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Correlation Analysis of Rice Seed Setting Rate and Weight of 1000-Grain and Agro-Meteorology over the Middle and Lower Reaches of the Yangtze River, China
Available online at www.sciencedirect.com
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Agricultural Sciences in China 2007, 6(4): 430-436
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Apnl2007
@'
Correlation Analysis of Rice Seed Setting Rate and Weight of 1 000-Grain and Agro-Meteorology over the Middle and Lower Reaches of the Yangtze River, China ZHAO Hai-yanl, YAO Feng-rnei1.2, ZHANG Yong1.2.3, XU Bin', YUAN Jingl, HU Ya-nanl and XU Yin-long' institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences, Beijing 100081, P.R. China Graduate University, Chinese Academy of Sciences, Beijing 100039, P.R. China
! 1
institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, P.R.China
Abstract The purpose of this study is to reveal the effects of historic climate change on rice yield over the middle and lower reaches of the Yangtze River, China, and to better adapt to climate change in the future. This study presents the relation of temperature and precipitation and rice components from 1981 to 2003 at 48 early rice stations and 30 middle rice stations. It focuses on an analysis of three stages: flowering, pre-milk, and late milk. The results show that mean maximum temperature and mean daily precipitation at the stages of flowering and pre-milk are most related to early rice yield. Yield change of middle rice is mainly because of mean precipitation change at the flowering stage. Furthermore, percentage of undeveloped grain increases as mean maximum temperature rises at the flowering stage. Over-precipitation in the reproductive stage is a major reason for reduction in yield of early rice. Consecutive rainfall and continuous high temperature can have negative effects on middle rice yield. Global warming would affect middle rice more seriously than early rice. Key words: mean maximum temperature, mean daily precipitation, percentage of undeveloped grain, percentage of partially developed grain, weight of 1 000-grain
INTRODUCTION It is concluded in the Third Assessment Report of Intergovernmental Panel on Climate Change (IPCC) that the global average surface temperature has increased by 0.6 -1- 0.2"C and there have been higher maximum temperatures and more hot days over nearly all land areas since the nineteenth century (Houghton et al. 2001). There is an increasing trend of the frequency and intensity of hot temperatures in Jiangsu, Hubei, Hunan and Anhui provinces, China, which would cause greater risks to rice production (Xu et al. 2005; Satake and Yoshida 1978; the Phytotron, Shanghai Institute of
Plant Physiology 1976a, b, 1977). On the other hand, plantation area has been reduced since the implementation of reform and opening-up policy; for example, plantation area around the Yangtze River, China, was decreased from 291 953 000 in 1949 to 257 529 000 ha in 1998 (Yu 2003), accounting for a 11.8% drop-off, so total rice production mainly relies on the rising of yield per unit. In this article, the impacts of climate change characterizing with global warming, on the components of rice yield will be analyzed from the historic record over the middle and lower reaches of the Yangtze River, providing scientific evidence for adaptive options to hot temperature events. Rice production over the Yangtze River is affected
This paper is translated from its Chinese version in Scienria Agricultura Sinica. ZHAO Hai-yan, MSc, E-mail: zhaohaiyan01234CO 163.corn; Correspondence XU Yin-long, E-mail: [email protected]
02007,CAAS. All rights reserved.Publishedby ElsevierLtd.
Correlation Analysis of Rice Seed Setting Rate and Weight of 1000-Grain and Agro-Meteorology over the Middle and Lower
by high temperatures at the flowering and grain filling stages. Regarding 30% of undeveloped-grain percentage as damaged index of fixed-number seed-setting rate, when average daily mean temperature is higher than 29-30°C and mean daily maximum temperature is higher than 35°C during 1-5 days after flowering, the damage to rice would occur because high temperature at the flowering stage would affect anther's splitting and shorten life of pollens, so as to lower fertilizing percentage of rice. The temperature between 22-28°C is condign at the filling stage of rice and 35°C will shorten the rice grain filling period (Tai et al. 1994; Kim et at. 1996a, b; Matsui et al. 1997; Imai and Okamoto-Sat0 1991; Tao et al. 1983; Xie et al. 1989; Liu et al. 2005; Yang et al. 1994; Tan et al. 1985; Huang et al. 2004; Wang C H et al. 2000; Zheng 2003). Otherwise, overcast s h e s and rain would also affect rice seeding. If there are 3 days of precipitation over 5 mm d-' during the 5 days after flowering, the seed setting rate would decrease because the bad weather could make spikelets degenerate and reduce fertilizing percentage (Tao et ul. 1983; Zhang et al. 1995). Previous studies were mainly carried out in the laboratory; limited field studies were performed in a relatively small area and short period with few species (Li 2003; He 1999; Zou 2002; Wang D P et al. 2000; Lou and Hou 2003). Past research on the impacts of climate change on agricultural production were mainly focused on seeking statistical relationships of crop yield and climatic variability, or simulating yield changes with the help of crop and climate models, whereas how climate change would impact on yield components is less investigated. In this article, 48 early rice stations and 30 middle rice stations over the middle and lower reaches of the Yangtze River in a long time series (1981-2003), are selected to analyze the correlation of rice seed setting rate and weight of 1 000-grain with mean maximum temperature and mean daily precipitation. The aim is to investigate the mechanism of rice yield change over the middle and lower reaches of the Yangtze River under the background of global warming from the relationship of rice yield components (percentage of undeveloped grain, percentage of partially developed grain, and weight of 1 000-grain) with the meteorological factors, consequently providing a scientific basis for coping measures with the hot temperature events.
