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Journal of Geographical Sciences >

2019 , Vol. 29 >Issue 3: 351 - 362

DOI: https://doi.org/10.1007/s11442-019-1602-5

Research Articles

Spatiotemporal differentiation of changes in maize phenology in China from 1981 to 2010

  • LIU Yujie , 1, 3, * ,
  • QIN Ya 1, 2 ,
  • GE Quansheng 1, 3
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  • 1. Key Laboratory of Land Surface Pattern and Simulation, Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China
  • 2. College of Surveying and Mapping Science and Technology, Xi'an University of Science and Technology, Xi'an 710054, China
  • 3. University of Chinese Academy of Sciences, Beijing 100049, China
*Corresponding author: Liu Yujie, PhD and Associate Professor, specialized in climate change. E-mail:

Received date: 2018-01-15

  Accepted date: 2018-07-12

  Online published: 2019-03-20

Supported by

National Natural Science Foundation of China, No.41671037

Youth Innovation Promotion Association of CAS, No.2016049

Key Research Program of Frontier Sciences, CAS, No.QYZDB-SSW-DQC005

Program for “Kezhen” Excellent Talents in IGSNRR, CAS, No.2017RC101

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Journal of Geographical Sciences, All Rights Reserved
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Abstract

Spatio-temporal changes in the differentiation characteristics of eight consecutive phenological periods and their corresponding lengths were quantitatively analyzed based on long-term phenological observation data from 114 agro-meteorological stations in four maize growing zones in China. Results showed that average air temperature and growing degree-days (GDD) during maize growing seasons showed an increasing trend from 1981 to 2010, while precipitation and sunshine duration showed a decreasing trend. Maize phenology has significantly changed under climate change: spring maize phenology was mainly advanced, especially in northwest and southwest maize zones, while summer and spring-summer maize phenology was delayed. The delay trend observed for summer maize in the northwest maize zone was more pronounced than in the Huang-Huai spring-summer maize zone. Variations in maize phenology changed the corresponding growth stages length: the vegetative growth period (days from sowing date to tasseling date) was generally shortened in spring, summer, and spring-summer maize, although to different degrees, while the reproductive growth period (days from tasseling date to mature date) showed an extension trend. The entire growth period (days from sowing date to mature date) of spring maize was extended, but the entire growth periods of summer and spring-summer maize were shortened.

Key words： maize; phenology; climate change; spatio-temporal differentiation; China

Cite this article

LIU Yujie , QIN Ya , GE Quansheng . Spatiotemporal differentiation of changes in maize phenology in China from 1981 to 2010[J]. Journal of Geographical Sciences, 2019 , 29(3) : 351 -362 . DOI: 10.1007/s11442-019-1602-5

1 Introduction

Phenology can intuitively indicate changes in seasons and climate (Zheng et al., 2012; He et al., 2015), thus being an important biological indicator for measuring regional climate change. According to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC, 2014), the average global surface temperature has increased by 0.89°C from 1901 to 2012. An increase in air temperature can promote enzyme activity and accelerate the phenological processes of plants, thus shortening plant growing seasons. In turn, changes in the length of plant growing seasons can modify vegetation productivity and structural composition, as well as water, heat, and carbon exchange rates in the soil-vegetation-atmosphere system, thereby affecting the climate system and exacerbating climate change (Wang et al., 2015; Cui et al., 2018). As agricultural production is directly affected by climate change (Guo, 2015), studying the patterns of phenological changes in crops is of great importance for guiding regional agricultural production and mitigating the negative impacts of climate change.
Under the scenario of climate change, maize phenology has been examined worldwide. Based on the Agro-IBIS model (a process-based ecosystem model adapted from the Integrated Biosphere Simulator), Sacks and Kucharik (2011) found that the sowing date and maturity date of maize advanced 0.40 day per year and delayed 0.10 day per year, respectively, between 1981 and 2005 in the US Corn Belt. Chinese scholars have found that, due to climate warming, the tasseling date and maturity date at more than 80% of the country’s maize production sites advanced by an average of 3.2 days and 6.0 days, respectively, over each 10-year period (Tao et al., 2014). In northeast China, the sowing date of maize advanced and the maturity date delayed by 4-21 days from 1981 to 2007 (Liu et al., 2013). In Inner Mongolia, the sowing date and maturity date of maize advanced by 1.0 day and delayed by 3.3 days per 10-year period, respectively, from 1981 to 2009 (Xiao, 2015). Fu et al. (2016) conducted temperature increment experiments in Tibet Autonomous Region and found that air temperature increments generally led to advancing trends in the phenological phases of maize to different degrees. Under the influence of increasing average air temperature, decreased precipitation with increased latitude, and substantial decline in sunshine duration, the seeding, jointing, and silking dates of summer maize in Jing-Jin-Ji (Beijing-Tianjin-Hebei) region and Shandong Province were significantly delayed, and the seeding, jointing, and silking dates of summer maize in Henan Province advanced considerably (Meng et al., 2015).
Based on the above results, previous studies mainly focused on the effect of air temperature increase on maize phenological phases in the context of climate change. In addition to temperature, moisture and sunshine duration can also affect crop growth (Liu et al., 2018a). For example, shortened sunshine duration can promote flowering of short-day plants and advance their flowering stage, while extended sunshine duration delays the flowering stage. Zheng et al. (2002) found that the main factor influencing flowering in winter and early spring plants is air temperature, whereas the flowering of late spring and early summer plants is simultaneously affected by air temperature and sunshine duration; the onset of pollen spreading in late summer plants is mainly affected by sunshine duration. Under certain sunshine conditions, changes in air relative humidity can also cause changes in plant phenology (Wang et al., 2010). In addition, limited by observation data and model simulation capabilities, studies conducted so far have mostly focused on individual key phenological phases, such as seeding, tasseling, and ripening dates, and lack a systematic analysis on the changing patterns of multiple phenological phases during crop growth. Moreover, due to the influence of local and regional climates, the same phenological stages of the same crop significantly differ among different regions, and most studies have been conducted at the regional scale or include only a few sites. For example, Zhao et al. (2015) explored the effects of sowing date adjustment and species change on maize growing season and yield in five maize production sites in northeast China (two in Heilongjiang, two in Jilin, and one in Liaoning). Wang et al. (2015) selected three to four representative sites in northeast, north, and southwest China to examine the uncertain factors in model simulation of maize phenology. The growth process of maize is influenced by multiple climate factors, but changes in the patterns of multiple consecutive phenological stages, especially changes in the trends of spatial differentiation patterns for each phenological stage during maize growth, hence further examination is still needed.
Therefore, based on long-term observation data (1981 to 2010) from 114 agro-meteorological stations in the four major maize growing zones in China, this study aims to: (1) quantify spatial and temporal changes occurring in the differentiation characteristics of maize regarding sowing, seedling, three-leaf, seven-leaf, jointing, tasseling, milk-ripe, and ripening dates; and (2) examine the changes in the patterns of the phenological phases and length of growing seasons for different planting types of maize in different regions in the context of changes in key climate factors (average air temperature, precipitation, and sunshine duration). The results obtained here could provide a theoretical reference for regional agricultural production practices.

