115 (2010) 158–164
a reduction in the root/shoot ratio (R/S) (Zhang et al., 1999a,b;
Zhang and Zhang, 2000; Song et al., 2009). In addition, a large root
system can result in rapid soil water consumption, which may not
be favorable in arid and semiarid areas that are not irrigated, such
as the Loess Plateau. In these areas, a key aspect of water-saving
technology is to increase the efficiency with which natural rainfall
is used (Li and Zhao, 1997).
Recent studies conducted to evaluate the relationship between
R/S and water use efficiency (WUE) have shown that the WUE of
wheat increased gradually as the R/S decreased from diploid to
hexaploid plants (Zhang et al., 2002; Li et al., 2003; Song et al.,
2009) and from older to modern varieties (Siddique et al., 1990; Li
and Chen, 2002; Fan et al., 2008). However, these findings were
based on different varieties of wheat; therefore, it was likely that
any improved grain yield and WUE did not result simply from a
reduced R/S, but possibly from a number of other traits. To remove
the effects of varying genotypes on grain yield and WUE, we used
root pruning to reduce the root system to determine if the yield
and WUE of winter wheat could be improved by lowering the R/S
among plants with the same genotype. The results of our previous
study showed that root pruning improved WUE and lowered the
competitive ability of wheat by reducing the root weight, but that
it had no effect on the R/S of plants (Ma et al., 2009). Furthermore,
root pruning also reduced the number of fertile tillers of wheat,
which can result in poor grain yield (Ma et al., 2008, 2009).
In this study, we conducted tiller pruning at the heading stage
to remove the effect of tiller number on grain yield, because
heading is the stage at which the root system of winter wheat is
largest. After tiller pruning, the R/S of plants that were subjected to
root pruning was expected to be lower than that of intact-root
plants. The specific goal of this study was to determine if the yield
and WUE of winter wheat could be improved by lowering the R/S
using root pruning at the stem elongation stage and tiller pruning
at the heading stage to ensure a similar number of fertile tillers.
159
spaced 6 cm apart. Pots were filled with 10 kg of sieved topsoil
(from farmland in the region, with a field water capacity of 26%).
Chemical fertilizers (N, P, and K) were applied to the pots at 120, 60,
and 48 kg ha1, respectively, to ensure sufficient nutrition. The
pots were maintained at 85% FWC (field water capacity) before the
jointing stage and 60% FWC after the jointing stage. There were five
replications per treatment and all pots were arranged randomly
under an automatic transparent rain-out shelter that covered the
pots whenever 1 mm of rain had accumulated. The pots were
weighed and rewatered at 8:00 a.m. and 4:00 p.m. every day
throughout the experimental period. At maturity, the shoot dry
weight, grain yield and spike number were measured.
The root/shoot ratio (R/S) was regulated by root pruning at the
stem elongation stage and tiller pruning at heading. The methods
used for root pruning and sowing are shown in Fig. 1. There were
approximately 4 cm between the root-pruned wheat and intact-root
plants in each row in the field experiment. Partial secondary lateral
roots were cut off from the winter wheat vertically to a depth of
10 cm along both sides, approximately 3 cm away from the plant
using a 25 cm long scale-marked single-edged knife at stem
elongation (Zadoks’ growth stage 30). At heading, the main stem
and largest tiller were retained to maintain the same fertile tiller
density between the root-pruned and intact-root plants, while all
other tillers were clipped under field conditions. In the pots, only the
main stem was retained and all other tillers were clipped. Rootpruned plants were designed to represent a cultivar with a small
root/shoot ratio (Rp), while intact-root plants were designed to
represent a cultivar that has a large root/shoot ratio (IR).
Competition between the root-pruned and intact-root plants was
examined using a simple replacement-series design (Fig. 1) in which
root-pruned plants and intact-root plants were combined at a ratio
of 0:1 (monoculture of intact-root plants), 1:1 (mixture of rootpruned and intact-root plants) and 1:0 (monoculture of root-pruned
plants). Root-pruned plants were labeled with a wire ring to
distinguish them from intact-root plants in the mixture plots (pots).
