Download Size and variability of crop productivity both impacted by CO 2

Size and variability of crop productivity both impacted by CO2
enrichment and warming-A case study of 4 year field experiment in a
Chinese paddy
Jianqing Wang1, Xiaoyu Liu1, Xuhui Zhang1, Pete Smith2, Lianqing Li1, , Timothy R.
Filley4, Kun Cheng1*, Mingxing Shen3, Yinbiao He1 and Genxing Pan1
1
Institute of Resource, Ecosystem and Environment of Agriculture, the Center of
Climate Change and Agriculture, Nanjing Agricultural University, 1 Weigang,
Nanjing, Jiangsu 210095, China
2
Institute of Biological and Environmental Sciences, University of Aberdeen, 23 St
Machar Drive, Aberdeen,
3
AB24 3UU, UK
Research Department of Agricultural Resources and Environment, Suzhou Academy
of Agricultural Sciences, Wangting Town, Suzhou, Jiangsu 215155, China
4
Department of Earth, Atmospheric & Planetary Sciences and the Purdue Climate
Change Research Center, Purdue University, West Lafayette, IN 47907, USA
Corresponding author: Kun Cheng
Email: [email protected]
Address: Institute of Resource, Ecosystem and Environment of Agriculture, Nanjing
Agriculture University, 1 Weigang, Nanjing, Jiangsu 210095, China
Tel.: +86 25 8439 9852
Fax: +86 25 8439 6507
Abstract
China is a key global region vulnerable to climate change; however, limited
studies have focused on of the combined impacts of atmospheric CO2 enrichment and
warming on crop production in arable land, especially in rice paddies in China. To
address this issue, a 4 year open-air field experiment during 2010 to 2014 was
conducted to simulate the impact of climate change on crop production in a rice paddy
in southeast of China. Four treatments including the ambient condition (CK), CO2
enrichment (500ppmv, CE), warming of canopy air (2 oC above the ambient, WA),
and the combined CO2 enrichment and warming (CW) were used to investigate the
responses of total biomass, crop yield and harvest index. In general, CE significantly
increased total biomass and grain yield of wheat and rice by 8.02%-17.63% and
6.39%-29.6% compared to CK. In contrast, total biomass and grain yield were
decreased by 4.38%-28.54% and 3.21%-37.08% under WA. However, there was no
significant difference of wheat biomass and yield between CW and CK, though rice
biomass was slightly decreased by 4.64% and 11.57% in 2011 and 2013, indicating
warming could offset and even reverse the positive effects of CO2 enrichment on
grain yield. The increases of 5.74% and 1.51% in harvest index of rice and wheat
were also observed under CW in 2013, respectively. The variation of rice yields
during 4 years was much lower than that of wheat yields; however, significant
changes in rice yield stability were observed under CE and WA, but no changes were
seen for wheat. The results indicated a significant uncertainty over future wheat and
rice production in response to climate change, and both stabilizing and increasing
grain yield under climate change are major challenges for agriculture in developing
countries.
Key words: Crop production; Climate change; CO2 enrichment; Warming;
Rice-wheat rotation
1. Introduction
The serious impact of global climate change on food production is well known
(Wheeler and von Braun, 2013). However, grain crop production will need to increase
by 70% to meet the demand for increasing population (Bruinsma, 2009). Feeding a
growing population in a changing climate presents an urgent challenge to global
society (Lobell et al., 2008; Ray et al., 2015). Coupled with population and
environmental pressures, it is important to understand the potential impacts of climate
change on crop production, and the means to alleviate these impacts. While
projections of the response of crop production to climate change at different regions
are known to vary, field experimental studies are needed to observe the impact of
climatic factors on crop growth, and to serve as an observational basis against which
to test models used to make future projections.