2 Data and methods

2.1 Data

This study examined spring, summer, and spring-summer maize grown in the northwest maize zone, northern spring maize zone, Huang-Huai spring-summer maize zone, and southwest maize zone, which are the four main maize production zones in China, based on the Chinese maize planting zonations (Tong, 1992). The sowing date of spring maize is from late April to early May, and that of summer maize is from early June to mid-July. Spring-summer maize is sowed at intervals between April and June or between May and June, and its sowing date is mainly affected by the planting time of the previous seasonal crops.
The research sites selected for the present study met the following four criteria: (1) typical site and representative of the agricultural production status of local maize; (2) with long-term (1981-2010) maize phenological observation data; (3) with meteorological observation station; and (4) with field management records, including information on maize variety, irrigation, and fertilization, among other features. According to data quality, 114 sites with complete observation records were selected (Figure 1). These sites were distributed in the northwest maize zone (17 sites), northern spring maize zone (54 sites), Huang-Huai spring-summer maize zone (32 sites), and southwest maize zone (11 sites). Maize growth season was divided into three key growth stages: vegetative growth stage (sowing to tasseling date), reproductive growth stage (tasseling to ripening date), and the entire growth stage (sowing to ripening date). The lengths of these three growth stages were calculated separately. Climate data for the 114 sites during the 1981-2010 period were obtained from the data sharing website (http://data.cma.cn/site/index.html).
Figure 1 Spatial distribution of agro-meteorological stations of China

2.2 Research methods

2.2.1 Trend analysis
The trends observed for changes in the length of phenological stages and growth stages of maize were calculated using the following linear regression equation, considering year as the independent variable (1):
${{\theta }_{k}}=\frac{n\times \sum\limits_{i=1}^{n}{(k\times {{P}_{i,k}})-\sum\limits_{i=1}^{n}{k\times \sum\limits_{i=1}^{n}{{{P}_{i,k}}}}}}{n\times \sum\limits_{i=1}^{n}{{{k}^{2}}-{{\left( \sum\limits_{i=1}^{n}{k} \right)}^{2}}}}$ (1)
where n is the number of years in the analyzed period, Pi,k is the length of phenological stage k in year i (DOY: Day of Year) or growth stage length (days) of the observation site in year i, i represents the ith year, and θk is the trend observed for changes in the length of phenological stage or growth stage (d/a). If θk is greater than 0, it means that the length of the phenological stage or growth stage is delayed or extended, respectively; for θk lower than 0, the length of the phenological stage or growth stage is advanced or shortened, respectively. A two-tailed t-test was used to evaluate the significance of the regression coefficients.
2.2.2 Calculation of growing degree-days
Growing degree-days (GDD) is a heat index for analyzing crop growth. In the present study, it refers to the effective GDD with a daily average air temperature ≥10°C. It was calculated according to McMaster and Wilhelm’s (1997) formula (2):
$GDD=\sum\limits_{{{d}_{s}}}^{{{d}_{e}}}{\left[ \left( \frac{{{T}_{\max }}+{{T}_{\min }}}{2} \right)-{{T}_{base}} \right]}$ (2)
where ds represents the starting date of the research phase, de represents the ending date of the research phase, Tmax represents the daily maximum air temperature, Tmin represents the daily minimum air temperature, and Tbase represents the minimum biological temperature in the maize growth stage.
Based on the observed dates for phenological phases, the starting date (i.e., the date of sowing) and the ending date (i.e. the date of ripening) of maize growth were determined. Daily meteorological data were used to calculate average air temperature, precipitation, sunshine duration, and GDD during each maize growth stage at each site. Trends in average air temperature, precipitation, sunshine duration, and GDD during maize growth stages in 1981-2010 were also calculated using equation (1).

3 Results

3.1 Spatio-temporal changes in climate factors

The spatial distribution of the trends in average air temperature, precipitation, sunshine duration, and GDD changes during maize growing season at each selected site from 1981 to 2010 is shown in Figure 2. Throughout the country, average air temperature and GDD increased from 1981 to 2010 by 0.03°C/yr and 4.92°C d/yr, respectively. Precipitation and sunshine duration showed decreasing trends, and the decrease rates were -0.16 mm/yr and -2.07 h/yr, respectively (Table 1). Average air temperature and GDD showed increasing trends at 90% and 83% of the selected sites, respectively, and the increase in air temperature was greater at high than at low latitudes.
Figure 2 Spatial distribution of climate factor changing trends during the growth period of maize in China from 1981 to 2010
Table 1 Changing trends of climate factors during the entire growth period of maize in different regions
Growing zones Average air
temperature (℃/a)		 Precipitation (mm/a) Sunshine duration (h/a) GDD (℃ d/a)
Nationwide 0.03** ‒0.16 ‒2.07** 4.92**
Northwest maize zone 0.05** 0.14 ‒0.99 5.26**
Northern spring maize zone 0.04** ‒2.26** 0.51 7.01**
Huang-Huai spring-summer maize zone 0.02** 2.61** ‒7.30** 0.87
Southwest maize zone ‒0.001 1.53 ‒1.15 5.81**

Note: “+” and “-” indicate that the climate factor increased or decreased, ** and * indicate significance levels at 0.01 or 0.05 respectively.

Precipitation showed obvious regional differences (Figure 2b). In most zones, precipitation showed a decreasing trend (55%), especially in northern spring maize zone, northwest maize zone, and southwest maize zone; however, precipitation in the Huang-Huai spring-summer maize zone showed an increasing trend. In terms of planting type, precipitation decreased by 1.30 mm/yr during the spring breeding growth stage of maize, while during the growth stage of summer maize and spring-summer maize it increased by 2.49 mm/yr and 1.44 mm/yr, respectively. Sunshine duration decreased by 63% of the selected sites, but it was most significant in the Huang-Huai spring-summer maize zone, showing a decrease of -7.30 h/yr (Figure 2c and Table 1); on the contrary, sunshine duration in the northern spring maize zone showed an increasing trend of 0.51 h/yr (Table 1). On average, sunshine duration during the growing season of spring maize was 0.31 h/yr, and -5.37 h/yr and -10.03 h/yr during the growing season of summer and spring-summer maize, respectively.

3.2 Spatio-temporal changes in the phenological stages of maize

The phenological stages of maize were mainly delayed nationwide, at 68%, 54%, 53%, 54%, 55%, 74%, and 77% of the sites showing a delaying trend in the sowing, seedling, three-leaf, jointing, tasseling, milk-ripe, and ripening dates, respectively. However, 54% of the sites showed an advancing trend in the seven-leaf stage. Sites with delayed sowing, seedling, three-leaf, jointing, and tasseling dates were mainly distributed across the Huang-Huai spring-summer maize zone, although there were some sites in the eastern part of the northern spring maize zone and in the northwest maize zone. Sites where the seven-leaf stage tended to advance were mainly located in the southeast of the northern spring maize zone (Figure 3d).
Figure 3 Spatial distribution of maize phenological trends in China from 1981 to 2010
There was a significant inter-regional difference in the changes observed in maize phenological stages (Figure 3 and Table 2). Within the same zone, the phenological phases were significantly different for different maize planting types. In the northwest maize zone, spring maize showed an advancing trend from the sowing to the jointing date (0.05<θ<0.24 d/yr), while the tasseling, milk-ripe, and ripening dates were delayed by 0.02, 0.12, and 0.06 d/yr; all phenological phases of summer maize, from sowing to ripening date, were delayed (0.21<θ<0.87 d/yr). All phenological phases of spring maize in the southwest maize zone were advanced (0.13<θ<0.53 d/yr). In contrast, the phenological phases of spring maize in northern China were mainly delayed (0.01<θ<0.30 d/yr), as only the seven-leaf stage was advanced (-0.14 d/yr). In the Huang-Huai spring-summer maize zone, the phenological phases of summer maize were delayed from the sowing to the ripening date (0.09<θ<0.35 d/yr). The phenological phases of spring-summer maize were also delayed, and sowing data had a significant delay (0.96 d/yr); the sowing date of spring-summer maize was significantly delayed, resulting in the shortening of the entire growth stage. Due to the implementation of the intermittent growth system comprising spring maize, winter wheat, and summer maize in this zone, the sowing date of maize was affected not only by climate factors but also by the planting and harvesting time of the previous seasonal crop.
Table 2 Changing trend of major phenological/growing stages length of maize in different regions from 1981 to 2010 (d/yr)
Growing
zones		 Planting type Sowing date Seedling date Three-leaf date Seven-leaf date Jointing date Tasseling date Milk-ripe date Ripening date Vegetative growth stage Reproductive growth stage Entire growth stage
Northwest maize zone Spring maize ‒0.05 ‒0.20** ‒0.16* ‒0.24** ‒0.18** 0.02 0.12 0.06 0.02* 0.03 0.10
Summer maize 0.87** 0.66** 0.64** 0.73** 0.21 0.46** 0.39** 0.22* ‒0.46 ‒0.24** ‒0.65**
Northern spring maize zone Spring maize 0.18** 0.04 0.01 ‒0.14** 0.10** 0.05* 0.23** 0.30** ‒0.12 0.25** 0.11**
Huang-Huai spring-summer maize zone Spring maize ‒0.52** ‒0.53** ‒0.45** ‒0.32** ‒0.24* ‒0.24* ‒0.13 ‒0.18 0.35** 0.10 0.41**
Southwest maize zone Summer maize 0.20** 0.17** 0.22** 0.15** 0.09* 0.09* 0.25** 0..35** ‒0.11* 0.26** 0.14**
Spring-summer maize 0.96** 0.17** 0.13 0.18* 0.12* 0.23** 0.22** 0.37** ‒0.83 0.14* ‒0.60**

Note: ”+” indicates the phenology / growing stages length delayed or prolonged; “‒” indicates the phenological / growing stages length advanced or shortened. ** and * indicate significance levels at 0.01 or 0.05 respectively.

