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European Journal of Agronomy
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patiotemporal changes of wheat phenology in China under the effects ofemperature, day length and cultivar thermal characteristics
ulu Taoa,∗, Shuai Zhanga,c, Zhao Zhangb
Institute of Geographical Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, ChinaState Key Laboratory of Earth Surface Processes and Resource Ecology, Beijing Normal University, Beijing 100875, ChinaGraduate University of Chinese Academy of Sciences, Beijing 100039, China
r t i c l e i n f o
rticle history:eceived 4 July 2012ccepted 6 July 2012
eywords:mpactdaptationrop cultivarlimate changeultivar thermal requirementrop growing period
a b s t r a c t
Investigating the spatiotemporal changes of crop phenology in field is important to understand theprocesses and mechanisms of crop response and adaption to ongoing climate change. Here, thewheat phenology at more than 100 national agro-meteorological experiment stations across Chinaspanning the years 1981–2007 was examined. Spatiotemporal changes of wheat phenology andseasonal temperature, as well as the correlations between them were presented. During the investi-gation period, heading dates advanced significantly at 43 stations from the 108 investigated stations;maturity dates advanced significantly at 41 stations from the 109 investigated stations. Lengths ofgrowing period (from sowing to maturity) and vegetative growing period (from sowing to heading)were significantly reduced at about 30% of the investigated stations, especially for spring wheat innorthwestern China, despite thermal accumulation during the periods increased. In contrast, althoughsignificantly and negatively related to mean temperature, lengths of reproductive growing period (fromheading to maturity) increased at 60% of the investigated stations, owing to increase in crop cultivars ther-mal requirements or/and decrease in mean temperature. The results showed that besides the complexinfluences of agronomic factors, climate change contributed substantially to the shift of wheat phenology.Mean day length during vegetative growing period had a decreasing trend at most of the investigatedstations owing to delay of sowing date or/and advancement of heading date, which counterbalanced
the roles of temperature in controlling the duration of vegetative growing period. In-depth analysesshowed that thermal requirements from sowing to almost each development stage increased, howeverthe thermal requirements to complete each single development stage changed differently, which tendedto increase yield and adapt to ongoing climate change. Our findings have important implications forimproving climate change impact studies, for breeding scientists to breed higher yielding cultivars, andfor agricultural production to cope with ongoing climate change.
. Introduction
Phenology, the study of the timing of recurring biological phases,he biotic and abiotic forces that cause the variation in timing, andhe interrelation among phases of the same or different speciesLieth, 1974), is experiencing a renaissance in global change sci-nce as it is providing society with an independent measure on howcosystems are responding to climate change (Myneni et al., 1997;hite et al., 1997; Menzel and Fabian, 1999; Zhang et al., 2004;
ao et al., 2008a; White et al., 2009). Plant phenology is stronglyontrolled by short- and long-term variability in climate and hasonsequently become one of the most reliable bio-indicators of
ongoing climate change (White et al., 1997; Badeck et al., 2004;Menzel et al., 2006). A shift in vegetation phenology influences thetiming and duration of a photosynthetically active canopy, influ-ences both the amplitude and timing of seasonal cycles of carbonand water fluxes, and could have a large impact on the global carboncycle (Keeling et al., 1996; Myneni et al., 1997). Researchers haveused numerous techniques to observe how phenology has shiftedin recent decades, including species-level observations from phe-nological network (e.g., Menzel and Fabian, 1999; Schwartz andReiter, 2000; Menzel et al., 2001; Parmesan and Yohe, 2003; Taoet al., 2006), and satellite remote-sensing based techniques (e.g.,Zhang et al., 2004; Beck et al., 2006; Tao et al., 2008a). Vegetation
phenological seasons have been shown to change spatially and tem-porally in response to trends in climate change across the northernhemisphere (e.g., Myneni et al., 1997; Menzel et al., 2001; Zhanget al., 2004). Many studies have documented an earlier onset of
pring for mid- and higher latitudes and a significant extension ofhe growing season particularly in the northern hemisphere, due tolimate warming (Menzel and Fabian, 1999; Penuelas and Filella,001; Walther et al., 2002; Parmesan and Yohe, 2003; Craufurd andheeler, 2009).However most studies focus on changes in the natural vegeta-