The increase of atmosphere CO2 concentration and air temperature are the main
features of climate and atmospheric change examined by many studies in recent years
(IPCC, 2013; Solomon et al., 2009; Walther et al., 2002). AtmosphericCO2
enrichment has been found to to enhance plant photosynthesis and then increase
crop biomass and yield (De Graaff et al., 2006; Rogers et al., 1995), but the
increments varied from 11 to 121% for wheat and 0.12% to 62% for rice, according to
the meta-analyses by Bender et al. (1999) and Ainsworth (2008). Limited attention,
however, has been paid to the effects of warming on plant growth. Several studies
have shown that warming decreased crop biomass and grain yield at sites in different
regions (Hatfield et al., 2011; Wheeler et al., 2000); however, a positive effect of
warming on rice biomass was observed at sites in Japan and Korea (Cheng et al., 2009;
Yun et al., 2012). Far fewer studies have focused on the interaction between warming
and CO2 enrichment on plant growth (Liu et al., 2014), and the combined effects are
still not well understood. For example, some studies suggest that warming could
negate the expected CO2 stimulation in crop photosynthesis and productivity (Baker
et al., 1992; Horie et al., 2000; Matsui et al., 1997; Prasad et al., 2006; Ruiz-Vera et
al., 2013; Ziska et al., 1996), but no effect or even a positive effect has been observed
in some agricultural and grassland ecosystems (Alberto et al., 1996; Dieleman et al.,
2012; Yun et al., 2012). In addition, yield stability is one of the key indicators used to
assess the food security, and this may also affected by climate change (Chloupek et al.,
2004; Schmidhuber and Tubiello, 2007). Therefore, there is an urgent need for a long
term multifactorial experiment to investigate the responses of crop production and its
variation to climate and atmospheric change.
Rice and wheat are both most important food crops, providing the staple grain
supply for about 8% of the world’s population (Ladha, 2003; Timsina and Connor,
2001). China is the one of most important food producing countries in the world, with
upland crop-paddy rice rotation accounting for 60% of the total rice paddies in China
(Frolking et al., 2002). Rice-winter wheat rotation is the major cropping system type
along the Yangtze River Basin (Zheng et al., 2000). In addition, there is a major
difference in irrigation management between rice and wheat. Therefore, assessing the
impact of climate change on rice-winter wheat systems provides an understanding of
the different responses of rice and upland crops, and the contribution of China to
global food security under climate change.
To address these issues, a simulated climatic change open field station has been
operated for four years in Southeast China. And the objectives of this study were to
determine: (i) responses of crop production to CO2 enrichment and warming, and their
interactions, (ii) differences between wheat and rice responses to CO2 enrichment and
warming, and (iii) effects of CO2 enrichment and warming on yield stability.
2. Materials and methods
2.1 Site description
This study was conducted in a field experimental station that simulates
atmospheric CO2 enrichment, warming and both in combination in an open air field.
The system was established in 2010 and is located at Kangbo village (31°30′N,
120°33′E), Guli Township, Changshu municipality in Jiangsu Province, China. The
site is a typical paddy field in the Taihu Lake region with a rice-winter wheat rotation.
The region has a subtropical monsoon climate with mean annual precipitation
between 1100-1200mm and the annual average temperature of 16 oC. The annual
average sunshine hours are > 2000h, and the annual average number of frost free days
is >230d. The daily rainfall and mean temperature during 2010-2014 are shown in Fig.
1. Daily weather data was obtained from the China Meteorological Data Sharing
Service System (http://new-cdc.cma.gov.cn:8081/home.do) for the station nearest to
the site. The soil is a Gleyic Stagnic Anthrosol formed on clayey lacustrine deposit
and cultivated under rice-wheat rotation for hundreds of years (loamy texture). The
major soil properties are listed in Table 1.
(Figure 1 here)
(Table 1 here)
2.2 Experiment design
The system was constructed under the state project of “Climate Change Impacts
on Crop Production and Mitigation” (2009-2013), and managed by the authors’
institute. An 8 m-diameter octagonal ring and area of 45 m2 each was treated with
atmospheric CO2 enrichment up to 500 ppm (CE) by pumping CO2 gas from a liquid
supplier, with warming of canopy air (WA) by 2oC over ambient with infrared heaters
over the crop canopy, and with interactive CO2 enrichment and warming as a
combination of the above two treatments (CW). An untreated ring with ambient
condition was set as control (CK). Each treatment was replicated in three rings with
the same infrastructure. A treatment ring plot is buffered by the surrounding untreated
paddy to minimize treatment cross-over effect. The actual average CO2 concentration
was monitored by Li-COR CO2 sensors (Li-COR Inc., Lincoln, NE, USA) and the
increment of canopy air temperature was monitored by infrared detector thermometers
(Model SI-121, Apogee instruments Inc, Logan, USA) as summarized in Table 2.