43 1
DATA AND METHODS In this article, 48 early rice stations and 30 middle rice stations from Hubei, Hunan, Anhui, Jiangxi, Jiangsu, and Zhejiang provinces between 198 1-2003, were selected. The data contain growth season (the first, general, and end of flowering stage), rice yield components (percentage of undeveloped grain; percentage of partially developed grain; and weight of 1 000-grain), as well as daily maximum temperature and precipitation in each selected rice station. The selected rice stations are shown in Fig.1, totally there are 1362 samples of indica rice, 872 for early rice with 332 species, and 490 for middle rice with 126 species. The mean daily maximum temperature and mean daily precipitation at the flowering stage (2 days before the first flowering to 5 days after the end of flowering), the pre-milk stage (6 days after the first flowering to 10 days after the end of flowering), and late milk stage (1 1 days after the first flowering to 15 days after the end of flowering) were firstly calculated, and then the correlation of rice yield components with mean daily maximum temperature and mean daily precipitation at the three stages were analyzed.
RESULTS Impacts of meteorologicalfactors on percentage of undeveloped grain of early and middle rice Fig.2 shows the relationship of percentage of undeveloped grain of early rice and mean maximum temperature at stages of the flowering, pre-milk, and late milk,
Fig. 1 Distribution of rice stations.
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and the positive relationship of undeveloped grain of early rice and mean daily precipitation at the three stages with the significance level of 0.01. As the flowering and late milk stages of early rice last from the middle of June to the middle of July, it is during the Meiyu season with a lot of rain and the daily maximum temperature is normally lower than 35°C over the middle and low reaches of the Yangtze River. Rice tassels more slowly in lower temperature conditions and some stems would be darkened. On the other hand, the flowers would disperse because of low temperature; the flowering stage would be lengthened with scarce pollen, which would result in decrease of insemination percentage of rice and increase of percentage of undeveloped grain. Therefore, percentage of undeveloped grain of early rice would rise with more precipitation and reduce with higher mean maximum temperature at the three stages. The positive relationship of percentage of undevel-
oped grain of middle rice and mean maximum temperature as well as mean precipitation at stages of flowering, pre-milk, and late milk is shown in Fig.3; the correlation of percentage of undeveloped grain with mean daily precipitation at the stages of flowering and pre-milk could get the significance level (P<0.05). The flowering and grain filling stages of middle rice usually last from late July to late August in Anhui and Jiangsu provinces, and from middle August to middle September in Hubei and Hunan provinces. During these periods, mean precipitation is 3.78-4.48 mm d-I,which is 2.46-4.18 mm d-' less than the corresponding stages of early rice. Meanwhile, hot days (daily maximum temperature 2 35°C) take place frequently. Anther's splitting would be damaged and pollen's life span would be shortened when daily maximum temperature is over 35°C. As a result, fertilizing rates of rice are decreased. The percentage of undeveloped grain is proportional to
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Fig. 2 The relationship between percentage of undeveloped grain of early rice and weather data at all stages. A, mean maximum temperature at flowering stage; B, mean maximum temperature at pre-milk stage; C, mean maximum temperature at late milk stage; D, mean daily precipitation at flowering stage; E, mean daily precipitation at pre-milk stage; F, mean daily precipitation at late milk stage.
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Correlation Analysis of Rice Seed Setting Rate and Weight of 1000-Grain and Agro-Meteorology over the Middle and Lower
precipitation and the mean maximum temperature, but the correlation is not significant ( P < 0.05). That is probably because of the response difference of various rice species to meteorological factors. Percentage of undeveloped grain is affected by daily precipitation and maximum temperature, especially at the flowering stage. The relationship between precipitation and percentage of undeveloped grain of early and middle rice is positive, whereas percentage of undeveloped grain decreases for early rice or increases for middle rice as mean maximum temperature rises.
Impacts of meteorological factors on percentage of partially developed grain of early and middle rice The percentage of partially developed grain of early rice is mainly affected by mean precipitation and mean maximum temperature in the late milk stage. It correlates positively with mean precipitation, but negatively with mean maximum temperature with the significance level P<0.05 (Fig.4). The middle rice is similar to the early rice, but the correlation is not significant ( P < 0.05) (Fig.5).