2. Materials and methods
2.1. Materials and experimental design
A field experiment and a pot experiment were conducted from
October 2006 to June 2007. The field experiment was conducted at
the Changwu Experimental Station of the Chinese Academy of
Sciences (1078400 E, 358140 N, 1200 m a.s.l.), which is located in a
typical area of the semiarid Loess Plateau, in the county of
Changwu, Shaanxi Province, China. The mean annual air temperature at the experimental station is 9.1 8C, while the cumulative
temperature above 10 8C is 3029 8C, and the annual frost-free
period is approximately 171 days. The average annual precipitation in the area is about 584 mm (rain and snow), 68% of which
occurs between June and September. The primary soil in the area is
Heilu soil (Calcic Kastanozems, FAO) with a bulk density of
1.36 g cm3, a field capacity of 26% (gravimetrically), and a
permanent wilting coefficient of 10%.
Chemical fertilizers (N, P and K) were applied basally at 120, 60
and 48 kg ha1, respectively. The cultivar of winter wheat (Triticum
aestivum L.) used in the experiment was ‘‘Changwu135’’, which is
widely used by farmers in the region. Wheat was sown in rows
20 cm apart on 20 September. The total density was 2.50 million
basic seedlings per hectare. Each plot was 2 m 2 m and each
treatment consisted of three replicated plots arranged in a
randomized block design.
The pot experiment was conducted at the Institute of Soil and
Water Conservation, Yangling, China (108870 E, 348120 N, 530 m
a.s.l.). Seeds of the same cultivar of winter wheat as used in the
field study were sown in plastic pots (28 cm diameter 50 cm
high) at a density of 12 seedlings per pot with seedlings being
Fig. 1. Methods of sowing and root pruning in (a) intact-root plants in a
monoculture plot (pot), (b) root-pruned plants grown in plot (pot) with a mixture of
intact-root plants, and (c) root-pruned plants in a monoculture plot (pot).
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S.-C. Ma et al. / Field Crops Research 115 (2010) 158–164
2.2. Experimental methods
2.2.1. Photosynthesis, root respiration rate (Rroot) and root efficiency
The instantaneous photosynthetic rate (Pn) of the flag leaf
was measured using a LI-6400 Portable Photosynthesis System
(LI-Cor, Inc., Lincoln, NE, USA) from 9:00 a.m. to 11:00 a.m. at
anthesis. 7–12 flag leaves in each plot (pot) were used to
determine the leaf Pn. Root respiration was measured 1 day after
Pn was measured. Shoots were first cut off at the soil level before
measuring the root respiration. After excision, the total CO2
efflux from the soil was immediately measured. Three samples
per plot (two samples per pot) were collected, each of which
consisted of two measurements, with one measurement centered
over the cut stem of sampled plants and the other measurement
from the mid-point between the rows. This value was taken to
represent the total soil respiration. The bare soil respiration was
measured in three bare experimental plots (pots). Root respiration was estimated by subtracting the bare soil respiration from
the total soil respiration. The soil CO2 efflux was measured using
a closed system chamber (SRC-1 with EGM-4, PP-Systems,
Boston, USA). The chamber was held in the air to allow it to
flush out prior to placing it on the soil, after which it was inserted
into the soil to a depth of 3 cm. After approximately 5 s, the
measurement was taken.
Root efficiency reflects the relationship between the amount of
carbon allocated to the roots and assimilate supply (Liu and Li,
2003), which was estimated using Pn/Rroot in this study.
2.2.2. Transpiration rate
The rate of leaf transpiration was measured using a steady-state
PMR-5 porometer (PP-Systems, Boston, USA) from 9:00 a.m. to
11:00 a.m. during the stem elongation stage and the heading stage.
Leaves used for measurement were fully expanded from each
randomly chosen plant. Ten replicate samples of each plot (pot)
were used to determine the Tr.
2.2.3. Plant and soil water content sampling
In the field experiment, root samples were collected during the
heading stage. Samples were collected in 20-cm increments to the
maximum possible depth using a drill. Two samples per plot were
collected, each of which consisted of two cores with one core
centered over the cut stem of sampled plants and the other at the
mid-point between the rows. In the pot experiment, root samples
were collected during the heading stage. Samples were washed
free of soil on a 0.5 mm sieve. New roots (light brown) were then
separated by hand from previous year roots (dark brown), soil
particles and debris. The root samples were then dried in a forceddraught oven at 75 8C.
