Double-and triple-cropping in a year have played a very important role in meeting the rising need for food in China.However,the intensified agricultural practices have significantly altered biogeochemical cycles and s...Double-and triple-cropping in a year have played a very important role in meeting the rising need for food in China.However,the intensified agricultural practices have significantly altered biogeochemical cycles and soil quality.Understanding and mapping cropping intensity in China′s agricultural systems are therefore necessary to better estimate carbon,nitrogen and water fluxes within agro-ecosystems on the national scale.In this study,we investigated the spatial pattern of crop calendar and multiple cropping rotations in China using phenological records from 394 agro-meteorological stations(AMSs)across China.The results from the analysis of in situ field observations were used to develop a new algorithm that identifies the spatial distribution of multiple cropping in China from moderate resolution imaging spectroradiometer(MODIS)time series data with a 500 m spatial resolution and an 8-day temporal resolution.According to the MODIS-derived multiple cropping distribution in 2002,the proportion of cropland cultivated with multiple crops reached 34%in China.Double-cropping accounted for approximately 94.6%and triple-cropping for 5.4%.The results demonstrat that MODIS EVI(Enhanced Vegetation Index)time series data have the capability and potential to delineate the dynamics of double-and triple-cropping practices.The resultant multiple cropping map could be used to evaluate the impacts of agricultural intensification on biogeochemical cycles.展开更多
In the summer of 2012, the US Midwest, the most productive agricultural region in the world, experienced the most intense and widespread drought on record for the past hundred years. The 2012 drought, characterized as...In the summer of 2012, the US Midwest, the most productive agricultural region in the world, experienced the most intense and widespread drought on record for the past hundred years. The 2012 drought, characterized as ‘flash drought’, developed in May with a rapid intensification afterwards, and peaked in mid-July. ~76% of crop region and 60% of grassland and pasture regions have been under moderate to severe dry conditions. This study used multiple lines of evidences, i.e., in-situ AmeriFlux measurements, spatial satellite observations, and scaled ecosystem modeling, to provide independent and complementary analysis on the impact of 2012 flash drought on the US Midwest vegetation greenness and photosynthesis carbon uptake. Three datasets consistently showed that 1) phenological activities of all biomes advanced 1–2 weeks earlier in 2012 compared to the other years of 2010–2014;2) the drought had a more severe impact on agroecosystems(crop and grassland) than on forests;3) the growth of crop and grassland was suppressed from June with significant reduction of vegetation index, sun-induced fluorescence(SIF) and gross primary production(GPP), and did not recover until the end of growing season. The modeling results showed that regional total GPP in 2012 was the lowest(1.76 Pg C/yr) during 2010–2014, and decreased by 63 Tg C compared with the other-year mean. Agroecosystems, accounting for 84% of regional GPP assimilation, were the most impacted by 2012 drought with total GPP reduction of 9%, 7%, 6%, and 29% for maize, soybean, cropland, and grassland, respectively. The frequency and severity of droughts have been predicted to increase in future. The results imply the importance to investigate the influences of flash droughts on vegetation productivity and terrestrial carbon cycling.展开更多