ion; only a few deal with trends in agricultural and horticulturalarieties so far (e.g., Chmielewski et al., 2004; Hu et al., 2005;ao et al., 2006; Estrella et al., 2009; Peltonen-Sainio and Rajala,007; Sacks and Kucharik, 2011; Siebert and Ewert, 2012). Sinceultivated land accounts for a large proportion (about 12%) ofhe global land-surface area (Ramankutty and Foley, 1998), shiftsn crop phenology can have important impacts on land surfacearbon and water fluxes, hydrological processes, regional climatend global carbon cycle. Crop phenology is also closely related togro-meteorological disasters and productivity, and consequentlyas important economic implications. Crop phenology is relativelyomplex due to the confounding effects of climatic and agronomicactors (Porter and Delecolle, 1988; Hilden et al., 2005; Estrella et al.,009). Nevertheless some phases of annual crop, such as heading,owering and maturity date, were found to be strongly affectedy weather and climate (e.g., Chmielewski et al., 2004; Hu et al.,005; Tao et al., 2006; Estrella et al., 2009; Peltonen-Sainio andajala, 2007; Sacks and Kucharik, 2011; Siebert and Ewert, 2012).or instance, in Germany, a shift in phenology of fruit trees and fieldrops due to increased temperature from 1961 to 2000 had beenbserved, but the changes in plant development were still mod-rate so no strong impacts on yield formation processes had beenbserved so far (Chmielewski et al., 2004). In the U.S. Great Plains,consistent trend of earlier heading or flowering dates across six
ites, with rates of the trend varying from 0.8 to 1.8 days/decade,as indicated, due to increase in spring daily minimum temper-
tures (Hu et al., 2005). In China, significant warming trends ineasonal temperature had shifted crop phenology and affected cropields at 5 investigated stations across China during 1981–2000Tao et al., 2006). Estrella et al. (2009) examined the phenology of8 agricultural and horticultural events from a national survey inermany spanning the years 1951–2004. They found the majorityf events advanced significantly, 78% of mean trends in emergencend flowering dates of annual crops were significant, and morehan 80% of the correlation coefficients between crop phenologyhanges and seasonal temperatures were significant. Siebert andwert (2012) documented that the significant warming trend since959 resulted in an earlier onset of all phenological stages and ahortening of most phenological phases for oat in Germany.
Here, we emphasize the necessity to investigate the spatiotem-oral changes of crop phenology in field, as well as the roles ofemperature, day length and crop cultivars thermal characteristics,o understand the processes and mechanisms of crop response tongoing climate change. We believe it is important to investigatehe shift of crop phenology and the development of cultivar ther-
al and phenological characteristics in the past few decades inesponse and adaptation to climate change. Such studies can accel-rate our understanding on the mechanisms of crop phenologyhift under the combined effects of climate and agronomic fac-ors, as well as the potential impacts on crop productivity (Migliettat al., 1995; Tao et al., 2009). For example, crop productivity wasrojected to decrease under climate warming due to acceleratedevelopment and shortened growing period (Estrella et al., 2009;
PCC, 2007; Tao et al., 2008b), how has the growing period of fieldrop, particularly the grain-filling period, been shortened in theast few decades?
The purposes of the present study are (1) to investigatehe spatiotemporal change in patterns of wheat phenologyased on the long-term records at more than 100 agro-eteorological experiment stations across China; (2) to analyze
my 43 (2012) 201–212
how climate and day length has changed and how climatechange and day length has influenced the wheat phenologi-cal events during the period of 1981–2007; and further (3)to understand the development of crop cultivar phenologicaland thermal characteristics, as well as the implications for foodproduction prediction and agricultural adaptation to climatechange.
2. Materials and methods
2.1. Wheat phenology and climate data
The data on wheat phenology, yields and climate come fromChina agro-meteorological experiment stations, which were main-tained by the Chinese Meteorological Administration. The recordson wheat phenology were available from 1981 to 2007 at 20stations and from 1992 to 2007 at additional more than 300 sta-tions, however with missing records. In the present study, onlystations with more than 10 years records were used for analysis.Finally there were 105, 108 and 109 stations selected to analyzethe spatial and temporal patterns of wheat sowing dates, head-ing dates and maturity dates, respectively. The datasets of dailyand monthly mean temperature at these stations were used in thestudy.