433
Percentage of partially developed grain is an index of grain filling, which is a process of photosynthate transportation and dry-matter accumulation. On one hand, photosynthate would be reduced by lower temperature and rainy days; on the other hand, transportation system could be blocked by low temperature. Percentage of partially developed grain would increase because of insufficient grain filling.
Impacts of meteorological factors on weight of 1000-grain of early and middle rice The fruiting stage, especially the grain-filling stage, is crucial to weight of 1 000-grain of rice. Mean temperature between 22-28°C is optimal at this stage. Warmer conditions would accelerate grain filling and shorten grain-filling period, which can result in a decrease of fruiting rate. In contrast, lower temperature could prolong grain-filling period and is beneficial to weight of 1000-grain of rice. It is shown from Fig.6 that weight of 1 000-grain of early rice is positively correlated to mean maximum temperature with a significance level of PcO.05, and negatively to mean daily precipitation at stages of pre-milk and late milk, which
Fig. 3 The relationship between percentage of undeveloped grain of middle rice and weather data at flowering stage. A, mean maximum temperature; B, mean daily precipitation.
Fig. 4 The relationshipbetween percentage of partially developed grain of early rice and weather data at late milk stage. A, mean maximum temperature; B, mean daily precipitation.
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ZHAO Hai-yan ef al.
Fig. 5 The relationship between percentage of partially developed grain of middle rice and weather data at late milk stage. A, mean maximum temperature; B, mean daily precipitation.
Fig. 6 The relationshipbetween thousand grains weight of early rice and mean maximum temperature at all stage. A, pre-milk stage; B, late milk stage.
indicates that the most important factor affecting weight of 1000-grain of early rice is mean maximum temperature at the whole milk stage, and precipitation is the second. Weight of 1 000-grain of middle rice is negatively correlated with mean daily precipitation and positively with mean maximum temperature at late milk stage, but it is not significant (P<0.05).Sunshine is not considered in the research of this paper, whereas, insufficient sunshine would weaken the photosynthesis and lower the filling of rice grains (Zheng 2003).
DISCUSSION Over the middle and lower reaches of the Yangtze River, rice is grown mainly in Meiyu season, when the climate is characterized by plenty of precipitation of large variability, and seed setting rate of early rice is hampered and weight of 1000-grain is decreased by overcast weather. After Meiyu period, the middle and lower reaches of the Yangtze River are dominated by the Subtropical High, and downward flow prevails with more hot days. Continuous hot weather would damage middle rice production.
Percentage of undeveloped grain of rice is closely related to daily precipitation and maximum temperature. For early rice, it would drop when mean maximum temperature decreases and mean daily precipitation increases at the flowering, pre-mill and late milk stages; whereas for middle rice, meteorological factors at the flowering stage are vital. It is positively correlated with the mean maximum temperature at the flowering stage. It has been proven that overcast skies and rain can impact flowering and fertilization of early rice, and consecutive hot days are the major reason for higher percentage of undeveloped grain for middle rice (Liu et al. 2005; Zhang et al. 1995; Li 2003). However, because of the lower occurrence of hot temperatures during the milk stage for race sampling in this study, the weight of 1 000-grain over the middle and lower reaches of the Yangtze River is slightly affected by global warming. Percentage of partially developed grain of early rice is mainly affected by mean daily precipitation and mean maximum temperature at the late milk stage. It is positively correlated with precipitation, but negatively with temperature. The relationship for middle rice is similar to early rice, but not significant (P<0.05). Weight of 1000-grain of early rice increases as mean temperature goes up and deceases as mean precipita-
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Correlation Analysis of Rice Seed Setting Rate and Weight of 1 000-Grain and Agro-Meteorology over the Middle and Lower
435
tion goes down at pre-milk and late milk stages. Similarly, the relationship of middle rice at late milk stage is identical to early rice, but not significant ( P c 0.05). Some research results show that consecutive hot temperature has negative effects on the weight of 1000-grain (The Phytotron, Shanghai Institute of Plant Physiology 1976a, b, 1977). There is no significant correlation between the percentage of undeveloped, partially developed grain, and weight of 1 000-grain of middle rice and temperature. Many other factors could affect yield component of rice, including inherent genotypes, physiological factors, ecology, and planting skill factors. Though all the selected genotypes in this study were indica rice, they possess some similar genetic characteristics. The relation between percentage of undeveloped, partially developed grain, weight of 1 000-grain, and meteorological factors were significant on P c 0.05 level, which means the responses of indica rice to temperature was identical. But middle rice differed from early rice. The responses of fruiting rate and weight of 1000-grain of middle rice to temperatureand precipitation are different. It means that more factors, including meteorological factors (e.g., sunshine) and non-meteorological factors (e.g.,soil moisture content) should be considered in the impacts on percentage of partially developed grain and weight of 1 000-grain of middle rice. Multiplefactor correlation analysis should be done in future study.