(Table 2 here)
For treatment CE and CW, pure CO2 (purity 99.99%) via a liquid tank was
injected into the ring plot with perforated pipes surrounding the ring. The consistency
of the CO2 concentration over the ring was controlled by automatic adjustment to
wind direction and velocity to ensure its stable distribution both temporally and
spatially. 17 Li-COR CO2 sensors (Li-COR Inc., Lincoln, NE, USA) are equipped
both over canopy and around the ring to automatically control the CO2 pumping (Fig.
2a).
Twleve ceramic infrared heaters (IR) (2000 W, 240 V, 1.65 m long × 0.14 m wide;
HS-2420, Kalglo Electronics Co., Inc., Bethlehem, PA, USA) supplying 140 W/m2 of
infrared radiation were equipped for each ring plot, and used to warm the canopies of
the heated plots to 2°C higher than the ambient temperature (Fig. 2b). The IR lamps
produced invisible radiation to elevate the canopy air temperature during the growing
season. The 6 infrared detector thermometers (Model SI-121, Apogee instruments Inc,
Logan, USA) were installed over the canopy and around the ring for feedback to the
air heating systems.
(Figure 2 here)
2.3 Field management
The field experiment was established between November in 2010 and November
in 2014. The winter wheat (Triticum aestivum L. cv. of yangmai No.14) was a locally
dominant cultivar, and was planted at a density of 300 seedlings m-2 with a row
spacing of 20cm, and the rice (Oryza sativa L. cv., Changyou No.5) was a japonica
hybrid cultivar, transplanted with the space of 3 seedlings per hill and 28 hills per m 2.
The rice transplanting date, wheat seeding date and harvest date are listed in Table 2.
Field management was carried out following local agronomic practices including
weed control, fertilization, water irrigation and insecticide application on the
experiment plots. Urea (46% N) and compound fertilizer (15 N: 15 P2O5: 15 K2O) for
N and compound fertilizer for P and K were used throughout the experiments. The
fertilizers were applied four times during the rice season and three times during the
wheat season. Urea was applied 2 days before rice transplanting and wheat seeding, at
an average rate of 187.5 kg ha-1 as basal fertilizers. Compound fertilizer (375kg ha-1
on average) was applied as topdressing after heading. Urea was applied two times in
the rice season and once in the wheat season as topdressing fertilizer at an average
rate of 150 kg ha-1. The basal fertilizer was thoroughly incorporated into the soil by
ploughing to a depth of 10 cm, and the topdressing was surface broadcast. Paddy rice
was irrigated with the regimes of continuous flooding, with two periods of drainage in
mid-season.
2.4 Sampling and data collection
Crop biomass and grain yield
Crop biomass was determined in this study to evaluate the response of crop
growth to different treatments. Firstly, all of the fresh boveground biomass in each
ring was collected and weighed, then three samples were randomly collected and
air-dried to calculate the water content (105 oC for 30 min, then 70 oC for 24 hours);
so that the aboveground biomass (AB, t ha-1) could be determined. Secondly, the roots
from 60 plants of wheat and 20 hills of rice were randomly collected and carefully
separated from soil in each ring; water content of the roots were also calculated
through air-drying, so that root biomass for each plant and hill could be determined;
belowground biomass (BB, t ha-1) could then be determined after the number of plants
and hills was counted for each ring. Total crop biomass (CB, t ha-1) was calculated
using the following equation:
𝐶𝐵 = 𝐴𝐵 + 𝐵𝐵
Grain yield was also determined to evaluate the impact of CO2 enrichment and
warming on crop economic characteristics. All of the crop grain was collected from
each ring and then threshed by portable thresher. Water content was measured from
three randomly collected samples were taken to determine the grain yield of wheat
and rice.