2.2. Mean temperature and accumulated thermal developmentunit during crop growing period
Wheat growing period (GP) is defined as the period from sow-ing to maturity; vegetative growing period (VGP) is defined as theperiod from sowing to heading; and reproductive growing period(RGP) is defined as the period from heading to maturity. Mean tem-perature (Tmean) during GP is calculated based on the daily meantemperature from sowing date to maturity date in a year. Tmean dur-ing VGP (RGP) is calculated based on the daily mean temperaturefrom sowing date to heading date (from heading date to maturitydate) in a year.
Accumulated thermal development unit (ATDU) during a devel-opment period such as GP, VGP and RGP was calculated as themethods used by the CROPSIM/CERES-Wheat version 4.0 model inDSSAT 4.0 (Hoogenboom et al., 2004). The methods were describedin details by McMaster et al. (2008). The rate of developmentvaries with temperature per se, vernalization and photoperiod(Kirby et al., 1985; Porter and Delecolle, 1988), the use of ATDUin many crop models can simulate crop development rate fairlywell (e.g., Porter et al., 1987; Jamieson et al., 1995; Ewert et al.,1996; McMaster et al., 2008; Xiao et al., 2012; Liu and Tao,submitted for publication). ATDU represents comprehensively thecharacteristics of cultivars including thermal requirements, ver-nalization requirements, and photoperiod sensitivity. Therefore,trend in ATDU represents the comprehensive effects of changesin cultivars characteristics, temperature and day lengths on cropphenology.
ATDU during a development period is the sum of daily thermaldevelopment unit (DTDU) during the period. DTDU before headingdate is calculated as:
DTDU = DTT × VF × DF (1)
where DTT (degree days, ◦C d) is the daily thermal time, VF(0 ≤ VF ≤ 1) is a vernalization factor and DF (0 ≤ DF ≤ 1) is a pho-toperiod factor. DTT is calculated by comparing daily Tmean with
F. Tao et al. / Europ. J. Agronomy 43 (2012) 201–212 203
ical zo
ci
D
Itiit
V
w(la
V
T
D
Wd
D
Wztw
Fig. 1. Classifications of wheat ecolog
ardinal temperatures, and reducing DTT by a 0 to 1 factor if Tmean
s outside the optimal range of temperature:
TT =
⎧⎪⎪⎪⎪⎪⎪⎨⎪⎪⎪⎪⎪⎪⎩
0.0 Tmean < Tb E Tmean ≥ Tmax
Tmean
Tol× Tmean Tb ≤ Tmean < Tol
Tmean Tol ≤ Tmean < Tou
Tmax − Tmean
Tmax − Tou× Tmean Tou ≤ Tmean < Tmax
(2)
n this study, the base temperature (Tb), lower optimum tempera-ure (Tol), upper optimum (Tou) and maximum temperature (Tmax)s set to be 0 ◦C, 30 ◦C, 50 ◦C and 60 ◦C, respectively, which has beenndicated to be accurate for a wide range of sowing dates and geno-ypes (McMaster et al., 2008).
VF is calculated as:
F = VF0 +(
CUMVD
P1V
)(3)
here VF0 is the relative development rate when unvernalizedVF0). CUMVD is the accumulated vernalization-days and calcu-ated as McMaster et al. (2008). P1V is required vernalization days,cultivar-specific parameter. VF0 is calculated as:
F0 = 1 −(
P1V
50
)(4)
he photoperiod factor DF is calculated as:
F = 1 −[(
P1D
10, 000
)× (20 − PP)2
](5)
heat development rate after heading date is assumed to be onlyependent on temperature, and DTDU is calculated as:
TDU = DTT (6)
heat cultivation areas in China were classified into nine ecologicalones (Jin, 1991) (Fig. 1). The values of P1V and P1D parameters forhe typical cultivar in each ecological zone were listed in Table 2,hich had been calibrated and validated in previous studies (Xiao
nes across China based on Jin (1991).
et al., 2012; Liu and Tao, submitted for publication; Xiong et al.,2008).