developed grain because of overcast and raining. The Erequency of percentage of undeveloped grain of early rice 3 30% is 3.9% in this study. The frequency of mean daily precipitation 3 10 mm is 8.6, 9.0% at the flowering and late milk stages respectively. However, the frequency of mean maximum temperature 3 35°C is 4.0, 2.0% at the flowering and late milk stages respectively. Hence, precipitation and temperature at the flowering and late milk stages are both contributing to the percentage of undeveloped grain of middle rice. Higher temperature over the middle and low reaches of the Yangtze River in the future will mainly affect middle rice. The frequency of mean maximum temperature 3 35°C is 4.0% at the flowering stage of middle rice, which is more than twice early rice at the same stage. Hence, global warming would have more negative impacts on middle rice over the middle and lower reaches of the Yangtze River than early rice. As global warming would increase the frequency of high temperature, it is very important to investigate adaptive measures to high temperature over the middle and lower reaches of the Yangtze River.
CONCLUSION
References
According to the analysis above, it can be concluded that growth season of early rice is hampered by cloudy and rainy weather; rising temperature is favorable to early rice growth. The frequency of percentage of undeveloped grain of early rice 2 30% is 7.0% in this study. The frequency of mean daily precipitation 3 10 mm is 31.5, 29.0, and 20.7% at the flowering, premilk, and late milk stages respectively. However, the frequency of mean maximum temperature 3 35°C is only 2.0,7.3, and 15.2%. So, precipitation is attributing to percentage of undeveloped grain of early rice at the reproductive stage more than temperature. Middle rice production is negatively affected by increase of percentage of undeveloped grain and partial
He S R. 1999. Climatic conditions analyses of early rice yield fluctuation at Nanfeng. Jiangxi Meteorological Science and Technology, 22,30-31. (in Chinese) Houghton J T, Ding Y, Griggs D J, Noguer M, Linden P J, Dai X, Maskell K, Johnson C A. 2001. Climate Change 2001: The Scientific Basis. Cambridge University Press, London. pp. 26. Huang Y D, Cao L J, Wu L Q, Yan P, Chen D P,Yang A Z. 2004. Investigation and analysis of heat damage on rice at blossoming stage in Anhui Province in 2003. Journal of Anhui Agricultural University, 31,385-388. (in Chinese) Imai K, Okamoto-Sato M. 1991. Effect of temperature on CO, dependence of gas exchanges in C, and C, crop plants. Japanese Journal of Crop Science, 60, 139-145. Kim H Y, Horie T, Nakagawa H, Wada K. 1996a. Effects of elevated CO, concentration and high temperature on growth
Acknowledgements This study is supported by National Key Technology R&D Program in 10th Five-Year Plan of China (2004BA611B-02). The authors are grateful to Meteorological Information Centre, China Meteorological Administration, for providing the observation data.
02007,CAAS. All dghts reselved.Published by EisevkrLtd.
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and yield of rice. I . The effect on development, dry matter production and some growth characteristics.Japanese Journal of Crop Science, 65,634-643. Kim H Y, Horie T, Nakagawa H, Wada K. 1996b. Effects of elevated CO, concentration and high temperature on growth and yield of rice. 11. The effect on yield and its components of Akihikari rice. Japanese Journal of Crop Science, 65,644651. Li C D. 2003. Analyses of high temperature and undeveloped grain. Shaanxi Journal of Agricultural Sciences, (S), 45-47. (in Chinese) Liu Y K, Xia S P, Luo X F, Li W Z. 2005. Effect of high temperature on seed setting rate and yield and its defense technique in single-cropping late rice. Chinese Agriculture Bulletin, 21, 155-158. (in Chinese) Lou X R, Hou Y Y. 2003. Evaluation merhod of national late rice climate year’s harvest. Meteorology, 29,21-25. (in Chinese) Matsui T, Omasa K, Horie T. 1997. High temperature-induced spikelet sterility of Japonica rice at flowering in relation to air temperature, humidity and wind velocity conditions. Japanese Journal of Crop Science, 66,449-455. Satake T, Yoshida S. 1978. High temperature-inducedsterility in Indica rices at flowering. Japanese Journal of Crop Science, 47,6-17. Tai H J, Yao K M, Liu W Z, Lou X R . 1994. Introduction of China Agro-Meteorology Information. China Meteorology Press, Beijing. pp. 146. (in Chinese) Tan Z H, Lan T Y, Ren C F, Fang W. 1985. Harm of high temperature on hybrid rice and its countermeasure. Acta Agronornica Sinica, 11, 103-108. (in Chinese) Tao B Y, Tang Z C, Peng Z A, Zhang D Q. 1983. Hybrid Rice and Meteorology. Jiangsu Scienceand TechnologyPress, Nanjing. pp. 52-54. (in Chinese) The Phytotron, Shanghai Institute of Plant Physiology. 1976a. The influence of high temperatures on flowering and fruiting of early rice. 11. High temperature sensitivity of flowering and fruiting of early rice. Acta Botanica Sinica, 18,323-329, (in Chinese) The Phytotron, Shanghai Institute of Plant Physiology. 1976b. The influence of high temperatures on flowering and fruiting