The soil water content was measured gravimetrically at 10-cm
intervals to 30 cm and at 10-cm intervals from 30 cm to 200 cm by
the neutron scattering technique (Model 503DR CPN, Martinez, CA,
USA) at sowing, stem elongation, heading and final harvest. The
neutron probe was calibrated against the soil water content
determined gravimetrically at the experimental sites. Readings
were taken after 64 s.
At maturity, the yield of the grain and shoot dry weight was
measured. In the field experiment, each plot had nine rows, three
of which were used to assess the grain yield and shoot dry weight.
where RYij is the relative shoot dry weight for treatment i in a
mixture with treatment j, Yij is the shoot dry weight per plant for
treatment i in a mixture with treatment j, Yi is the shoot dry weight
per plant for treatment i in monoculture.
2.4. Water use efficiency
Water use efficiency (WUE) was calculated based on the
following equation:
WUEgr ¼
Y
ET
(2)
where WUEgr is the water use efficiency for grain yield, Y is the
grain yield per pot (the grain yield per unit area in the field
experiment), and ET (evapotranspiration) is the recorded total
water consumption per pot (plot) over the entire growing season.
ET for a given period was determined according to the equation:
ET ¼ P þ DW
(3)
where DW was the change in water stored in the soil in the pot and
profile between 0 and 200 cm in the field during the period
considered, and P was the recorded rainfall in the field and
irrigated water in the pot.
Statistical analyses were conducted using Microsoft Excel 2000.
Treatment effects were compared using a t-test (p = 0.05).
3. Results
3.1. Leaf transpiration
Root pruning inevitably disturbs the balance between water
uptake and loss during the early growth stage. Thus, the rate of
transpiration (Tr) of the root-pruned plants was lower than that of
intact-root plants at stem elongation in both experiments (Table
1). At heading, there was no significant difference in Tr between
root-pruned and intact-root plants in the pots, but Tr of rootpruned plants was significantly higher than that of intact-root
plants in the field (Table 1).
3.2. Tiller number and root/shoot ratio
Root pruning led to a significant reduction in the root dry
weight of wheat, but had no effect on their root/shoot ratio (R/S)
under field and pot conditions at heading (Table 2). Root pruning
reduced the number of tillers per plant, which led to a significantly
lower tiller density under both experimental conditions. To retain
the same tiller density between root-pruned and intact-root
plants, all treatments were subjected to tiller pruning at heading.
After tiller pruning, the R/S of root-pruned wheat was significantly
lower compared to intact-root plants in both the pot and field
experiments.
Table 1
The rate of leaf transpiration (Tr) (mmol m2 s1) of intact-root (IR) and root-pruned
wheat plants (Rp) in monoculture at two stages of development.
Pot experiment
2.3. Estimation of competitive ability
Competitive ability was analyzed by calculating the relative
shoot dry weight (RYij) according to the following equation:
RY i j ¼
Yi j
Yi
(1)
Stem elongation
stage
Heading stage
Field experiment
IR
Rp
IR
3.61 0.4a
2.66 0.8b
3.8 0.4a
Rp
2.7 0.8b
4.45 0.7a
4.70 0.6a
4.2 0.3b
5.62 0.7a
Values are the means standard errors (n = 10). Different letters in the same
experiment indicate a significant difference between IR and Rp at p = 0.05 according to
a t-test.
S.-C. Ma et al. / Field Crops Research 115 (2010) 158–164
161
Table 2
Spike number (SN) and root/shoot ratio (R/S) before and after tiller pruning at heading of intact-root wheat (IR) and root-pruned wheat (Rp) in the pot and field experiments.
Treatment
Items
Pot experiment
SN (per pot)
Root (g pot1)
Shoot (g pot1)
R/S
SN (per m2)
Root (g m2)
Shoot (g m2)
R/S
Field experiment
Before tiller pruning
After tiller pruning
IR
Rp
IR
Rp
17.2 2.8a
8.2 0.4a
32.57 0.72a
0.25a
682 88a
364 12.7a
1125 35a
0.32a
14.1 0.7b
6.8 0.3b
26.09 0.84b
0.26a
624 44b
312 8.4b
1006 42a
0.31a
12
8.2 0.4a
24.24 0.68a
0.34a
500
364 12.74a
842 12a
0.43a
12
6.8 0.3b
23.8 0.49a
0.28b
500
312 8.4b
827 18a
0.37b
Values are the means standard errors (n = 5 in the pot experiment and n = 3 in the field experiment). Different letters in the same experiment indicate a significant difference
between IR and Rp at p = 0.05 according to a t-test.