2.3. Description of representative stations for detailed analyses
To further investigate the changes of day lengths, the develop-ment of cultivar thermal characteristics and its potential effects oncrop phenology, detailed analyses were conducted at three rep-resentative stations, i.e. Zhengzhou station in the NCP, Tianshuistation and Dunhuang station in northwestern China (Fig. 2A). Theinformation about climate during 1981–2000, as well as the typicalcropping system at these stations, was detailed in Table 1.
2.4. Analysis
We distinguished spring wheat from winter wheat by sowingdate. Spring wheat had sowing dates generally within the periodfrom the beginning of the year till the end of May (DOY 1–151).Trends in wheat phenological events during 1981–2007 wereinvestigated using linear regression analyses. Trends in lengths ofGP, VGP and RGP, Tmean and ATDU during GP, VGP and RGP, as wellas the correlations between them, were investigated using linearregression and Pearson correlation analyses. Statistical significancewas tested using the two-tailed t-test.
3. Results
3.1. Spatiotemporal changes of wheat sowing dates, headingdates and maturity dates
Mean wheat sowing dates had an obvious regional pattern dur-ing the investigation period (Fig. 2A). Spring wheat, cultivated innorthwestern and northeastern China, had sowing dates before the
end of May (DOY 151). Winter wheat, cultivated widely from theNorth China Plain (NCP) to southwestern China, had sowing datesgenerally from the beginning of October (DOY 274) to the middleof November (DOY 320). During the investigation period, trends
204 F. Tao et al. / Europ. J. Agronomy 43 (2012) 201–212
F wheat signip ted by
itas
t
TD
ig. 2. Mean date of wheat sowing (A) and trend in sowing date (B), mean date ofrend in maturity date (F), during the period of 1981–2007. The stations with trenderiod from the beginning of the year till the end of May (DOY 1–151) were cultiva
n sowing dates across the stations were diverse (Fig. 2B). Fromhe 105 investigated stations, sowing dates advanced significantlyt 6 stations by up to 9.1 days/decade (p < 0.05), however delayed
ignificantly at 11 stations by up to about 10 days/decade.
Mean wheat heading dates also had an obvious regional pat-ern during the investigation period (Fig. 2C). Spring wheat in
able 1escriptions of three representative stations that were selected for detailed analyses.
Stations Latitude Longitude Annual meantemperature (◦C)
Zhengzhou 34◦43′N 113◦39′E 14.4
Tianshui 34◦35′N 105◦45′E 11.2
Dunhuang 40◦09′N 94◦41′E 9.6
t heading (C) and trend in heading date (D), mean date of wheat maturity (E) andficant at 0.05 level are marked by a flag. The stations with sowing dates within thespring wheat, and all other stations were cultivated by winter wheat.
northwestern and northeastern China had heading dates gener-ally from end of May to beginning of July (DOY 139–193). Winterwheat had heading dates generally from middle of February (DOY
46) to middle of May (DOY 138). During the study period, head-ing dates advanced to some extent at most of the investigatedstations (Fig. 2D). From the 108 investigated stations, heading
Annual totalprecipitation (mm)
Typical cropping system
623 Rotation between winterwheat and maize
494 Rotation between winterwheat and maize
424 Spring wheat
F. Tao et al. / Europ. J. Agronomy 43 (2012) 201–212 205
Table 2The values of P1V and P1D parameters used for calculating ATDU in different ecological zones across China.
Ecological zone Wheat types P1V P1D References
I Winter wheat 40 40 Xiao et al. (2012), Liu and Tao (submitted for publication)II Winter wheat 40 40 Xiao et al. (2012), Liu and Tao (submitted for publication)III Winter wheat 30 40 Liu and Tao (submitted for publication)IV Winter wheat 30 40 Liu and Tao (submitted for publication)
Winter wheat 30 40 Liu and Tao (submitted for publication)V Spring wheat 0.1 65 Xiong et al. (2008)
Winter wheat 68 22 Xiong et al. (2008)VI Spring wheat 0.1 67 Xiong et al. (2008)VII Spring wheat 0.1 86 Xiong et al. (2008)VIII Spring wheat 0.1 67 Xiong et al. (2008)IX Spring wheat 0.1 67 Xiong et al. (2008)
Fig. 3. Trends in length of wheat growing period (GP) (A) and Tmean during GP (B), the correlation between length of GP and Tmean (C), trend in ATDU during GP (D), and thecorrelation between ATDU and Tmean during GP (E), during the period of 1981–2007 at 93 agro-meteorological experiment stations across China. The stations with the trendssignificant at 0.05 level were marked by a flag.