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of early rice. I . The influence of high temperature on the fruiting from milky stage to ripening stage. Acta Botanica Sinica, 18,250-256. (in Chinese) The Phytotron, Shanghai Institute of Plant Physiology. 1977. The influence of high temperatures on flowering and fruiting of early rice.111. High temperature sensitivity of flowering and fruiting of early rice. Acta Botanica Sinica, 19, 126-131. (in Chinese) Wang C H, Zhang Y Z, Zou Y H, Zhou J C. 2000. Review of ripening of hybrid rice. Liaoning Agricultural Sciences, (l), 41-43. (in Chinese) Wang D P, Tang J, Li R F. 2000. Effects of climatic conditions on hybrid rice at flowering and grain filling stages. Journal of Shaanxi Meteorology, (l),18-20. (in Chinese) Xie P Q, Long G B, Li Z W, Xu Q S. 1989. Primary analysis of climatic ecological conditions and ripening rate of subspecies of hybrid rice F,. Hunan Agricultural Science, (3), 7-8. (in Chinese) Xu Y L, Zhao H Y, Yao F M, Zhang Y, Xu B, Hu Y N, Yuan J. 2005. Statistical analysis of impacts of high temperature events on rice yiled components over middle and lower reaches of the Yangtze River. Chinese Journal of Agrometerology, 25 (suppl.), 20-23. (in Chinese) Yang J C, Zhu Q S, Wang Z Q, Lang Y Z. 1994. A study on the setting percentage and grain filling percentage of Yayou 2. Journal of Jiangsu Agriculture College, 15, 14-18. (in Chinese). Yu X G.2003. Persistent Development Study of the Yangtze River. Science Press, Beijing. pp. 77-82. (in Chinese) Zhang Y Z, Zhang G H, Zhu G Q, Deng Q Y, Zhan Q C. 1995. Effects of overcast and raining on flowering, fertilizing and seed setting of early rice. Chinese Journal of Rice Science, 9, 173-178. (in Chinese) Zheng Z G.2003. The influence of temperature and light on grain-filling, dry matter production of rice. Journal of Beijing Agricultural College, 18,13-16. (in Chinese) Zou L Y. 2002. Analysis of disasters influencing paddy yield in Yunnan. Chinese Journal of Agrometeomlogy, 23, 12-15. (in Chinese) (Edited by ZHANG Yi-min)
02007, CAAS. All d g k mserved. Publlshedby ElsevlerLtd.
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Agricultural Sciences in China 2007, 6(4): 430-436
~i ScienceDirect
Apnl2007
@'
Correlation Analysis of Rice Seed Setting Rate and Weight of 1 000-Grain and Agro-Meteorology over the Middle and Lower Reaches of the Yangtze River, China ZHAO Hai-yanl, YAO Feng-rnei1.2, ZHANG Yong1.2.3, XU Bin', YUAN Jingl, HU Ya-nanl and XU Yin-long' institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences, Beijing 100081, P.R. China Graduate University, Chinese Academy of Sciences, Beijing 100039, P.R. China
! 1
institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, P.R.China
Abstract The purpose of this study is to reveal the effects of historic climate change on rice yield over the middle and lower reaches of the Yangtze River, China, and to better adapt to climate change in the future. This study presents the relation of temperature and precipitation and rice components from 1981 to 2003 at 48 early rice stations and 30 middle rice stations. It focuses on an analysis of three stages: flowering, pre-milk, and late milk. The results show that mean maximum temperature and mean daily precipitation at the stages of flowering and pre-milk are most related to early rice yield. Yield change of middle rice is mainly because of mean precipitation change at the flowering stage. Furthermore, percentage of undeveloped grain increases as mean maximum temperature rises at the flowering stage. Over-precipitation in the reproductive stage is a major reason for reduction in yield of early rice. Consecutive rainfall and continuous high temperature can have negative effects on middle rice yield. Global warming would affect middle rice more seriously than early rice. Key words: mean maximum temperature, mean daily precipitation, percentage of undeveloped grain, percentage of partially developed grain, weight of 1 000-grain
INTRODUCTION It is concluded in the Third Assessment Report of Intergovernmental Panel on Climate Change (IPCC) that the global average surface temperature has increased by 0.6 -1- 0.2"C and there have been higher maximum temperatures and more hot days over nearly all land areas since the nineteenth century (Houghton et al. 2001). There is an increasing trend of the frequency and intensity of hot temperatures in Jiangsu, Hubei, Hunan and Anhui provinces, China, which would cause greater risks to rice production (Xu et al. 2005; Satake and Yoshida 1978; the Phytotron, Shanghai Institute of
Plant Physiology 1976a, b, 1977). On the other hand, plantation area has been reduced since the implementation of reform and opening-up policy; for example, plantation area around the Yangtze River, China, was decreased from 291 953 000 in 1949 to 257 529 000 ha in 1998 (Yu 2003), accounting for a 11.8% drop-off, so total rice production mainly relies on the rising of yield per unit. In this article, the impacts of climate change characterizing with global warming, on the components of rice yield will be analyzed from the historic record over the middle and lower reaches of the Yangtze River, providing scientific evidence for adaptive options to hot temperature events. Rice production over the Yangtze River is affected
This paper is translated from its Chinese version in Scienria Agricultura Sinica. ZHAO Hai-yan, MSc, E-mail: zhaohaiyan01234CO 163.corn; Correspondence XU Yin-long, E-mail: [email protected]
02007,CAAS. All rights reserved.Publishedby ElsevierLtd.