Harvest index
Harvest index (HI) could characterize the ability of a crop to transfer the
photosynthetic product to the grain which is the economically important part of the
plant. Some meta-analyses suggest that the harvest index could change by -10% to 21%
under CO2 enrichment compared to ambient condition (Ainsworth, 2008; Wang et al.,
2015). HI was calculated here as grain yield (GY, t ha-1) divided by aboveground
biomass using the equation:
𝐻𝐼 =
𝐺𝑌
𝐴𝐵
Stability of crop production
Given that the same cultivars and farm management were used over the four year
experiment, the coefficient of variability (C.V.) could be used to reflect the stability of
crop production in response to climate change. Therefore, the C.V. was also calculated
in this study as follows:
2
∑(𝐶𝑖,𝑗,𝑘 − 𝑀𝐶𝑖,𝑗 ) /3
𝐶𝑉𝑖,𝑗 =
× 100
𝑀𝐶𝑖,𝑗
Where, CVi,j represents the C.V. of ring i under treatment j; Ci,j,k is the crop
biomass, grain yield or harvest index of ring i under treatment j in kth year; and MCi,j
is the mean crop biomass, grain yield or harvest index of ring i under treatment j.
2.5 Statistical analysis
All data were expressed as means plus or minus one standard deviation of three
replicates. Two-way ANOVA followed by Duncan’s test was used to test the
differences between different treatments with a probability defined at p<0.05. All
statistical analyses were carried out using SPSS19.0.
3. Results
3.1 Total biomass
Total biomass of rice and wheat under different treatments were observed for
four years (Table 3). In general, CO2 enrichment increased rice biomass by 8.0%-17.6%
in most years (except 2013); however, the wheat biomass was significantly increased
by 13.5% and 17.6% only in 2013 and 2014. Warming could greatly decrease the
biomass of wheat and rice by 17.2%-28.5% and 4.4%-23.0% compared to current
climatic conditions, though the decrease in rice biomass was not significant in 2012.
Concurrent warming and CO2 concentration enrichment decreased rice biomass in
2011 and 2013 by 4.6% and 11.6%, respectively, but no response was observed in
wheat biomass over the four years.
(Table 3 here)
The coefficient of variation (C.V.) was calculated to characterize the inter-annual
variability of rice and wheat biomass under different treatments (Fig. 3). In general,
the C.V. of wheat was higher than that of rice. However, there was no significant
difference in wheat biomass between different treatments, while the inter-annual
variability of rice biomass under warming (18.4%) was significantly higher than that
under current climatic state (12.6%). In addition, concurrent warming and CO2
concentration enrichment increased rice biomass variability in this study.
(Figure 3 here)
3.2 Grain yield
The responses of grain yield to CO2 enrichment were different between rice and
wheat. As shown in Fig. 4, rice grain yield was
increased by 6.4% to 14.2% under
CO2 enrichment compared to current climatic conditions in most years (except 2013),
but there was no significant change in wheat grain yield under CO2 enrichment over
the 4 years. Warming reduced the grain yield of wheat and rice by 13.3%-37.1% and
3.2%-20.3%, respectively, in almost all years. Compared to current climate, no
changes in grain yield of wheat and rice were observed under concurrent warming and
CO2 concentration enrichment in any year.
(Figure 4 here)
Similarly to total biomass, there was no significant difference in the C.V. in
wheat grain yield between different treatments. However, rice yield had the lower C.V.
of 7.9% under CO2 enrichment, but the higher C.V. of 16.8% under warming
compared to current climate (12.7%). No inter-annual variability was observed in rice
grain yield under concurrent warming and CO2 concentration enrichment.
3.3 Harvest index
In this study, harvest index was calculated as the ratio of grain yield to
aboveground biomass. Harvest index is an important indicator for assessing the ability
of a crop to transfer the photosynthetic product to the grain. As indicated in Table 4,
no significant change of harvest index was observed in wheat or rice production in
most years. An increase of 8.2% was only found in wheat production under warming
in 2013, and the harvest index of wheat and rice was increased by 11.4% and 7.8%
respectively under concurrent warming and CO2 concentration enrichment, both in
2013.