Different growing zones also presented significant differences in the direction and magnitude of the trends observed for changes in the phenological phases of maize of the same planting type. For instance, the phenological phases of spring maize were mainly advanced in the southwest maize zone, but mainly delayed in the northern spring maize zone. The delay in the phenological phases in the northwest maize zone (0.21<θ<0.87 d/yr) was significantly greater than the delay of the phenological phases of summer maize in the Huang-Huai spring-summer maize zone (0.09<θ<0.35 d/yr).

3.3 Changes in the length of key growth stages

Maize vegetative growth, reproductive growth, and entire growth stages were extended at 34%, 71%, and 57% of the selected sites, respectively, with extension ranges of 0.08-0.76, 0.61-0.97, and 0.03-1.07 d/yr, respectively. On average, the vegetative growth stage of spring maize was shortened by 0.06 d/yr. Reproductive growth and entire growth stages were extended by 0.18 d/yr and 0.16 d/yr, respectively. Spring maize in the northwest maize zone and southwest maize zone showed an extension trend at the three growth stages. The vegetative growth stage of spring maize in the northern spring maize zone was shortened, while reproductive growth and entire growth stages were mainly extended (Table 2). The vegetative growth and entire growth stages of summer maize were shortened by 0.20 d/yr and 0.05 d/yr, respectively. The reproductive growth stage was extended by 0.14 d/yr. The three growth stages of summer maize were shortened in the northwest maize zone, while vegetative growth stage was shortened in the Huang-Huai spring-summer maize zone; reproductive and entire growth stages of this maize type were extended in the Huang-Huai spring-summer maize zone (Table 2). The reproductive growth stage of spring-summer maize in the Huang-Huai spring-summer maize zone was extended (0.14 d/yr), but vegetative and entire growth stages were shortened by 0.83 d/yr and 0.60 d/yr, respectively (Figure 4).
Figure 4 Trends of three growing stages length of different planting types of maize from 1981 to 2010

4 Discussion

From 1981 to 2010, the average air temperature increased during the growth stage of spring, summer, and spring-summer maize in China (0.03, 0.02, and 0.05 °C/yr, respectively). In general, elevated air temperatures affect all stages of crop growth and development, including seedling, flowering, and ripening (Liu et al., 2010; Hou et al., 2014; Liu et al., 2017). For progressing from one growth stage to the next, crops need to accumulate enough effective accumulated temperature. Thus, an increase in air temperature can accelerate the accumulation of effective accumulated temperature and shorten each growth stage (Zhang et al., 2013; Zhang et al., 2018), leading to earlier phenological phases or shorter growth stages (Vitasse et al., 2011; Liu et al., 2018b). Precipitation and sunshine duration can also affect crop growth. According to our results, except for the slight decrease in average air temperature (-0.001 °C/yr) during the maize growth stage in the southwest maize zone, average air temperature and GDD in the four maize zones showed an increasing trend, whereas precipitation and sunshine duration showed mainly increasing and decreasing trends, respectively. The phenological phases of spring maize in China mainly advanced in the past 30 years. For example, phenological phases from the sowing date to the jointing date were advanced (0.05<θ<0.24 d/yr) in the northwest maize zone. The vegetative, reproductive, and entire growth stages in this zone were extended by 0.02, 0.03, and 0.10 d/yr, respectively, which is consistent with the findings of Xiao et al. (2015). The phenological stages of spring maize from seeding to maturation were advanced in the southwest maize zone (0.13<θ<0.53 d/yr), however, in the northern spring maize zone, the seven-leaf date showed an advancing trend (-0.14 d/yr); sowing, seedling, and ripening dates were delayed by 0.18, 0.04, and 0.30 d/yr, respectively. This is consistent with the findings of Li et al. (2009). From 1961 to 2010, the air temperature during the maize breeding growth stage in northeast farming areas increased significantly (Yin et al., 2015). Since 1991, the precipitation in the maize growing season (April-September) continued to decrease in northeast China. Since 1971, the accumulated temperature ≥10°C in this area has increased by 262.8°C, and the accumulated temperature ≥10°C (at 2700°C for example) has shifted about 200-300 km to the north and 50-150 km to the east (Ji et al., 2012). The northeast region is dominated by the planting of spring maize, and changes in climate factors during the maize growth stage are similar to the spatial variations of climatic factors observed for northeast spring maize in the northern spring maize zone. Accordingly, the three provinces in northeast China showed an advanced seedling date (0.02<θ<0.15 d/yr) and a delayed ripening date (0.18<θ<0.38 d/yr) for spring maize from 1990 to 2009 (Li et al., 2013). Liu et al. (2013) also reported that the sowing date in northeast China was advanced from 1981 to 2007, while the ripening date was delayed. Nationwide, the vegetative growth stage was shortened (-0.06 d/yr), while the reproductive and entire growth stages of spring maize were extended (by 0.18 and 0.16 d/yr, respectively). Summer maize and spring-summer maize showed a delaying trend in the phenological stages until the ripening stage. Whereas, due to the influence of local regional climate, the differences among regions were significant (Figure 3 and Table 2). The growth stages of summer maize in the northwest maize zone and spring-summer maize in Huang-Huai spring-summer maize zone were shortened (-0.65 and -0.60 d/yr, respectively), while the growth stage of summer maize in Huang-Huai spring-summer maize zone was extended (0.14 d/yr). Previous studies have found that during the growth stage of the summer maize in the North China Plain, air temperature decreased with latitude, sunshine duration declined significantly, and the number of days in the entire growth stage increased significantly from 1981 to 2009 (Meng et al., 2015). Our results for the changes in sunshine duration in the growth stage in Huang-Huai spring-summer maize zone are consistent with these findings. Therefore, the decrease in sunshine duration might be an important factor for extending maize growth season.
Many studies have examined spatio-temporal differences in changes in maize phenology and in the duration of each growth stage in China under different climate change scenarios. However, the effects of human activity such as cultivar shifts, use of fertilizers, and irrigation on crop phenology still need further investigation. Thus, combined crop models including the effect of climate changes, management measures, and other variables that might affect crop growth, should be considered in future studies. Changes in the length of each growth stage of maize are caused by changes in the corresponding phenological phases; therefore, discussing changes in maize phenological stages and growth stages at different scales, such as site, regional, and inter-regional levels, and including different planting types could help gain insight into the effects of climate change on crop phenology.

5 Conclusions

(1) During the past three decades (1981-2010), there were significant changes in maize phenological phases of China. While the phenological phases of spring maize were mainly advanced, those of summer maize showed a delaying trend in different regions. Specifically, sowing to jointing dates of spring maize in the northwest maize zone were advanced (0.05<θ<0.24 d/yr), as well as sowing to ripening dates in the southwest maize zone (0.13<θ<0.53 d/yr). Spring maize in the northern spring maize zone only advanced at the seven-leaf stage (0.14 d/yr). The delayed range of summer maize phenological phases in the northwest maize zone (0.21<θ<0.87 d/yr) was generally greater than in the Huang-Huai spring-summer maize zone (0.09<θ<0.35 d/yr).
(2) All phenological stages of spring and summer maize in Huang-Huai spring-summer maize zone showed a delaying trend (0.12<θ<0.96 d/yr). The changes in the phenological phases resulted in changes in the length of the corresponding growth stage. The vegetative growth stage of spring maize showed a shortening trend (-0.06 d/yr), and the reproductive growth and entire growth stages showed an extending trend (0.18 and 0.16 d/yr, respectively).
(3) The vegetative growth (-0.20/-0.83 d/yr) and entire growth (-0.05/-0.60 d/yr) stages of summer and spring-summer maize were shortened, while their reproductive growth stages were extended (0.14/0.14 d/yr). In general, the phenological phases of spring maize in China were advanced, while the phenological phases of summer and spring-summer were delayed; the length of each growth stage was mainly extended in different regions.