2 grono
d1
seSett(
F(w
06 F. Tao et al. / Europ. J. A
ates advanced significantly at 40 stations (p < 0.05) by up to about2.8 days/decade.
The regional patterns of mean wheat maturity dates during thetudy period were shown in Fig. 2E. Spring wheat in northwest-rn and northeastern China became mature generally from July toeptember (DOY 182–253). Winter wheat had maturity dates gen-rally from April (DOY 94) to June (DOY 181), from southwestern to
he NCP. During the study period, from all the 109 investigated sta-ions, maturity dates advanced significantly at 41 stations (p < 0.05)Fig. 2F).
ig. 4. Trends in length of wheat vegetative growing period (VGP) (A) and Tmean during VGD), and the correlation between ATDU and Tmean during VGP (E), during the period of 19ith the trends significant at 0.05 level were marked by a flag.
my 43 (2012) 201–212
3.2. Spatiotemporal changes of wheat growing period, Tmean, andATDU
Length of GP showed a decreasing trend at most of the stations(Fig. 3A). It decreased significantly at 26 stations from the 93 inves-tigated stations, mainly in central and northwestern China. Tmean
during GP increased significantly at 47 stations (Fig. 3B). Length of
GP was significantly and negatively correlated with Tmean duringGP at 21 stations (Fig. 3C), mainly for spring wheat. ATDU dur-ing GP increased significantly at 18 stations mainly in central and
P (B), the correlation between length of VGP and Tmean (C), trend in ATDU during VGP81–2007 at 94 agro-meteorological experiment stations across China. The stations
gronom
nzp
isu2cwTts
FRw
F. Tao et al. / Europ. J. A
orthwestern China, and decreased in some areas in ecologicalones III and V (Fig. 3D). ATDU during GP was significantly andositively correlated with Tmean at most of the stations (Fig. 3E).
Further analyses showed that length of VGP also had a decreas-ng trend at most of the investigated stations (Fig. 4A). It decreasedignificantly at 26 stations from all the 94 investigated stations byp to 14 days/decade. Tmean during VGP increased significantly at6 stations (Fig. 4B). Length of VGP was significantly and negativelyorrelated with Tmean at 20 stations, mainly for spring wheat. Forinter wheat, length of VGP was not significantly correlated with
mean for most cases owing to the effects of vernalization and pho-operiod (Fig. 4C). ATDU during VGP increased significantly at 15tations, however decreased significantly at 5 stations (Fig. 4D).
ig. 5. Trend in length of wheat reproductive growing period (RGP) (A) and Tmean duringGP (D), and the correlation between ATDU and Tmean during RGP (E), during the period of 1ith the trends significant at 0.05 level were marked by a flag.
y 43 (2012) 201–212 207
ATDU during VGP was significantly and positively correlated withTmean at most of the stations (Fig. 4E).
The length of RGP increased at 58 stations, although alsodecreased at 40 stations. It increased significantly at 11 stationsfrom the 98 investigated stations by up to 6.3 days/decade, in con-trast decreased significantly at 3 stations (Fig. 5A). Tmean duringRGP increased significantly at 17 stations in northwestern China,in contrast decreased at some stations in the southern part of NCP(ecological zone III) and southwestern China (ecological zone V)(Fig. 5B), owing to the advancement of heading and maturity date.
Length of RGP was significantly and negatively correlated withTmean during RGP at 53 stations (Fig. 5C), suggesting Tmean con-tribute much to changes of RGP, besides the influences of cultivars
RGP (B), the correlation between length of RGP and Tmean (C), trend in ATDU during981–2007 at 98 agro-meteorological experiment stations across China. The stations
208 F. Tao et al. / Europ. J. Agronomy 43 (2012) 201–212
the tr
tan
3p
(wolgoasdctcwwlfZdt
Fig. 6. Correlation between length of VGP and sowing date (A), as well as
urnover. ATDU during RGP increased significantly at 24 stations,nd decreased significantly at 4 stations (Fig. 5D), which was sig-ificantly correlated with Tmean at most of the stations (Fig. 5E).