Many cities face heat wave(HW) events, combined with the existent surface urban heat island(SUHI) effects. This places pressure on human settlements and sustainable development. However, few studies have investigated ...Many cities face heat wave(HW) events, combined with the existent surface urban heat island(SUHI) effects. This places pressure on human settlements and sustainable development. However, few studies have investigated the SUHI effects from the perspective of HWs. In this study, the summer HWs in Beijing from 2001 to 2021 were calculated, and the evolution of HWs and SUHIs was quantitatively analyzed based on the dynamic nature of the urban-rural boundary. Beijing experienced 27 HWs in the 21 years, including 10 instances in June, four in July, and 13 in August. The SUHI varied during HWs, between 2–3℃ in most years. The highest SUHI occurred in 2019, reaching 3.99℃ and covering the largest area(10,887 km^(2)). The fluctuation in HWs and SUHIs generally displayed the same spatiotemporal pattern, and HWs amplified the SUHIs to a certain extent, with the highest correlation coefficient being 0.44. Additionally, impervious surfaces and cropland contributed most to SUHIs,and night light enhanced SUHIs. Observing the co-evolution of HWs and SUHIs will be helpful for ecological maintenance and urban infrastructure optimization and provide theoretical support for reducing heat risk and improving the human settlement environment.展开更多
目的探讨高分辨率食管测压(HRM)联合24 h pH阻抗技术技术在胃食管反流病合并食管裂孔疝的诊断及腹腔镜胃底折叠术式选择。方法回顾性分析2015年4月至2019年10月,潍坊市人民医院胃肠外科行胃镜及HRM检查联合24 h pH阻抗技术,确诊为胃食...目的探讨高分辨率食管测压(HRM)联合24 h pH阻抗技术技术在胃食管反流病合并食管裂孔疝的诊断及腹腔镜胃底折叠术式选择。方法回顾性分析2015年4月至2019年10月,潍坊市人民医院胃肠外科行胃镜及HRM检查联合24 h pH阻抗技术,确诊为胃食管反流病合并食管裂孔疝并收住普外科的167例患者的临床资料,统计胃镜及HRM检查联合24 h pH阻抗技术诊断胃食管反流病合并食管裂孔疝的确诊率。结果HRM检查联合24 h pH阻抗技术的检出率为83.32%(139/167),特异性为100%(139/139);胃镜确诊为67.06%(112/167):其中由胃镜和HRM均确诊112例患者,约占80.57%(112/139),HRM技术的检出率明显高于胃镜;其中105例行腹腔镜治疗食管裂孔疝修补术联合胃底折叠术,7例患者及家属因各种原因放弃手术选择内科保守治疗。结论HRM检查联合24 h pH阻抗技术较胃镜对胃食管反流病合并食管裂孔疝的诊断具有更高的特异性,并能够有效地指导胃底折叠手术方案。展开更多
Rice cropping systems not only characterize comprehensive utilization intensity of agricultural resources but also serve as the basis to enhance the provision services of agro-ecosystems. Yet, it is always affected by...Rice cropping systems not only characterize comprehensive utilization intensity of agricultural resources but also serve as the basis to enhance the provision services of agro-ecosystems. Yet, it is always affected by external factors, like agricultural policies. Since 2004, seven consecutive No.1 Central Documents issued by the Central Government have focused on agricultural development in China. So far, few studies have investigated the effects of these policies on the rice cropping systems. In this study, based upon the long-term field survey information on paddy rice fields, we proposed a method to discriminate the rice cropping systems with Landsat data and quantified the spatial variations of rice cropping systems in the Poyang Lake Region （PLR）, China. The results revealed that： （1） from 2004 to 2010, the decrement of paddy rice field was 46.76 km2 due to the land use change. （2） The temporal dynamics of NDVI derived from Landsat historical images could well characterize the temporal development of paddy rice fields. NDVI curves of single cropping rice fields showed one peak, while NDVI curves of double cropping rice fields displayed two peaks annually. NDVI of fallow field fluctuated between 0.15 and 0.40. NDVI of the flooded field during the transplanting period was relatively low, about 0.20±0.05, while NDVI during the period of panicle initiation to heading reached the highest level （above 0.80）. Then, several temporal windows were determined based upon the NDVI variations of different rice cropping systems. （3） With the spatial pattern of paddy rice field and the NDVI threshold within optimum temporal windows, the spatial variation of rice cropping systems was very obvious, with an increased multiple cropping index of rice about 20.2% from 2004 to 2010. The result indicates that agricultural policies have greatly enhanced the food provision services in the PLR, China.展开更多