The authors have declared that no competing interests exist.

References

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Fu G, Zhong Z M, 2016. Initial response of phenology and aboveground biomass to experimental warming in a maize system of the Tibet.Ecology and Environmental Sciences, 25(7): 1093-1097. (in Chinese)http://www.en.cnki.com.cn/Article_en/CJFDTOTAL-TRYJ201607001.htmThere remains uncertainty on effects of climatic warming on crop phenology and biomass on the Tibetan Plateau.A field warming experiment was conducted in a maize system located at the Dazi county of the Tibet since late April,2015.This study examined the effect of warming on maize phenology(i.e.sowing time,seeding stage,trefoil stage,five-leaf stage,jointing stage,pustulation period,milk-ripe stage,mature period),aboveground biomass and plant height.The trefoil stage and five-leaf stage completed 2 days earlier;the jointing stage completed 1.3 days earlier(t=2.00,P=0.184),the pustulation period completed 3.3 days earlier(t=2.00,P=0.184),the milk-ripe stage completed 4.7 days earlier(t=2.80,P=0.119),and the mature period completed 6.7 days earlier(t=3.78,P=0.050 2) under experimental warming conditions.Experimetal warming shorten 6.7 days of the interval between seeding stage and mature period(t=2.77,P=0.050 2),and 3.3 days of the interval between pustulation period and mature period(t=2.43,P=0.122).Experimental warming increased cumulative temperature by 11.89 during the period from sowing time to seeding stage(t=11.21,P=0.000),decreased cumulative temperature by 7.58 during the period from seeding stage to trefoil stage(t=77.55,P=0.000).However,experimental warming had no obvious effects on cumulative temperature during the period from trefoil stage to five-leaf stage,from five-leaf stage to jointing stage,from jointing stage to pustulation period,from pustulation period to milk-ripe stage,from milk-ripe stage to mature stage,and from sowing stage to mature stage.Experimental warming had no significant effects on aboveground plant biomass and plant height.Therefore,warming may alter maize phenology but did not significantly affect aboveground plant biomass.

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Guo J P, 2015. Advances in impacts of climate change on agricultural production in China.Journal of Applied Meteorological Science, 26(1): 1-11. (in Chinese)http://en.cnki.com.cn/Article_en/CJFDTotal-YYQX201501001.htmClimate change,the main feature of which is global warming,has become one of the important environmental problems in the world.Also,it is a matter of general concern by the scientific community,governments and the social public.Climate change has brought a series of problems that beyond the range of nature changes in the earth itself,which poses a serious threat to human survival and social economy.Agriculture,especially crop production and food security,is one of the largest and the most direct industry affected by climate change.Therefore,the impact of climate change on agricultural production is always one of the hottest issues in the field of climate change.The present situation and progress in the research field of climate change impact on agricultural production in China is summarized systematically,introducing research methods,the progress in the experiment of greenhouse gases concentration enrichment in the atmosphere impact on crops,impacts and future trends of climate change on agricultural climate resources,the possible impact of climate change on crop growth and yield,impacts and future trends of climate change on agricultural planting system and varieties distribution,impact of climate change on crop potential productivity,impact of measures of adapting to climate change to increase the utilization ratio of agricultural climate resources and so on.On the basis,current problems in the impact assessment of climate change on agriculture is proposed too.In order to improve the reliability and rationality of the impact assessment for climate change on agriculture,more attention needs to be paid to the research of uncertainty of future climate change scenarios,model prediction and evaluation method.In addition,further researches are also needed about the impact of extreme weather events under climate change on agricultural production,the impact of climate change on agricultural plant diseases and insect pests,impacts of climate change on cash crops,fruit,animal husbandry and farmland ecosystem.

[4]
He L, Asseng S, Zhao Get al., 2015. Impacts of recent climate warming, cultivar changes, and crop management on winter wheat phenology across the Loess Plateau of China.Agricultural and Forest Meteorology, 200: 135-143.https://linkinghub.elsevier.com/retrieve/pii/S0168192314002226Crop yields are influenced by growing season length, which are determined by temperature and agronomic management, such as sowing date and changes in cultivars. It is essential to quantify the interaction between climate change and crop management on crop phenology to understand the adaptation of farming systems to climate change. Historical changes in winter wheat phenology have been observed across the Loess Plateau of China during 1981–2009. The observed dates of sowing, emergence, and beginning of winter dormancy were delayed by an average of 1.2, 1.3, and 1.2daysdecade611, respectively. Conversely, the dates of green-up (regrowth after winter dormancy), anthesis, and maturity advanced by an average of 2.0, 3.7, and 3.1daysdecade611, respectively. Additionally, the growth duration (sowing to maturity), overwintering period, and vegetative phase (sowing to anthesis) shortened by an average of 4.3, 3.1, and 5.0daysdecade611, respectively. The changes in phenological stages and phases were significantly negatively correlated with a temperature increase during this time. Differently to most other phase changes, the reproductive phase (anthesis to maturity) prolonged by an average of 0.7daydecade611, but this was spatially variable. The prolonged reproductive phase was due to advanced anthesis dates and consequently caused the reproductive phase to occur during a cooler part of the season, which led to an extended reproductive phase. Applying a crop simulation model using a field-tested standard cultivar across locations and years indicated that the simulated phenological stages have accelerated with the warming trend more than the observed phenological stages. This indicated that, over the last decades, later sowing dates and the introduction of new cultivars with longer thermal time requirement have compensated for some of the increased temperature-induced changes in wheat phenology.

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[5]
Hou P, Liu Y E, Xie R Zet al., 2014. Temporal and spatial variation in accumulated temperature requirements of maize.Field Crops Research, 158: 55-64.https://linkinghub.elsevier.com/retrieve/pii/S0378429013004358Temperature, especially accumulated temperature, is an important environmental factor that plays a fundamental role in agricultural productivity. To examine temporal and spatial variation in accumulated temperature requirements of maize as indicated by ≥10°C accumulated temperature and growing degree days (GDD), we conducted experiments during 2007–2012 at 35 locations in seven provinces in the north spring maize region between 35°11′N and 48°08′N and 6 locations in four provinces in the Huanghuaihai maize region between 32°52′N and 41°05′N in China. The most widely cultivated maize hybrids of ZD958 and XY335 were used in this study. We found that the coefficients of variation for ≥10°C accumulated temperature and GDD requirements were different during different growth periods, with a descending rank order of sowing to emergence>silking to maturity>emergence to silking>sowing to maturity and greater in the north spring maize region than in the Huanghuaihai maize region. The coefficients of variation were lower for ≥10°C accumulated temperature than GDD requirements for both cultivars in both planting regions. Significant differences existed between locations and years for the ≥10°C accumulated temperature and GDD requirements. These have implications for appropriate maize cultivars recommendation, and high and stable yield achieving by reasonably using accumulated temperature across different regions of China.

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[6]
IPCC, 2014. Climate change 2014: The physical science basis. Contribution of Working Group 1 to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge: Cambridge University Press, 5-7.