Correlation Analysis of Rice Seed Setting Rate and Weight of 1000-Grain and Agro-Meteorology over the Middle and Lower
by high temperatures at the flowering and grain filling stages. Regarding 30% of undeveloped-grain percentage as damaged index of fixed-number seed-setting rate, when average daily mean temperature is higher than 29-30°C and mean daily maximum temperature is higher than 35°C during 1-5 days after flowering, the damage to rice would occur because high temperature at the flowering stage would affect anther's splitting and shorten life of pollens, so as to lower fertilizing percentage of rice. The temperature between 22-28°C is condign at the filling stage of rice and 35°C will shorten the rice grain filling period (Tai et al. 1994; Kim et at. 1996a, b; Matsui et al. 1997; Imai and Okamoto-Sat0 1991; Tao et al. 1983; Xie et al. 1989; Liu et al. 2005; Yang et al. 1994; Tan et al. 1985; Huang et al. 2004; Wang C H et al. 2000; Zheng 2003). Otherwise, overcast s h e s and rain would also affect rice seeding. If there are 3 days of precipitation over 5 mm d-' during the 5 days after flowering, the seed setting rate would decrease because the bad weather could make spikelets degenerate and reduce fertilizing percentage (Tao et ul. 1983; Zhang et al. 1995). Previous studies were mainly carried out in the laboratory; limited field studies were performed in a relatively small area and short period with few species (Li 2003; He 1999; Zou 2002; Wang D P et al. 2000; Lou and Hou 2003). Past research on the impacts of climate change on agricultural production were mainly focused on seeking statistical relationships of crop yield and climatic variability, or simulating yield changes with the help of crop and climate models, whereas how climate change would impact on yield components is less investigated. In this article, 48 early rice stations and 30 middle rice stations over the middle and lower reaches of the Yangtze River in a long time series (1981-2003), are selected to analyze the correlation of rice seed setting rate and weight of 1 000-grain with mean maximum temperature and mean daily precipitation. The aim is to investigate the mechanism of rice yield change over the middle and lower reaches of the Yangtze River under the background of global warming from the relationship of rice yield components (percentage of undeveloped grain, percentage of partially developed grain, and weight of 1 000-grain) with the meteorological factors, consequently providing a scientific basis for coping measures with the hot temperature events.
43 1
DATA AND METHODS In this article, 48 early rice stations and 30 middle rice stations from Hubei, Hunan, Anhui, Jiangxi, Jiangsu, and Zhejiang provinces between 198 1-2003, were selected. The data contain growth season (the first, general, and end of flowering stage), rice yield components (percentage of undeveloped grain; percentage of partially developed grain; and weight of 1 000-grain), as well as daily maximum temperature and precipitation in each selected rice station. The selected rice stations are shown in Fig.1, totally there are 1362 samples of indica rice, 872 for early rice with 332 species, and 490 for middle rice with 126 species. The mean daily maximum temperature and mean daily precipitation at the flowering stage (2 days before the first flowering to 5 days after the end of flowering), the pre-milk stage (6 days after the first flowering to 10 days after the end of flowering), and late milk stage (1 1 days after the first flowering to 15 days after the end of flowering) were firstly calculated, and then the correlation of rice yield components with mean daily maximum temperature and mean daily precipitation at the three stages were analyzed.
RESULTS Impacts of meteorologicalfactors on percentage of undeveloped grain of early and middle rice Fig.2 shows the relationship of percentage of undeveloped grain of early rice and mean maximum temperature at stages of the flowering, pre-milk, and late milk,
Fig. 1 Distribution of rice stations.
02007,CAAS. All rightsm6erVBd.Publishedby Elsevier Ltd.
ZHAO Hai-yan et al.