.3. Effects of day length on spatiotemporal changes of wheathenology
Length of VGP was not significantly correlated with Tmean
Fig. 4C); by contrast, it was significantly and negatively correlatedith sowing date (Fig. 6A). This indicated the obvious dependence
f length of VGP on photoperiod (Miglietta et al., 1995). Mean dayength during VGP had a decreasing trend at most of the investi-ated stations owing to delay of sowing date or/and advancementf heading date (Fig. 6B). It decreased significantly at 39 stations,lthough the actual changes of day length were generally quitemall at most of the stations. Decrease in day length reduced wheatevelopment rate during the period from emergence to heading,ounterbalancing the roles of temperature to some extent in con-rolling the duration of VGP. For examples, at a station, withouthange of latitude, the change of mean day length during VGPas mainly induced by shift of sowing and heading dates, whichere generally quite small (Fig. 7). The small changes in mean day
ength caused slight changes in trends of heading dates in the past
ew decades. For example, at the three representative stations, i.e.hengzhou, Tianshui and Dunhuang, mean day length during VGPecreased by 0.008, 0.003, and 0.01 h/year, respectively; by con-rast, Tmean during VGP increased by 0.067, 0.07 and 0.05 ◦C/year.
end in mean day length during VGP during the period of 1981–2007 (B).
While comparing the ATDU with and without accounting for DFfactor, we found ATDU was obviously reduced if the effects of daylength were taken into account, and the changes in day length dur-ing VGP caused slight changes in the interannual variability andlong-term trend of ATDU (Fig. 7). The significant increases in Tmean
during VGP played a key role in affecting trends in ATDU and con-sequently heading dates.
3.4. Development of cultivar thermal characteristics and its rolein crop phenology
Besides climatic factors, cultivar thermal characteristics couldplay important role in affecting crop phenology. We furtherillustrated changes in wheat phenology and the roles of temper-ature and cultivar thermal characteristics at three representativestations, i.e. Zhengzhou, Tianshui and Dunhuang station. AtZhengzhou station, from 1981 to 2007, wheat sowing datesadvanced not significantly. Wheat heading dates advanced signif-icantly by 6.0 days/decades. Maturity dates advanced significantlyby 2.4 days/decades. Crop cultivars were frequently replaced dur-ing the period. The thermal requirements of cultivars from sowingto each development stage increased (Fig. 8A), however the ther-mal requirements for completing each single development stage
changed differently. The thermal accumulation during winter dor-mancy increased. The thermal requirements from spring green-upto heading and from milky ripe to physiological maturity decreased.By contrast, the thermal requirements from heading to milky
F. Tao et al. / Europ. J. Agronomy 43 (2012) 201–212 209
F ith aa
ria
isriplaa
ssaftifl
4
4c
satc
ig. 7. Trends in day length and Tmean during VGP, as well as the calculated ATDU wnd Dunhuang station (C).
ipe (i.e. grain-filling stage) increased significantly. Length of RGPncreased significantly (p < 0.01), although length of VGP (p < 0.01)nd GP decreased (Fig. 8A).
At Tianshui station, from 1981 to 2003, sowing dates and head-ng dates advanced not significantly. Maturity dates advancedignificantly by 3.8 days/decades. During the period, the thermalequirements of cultivars from sowing to each development stagencreased (Fig. 8B). The thermal requirements from milky ripe tohysiological maturity decreased. By contrast, the thermal accumu-
ation during winter dormancy, from spring green-up to heading,nd from heading to milky ripe, all increased. Lengths of VGP, RGPnd GP decreased not significantly (Fig. 8B).
For spring wheat at Dunhuang station, from 1981 to 2007,owing dates advanced not significantly. Heading dates advancedignificantly by 5.3 days/decade during 1992–2007. Maturity datesdvanced not significantly. The thermal requirements of cultivarsrom sowing to jointing, from sowing to heading, and from sowingo maturity, all increased (Fig. 8C). ATDU from jointing to head-ng decreased. By contrast, ATDU from heading to milky ripe, androm milky ripe to maturity increased. Length of RGP increased, andength of VGP and GP decreased slightly (Fig. 8C).