[7]
Ji R P, Zhang Y S, Jiang L Xet al., 2012. Effect of climate change on maize production in Northeast China.Geographical Research, 31(2): 290-298. (in Chinese)http://en.cnki.com.cn/Article_en/CJFDTOTAL-DLYJ201202009.htmThis paper analyzed the facts of climate change and its effects on the maize production in Northeast China according to the meteorological,maize yield and planting area data.The results are as follows.The heat resources in this region have been increasing continually since 1971.The accumulated temperature over 10℃ has increased by 262.8℃ averaged for the whole region.The plain area with accumulated temperature(≥10℃) higher than 2700℃ has extended northward 200-300 km,and eastward 50-150 km respectively.The precipitation in growing period(from April to September) during 1981-1990 had an increasing trend,but has been decreasing continually since 1991.Annual average water deficiency amounts to 391.5 mm.Humid area is decreasing and the whole region has a drying trend.The early frost date(the date with the lowest temperature ≤0℃) has postponed 7-9 days,and the frostless period has prolonged 14-21 days,so the probability of frost disaster occurrence is reduced.The period with high probability of lingering low temperature disaster on maize was observed in the 1960s and 1970s,and the period with low probability started in the 1990s.Heilongjiang Province had a high probability of frost disasters.With the heat resources increasing continually,adaptive area of maize planting is growing,with its north boundary extending northward and eastward,so the adaptive seeding date comes earlier.With steady increase of maize planting area and yield,the total yield and total planting area will increase by 9,670,000 t and 720,000 ha per decade respectively. Although climate change has supplied more heat resources for maize production in Northeast China,it is enhancing drought.So,we should adjust maize distribution and varieties.Additionally,using irrigation engineering and dry-farming technology widely,and selecting varieties with disease-resistance,drought-endurance and strong stress-resistance are the important measures to realize sustainable development of maize production in Northeast China.

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[8]
Li R P, Zhou G S, Shi K Qet al., 2009. Phenological characteristics of maize and their response to the climate from 1980 to 2005.Journal of Anhui Agricultural Science, 37(31): 15197-15199, 15267. (in Chinese)http://en.cnki.com.cn/Article_en/CJFDTOTAL-AHNY200931047.htmThe phonological data at 16 stations of Liaoning Province from 1980 to 2005 were analyzed.The results showed that the sowing and seedling emergence of maize appeared slightly earlier.But the mature was significantly postponed,which led to longer growing season.The stages of sowing,seedling emergence,mature and growing season all showed a significant negative correlation with temperature.Except sowing stage,all phenological stages of maize showed a significant positive correlation with precipitation.The increase of annual average temperature caused the shortening of maize growth stage.The decrease of annual precipitation brought about the longer growth stage.Therefore,warming and drought of the future climate would have fatal effects on the growth,quality and yield of maize.

[9]
Li Z G, Yang P, Tang H Jet al., 2013. Trends of spring maize phenophases and spatio-temporal responses to temperature in three provinces of Northeast China during the past 20 years.Acta Ecologica Sinica, 33(18): 5818-5827. (in Chinese)http://www.ecologica.cn/

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[10]
Liu Y, Wang E L, Yang X Get al., 2010. Contributions of climatic and crop varietal changes to crop production in the North China Plain, since 1980s.Global Change Biology, 16(8): 2287-2299.http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2486.2009.02077.x/pdfThe North China Plain (NCP) is the most important agricultural production area in China. Crop production in the NCP is sensitive to changes in both climate and management practices. While previous studies showed a negative impact of climatic change on crop yield since 1980s, the confounding effects of climatic and agronomic factors have not been separately investigated. This paper used 25 years of crop data from three locations (Nanyang, Zhengzhou and Luancheng) across the NCP, together with daily weather data and crop modeling, to analyse the contribution of changes in climatic and agronomic factors to changes in grain yields of wheat and maize. The results showed that the changes in climate were not uniform across the NCP and during different crop growth stages. Warming mainly occurred during the vegetative (preflowering) growth stage of wheat and maize, while there was a cooling trend or no significant change in temperatures during the postflowering stage of wheat (spring) or maize (autumn). If varietal effects were excluded, warming during vegetative stages would lead to a reduction in the length of the growing period for both crops, generally leading to a negative impact on crop production. However, autonomous adoption of new crop varieties in the NCP was able to compensate the negative impact of climatic change. For both wheat and maize, the varietal changes helped stabilize the length of preflowering period against the shortening effect of warming and, together with the slightly reduced temperature in the postflowering period, extend the length of the grain-filling period. The combined effect led to increased wheat yield at Zhengzhou and Luancheng; increased maize yield at Nanyang and Luancheng; stabilized wheat yield at Nanyang, and a slight reduction in maize yield at Zhengzhou, compared with the yield change caused entirely by climatic change.

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[11]
Liu Y J, Chen Q M, Ge Q Set al., 2018a. Modelling the impacts of climate change and crop management on phenological trends of spring and winter wheat in China.Agricultural and Forest Meteorology, 248: 518-526.https://linkinghub.elsevier.com/retrieve/pii/S0168192317303039Crop yields are influenced by growing season length, which are determined by temperature and agronomic management, such as sowing date and changes in cultivars. It is essential to quantify the interaction between climate change and crop management on crop phenology to understand the adaptation of farming systems to climate change. Historical changes in winter wheat phenology have been observed... [Show full abstract]

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[12]
Liu Y J, Chen Q M, Ge Q Set al., 2018b. Spatiotemporal differentiation of changes in wheat phenology in China under climate change from 1981 to 2010.Science China-Earth Sciences, 61: 1088-1097.http://www.cnki.com.cn/Article/CJFDTotal-JDXG201808008.htmPhenology is a reliable biological indicator for reflecting climate change. An examination of changes in crop phenology and the mechanisms driving them is critical for guiding regional agricultural activities in attempts to adapt to climate change. Due to a lack of records based on continuous long-term observation, studies on changes in multiple consecutive phenological stages throughout a whole growing season on a national scale are rarely found, especially with regard to the spatiotemporal differentiation of phenological changes. Using a long-term dataset (1981-2010) of wheat phenology collected from 48 agro-meteorological stations in China, we qualified the spatiotemporal changes of 10 phenological stages as well as the length of wheat growth phases. Results showed that climate and wheat phenology changed significantly during the growing seasons from 1981 to 2010. On average, on a national scale, dates of sowing (0.19 d a -1 ), emergence (0.06 d a -1 ), trefoil (0.05 d a -1 ), and milk ripe (0.06 d a -1 ) showed a delaying trend, whereas dates of tillering (-0.02 d a -1 ), jointing (-0.15 d a -1 ), booting (-0.21 d a -1 ), heading (-0.17 d a -1 ), anthesis (-0.19 d a -1 ), and maturity (-0.10 d a -1 ) showed an advancing trend. Furthermore, the vegetative growth phase and growing season were shortened by 0.23 and 0.29 d a -1 , respectively, whereas the reproductive growth phase was lengthened by 0.06 d a -1 . Trends in dates of phenological stages or length of growing phases varied across wheat-planting regions. Moreover, spatiotemporal differentiation of sensitivity in growing season length (GSL) to variations in climatic factors during the growing season between spring and winter wheat were remarkable. The GSL of spring (winter) wheat decreased (increased) with an increase in average temperature during the growing season. In all wheat-planting regions, the GSL increased with the increasing of total precipitation and sunshine duration during the growing season. In particular, the sensitivity of GSL to precipitation for spring wheat was weaker than for winter wheat, while the sensitivity of GSL to sunshine duration for spring wheat was stronger than for winter wheat. Recognition of the spatiotemporal differentiation of phenological changes and their response to various climatic factors will provide scientific support for decision-making in agricultural production.

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[13]
Liu Y J, Qin Y, Ge Q Set al., 2017. Reponses and sensitivities of maize phenology to climate change from 1981 to 2009 in Henan Province, China.Journal of Geographical Sciences, 27(9): 1072-1084.http://link.springer.com/10.1007/s11442-017-1422-4With the global warming, crop phenological shifts in responses to climate change have become a hot research topic. Based on the long-term observed agro-meteorological phenological data (1981–2009) and meteorological data, we quantitatively analyzed temporal and spatial shifts in maize phenology and their sensitivities to key climate factors change using climate tendency rate and sensitivity analysis methods. Results indicated that the sowing date was significantly delayed and the delay tendency rate was 9.0 d·10a -1 . But the stages from emergence to maturity occurred earlier (0.1 d·10a -1 <θ<1.7 d·10a -1 , θ is the change slope of maize phenology). The length of vegetative period (VPL) (from emergence to tasseling) was shortened by 0.9 d·10a -1 , while the length of generative period (GPL) (from tasseling to maturity) was lengthened by 1.7 d·10a -1 . The growing season length (GSL) (from emergence to maturity) was lengthened by 0.4 d·10a -1 . Correlation analysis indicated that maize phenology was significantly correlated with average temperature, precipitation, sunshine duration and growing degree days (GDD) ( p <0.01). Average temperature had significant negative correlation relationship, while precipitation, sunshine duration and growing degree days had significant positive correlations with maize phenology. Sensitivity analysis indicated that maize phenology showed different responses to variations in key climate factors, especially at different sites. The conclusions of this research could provide scientific supports for agricultural adaptation to climate change to address the global food security issue.