Carbon fluxes in temperate grassland ecosystems are characterized by large inter-annual variations due to fluctuations in precipitation and land water availability. Since an eddy flux tower has been in operation in th...Carbon fluxes in temperate grassland ecosystems are characterized by large inter-annual variations due to fluctuations in precipitation and land water availability. Since an eddy flux tower has been in operation in the Xilin Gol grassland, which belongs to typical temperate grassland in North China, in this study, observed eddy covariance flux data were used to critically evaluate the biophysical performance of different remote sensing vegetation indices in relation to carbon fluxes. Furthermore, vegetation photosynthesis model (VPM) was introduced to estimate gross primary production (GPP) of the grassland ecosystem for assessing its dependability. As defined by the input variables of VPM, Moderate Resolution Imaging Spectroradimeter (MODIS) and standard data product MOD09A1 were downloaded for calculating enhanced vegetation index (EVI) and land surface water index (LSWI). Measured air temperature (Ta) and photosynthetically active radiation (PAR) data were also included for model simulating. Field CO2 flux data, during the period from May, 2003 to September, 2005, were used to estimate the “observed” GPP (GPP obs) for validation. The seasonal dynamics of GPP predicted from VPM (GPP VPM) was compared quite well (R 2=0.903, N=111, p<0.0001) with the observed GPP. The aggregate GPP VPM for the study period was 641.5 g C·m?2, representing a ～6% over-estimation, compared with GPP obs. Additionally, GPP predicted from other two typical production efficiency model (PEM) represents either higher overestimation or lower underestimation to GPP obs. Results of this study demonstrate that VPM has potential for estimating site-level or regional grassland GPP, and might be an effective tool for scaling-up carbon fluxes.展开更多
The changes in cropland quantity and quality due to land use are critical concerns to national food security, particularly for China. Despite the significant ecological effects, the ecological restoration program （ER...The changes in cropland quantity and quality due to land use are critical concerns to national food security, particularly for China. Despite the significant ecological effects, the ecological restoration program （ERP）, started from 1999, has evidently altered the spatial patterns of China＇s cropland and agricultural productivity. Based on cropland dynamic data from 2000 to 2008 primarily derived from satellite images with a 30-m resolution and satel- lite-based net primary productivity models, we identified the impacts on agricultural produc- tivity caused by ERP, including ＂Grain for Green＂ Program （GFGP） and ＂Reclaimed Cropland to Lake＂ （RCTL） Program. Our results indicated that the agricultural productivity lost with a rate of 132.67×104 t/a due to ERP, which accounted for 44.01% of the total loss rate caused by land use changes during 2000-2005. During 2005-2008, the loss rate due to ERP de- creased to 77.18×104 t/a, which was equivalent to 58.17% of that in the first five years and 30.22% of the total loss rate caused by land use changes. The agricultural productivity loss from 2000-2008 caused by ERP was more attributed to GFGP （about 70%） than RCTL. Al- though ERP had a certain influence on cropland productivity during 2000-2008, its effect was still much less than that of urbanization; moreover, ERP was already converted from the project implementation phase to the consolidation phase.展开更多
Bangladesh is one of the most vulnerable countries to natural disasters such as droughts in the world.The pre-monsoon Aus rice in Bangladesh depends on rainfall and is threatened by increasing droughts.However,limited...Bangladesh is one of the most vulnerable countries to natural disasters such as droughts in the world.The pre-monsoon Aus rice in Bangladesh depends on rainfall and is threatened by increasing droughts.However,limited information on the changes in Aus rice as well as droughts hamper our understanding of the country’s agricultural resilience and adaption to droughts.Here,we collected all the official statistical data of Aus rice at the district level from 1980 to 2018,and examined the interannual variations of area,yield,and production.The results showed both area and production of Aus rice decreased significantly(61.58×103 ha yr-1 and 17.21×103 M.tons yr-1,respectively),while yield increased significantly(0.03 M.tons ha-1 yr-1).We also found a significantly increasing trend of droughts in 88%of area based on the Palmer Drought Severity Index(PDSI)data,especially in those rainfed agricultural areas.Moreover,we found significant positive correlations between PDSI and Aus rice area(production)in 33(25)out of 64 districts.There is hardly a relationship between PDSI and yield,likely due to the improved management and increasing irrigated areas.Implementing continuous drought monitoring,combined irrigation(surface and groundwater)systems,and conservation and precision agriculture are highly recommended in these drought-prone districts to ensure food security in Bangladesh.展开更多