(Table 4 here)
Some significant differences of harvest index C.V. were observed in both wheat
and rice production (Fig. 3). The C.V. of wheat harvest index was 22.4% under
warming, and was higher than the 13.2% under current climate. However, concurrent
warming and CO2 concentration enrichment increased the inter-annual variability of
the rice harvest index by as much as 117.9% compared to current climatic conditions.
4. Discussion
4.1 Responses of wheat and rice production to CO2 enrichment and warming
Clarifying the impact of climate and atmospheric change on agricultural
production is essential to ensure food security and future human well-being. There
have been many studies focused on simulating the impact of various climate change
scenarios on agriculture, based on climatic and ecosystem models (Adams et al., 1998;
Lobell et al., 2006; Olesen et al., 2007; Tubiello et al., 2000). However, field-based
experiments, especially open air experiments are still limited for climate change and
agricultural research, though a number of FACE (Free-air CO2 enrichment) and OTC
(Open-top chamber) experiments for agriculture have been conducted in some
countries such as Japan, USA, Germany and China (Baker et al., 1997; Weigel and
Manderscheid, 2012; Zhang et al., 2015; Zhu et al., 2015; Ziska et al., 1997).
Furthermore, experiments considering the interaction of CO2 enrichment and warming
on plant growth are scarce globally (Baker et al., 1992; Liu et al., 2014). To address
the above issues, a 4 year open-air field experiment was conducted to observe the
responses of total biomass, grain yield and harvest index of wheat and rice to both of
CO2 enrichment and warming in this study.
Most previous studies have reported an increase in biomass and yield stimulated
by CO2 enrichment,
mainly due to increased photosynthesis, and decreased
photorespiration, stomatal conductance and accelerated carboxylation (Ainsworth and
Rogers, 2007; Leakey et al., 2006; Long et al., 2004). As indicated in this 9study, rice
biomass and grain yield were increased by 7.4% and 9.9% on average under CO2
enrichment compared to current climate in most years. These results are consistent
with previous findings of an increase of 2.9% for rice biomass with a CO2
concentration of 673 ppm from a field study of Korea (Yun et al., 2012), and yet rice
yields were increased by 26.9% under CO2 enrichment (680 ppm) in a paddy field in.
Japan (Cheng et al., 2009). The total biomass of wheat was not changed under CO2
enrichment in the first two years, though an average 15.5% increase was observed in
2013 and 2014. Similarly, (Kou et al., 2007) observed an increase of 8.3-19% for
wheat biomass in the later period under CO2 enrichment based on an a FACE
experiment conducted in China. Some FACE experiments in Germany also found
10.6%-14% increases of wheat biomass under CO2 enrichment (Weigel and
Manderscheid, 2012). In most studies, CO2 enrichment can significantly increase the
grain yield of wheat by 7% to 15% (Amthor, 2001; Weigel and Manderscheid, 2012).
However, no change in wheat yield under CO2 enrichment was observed in any year
of this study, which indicates the spatial variation of CO2 enrichment effects exists in
agriculture (Ray et al., 2015; Wang et al., 2015).
In contrast, negative responses of both total biomass and grain yield to warming
were observed in most of years. Warming shortened the growing period, and led to
lower photosynthetic carbon assimilation, which can largely be attributed to declines
in stomatal conductance and intercellular CO2 concentration, which led in turn to
lower yields (Ainsworth and Ort, 2010; Hatfield et al., 2011; Kim et al., 2013;
Ruiz-Vera et al., 2013). In this study, rice yield was reduced by 3.2% to 20.3% under
warming, which is comparable with previous findings of 5.7% and 11% decreeases of
rice yield observed under warming in experiments from Japan (+10 oC) and Korea
(+1.7 oC) (Cheng et al., 2009; Yun et al., 2012). However, significant increases in total
biomass were found under warming in these two experiments (Cheng et al., 2009; Yun
et al., 2012). Again, our results show that responses are condition and region specific.