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[14]
Liu Z J, Hubbard Kenneth G, Lin X Met al., 2013. Negative effects of climate warming on maize yield are reversed by the changing of sowing date and cultivar selection in Northeast China.Global Change Biology, 19(11): 3481-3492.http://europepmc.org/abstract/MED/23857749Northeast China (NEC) accounts for about 30% of the nation's maize production in China. In the past three decades, maize yields in NEC have increased under changes in climate, cultivar selection and crop management. It is important to investigate the contribution of these changing factors to the historical yield increases to improve our understanding of how we can ensure increased yields in the future. In this study, we use phenology observations at six sites from 1981 to 2007 to detect trends in sowing dates and length of maize growing period, and then combine these observations with in situ temperature data to determine the trends of thermal time in the maize growing period, as a measure of changes in maize cultivars. The area in the vicinity of these six sites accounts for 30% of NEC's total maize production. The agricultural production systems simulator, APSIM-Maize model, was used to separate the impacts of changes in climate, sowing dates and thermal time requirements on maize phenology and yields. In NEC, sowing dates trended earlier in four of six sites and maturity dates trended later by 4 21 days. Therefore, the period from sowing to maturity ranged from 2 to 38 days longer in 2007 than it was in 1981. Our results indicate that climate trends alone would have led to a negative impact on maize. However, results from the adaptation assessments indicate that earlier sowing dates increased yields by up to 4%, and adoption of longer season cultivars caused a substantial increase in yield ranging from 13% to 38% over the past 27 years. Therefore, earlier sowing dates and introduction of cultivars with higher thermal time requirements in NEC have overcome the negative effects of climate change and turned what would have otherwise been a loss into a significant increase in maize yield.

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[15]
McMaster G S, Wilhelm W W, 1997. Growing degree-days: One equation, two interpretations.Agricultural and Forest Meteorology, 87(4): 291-300.http://linkinghub.elsevier.com/retrieve/pii/S0168192397000270Heat units, expressed in growing degree-days (GDD), are frequently used to describe the timing of biological processes. The basic equation used is GDD = [(TMAX + TMIN)/2] - TBASE where TMAX and TMIN are daily maximum and minimum air temperature, respectively, and TBASE is the base temperature. Two methods of interpreting this equation for calculating GDD are: (1) if the daily mean temperature is less than the base, it is set equal to the base temperature, or (2) if TMAX or TMIN < TBASE they are reset equal to TBASE. The objective of this paper is to show the differences which can result from using these two methods to estimate GDD, and make researchers and practitioners aware of the need to report clearly which method was used in the calculations. Although percent difference between methods of calculation are dependent on TMAX and TMIN data used to compute GDD, our comparisons have produced differences up to 83% when using a 0 C base for wheat (Triticum aestivum L.). Greater differences were found for corn (Zea mays L.) when using a base temperature of 10 C. Differences between the methods occur if only TMIN is less than TBASE and then Method 1 accumulates fewer GDD than Method 2. When incorporating an upper threshold, as commonly done with corn, there was a greater difference between the two methods. Not recognizing the discrepancy between methods can result in confusion and add error in quantifying relationships between heat unit accumulation and timing of events in crop development and growth, particularly in crop simulation models. This paper demonstrates the need for authors to clearly communicate the method of calculating GDD so others can correctly interpret and apply reported results.

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[16]
Meng L, Liu X J, Wu D Ret al., 2015. Responses of summer maize main phenology to climate change in the North China Plain.Chinese Journal of Agrometeorology, 36(4): 375-382. (in Chinese)http://en.cnki.com.cn/Article_en/CJFDTOTAL-ZGNY201504001.htmKnowledge about response of crop phenology to current climate change is of much importance to predict its response to future climate change scenario,since it helps reduce the prediction uncertainty.In this paper,based on phonological observation data of summer maize from agricultural meteorological station records and daily meteorological data during 1981-2009 in the North China Plain(NCP),responses of summer maize phenology to climate change were analyzed using linear regression method and significance analysis.Results showed that:(1)over the past 30 years,minimum and average temperature increased significantly(P0.05) during summer maize growing season in NCP with a trend of decline negatively correlated with latitude.Sunshine hours declined substantially(P0.01) and precipitation change was not significant;(2) The dates of main growth period of summer maize in the Beijing-Tianjin-Hebei region and Shandong province delayed significantly(P0.05),while in the Henan province they advanced significantly(P 0.05);(3) The whole growth days in NCP increased with a rate of2.72d 10y~(-1)(P0.01),and those in the Beijing-Tianjin-Hebei region had the highest rate of 3,36d 10y~(-1);(4) The whole growth days were mainly negatively correlated with average temperature during the same period.Regression coefficient varied in-7.16~3.17.The reproductive days were also negatively correlated with average temperature.Regression coefficient varied in-3.56~1.87.The results indicated that while temperature increased by 1 ,the days of whole growth period and reproductively stage of summer maize would shorten by 2.71 d and 1.07 d,respectively.Summer maize in different regions of NCP had different ways of responding to climate change.Suitable seeding time and variety types should be selected according to local response features.

[17]
Sacks William J, Kucharik Christopher J, 2011. Crop management and phenology trends in the US Corn Belt: Impacts on yields, evapotranspiration and energy balance.Agricultural and Forest Meteorology, 151(7): 882-894.https://linkinghub.elsevier.com/retrieve/pii/S0168192311000761Crop yields are affected by many factors, related to breeding, management and climate. Understanding these factors, and their relative contributions to historical yield increases, is important to help ensure that these yield increases can continue in the future. Two important factors that can affect yields are planting dates and the crop's growing degree day (GDD) requirements. We analyzed 25 years of data collected by the USDA in order to document trends in planting dates, lengths of the vegetative and reproductive growth periods, and the length of time between maturity and harvest for corn and soybeans across the United States. We then drove the Agro-IBIS agroecosystem model with these observations to investigate the effects of changing planting dates and crop GDD requirements on crop yields and fluxes of water and energy. Averaged across the U.S., corn planting dates advanced about 10 days from 1981 to 2005, and soybean planting dates about 12 days. For both crops, but especially for corn, this was accompanied by a lengthening of the growth period. The period from corn planting to maturity was about 12 days longer around 2005 than it was around 1981. A large driver of this change was a 14% increase in the number of GDD needed for corn to progress through the reproductive period, probably reflecting an adoption of longer season cultivars. If these changes in cultivars had not occurred, yields around 2005 would have been 12.6 bu ac 1 lower across the U.S. Corn Belt, erasing 26% of the yield increase from 1981 to 2005. These changes in crop phenology, together with a shortening of the time from maturity to harvest, have also modified the surface water and energy balance. Earlier planting has led to an increase in the latent heat flux and a decrease in the sensible heat flux in June, while a shorter time from maturity to harvest has meant an increase in net radiation in October.