432
and the positive relationship of undeveloped grain of early rice and mean daily precipitation at the three stages with the significance level of 0.01. As the flowering and late milk stages of early rice last from the middle of June to the middle of July, it is during the Meiyu season with a lot of rain and the daily maximum temperature is normally lower than 35°C over the middle and low reaches of the Yangtze River. Rice tassels more slowly in lower temperature conditions and some stems would be darkened. On the other hand, the flowers would disperse because of low temperature; the flowering stage would be lengthened with scarce pollen, which would result in decrease of insemination percentage of rice and increase of percentage of undeveloped grain. Therefore, percentage of undeveloped grain of early rice would rise with more precipitation and reduce with higher mean maximum temperature at the three stages. The positive relationship of percentage of undevel-
oped grain of middle rice and mean maximum temperature as well as mean precipitation at stages of flowering, pre-milk, and late milk is shown in Fig.3; the correlation of percentage of undeveloped grain with mean daily precipitation at the stages of flowering and pre-milk could get the significance level (P<0.05). The flowering and grain filling stages of middle rice usually last from late July to late August in Anhui and Jiangsu provinces, and from middle August to middle September in Hubei and Hunan provinces. During these periods, mean precipitation is 3.78-4.48 mm d-I,which is 2.46-4.18 mm d-' less than the corresponding stages of early rice. Meanwhile, hot days (daily maximum temperature 2 35°C) take place frequently. Anther's splitting would be damaged and pollen's life span would be shortened when daily maximum temperature is over 35°C. As a result, fertilizing rates of rice are decreased. The percentage of undeveloped grain is proportional to
k
O
-
.E!
5
3" % g 3
a C
=
0 I 20
25
10
4 5
50
R* = 0.047 1
40 30 20 10
0
40
Mean maximum temperature ( " C )
Mean daily precipitation (mm d ')
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20
30
40
35
0
45
20
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Mean daily prccipitation (mm d
Mean maximimi tempcrature ('C)
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Mean maxlmum temperanire ( 'c )
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Mean daily precipitation (mm d '1
Fig. 2 The relationship between percentage of undeveloped grain of early rice and weather data at all stages. A, mean maximum temperature at flowering stage; B, mean maximum temperature at pre-milk stage; C, mean maximum temperature at late milk stage; D, mean daily precipitation at flowering stage; E, mean daily precipitation at pre-milk stage; F, mean daily precipitation at late milk stage.
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Correlation Analysis of Rice Seed Setting Rate and Weight of 1000-Grain and Agro-Meteorology over the Middle and Lower
precipitation and the mean maximum temperature, but the correlation is not significant ( P < 0.05). That is probably because of the response difference of various rice species to meteorological factors. Percentage of undeveloped grain is affected by daily precipitation and maximum temperature, especially at the flowering stage. The relationship between precipitation and percentage of undeveloped grain of early and middle rice is positive, whereas percentage of undeveloped grain decreases for early rice or increases for middle rice as mean maximum temperature rises.
Impacts of meteorological factors on percentage of partially developed grain of early and middle rice The percentage of partially developed grain of early rice is mainly affected by mean precipitation and mean maximum temperature in the late milk stage. It correlates positively with mean precipitation, but negatively with mean maximum temperature with the significance level P<0.05 (Fig.4). The middle rice is similar to the early rice, but the correlation is not significant ( P < 0.05) (Fig.5).
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Percentage of partially developed grain is an index of grain filling, which is a process of photosynthate transportation and dry-matter accumulation. On one hand, photosynthate would be reduced by lower temperature and rainy days; on the other hand, transportation system could be blocked by low temperature. Percentage of partially developed grain would increase because of insufficient grain filling.
Impacts of meteorological factors on weight of 1000-grain of early and middle rice The fruiting stage, especially the grain-filling stage, is crucial to weight of 1 000-grain of rice. Mean temperature between 22-28°C is optimal at this stage. Warmer conditions would accelerate grain filling and shorten grain-filling period, which can result in a decrease of fruiting rate. In contrast, lower temperature could prolong grain-filling period and is beneficial to weight of 1000-grain of rice. It is shown from Fig.6 that weight of 1 000-grain of early rice is positively correlated to mean maximum temperature with a significance level of PcO.05, and negatively to mean daily precipitation at stages of pre-milk and late milk, which
Fig. 3 The relationship between percentage of undeveloped grain of middle rice and weather data at flowering stage. A, mean maximum temperature; B, mean daily precipitation.
Fig. 4 The relationshipbetween percentage of partially developed grain of early rice and weather data at late milk stage. A, mean maximum temperature; B, mean daily precipitation.
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Fig. 5 The relationship between percentage of partially developed grain of middle rice and weather data at late milk stage. A, mean maximum temperature; B, mean daily precipitation.