Table 3
The shoot dry weight (SDW) per plant and relative shoot dry weight (RY) of intactroot wheat (IR) and root-pruned wheat (Rp) grown in monoculture and mixed
cultures.
Treatments
Monoculture
Mixture
Pot experiment
IR
Rp
IR
Rp
Field experiment
SDW (g plant1)
RY
SDW (g plant1)
RY
3.18b
3.29b
3.95a
2.58c
1
1
1.24a
0.78b
2.51b
2.55b
2.90a
2.19c
1
1
1.16a
0.86b
Different letters in the same experiment indicate a significant difference between IR
and Rp at p = 0.05 according to a t-test.
3.3. Competitive ability
There were no significant differences in shoot dry weight per
plant at maturity between root-pruned and intact-root plants
grown in monoculture under either experimental condition (Table
3). In the mixed treatment, the growth of root-pruned plants was
restrained by that of intact-root plants in both the pot and field
experiments (Table 3). Furthermore, the relative shoot dry weight
of the root-pruned plants (0.78 and 0.86 in the pots and field,
respectively) was lower than that of the intact-root plants (1.24
and 1.16 in the pots and field, respectively) when plants with
pruned and intact roots were grown in mixture.
3.4. Photosynthesis, root respiration rate and root efficiency
In both the pot and field experiments, root-pruned wheat had
a higher rate of leaf photosynthesis (Pn) and a lower root
respiration rate (Rroot) than intact-root plants in the monoculture pots (plots) at anthesis (Fig. 2). Root efficiency was
estimated based on the Pn/Rroot. Root pruning significantly
increased the root efficiency (Pn/Rroot) of wheat (Fig. 2).
3.5. Water consumption and soil water content
Root pruning primarily led to a decrease in water use prior to
tiller pruning at heading. In the pot experiment, root pruning saved
about 2.16 kg water (Fig. 3). In the field experiment, there were no
significant differences in soil water content between the rootpruned plot and intact-root plot at stem elongation, but by heading
the soil water content of the root-pruned plot was greater than that
of the intact-root plot (p < 0.05) (Fig. 4). These findings clearly
demonstrate that the root-pruned wheat used less soil water than
plants with intact roots.
3.6. Grain yield and water use efficiency for grain yield
Root and tiller pruning had no significant effect on shoot dry
weight at maturity (Table 3), but root-pruned wheat had an
Fig. 2. Leaf photosynthetic rate (Pn), root respiration rate (Rroot) and root efficiency (Pn/Rroot) of intact-root plants (IR) and root-pruned wheat (Rp) in monoculture. Leaf Pn was
measured from 9:00 a.m. to 11:00 a.m. at anthesis. Root respiration was measured at 1 day after leaf photosynthesis. Vertical bars represent standard errors (n = 5 in the pot
experiment and n = 3 in the field experiment).
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S.-C. Ma et al. / Field Crops Research 115 (2010) 158–164
4. Discussion
Fig. 3. Water use (kg) before and after tiller pruning by intact-root wheat (IR) and
root-pruned wheat (Rp) in a pot experiment. Vertical bars represent the standard
errors (n = 5).
improved kernel weight per spike and harvest index. As a result,
root-pruned plants had a higher grain yield than intact-root plants
(Table 4). Based on water use, root-pruned wheat had a
significantly higher WUEgr than plants with intact roots
(p < 0.05) (Table 4).
The ability of a plant to acquire underground resources is
strongly influenced by the size of its root system (Kramer, 1969).