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[18]
Tao F L, Zhang S, Zhang Zet al., 2014. Maize growing duration was prolonged across China in the past three decades under the combined effects of temperature, agronomic management, and cultivar shift.Global Change Biology, 20(12): 3686-3699.http://doi.wiley.com/10.1111/gcb.12684Abstract Maize phenology observations at 112 national agro-meteorological experiment stations across China spanning the years 1981鈥2009 were used to investigate the spatiotemporal changes of maize phenology, as well as the relations to temperature change and cultivar shift. The greater scope of the dataset allows us to estimate the effects of temperature change and cultivar shift on maize phenology more precisely. We found that maize sowing date advanced significantly at 26.0% of stations mainly for spring maize in northwestern, southwestern and northeastern China, although delayed significantly at 8.0% of stations mainly in northeastern China and the North China Plain (NCP). Maize maturity date delayed significantly at 36.6% of stations mainly in the northeastern China and the NCP. As a result, duration of maize whole growing period (GPw) was prolonged significantly at 41.1% of stations, although mean temperature ( T mean) during GPw increased at 72.3% of stations, significantly at 19.6% of stations, and T mean was negatively correlated with the duration of GPw at 92.9% of stations and significantly at 42.9% of stations. Once disentangling the effects of temperature change and cultivar shift with an approach based on accumulated thermal development unit, we found that increase in temperature advanced heading date and maturity date and reduced the duration of GPw at 81.3%, 82.1% and 83.9% of stations on average by 3.2, 6.0 and 3.5 days/decade, respectively. By contrast, cultivar shift delayed heading date and maturity date and prolonged the duration of GPw at 75.0%, 94.6% and 92.9% of stations on average by 1.5, 6.5 and 6.5 days/decade, respectively. Our results suggest that maize production is adapting to ongoing climate change by shift of sowing date and adoption of cultivars with longer growing period. The spatiotemporal changes of maize phenology presented here can further guide the development of adaptation options for maize production in near future.

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[19]
Tong P Y, 1992. Maize planting regionalization in China. Beijing: Press of Chinese Agriculture Science and Technology, 6-24. (in Chinese)

[20]
Vitasse Y, Francois C, Delpierre Net al., 2011. Assessing the effects of climate change on the phenology of European temperate trees.Agricultural and Forest Meteorology, 151(7): 969-980.https://linkinghub.elsevier.com/retrieve/pii/S0168192311000840Modelling phenology is crucial to assess the impact of climate change on the length of the canopy duration and the productivity of terrestrial ecosystems. Focusing on six dominant European tree species, the aims of this study were (i) to examine the accuracy of different leaf phenology models to simulate the onset and ending of the leafy season, with particular emphasis on the putative role of chilling to release winter bud dormancy and (ii) to predict seasonal shifts for the 21st century in response to climate warming. Models testing and validation were done for each species considering 2 or 3 years of phenological observations acquired over a large elevational gradient (1500 m range, 57 populations). Flushing models were either based solely on forcing temperatures (1-phase models) or both on chilling and forcing temperatures (2-phases models). Leaf senescence models were based on both temperature and photoperiod. We show that most flushing models are able to predict accurately the observed flushing dates. The 1-phase models are as efficient as 2-phases models for most species suggesting that chilling temperatures are currently sufficient to fully release bud dormancy. However, our predictions for the 21st century highlight that chilling temperature could be insufficient for some species at low elevation. Overall, flushing is expected to advance in the next decades but this trend substantially differed between species (from 0 to 2.4 days per decade). The prediction of leaf senescence appears more challenging, as the proposed models work properly for only two out of four deciduous species, for which senescence is expected to be delayed in the future (from 1.4 to 2.3 days per decade). These trends to earlier spring leafing and later autumn senescence are likely to affect the competitive balance between species. For instance, simulations over the 21st century predict a stronger lengthening of the canopy duration for Quercus petraea than for Fagus sylvatica, suggesting that shifts in the elevational distributions of these species might occur.

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[21]
Wang L X, Chen H L, Li Qet al., 2010 Research advances in plant phenology and climate.Acta Ecologica Sinica, 30(2): 447-454. (in Chinese)

[22]
Wang N, Wang J, Wang E Let al., 2015. Increased uncertainty in simulated maize phenology with more frequent supra-optimal temperature under climate warming.European Journal of Agronomy, 71: 19-33.https://linkinghub.elsevier.com/retrieve/pii/S1161030115300204Crop phenology is related to the partitioning of assimilates to different organs, crop productivity and timing of crop management. Understanding the uncertainty in simulated crop phenology can help target future direction of model improvement and assess climate change impact more accurately. However, the uncertainty in maize phenology modelling across regions and under climate scenarios has not been properly addressed. This study investigated the uncertainty in simulated maize phenology using six widely used models (SIMCOY, MAIS, Beta, WOFOST, CERES, and APSIM). The models were firstly calibrated and validated using long-term observational data across China Maize Belt. The validated models were then used to simulate maize phenology changes in response to climate change. The results showed that the six models could reach acceptable precision (NRMSE<8% for all the six models) by the calibration under current climate. However, the uncertainty between models in simulated maize phenology increased with the coefficient of fluctuation from 3.2% under the baseline to 6.3% under RCP4.5 and 7.4% under RCP8.5 in 2030s and 8.9% under RCP4.5 and 14.5% under RCP8.5 in 2080s for the simulated silking date, and from 4.2% under the baseline to 7.0% under RCP4.5 and 7.7% under RCP8.5 in 2030s and 10.2% under RCP4.5 and 16.7% under RCP8.5 in 2080s for the simulated maturity date in North China Plain. This highlights a significant knowledge gap in understanding how the key physiological processes of maize respond to changing temperature, particularly temperatures beyond the optimum. The uncertainty in predicted phenology is largest for summer maize in North China Plain, smaller for spring maize in northeast and southwest China. The increased uncertainty in North China Plain was due to more frequent supra-optimal temperatures, where different models disagree most in terms of phenology response to temperature, highlighting a key area for future model improvement. This implies that there could be a large uncertainty in simulated maize yield under future climate change in previous modelling studies conducted with a single crop growth model due to the uncertainty in simulated maize phenology.

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[23]
Xiao D P, 2015. Changes of crop phenology in Inner Mongolia under the background of climate warming.Chinese Agricultural Science Bulletin, 31(26): 216-221. (in Chinese)http://en.cnki.com.cn/Article_en/CJFDTotal-ZNTB201526036.htmUsing long-term observed phenological data, research on the trends of crop phenology is a vital approach to understand the impact of climate warming on agricultural production. In this study, the trends inwheat and maize for 1981 to 2009 were investigated based on phenological data from 13 agro-experimental stations in Inner Mongolia by using statistical methods. The study showed that the response of wheat and maizephenology to climate change was different under the combined effect of management change(sowing date adjustment) and cultivar shift. Across the investigated stations, while sowing date of wheat was delayed on anaverage of 1.7 d/10 a, maize sowing date was in advance with an average of 1.0 d/10 a. The heading date andthe subsequent maturity date of wheat were delayed on an average of 1.7 d/10 a and 0.8 d/10 a. Althoughheading date of maize showed small changes, the maize maturity date was delayed on an average by up to 3.3 d/10 a. Furthermore, trends in duration of different growth stages for wheat and maize were significantly different.The duration from emergence to heading(VGP) of wheat was shortened by an average of 1.4 d/10 a, while VGP of maize was prolonged on an average of 1.2 d/10 a. Also the durations from heading to maturity(RGP) of wheat and maize were prolonged on an average of 0.2 d/10 a and 3.3 d/10 a, respectively. However, the duration fromemergence to maturity(WGP) of wheat was shortened by an average of 1.2 d/10 a, while that of maize wasprolonged on an average of 4.5 d/10 a.

[24]
Yin X G, Wang M, Kong Q Xet al., 2015. Impacts of high temperature on maize production and adaptation measures in Northeast China.Chinese Journal of Applied Ecology, 26(1): 186-198. (in Chinese)http://www.ncbi.nlm.nih.gov/pubmed/25985670Heat stress is one of the major agro-meteorological hazards that affect maize production significantly in the farming region of Northeast China( NFR). This study analyzed the temporal and spatial changes of the accumulated temperature above 30 ( AT) and the accumulated days with the maximum temperature above 30 ( AD) in different maize growing phases under global warming. It further evaluated the impacts of extreme heat on maize yield in different regions,and put forward some adaptation measures to cope with heat stress for maize production in NFR. The results showed that during 1961 to 2010,the temperature in the maize growing season increased significantly. The maximum temperature in flowering phase was much larger than that in the other growing phases. Temperature increased at rates of 0. 16,0. 14,0. 06 and 0. 23 every ten years in the whole maize growing season,vegetative growth phase( from sowing to 11 days before flowering),flowering phase,and late growth phase( from 11 days after flowering to maturity),respectively. The AT in the whole maize growing season increased in NFR during the last 50 years with the highest in the southwest part of NFR,and that in the vegetative growth phase increased faster than in the other two phases. The AD in the whole maize growing season increased during the last 50 years with the highest in the southwest part of NFR,and that in the late growth phase increased faster than in the other two phases. Heat stress negatively affected maize yield during the maize growing season,particularly in the vegetative growth phase. The heat stress in Songliao Plain was much higher in comparison to the other regions.The adaptation measures of maize production to heat stress in NFR included optimizing crop structure,cultivating high temperature resistant maize varieties,improving maize production management and developing the maize production system that could cope with disasters.