. Discussion
.1. Wheat phenology in field under the combined effects oflimate change, photoperiod and cultivar thermal characteristics
Wheat heading dates, consequently length of VGP can be mainly
ubjected to the effects of photoperiod, vernalization and temper-ture (Porter and Delecolle, 1988; Miglietta et al., 1995). Acrosshe investigated stations, the spatial patterns of VGP length andonsequently heading dates were significantly dependent on Tmean
nd without accounting for the effect of day length, at Zhengzhou (A), Tianshui (B),
during VGP (Fig. 9A), and mean day length during VGP (Fig. 9B). Ata station, although mean day length during VGP generally had adecreasing trend, and counterbalanced the roles of temperature incontrolling the duration of VGP, the significant increases in Tmean
during VGP play a key role in affecting trends in heading dates.Although significantly and negatively correlated with Tmean dur-
ing RGP at many stations, the lengths of RGP increased in 60% of theinvestigated stations since heading dates were advanced more thanmaturity dates that were more subjected to the effects of cultivarsturnover (i.e. changes of ATDU). The lengths of RGP were subjectedto changes in both Tmean and ATDU. Increases in the length of RGPin the southern part of NCP (ecological zone III) and southwesternChina (ecological zone V) could be ascribed to the decreasing trendin Tmean and the increasing trend in ATDU during RGP, which is con-sistent with Liu et al. (2010). However, at a fair number of stations innorthern part of the NCP and northwestern China, Tmean during RGPshowed an increasing trend, and RGP showed diverse trends. Ouranalyses at three representative stations illustrated such changesin more details.
The shifts in phonological phases could be assigned to the com-bined influences of both climatic and agronomic factors such asfarming practices and cultivars characteristics, particularly for sow-ing dates. Wheat sowing dates changed diversely because they maybe dominated by temperature at some stations, and by soil watercontent at others. To some extent, they can also be subjected tofarmers’ decision and influenced by agronomic factors such as croprotation. Farmers may respond to climate change by shifting sowingdates of their crops, with a stronger effect on earlier phenologi-
cal stages. At the same time, climate change influences phenology.The influences of agronomic factors and crop cultivars turnover oncrop phenology were partly described by changes of sowing datesand changes of crop cultivars thermal characteristics, i.e. changes
210 F. Tao et al. / Europ. J. Agronomy 43 (2012) 201–212
F ing ea( statio
oos
4c
mtPwhBigtcTgt
ig. 8. Trends in ATDU from sowing to each development stage, ATDU for completB), and Dunhuang station (C). The locations of Zhengzhou, Tianshui and Dunhuang
f ATDU. Our results showed that besides the complex influencesf agronomic factors, climate change contributed substantially tohift of wheat phenology during the study period.
.2. Implications for agricultural adaption to ongoing climatehange
In-depth analyses show that ATDU from sowing to each develop-ent stage increased at Zhengzhou and Tianshui. However ATDU
o complete each single development stage changed differently.articularly the thermal accumulation during winter dormancy ofinter wheat cultivars increased. ATDU from spring green-up toeading and from milky ripe to physiological maturity decreased.y contrast, the thermal requirements from heading to milky ripe
ncreased significantly. For spring wheat at Dunhuang, the case wasenerally true too. The different changes in cultivar thermal charac-eristics among development stages tell us an interesting story that
rop cultivars might be optimized in adaption to climate change.he thermal accumulation during winter dormancy increased, sug-esting thermal requirements during winter dormancy increase, orhe vernalization requirements of winter wheat cultivars decrease.
ch single stage, as well the lengths of GP, VGP and RGP at Zhengzhou (A), Tianshuin were shown in Fig. 2A.
For wheat, the size of heads, or number of spikelets per spike,is determined in the duration from spring green-up to headingstage. No effect on yield is expected from tillers developed later(Miller, 1992). Another study on the yield responses and phenologi-cal characteristics of a wide range of winter wheat cultivars showedthat the selection of early-heading winter wheat varieties secureshigher yields; grains/head alone explained about 13% of the varia-tion in yield. Grain weight alone accounted for 24% of the variationin yield. The duration of the grain filling period alone accountedfor about 30% of the yield variations. Cultivars with earlier head-ing dates usually have longer grain filling period, and grain fillingperiod is positively correlated with grain weight (Fernández et al.,1998). Therefore, all the changes in cultivar thermal characteristicsin the past few decades, as we identified above, tend to increasecrop yield.