In both the field and pot experiments, root pruning led to a
reduced root system and decreased soil water uptake by winter
wheat during vegetative growth. This decreased uptake, in turn,
led to the death of some tillers during the tiller survival period,
resulting in a reduced tiller numbers. Furthermore, root pruning
also reduced soil water use due to reduced transpiration during
the vegetative growth. In arid or semiarid areas, especially the
semiarid area of the Loess Plateau, winter wheat does not suffer
water shortage during the vegetative phase, but it is always
subjected to late-season or terminal drought. Therefore, if more
soil water is saved prior to anthesis and supplied to plants after
anthesis, it is beneficial for crop production and WUE (Li et al.,
2001).
Root pruning leads to a reduced R/S during the early growth;
however, there is a controlling mechanism balancing the growth
of above- and below-ground plant parts (Jackson, 1993;
Vysotskaya et al., 2001). This mechanism enables plants to
restore their R/S after perturbations such as root pruning. In the
present study, the R/S of root-pruned plants was similar to that
of intact-root plants at heading. As a result when plants were
grown in pots, the transpiration of root-pruned plants was
similar to that in plants with intact roots by heading. However,
under field conditions, root pruning reduced soil water use
during the vegetative growth period, which resulted in soil
Fig. 4. Soil water content in the plots of intact-root wheat (IR) and root-pruned wheat (Rp) in a field experiment at (a) stem elongation, and (b) at heading. Horizontal bars
represent the standard errors (n = 3).
Table 4
Kernel weight per spike (KWS), grain yield, harvest index (HI), and water use efficiency for grain yield (WUEgr) of intact-root wheat (IR) and root-pruned wheat (Rp) grown in
monoculture.
Items
Units
Pot experiment
IR
KWS
(g)
Yield
(g pot1)
(g m2)
HI
WUEgr
(g kg1)
(g m2 mm1)
1.51 0.03b
18.12 2b
Field experiment
Rp
1.72 0.02a
IR
Rp
1.07 0.02b
1.19 0.03a
535 18.2b
0.42 0.03b
593 15.5a
0.46 0.05a
2.13 0.04b
2.43 0.06a
20.64 3a
0.47 0.02b
0.52 0.03a
1.19 0.2b
1.57 0.4a
Values are the means standard errors (n = 5 in pot experiment and n = 3 in field experiment). Different letters in the same experiment indicate a significant difference between IR
and Rp at p = 0.05 according to a t-test.
S.-C. Ma et al. / Field Crops Research 115 (2010) 158–164
water being saved and available to plants after heading. This
facilitated the physiological activities of the plants so that the
transpiration of root-pruned plants was significantly higher than
that of intact-root plants at heading.
Passioura (1983) demonstrated that roots are a major sink for
assimilates, requiring twice as much photosynthate to produce
dry matter as the shoots. Moreover, the maintenance of the root
system consumes more energy than its construction (McCree,
1986). Indeed, it has been shown that more than 50% of
assimilates are lost through root respiration (Lambers et al.,
1996; Liu et al., 2004). As a result, the amount of energy utilized to
maintain the root biomass increases as the amount of root
biomass increases. Because the root systems of crop plants may
be unnecessarily large (Passioura, 1983), their reduction may
result in more photosynthate being available for shoots and
higher grain production. In this study, root-pruned plants had a
smaller root/shoot ratio than plants with intact roots following
tiller pruning at heading, which demonstrated that we successfully simulated a cultivar of wheat with a smaller R/S. Due to the
reduced root system, root-pruned plants had lower root
respiration and higher leaf photosynthesis when compared to
plants with intact roots at heading. This decreased root
respiration resulted in a higher proportion of photosynthate
being allocated to the shoot biomass and may explain why rootpruned plants had higher grain yield when compared with intactroot plants. A study conducted by Fan et al. (2008) demonstrated
that WUEgr was greater for modern varieties of wheat than for old
varieties and was correlated with the root efficiency. Our results
also showed that a significantly higher WUEgr in root-pruned
plants was correlated with the root efficiency.
There is mutual competition for limited resources (light,
water, minerals, etc.) among neighboring individuals in a crop
population. Although above-ground interactions are important,
much of this competition takes place below the ground for soil
resources such as nutrients and water (Caldwell, 1987; Jastrow
and Miller, 1993). Accordingly, plants with larger root systems
in a water-limited environment will gain more of the limited
resources and usually be more productive if surrounded by
plants with a smaller root system (Zhang et al., 1999a). Root
pruning reduces the size of the root system, thereby lowering
the ability of the individual plants to compete for underground
resources such as water. In the present study, the relative yield
suggested by de Wit (1960) was adopted to estimate the
competitive ability of plants. Root-pruned plants had a lower
relative shoot dry weight than intact-root plants when grown
under mixed conditions, which indicates that root-pruned
plants lost some of their competitive ability.