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[25]
Zhao J, Yang X G, Dai S Wet al., 2015. Increased utilization of lengthening growing season and warming temperatures by adjusting sowing dates and cultivar selection for spring maize in Northeast China.European Journal of Agronomy, 67: 12-19.https://linkinghub.elsevier.com/retrieve/pii/S1161030115000416Highlights 61 Both the actual and theoretical growing seasons are lengthening in Northeast China. 61 Adjusting the sowing dates decreased the unutilized thermal time (TT) before sowing. 61 Cultivar selection increased the utilized TT and decreased the unutilized TT after maturity. 61 The increased grain yield by adjusting sowing dates far less than by switching to late maturing cultivars. 61 If the currently unutilized TT were fully explored, the local spring maize grain yield would have increased by 12.0–38.4%. Abstract Global warming has lengthened the theoretical growing season of spring maize in Northeast China (NEC), and the temperatures during the growing season have increased. In practise, crop producers adjust sowing dates and alternate crop cultivars to take advantage of the lengthening growing season and increasing temperatures. In this study, we used crop data and daily weather data for 1981–2007 at five locations in NEC to quantify the utilization of the lengthening growing season and increasing temperatures by adjusting sowing dates and cultivar selection for spring maize production. If these two positive factors are not fully utilized, then it is important to know the potential impacts of these climatic trends on spring maize grain yields. The results show that in NEC, both the actual and theoretical growing seasons are lengthening, i.e., the sowing dates have been advanced and the maturity dates have been delayed. The actual sowing dates are 1–8&nbsp;days later and the actual maturity dates are 6–22&nbsp;days earlier than the theoretical perspective. Advancing sowing dates and changing cultivars led to 0–5&nbsp;days and 6–26&nbsp;days extension of the growing season. For the potential thermal time (TT), adjusting the sowing dates decreased the unutilized TT before sowing, while the cultivar selection increased the utilized TT and decreased the unutilized TT after maturity. On average, the unutilized heating resource before sowing is less than that after the maturity date (0.3–1.9% vs. 2.1–7.8%). During 1981–2007, for per day extension of the growing season, the spring maize grain yield increased by 75.2&nbsp;kg&nbsp;ha611. The spring maize grain yields have increased by 7.1–57.2% when both early sowing and changing cultivars during 1981–2007. In particular, adjusting the sowing dates increased the grain yield by 1.1–7.3%, which was far less than the increase effect (6.5–43.7%) from switching to late maturing cultivars. Therefore, selecting late maturing cultivars is an important technique to improve maize grain yields in NEC under the global warming context. Nevertheless, if the currently unutilized TT were fully explored, the local spring maize grain yield would have increased by 12.0–38.4%.

DOI

[26]
Zhang T Y, Huang Y, Yang X G, 2013. Climate warming over the past three decades has shortened rice growth duration in China and cultivar shifts have further accelerated the process for late rice.Global Change Biology, 19(2): 563-570.http://doi.wiley.com/10.1111/gcb.2012.19.issue-2An extensive dataset on rice phenology in China, including 202 series broadly covering the past three decades (1980s–2000s), was compiled. From these data, we estimated the responses of growth duration length to temperature using a regression model based on the data with and without detrending. Regression coefficients derived from the detrended data reflect only the temperature effect, whereas those derived from data without detrending represent a combined effect of temperature and confounding cultivar shifts. Results indicate that the regression coefficients calculated from the data with and without detrending show an average shortening of the growth duration of 4.1–4.4 days for each additional increase in temperature over the full growth cycle. Using the detrended data, 95.0% of the data series exhibited a negative correlation between the growth duration length and temperature; this correlation was significant in 61.9% of all of the data series. We then compared the difference between the two regression coefficients calculated from data with and without detrending and found a significantly greater temperature sensitivity using the data without detrending (612.9 days °C611) than that derived from the detrended data (612.0 days °C611) in the period of emergence to heading for the late rice, producing a negative difference in temperature sensitivity (610.9 days °C611). This implies that short-duration cultivars were planted with increase in temperature and exacerbated the undesired phenological change. In contrast, positive differences were detected for the single (0.6 days °C611) and early rice (0.5 days °C611) over the full growth cycle, which might indicate that long-duration cultivars were favoured with climate warming, but these differences were insignificant. In summary, our results suggest that a major, temperature induced change in the rice growth duration is underway in China and that using a short-duration cultivar has been accelerating the process for late rice.

DOI PMID

[27]
Zhang W X, Liu P X, Feng Q Ret al., 2018. The spatiotemporal responses ofPopulus euphratica to global warming in Chinese oases between 1960 and 2015. Journal of Geographical Sciences, 28(5): 579-594.

[28]
Zheng J Y, Ge Q S, Hao Z X, 2002. Impacts of climate warming on plants phenophases in China for the last 40 years.Chinese Science Bulletin, 47(21): 1826-1831.http://www.scichina.com/ky/0221/ky1826.stmBased on plant phenology data from 26 stations of the Chinese Phenology Observation Network of the Chinese Academy of Sciences and the climate data, the change of plant phenophase in spring and the impact of climate warming on the plant phenophase in China for the last 40 years are analyzed. Furthermore, the geographical distribution models of phenophase in every decade are reconstructed, and the impact of climate warming on geographical distribution model of phenophase is studied as well. The results show that ( ) the response of phenophase advance or delay to temperature change is nonlinear. Since the 1980s, at the same amplitude of temperature change, phenophase delay amplitude caused by temperature decrease is greater than phenophase advance amplitude caused by temperature increase; the rate of phenophase advance days decreases with temperature increase amplitude, and the rate of phenophase delay days increases with temperature decrease amplitude. ( ) The geographical distribution model between phenophase and geographical location is unstable. Since the 1980s, with the spring temperature increasing in the most of China and decreasing in the south of Qinling Mountains, phenophases have advanced in northeastern China, North China and the lower reaches of the Changjiang River, and have delayed in the eastern part of southwestern China and the middle reaches of the Changjiang River; while the rate of the phenophase difference with latitude becomes smaller.

DOI

[29]
Zheng J Y, Ge Q S, Hao Z Xet al., 2012. Changes of spring phenodate in Yangtze River Delta region in the past 150 years.Acta Geographica Sinica, 67(1): 45-52. (in Chinese)http://en.cnki.com.cn/Article_en/CJFDTOTAL-DLXB201201007.htmBased on phenological records extracted from Chinese historical dairies, the series of spring phenodate in the Yangtze River Delta region of China since 1834 is reconstructed. Together with the temperature and phenology observation data, the interpretation of the phenodate variation to temperature change is also analyzed. The results are shown as follows. (1) Spring phenology in the Yangtze River Delta region is gradually delayed during 1834-1893 and greatly advances after 1893; and exhibits inter-decadal fluctuation during 1900-1990 and greatly advances after 1990. The latest year of the spring phenodate is delayed by 27 days and occurs in 1893, while the earliest year is advanced by 17 days and occurs in 2007. (2) Correlation coefficient between spring phenodate in the Yangtze River Delta region and temperature (previous December to March and January to March) is higher significant up to the level at 99.9% with the value over -0.75 and -0.80, respectively. The variation of spring phenodate well indicates the change of temperature from previous winter to early spring, especially from January to March. These results will provide a data basis for the further study on temperature change reconstruction using multi-proxy data, including phenological records during historical times.

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