There are a very limited number of studies that have focused on the interaction
between CO2 enrichment and warming on crop growth (Cheng et al., 2009; Yun et al.,
2012). Both Cheng et al. (2009) and Yun et al. (2012) reported that there were no
significant changes of rice yield observed under concurrent warming and CO2
concentration enrichment compared to current climatic conditions, but that there was
a significant increase (8%~18%) in total rice biomass. Our study also shows no
changes in biomass and grain yield for wheat or rice under concurrent warming and
enriching CO2 concentration over 4 years. However, in contrast to previous studies,
decreases in rice biomass were found in individual years (2011 and 2013). Given the
positive effect of CO2 enrichment and negative effect of warming, this study shows
that warming may offset or even reverse the positive effect of CO2 enrichment on
biomass and grain yield (Baker et al., 1992; Ruiz-Vera et al., 2013). We also found
harvest index of both wheat and rice was increased under concurrent warming and
CO2 concentration enrichment, though this result is inconsistent with Cheng et al.
(2009) who reported a decrease of 13%. Increased harvest index in this study did not
result in an increase of grain yield in this study, mainly due to the strong negative
effect of warming. Given the complex responses detailed above, the interaction of
CO2 enrichment and warming should not be ignored in studies on climate change and
agriculture.
4.2 Variability of climate change effect on wheat and rice production
The C.V. was calculated to characterize the inter-annual variability of rice and
wheat production. Consistent with previous studies (Cheng et al., 2011; Wang et al.,
2009), wheat production had the higher inter-annual variability than rice, due to
management practices such as flooding irrigation in rice production (Fig. 3). While
there was no significant difference in the C.V. of wheat biomass and grain yield
between different treatments, both warming and concurrent warming and CO2
enrichment increased the variability of rice biomass. In addition, warming could also
intensify the variability of rice yield, though CO2 enrichment lowered it in this study
(Fig. 3). Ray et al. (2015) suggested that climate variation could explain one third of
the global crop yield variability. Recently, a study by Li et al. (2015) indicated that
there was a large uncertainty in accurately predicting rice yield in response to
increasing CO2 concentration and temperature.
The present study also found the variance of the responses of wheat and rice to
different treatments (Fig. 3; Table 5). The CO2 enrichment effect was not significant
in most years for wheat despite being found in previous studies (Amthor, 2001;
Aranjuelo et al., 2013; Weigel and Manderscheid, 2012). The significant response of
wheat and rice to concurrent warming and CO2 enrichment was not observed in most
years, but rice biomass was decreased under the CW treatment in 2011 and 2013. In
addition, the decreases of biomass and grain yield by warming varied from 4.4% to
28.5% and 3.2% to 37.1%. Taken together, our results suggest a large uncertainty
concerning the effect of climate and atmospheric change on crop production.
(Table 5 here)
To examine the causes of the inter-annual variance, we analyzed the daily mean
temperature at the grain filling stage of wheat and rice (Fig. 5). The grain filling stage
is critical for producing high yields because kernel size and weight are determined
during this stage (Herbek and Lee, 2009). Environmental factors affect the rate and
duration of the grain filling stage, and yields will be reduced by any environmental
stress (high temperatures, low soil moisture, etc.) occurring during the grain filling
stage. A previous study indicated an optimal temperature of 20.7 oC for grain filling in
wheat (Luo, 2011; Porter and Gawith, 1999). In comparison, the temperature during
the grain filling stage of wheat had the higher mean values of 20.8 oC and 20.3 oC, and
variations with the C.V. of 22.6% and 15.5% in 2011 and 2012 compared to 2013
(mean temperature of 18.1 oC and C.V. of 12.2%) and 2014 (mean temperature of
17.9 oC and C.V. of 11.7%) (Fig. 5). Furthermore, as many as 6 days when the
temperature exceeded 20.7 oC were found in the grain filling stages in 2011 and 2012,
compared to 2013 and 2014. The treatments of WA and CW still increased the
temperature by nearly 2 oC. Therefore, no CO2 effect but a significant decrease under
warming was observed in wheat grain yield in 2011 and 2012 (Table 5). In addition,
the decreases of wheat grain yield were much higher in 2011 and 2012 than in 2013
and 2014 (Table 3; Fig. 4). Given that the optimal temperature for rice grain formation
is about 25 oC (Baker et al., 1995), the number of days when the temperature
exceeded 25 oC in 2013 was 4, which was higher than in other years. The grain filling
stage of rice in 2013 also had the highest mean temperature (23 oC) and variation
(12.3%) (Fig. 5). Correspondingly, CO2 enrichment did not increase the rice yield
(only in 2013), and the decrease by warming was as high as 20.3% in 2013 compared
to other years (Table 5; Fig. 4). With a calculation of cumulative rainfall during the
grain filling stage, water supply was not an environmental stressor for wheat or rice in
this experiment (data not shown). Hence, inter-annual variation of air temperatures in
key growth stages may be one of the major factors determining the variability of
wheat and rice production under warming and CO2 enrichment in southeast China.