Most plant breeders regard increased crop yield per unit area
as an important, high-priority objective (Evans, 1993). Donald
(1968) suggested that, to increase yield potential, crop breeders
will be forced to develop a ‘communal’ ideotype that will not
perform well in competition with other genotypes and may give
low individual yields when plants are grown in isolation, but
that are capable of higher yields when grown in monoculture at
densities sufficient to induce interplant competition. Reynolds
et al. (1994) also provided substantial evidence that genes
conferring yield potential through improved adaptation to the
crop environment are associated with a less competitive
phenotype. If all individuals are poor competitors in the field,
the entire population will use fewer resources on competitive
structures such as leaves, stems and the root system, and will
therefore have more resources available for reproduction. As a
result, the yield of a population composed of poor competitors
will be higher than if all individuals are good competitors
(Weiner, 2003). Dennison et al. (2003) suggested that further
genetic improvement of crop yield potential over the next
163
decade will primarily involve tradeoffs between individual
competition and the collective performance of plant communities. In this study, root and tiller pruning improved grain yield
and WUE by lowering the competitive ability of winter wheat,
which suggests that attempts at drought-resistance breeding, at
least for wheat, should be made by targeted selection of a less
competitive progeny with a small R/S, and this study also
indicates that finding methods to manage the root system/
tillering pattern would be a potential approach to increase grain
yield and water use efficiency in arid and semiarid areas.
Acknowledgements
The authors appreciate the anonymous referees for their
valuable comments. We are also thankful to Dr. N C Turner for
editing the manuscript. This research was supported by NSFC
(30625025), ‘‘973’’ program (2007CB106804) and ‘‘111’’ project,
the Cultivation Fund of the Key Scientific and Technical Innovation
Project (704041) and Innovation Team Program, Ministry of
Education of China.
References
Caldwell, M.M., 1987. In: Gregory, P.J., Lake, J.V., Rose, D.A. (Eds.), Competition
Between Root Systems in Natural Communities. Root Development and
Function. Cambridge University Press, Cambridge, England, pp. 167–185.
de Wit, C.T., 1960. On competition. Verslagen van landbouwkundige onderzoekingen. Wageningen 66, 1–81.
Deng, X.P., Shan, L., Zhang, H., Turner, N.C., 2006. Improving agricultural water
use efficiency in arid and semiarid areas of China. Agric. Water Manage. 80,
23–40.
Dennison, R.F., Kiers, E.T., West, S.A., 2003. Darwinian agriculture: when can
humans find solutions beyond the reach of natural selection? Q. Rev. Biol.
78, 145–168.
Donald, C.M., 1968. The breeding of crop ideotype. Euphytica 17, 385–403.
Evans, L.T., 1993. Crop Evolution, Adaptation and Yield. Cambridge University Press,
Cambridge, 500 pp.
Fan, X.W., Li, F.M., Xiong, Y.C., An, L.Z., Long, R.J., 2008. The cooperative relation
between non-hydraulic root signals and osmotic adjustment under water
stress improves grain formation for spring wheat varieties. Physiol. Plant. 132,
283–292.
Hurd, E.A., 1974. Phenotype and drought tolerance in wheat. Agric. Meteorol. 14,
39–45.
Jackson, M., 1993. Are plants hormones involved in root to shoot communication?
In: Callow, J.A. (Ed.), Advances in Botanical Research, vol. 19. Academic Press,
pp. 103–187.
Jastrow, J.D., Miller, R.M., 1993. Neighbor influences on root morphology
and mycorrhizal fungus colonization in tall grass prairie plants. Ecology
72, 561–569.
Kramer, P.J., 1969. Plant and Soil Water Relationships: A Modern Synthesis.
McGraw-Hill, New York, NY, p. 482.