4.3. Implications for improving climate change impacts studies
Our findings have important implications for improving the cur-rent climate change impacts studies. Due to increasing concernsabout the risk of agricultural production to future climate change,
F. Tao et al. / Europ. J. Agronom
1612840
50
100
150
200
250
Length
of V
GP
(days)
Tmean during VGP (degree)
y = -15.35x+284.77, r=-0.96, p<0.01
16151413121110
50
100
150
200
250
Length
of V
GP
(days)
Day length (hours)
y = -31.75+530.86, r=-0.82, p<0.01
(A)
(B)
Fbg
ecmsHtsdcnpeodsm
5
tSaDdt3
ig. 9. Relationships between mean length of VGP and Tmean during VGP (A), andetween mean length of VGP and day length during VGP (B), across all the investi-ated stations.
xtensive studies have projected the impacts of future climatehange on agricultural production using crop models and future cli-ate scenarios. Adaptation is a key factor that will shape the future
everity of climate change impacts on food production (IPCC, 2007).owever current climate change impact studies generally fail to
ake into account future adaptations well enough. Although sometudies account for agronomic adaptations such as shifting sowingates, automatic fertilization and irrigation, the adoption of newultivars with different thermal and phenological characteristics isot considered, which contribute to the large uncertainties of therojections of future production (Tao et al., 2008b, 2009; Zhangt al., 2008). Besides the length of the growing period, the timingf phenological events is also important, for example heat stressuring anthesis might reduce yields, therefore impact assessmenttudies that account for the changes in cultivar thermal require-ents and timing of phenological events should be developed.
. Conclusion
The wheat phenology at more than 100 agro-meteorological sta-ions across China spanning the years 1981–2007 was examined.patiotemporal changes of wheat phenology and temperature,s well as temperature response of phenology were presented.
uring the investigation period, heading dates and maturityates advanced significantly at about 40% of the investigated sta-ions. Lengths of GP and VGP were significantly reduced at about0% of the investigated stations, especially for spring wheat in
y 43 (2012) 201–212 211
northwestern China, although ATDU during GP and VGP increased.In contrast, although significantly and negatively related to Tmean,lengths of RGP increased at 60% of the investigated stations, owingto increased ATDU or/and decrease in Tmean. Our results showedthat besides the complex influences of agronomic factors, climatechange contributed substantially to shift of wheat phenology dur-ing the study period. Mean day length during VGP had a decreasingtrend at most of the investigated stations, which counterbalancedthe roles of temperature in controlling the duration of VGP. In-depth analyses showed that the thermal requirements of cropcultivars from sowing to almost every development stage increasedgenerally. However the thermal requirements of crop cultivars tocomplete each single development stage changed differently. Thedifferent changes in cultivar thermal characteristics among devel-opment stages tend to increase crop yield, suggesting crop cultivarsmight be optimized in adaption to ongoing climate change in thepast few decades.
Our findings have important implications for improving climatechange impacts studies, for breeding scientists to breed higheryielding cultivars, and for agricultural production to cope withfuture climate change. The results provided the information onthe development of crop cultivars thermal and phenological char-acteristics in the past few decades, suggesting climate changeimpacts studies should be improved by taking into account thedevelopment of cultivars thermal and phenological characteristics.Since the lengths of GP, particularly the lengths of RGP, are closelyrelated to crop productivity, our results suggest that new crop cul-tivars with higher thermal requirements and longer RGP should beadopted in northern and northwestern China to take advantage ofincreased heat resources from climate warming. The selection ofcultivars with earlier heading dates and longer grain filling periodsecures higher yields, suggesting further development and opti-mization of cultivar thermal characteristics should be a potentialadaption to ongoing climate change.
Acknowledgments
This study is supported by the National Science Foundationof China (Project Number 41071030), the science and technologystrategic pilot projects of the Chinese Academy of Sciences (ProjectNumber XDA05090308), and National Key Programme for Devel-oping Basic Science (Project Number 2010CB950902), China. F. Taoacknowledges the support of the “Hundred Talents” Program of theChinese Academy of Sciences. We acknowledge that wheat phe-nological and climate data used in the study were from ChineseMeteorological Administration. We are grateful to the two anony-mous reviewers, Dr. S. Siebert in University of Bonn, and editor fortheir insightful comments on an earlier version of this manuscript.
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