基金Under the auspices of Strategic Priority Research Program-Climate Change:Carbon Budget and Relevant Issues of Chinese Academy of Sciences(No.XDA05050602)Major State Basic Research Development Program of China(No.2010CB950904)+1 种基金National Natural Science Foundation of China(No.40921140410,41071344)Land Cover and Land Use Change Program of National Aeronautics and Space Administration,USA(No.NAG5-11160,NNG05GH80G)
文摘Double-and triple-cropping in a year have played a very important role in meeting the rising need for food in China.However,the intensified agricultural practices have significantly altered biogeochemical cycles and soil quality.Understanding and mapping cropping intensity in China′s agricultural systems are therefore necessary to better estimate carbon,nitrogen and water fluxes within agro-ecosystems on the national scale.In this study,we investigated the spatial pattern of crop calendar and multiple cropping rotations in China using phenological records from 394 agro-meteorological stations(AMSs)across China.The results from the analysis of in situ field observations were used to develop a new algorithm that identifies the spatial distribution of multiple cropping in China from moderate resolution imaging spectroradiometer(MODIS)time series data with a 500 m spatial resolution and an 8-day temporal resolution.According to the MODIS-derived multiple cropping distribution in 2002,the proportion of cropland cultivated with multiple crops reached 34%in China.Double-cropping accounted for approximately 94.6%and triple-cropping for 5.4%.The results demonstrat that MODIS EVI(Enhanced Vegetation Index)time series data have the capability and potential to delineate the dynamics of double-and triple-cropping practices.The resultant multiple cropping map could be used to evaluate the impacts of agricultural intensification on biogeochemical cycles.
基金Under the auspices of the National Natural Science Foundation of China(No.41801340)Natural Science Foundation of Liaoning,China(No.20180550238)the Key Research Program of Frontier Sciences by Chinese Academy of Sciences(No.QYZDB-SSW-DQC005)
文摘In the summer of 2012, the US Midwest, the most productive agricultural region in the world, experienced the most intense and widespread drought on record for the past hundred years. The 2012 drought, characterized as ‘flash drought’, developed in May with a rapid intensification afterwards, and peaked in mid-July. ~76% of crop region and 60% of grassland and pasture regions have been under moderate to severe dry conditions. This study used multiple lines of evidences, i.e., in-situ AmeriFlux measurements, spatial satellite observations, and scaled ecosystem modeling, to provide independent and complementary analysis on the impact of 2012 flash drought on the US Midwest vegetation greenness and photosynthesis carbon uptake. Three datasets consistently showed that 1) phenological activities of all biomes advanced 1–2 weeks earlier in 2012 compared to the other years of 2010–2014;2) the drought had a more severe impact on agroecosystems(crop and grassland) than on forests;3) the growth of crop and grassland was suppressed from June with significant reduction of vegetation index, sun-induced fluorescence(SIF) and gross primary production(GPP), and did not recover until the end of growing season. The modeling results showed that regional total GPP in 2012 was the lowest(1.76 Pg C/yr) during 2010–2014, and decreased by 63 Tg C compared with the other-year mean. Agroecosystems, accounting for 84% of regional GPP assimilation, were the most impacted by 2012 drought with total GPP reduction of 9%, 7%, 6%, and 29% for maize, soybean, cropland, and grassland, respectively. The frequency and severity of droughts have been predicted to increase in future. The results imply the importance to investigate the influences of flash droughts on vegetation productivity and terrestrial carbon cycling.