Lambers, H., Atkin, O.K., Scheureater, I., 1996. Respiratory patterns in root in relation
to their function. In: Waisel, Y., Eshel, A., Kafkafi, U. (Eds.), Plant Roots: The
Hidden Half. Marcel Dekker, New York, pp. 323–362.
Li, F.M., Liu, X.L., Li, S.Q., 2001. Effects of early soil water distribution on the dry
matter partition between roots and shoots of winter wheat. Agric. Water
Manage. 49, 163–171.
Li, F.M., Zhao, S.L., 1997. New approaches in researches of water use efficiency in
semiarid area of Loess Plateau. Chin. J. Appl. Ecol. 8, 104–109 (in Chinese with
English abstract).
Li, L.H., Chen, S.B., 2002. Study on root function efficiency of spring wheat under
different moisture condition. Sci. Agric. Sin. 35, 867–871 (in Chinese with
English abstract).
Li, Y.Y., Zhang, S.Q., Shao, M.A., 2003. Interrelationship between water use efficiency
and nitrogen use efficiency of different wheat evolution materials. Chin. J. Appl.
Ecol. 14, 1478–1480 (in Chinese with English abstract).
Liu, H.S., Li, F.M., 2003. The study of spring wheat root function efficiency under
water stress conditions. Acta Bot. Boreal. Occident. Sin. 23, 942–948 (in Chinese
with English abstract).
Liu, H.S., Li, F.M., Xu, H., 2004. Carbon consumption of roots and its relationship to
yield formation in spring wheat as affected by soil moisture. Acta Phytoecol. Sin.
28, 191–197 (in Chinese with English abstract).
Ma, S.C., Xu, B.C., Li, F.M., Liu, W.Z., Huang, Z.B., 2008. Effects of root pruning on
competitive ability and water use efficiency in winter wheat. Field Crops Res.
105, 56–63.
Ma, S.C., Li, F.M., Xu, B.C., Huang, Z.B., 2009. Effects of root pruning on the growth
and water use efficiency of winter wheat. Plant Growth Regul. 57, 233–241.
McCree, K.J., 1986. Measuring the whole-plant daily carbon balance. Photosynthetica 2, 82–93.
164
S.-C. Ma et al. / Field Crops Research 115 (2010) 158–164
Passioura, J.B., 1983. Roots and drought resistance. Agric. Water Manage. 7, 265–
280.
Reynolds, M.P., Acevedo, E., Sayre, K.D., Fischer, R.A., 1994. Yield potential in modem
wheat varieties: its association with a less competitive ideotype. Field Crops
Res. 37, 149–160.
Siddique, K.H.M., Belford, R.K., Tennant, D., 1990. Root:shoot ratio of old and
modern, tall and semidwarf wheat in a Mediterranean environment. Plant Soil
121, 89–98.
Song, L., Li, F.M., Fan, X.W., Xiong, Y.C., Wang, W.Q., Wu, X.B., Turner, N.C., 2009. Soil
water availability and plant competition affect the yield of spring wheat. Eur. J.
Agron. 31, 51–60.
Vysotskaya, L., Timergalina, L., Simonyan, M., Veselov, S., Kudoyarova, G., 2001.
Growth rate, IAA and cytokinin content of wheat seedlings after root pruning.
Plant Growth Regul. 33, 51–57.
Weiner, J., 2003. Ecology—the science of agriculture in the 21st century. J. Agric. Sci.
141, 371–377.
Zhang, D.Y., Sun, G.J., Jiang, X.H., 1999. Donald’s ideotype and growth redundancy: a
game theoretical analysis. Field Crops Res. 61, 179–187.
Zhang, R., Zhang, D.Y., Yuan, B.Z., 1999. A study on the relationship between
competitive ability and productive performance of spring wheat in semiarid
regions of Loess Plateau. Acta Phytoecol. Sin. 23, 205–210 (in Chinese with
English abstract).
Zhang, R., Zhang, D.Y., 2000. A comparative study on root redundancy in spring
wheat varieties released in different years in semi-arid area. Acta Phytoecol. Sin.
24, 298–303 (in Chinese with English abstract).
Zhang, S.Q., Shan, L., Deng, X.P., 2002. Relation between growth of root system and
water use efficiency during the evolution process. Chin. Sci. Bull. 47, 1327–1331
(in Chinese with English abstract).