(Figure 5 here)
Although the responses of rice were greater than wheat in most years (Fig. 3),
drought may be a risk factor for wheat production under climate change, but not for
rice production due to irrigation management (De Vita et al., 2007; Eitzinger et al.,
2003). A study conducted by Farhangfar et al. (2015) suggested that crop production
will be extremely vulnerable to probable droughts under future climate change. Piao
et al. (2010) also reported that regional and inter-annual variability of rainfall will
increase in the future. In addition, as monitored and predicted by previous studies,
climate warming will expand the area suitable for rice cropping systems and
multiple-cropping systems (Ye et al., 2015), indicating an increasing exposure for
crop production under climate change. Combined with the uncertainties detailed
above, maintaining food security under severe climate change is great challenge faced
by agriculture, especially in developing countries.
Conclusion
The responses of total biomass, grain yield, harvest index and yield stability of
wheat and rice to CO2 enrichment and warming were investigated with an open air
experimental site in Southeast China. In general, CO2 enrichment increased, but
warming decreased, total biomass and grain yield of wheat and rice, though the
inter-annual variation of these responses was large. The results from the treatment of
concurrent CO2 enrichment and warming indicated that warming may offset or even
reverse the positive effect of CO2 enrichment. There was no significant response of
harvest index in most years, but the harvest index was increased under warming and
concurrent CO2 enrichment compared to current climatic conditions in 2013. The
yield stability of rice was higher than that of wheat; however, concurrent CO2
enrichment and warming significantly decreased the stability of rice yield. These
results indicate a large variability of wheat and rice production in response to climate
change in China.
Acknowledgement
This work was supported by Ministry of Science and Technology of the People's
Republic of China under a grant number 2012BAC19B01 and Ministry of Agriculture
of the People's Republic of China under a grant number 200903003. This work was
also funded by “111 project” (B12009) and the Priority Academic Program
Development of Jiangsu Higher Education Institutions (PAPD). The authors thank
Jiangsu Tianniang Agro-Technology Company LTD for the assistance in maintaining
the experiment system. The contribution of PS was funded under the Chinese
Ministry of Agriculture and the United Kingdom Department for Environment, Food
and Rural Affairs (DEFRA) UK-China Sustainable Agriculture Innovation Network
(SAIN).
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Table 1. The physical-chemical properties of the topsoil before the experiment at the
study field (0-15cm).
Organic
carbon
/g·kg-1
19.2
Total N
Total K
Total P
/g·kg-1
/g·kg-1
/g·kg-1
1.3
15.0
0.9
bulk
pH(H2O)
density
texture/%
porosity/ %
/g·cm-3
7.0
1.2
54.3
sand
silt
clay
33.8
38.6
27.6
Table 2. Date of rice transplanting or wheat seeding and harvest, and mean
temperature increments and atmospheric CO2 concentration under warming or CO2
enrichment treatments during 2011-2014.
Rice transplanting or
Year
Crop
2011
Wheat
8th November 2010
Rice
2012
2013
2014
Wheat seeding date
Harvest date
Warming
o
CO2 enrichment
( C)
(ppm)
8th June 2011
1.4±0.7
501±17
25th June 2011
31st October 2011
1.6±0.4
504±16
Wheat
6th November 2011
24th May 2012
1.4±0.5
505±18
Rice
15th June 2012
28th October 2012
1.8±0.6
514±55
Wheat
23th November 2012
2nd June 2013
1.5±0.7
505±26
th
th
Rice
20 June 2013
29 October 2013
1.8±0.7
535±21
Wheat
10th November 2013
28th May 2014
2.0±0.3
511±20
Rice
23th June 2014
1st
1.6±0.4
505±18
November 2014
Table 3 The total biomass (t ha-1) of wheat and rice under different treatments during
2011-2014.