Fig. 6 The relationshipbetween thousand grains weight of early rice and mean maximum temperature at all stage. A, pre-milk stage; B, late milk stage.
indicates that the most important factor affecting weight of 1000-grain of early rice is mean maximum temperature at the whole milk stage, and precipitation is the second. Weight of 1 000-grain of middle rice is negatively correlated with mean daily precipitation and positively with mean maximum temperature at late milk stage, but it is not significant (P<0.05).Sunshine is not considered in the research of this paper, whereas, insufficient sunshine would weaken the photosynthesis and lower the filling of rice grains (Zheng 2003).
DISCUSSION Over the middle and lower reaches of the Yangtze River, rice is grown mainly in Meiyu season, when the climate is characterized by plenty of precipitation of large variability, and seed setting rate of early rice is hampered and weight of 1000-grain is decreased by overcast weather. After Meiyu period, the middle and lower reaches of the Yangtze River are dominated by the Subtropical High, and downward flow prevails with more hot days. Continuous hot weather would damage middle rice production.
Percentage of undeveloped grain of rice is closely related to daily precipitation and maximum temperature. For early rice, it would drop when mean maximum temperature decreases and mean daily precipitation increases at the flowering, pre-mill and late milk stages; whereas for middle rice, meteorological factors at the flowering stage are vital. It is positively correlated with the mean maximum temperature at the flowering stage. It has been proven that overcast skies and rain can impact flowering and fertilization of early rice, and consecutive hot days are the major reason for higher percentage of undeveloped grain for middle rice (Liu et al. 2005; Zhang et al. 1995; Li 2003). However, because of the lower occurrence of hot temperatures during the milk stage for race sampling in this study, the weight of 1 000-grain over the middle and lower reaches of the Yangtze River is slightly affected by global warming. Percentage of partially developed grain of early rice is mainly affected by mean daily precipitation and mean maximum temperature at the late milk stage. It is positively correlated with precipitation, but negatively with temperature. The relationship for middle rice is similar to early rice, but not significant (P<0.05). Weight of 1000-grain of early rice increases as mean temperature goes up and deceases as mean precipita-
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Correlation Analysis of Rice Seed Setting Rate and Weight of 1 000-Grain and Agro-Meteorology over the Middle and Lower
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tion goes down at pre-milk and late milk stages. Similarly, the relationship of middle rice at late milk stage is identical to early rice, but not significant ( P c 0.05). Some research results show that consecutive hot temperature has negative effects on the weight of 1000-grain (The Phytotron, Shanghai Institute of Plant Physiology 1976a, b, 1977). There is no significant correlation between the percentage of undeveloped, partially developed grain, and weight of 1 000-grain of middle rice and temperature. Many other factors could affect yield component of rice, including inherent genotypes, physiological factors, ecology, and planting skill factors. Though all the selected genotypes in this study were indica rice, they possess some similar genetic characteristics. The relation between percentage of undeveloped, partially developed grain, weight of 1 000-grain, and meteorological factors were significant on P c 0.05 level, which means the responses of indica rice to temperature was identical. But middle rice differed from early rice. The responses of fruiting rate and weight of 1000-grain of middle rice to temperatureand precipitation are different. It means that more factors, including meteorological factors (e.g., sunshine) and non-meteorological factors (e.g.,soil moisture content) should be considered in the impacts on percentage of partially developed grain and weight of 1 000-grain of middle rice. Multiplefactor correlation analysis should be done in future study.
developed grain because of overcast and raining. The Erequency of percentage of undeveloped grain of early rice 3 30% is 3.9% in this study. The frequency of mean daily precipitation 3 10 mm is 8.6, 9.0% at the flowering and late milk stages respectively. However, the frequency of mean maximum temperature 3 35°C is 4.0, 2.0% at the flowering and late milk stages respectively. Hence, precipitation and temperature at the flowering and late milk stages are both contributing to the percentage of undeveloped grain of middle rice. Higher temperature over the middle and low reaches of the Yangtze River in the future will mainly affect middle rice. The frequency of mean maximum temperature 3 35°C is 4.0% at the flowering stage of middle rice, which is more than twice early rice at the same stage. Hence, global warming would have more negative impacts on middle rice over the middle and lower reaches of the Yangtze River than early rice. As global warming would increase the frequency of high temperature, it is very important to investigate adaptive measures to high temperature over the middle and lower reaches of the Yangtze River.
CONCLUSION
References
According to the analysis above, it can be concluded that growth season of early rice is hampered by cloudy and rainy weather; rising temperature is favorable to early rice growth. The frequency of percentage of undeveloped grain of early rice 2 30% is 7.0% in this study. The frequency of mean daily precipitation 3 10 mm is 31.5, 29.0, and 20.7% at the flowering, premilk, and late milk stages respectively. However, the frequency of mean maximum temperature 3 35°C is only 2.0,7.3, and 15.2%. So, precipitation is attributing to percentage of undeveloped grain of early rice at the reproductive stage more than temperature. Middle rice production is negatively affected by increase of percentage of undeveloped grain and partial
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