Crop
Treatments 2011
2012
2013
2014
CK
20.80±2.16a 14.94±0.57a 11.96±0.54b 13.07±0.11b
CE
22.71±2.00a 15.53±0.67a 14.06±0.93a 14.84±0.58a
Wheat
WA
14.87±0.39b 11.31±0.39b 9.90±0.48c
10.67±0.42c
CW
20.53±1.04a 15.20±1.33a 10.77±1.47bc 12.43±0.13b
CK
19.38±0.15b 15.21±1.14b 18.59±0.37a 20.52±0.42b
CE
20.94±0.39a 17.89±0.50a 19.39±0.67a 22.48±0.16a
Rice
WA
18.54±0.35c 13.37±1.03b 14.33±0.98c 19.19±0.11c
CW
18.49±0.59c 14.05±0.97b 16.44±0.33b 20.84±0.31b
CK: ambient CO2 and temperature; CE: elevated CO2 and ambient temperature; WA:
ambient CO2 and warming; CW: elevated CO2 and warming. Different letters indicate
significant differences of crop biomass between treatments in the same year at p<0.05.
Table 4 The Harvest index of wheat and rice under different treatments during
2011-2014.
Crop
Treatments 2011
2012
2013
2014
CK
0.44±0.003 0.42±0.01 0.51±0.02b 0.56±0.03
CE
0.45±0.02 0.44±0.05 0.54±0.02ab 0.57±0.02
Wheat
WA
0.43±0.01 0.36±0.01 0.55±0.02a 0.60±0.01
CW
0.45±0.002 0.46±0.08 0.57±0.01a 0.58±0.03
CK
0.48±0.001 0.50±0.01 0.52±0.003b 0.48±0.02
CE
0.47±0.01 0.49±0.01 0.51±0.02b 0.47±0.003
Rice
WA
0.48±0.03 0.49±0.01 0.54±0.03ab 0.49±0.01
CW
0.47±0.01 0.51±0.01 0.56±0.003a 0.47±0.02
No letters indicate the ANOVA was not significant at P>0.05. Different letters indicate
significant differences between treatments in the same year at p<0.05.
Table 5 Responses of total biomass, grain yield and harvest index to different treatments during 2011-2014.
Crop
WA
2011 2012 2013 2014
2011 2012 2013 2014
Harvest index
○
○
○
○
○
○
Total biomass
+
+
Grain yield
+
+
Harvest index
○
○
Wheat Total biomass
Grain yield
Rice
CE
—
—
—
○
○
○
○
○
○
—
—
—
—
—
—
○
○
○
+
+
○
○
—
—
○
+
—
○
○
+
○
2011 2012 2013 2014
—
+
○
○
○
○
CW
○
○
+
○
○
○
○
○
○
○
○
○
○
+
—
○
+
○
○
○
○
○
○
The ○ means no significant at p>0.05. + and - indicated a significant increase and decrease under the treatments compared to CK at p<0.05,
respectively.
Figure Captions:
Fig. 1 The daily rainfall and mean temperature during 2010-2014.
Fig. 2 Diagram for open air experimental field employed in this study. a, Li-COR CO2
sensors labeled as red point are equipped with in CE and CW; b, Ceramic infrared
heaters (IR) labeled as red line were equipped in WA and CW.
Fig. 3 Response of coefficient of variable (total biomass, and grain yield, and harvest
index) to different treatments during 2011-2014. No letters indicate the ANOVA was
not significant at P>0.05. Different letters indicate significant differences between
treatments in the same year at p<0.05.
Fig. 4 The grain yield of wheat and rice under different treatments during 2011-2014.
No letters indicate the ANOVA was not significant at P>0.05. Different letters indicate
significant differences between treatments in the same year at p<0.05.
Fig. 5 The daily mean temperature at filling stage of wheat and rice during
2010-2014.
Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5