基金National Natural Science Foundation of China,No.41771178, No.42030409Fundamental Research Funds for the Central Universities,No.N2111003Basic Scientific Research Project (Key Project) of the Education Department of Liaoning Province,No.LJKZ0964。
文摘Many cities face heat wave(HW) events, combined with the existent surface urban heat island(SUHI) effects. This places pressure on human settlements and sustainable development. However, few studies have investigated the SUHI effects from the perspective of HWs. In this study, the summer HWs in Beijing from 2001 to 2021 were calculated, and the evolution of HWs and SUHIs was quantitatively analyzed based on the dynamic nature of the urban-rural boundary. Beijing experienced 27 HWs in the 21 years, including 10 instances in June, four in July, and 13 in August. The SUHI varied during HWs, between 2–3℃ in most years. The highest SUHI occurred in 2019, reaching 3.99℃ and covering the largest area(10,887 km^(2)). The fluctuation in HWs and SUHIs generally displayed the same spatiotemporal pattern, and HWs amplified the SUHIs to a certain extent, with the highest correlation coefficient being 0.44. Additionally, impervious surfaces and cropland contributed most to SUHIs,and night light enhanced SUHIs. Observing the co-evolution of HWs and SUHIs will be helpful for ecological maintenance and urban infrastructure optimization and provide theoretical support for reducing heat risk and improving the human settlement environment.
文摘目的探讨高分辨率食管测压(HRM)联合24 h pH阻抗技术技术在胃食管反流病合并食管裂孔疝的诊断及腹腔镜胃底折叠术式选择。方法回顾性分析2015年4月至2019年10月,潍坊市人民医院胃肠外科行胃镜及HRM检查联合24 h pH阻抗技术,确诊为胃食管反流病合并食管裂孔疝并收住普外科的167例患者的临床资料,统计胃镜及HRM检查联合24 h pH阻抗技术诊断胃食管反流病合并食管裂孔疝的确诊率。结果HRM检查联合24 h pH阻抗技术的检出率为83.32%(139/167),特异性为100%(139/139);胃镜确诊为67.06%(112/167):其中由胃镜和HRM均确诊112例患者,约占80.57%(112/139),HRM技术的检出率明显高于胃镜;其中105例行腹腔镜治疗食管裂孔疝修补术联合胃底折叠术,7例患者及家属因各种原因放弃手术选择内科保守治疗。结论HRM检查联合24 h pH阻抗技术较胃镜对胃食管反流病合并食管裂孔疝的诊断具有更高的特异性,并能够有效地指导胃底折叠手术方案。
基金National Basic Research Program of China(973 Program),No.2009CB421106National Natural Science Foundation of China,No.40901285
文摘Rice cropping systems not only characterize comprehensive utilization intensity of agricultural resources but also serve as the basis to enhance the provision services of agro-ecosystems. Yet, it is always affected by external factors, like agricultural policies. Since 2004, seven consecutive No.1 Central Documents issued by the Central Government have focused on agricultural development in China. So far, few studies have investigated the effects of these policies on the rice cropping systems. In this study, based upon the long-term field survey information on paddy rice fields, we proposed a method to discriminate the rice cropping systems with Landsat data and quantified the spatial variations of rice cropping systems in the Poyang Lake Region （PLR）, China. The results revealed that： （1） from 2004 to 2010, the decrement of paddy rice field was 46.76 km2 due to the land use change. （2） The temporal dynamics of NDVI derived from Landsat historical images could well characterize the temporal development of paddy rice fields. NDVI curves of single cropping rice fields showed one peak, while NDVI curves of double cropping rice fields displayed two peaks annually. NDVI of fallow field fluctuated between 0.15 and 0.40. NDVI of the flooded field during the transplanting period was relatively low, about 0.20±0.05, while NDVI during the period of panicle initiation to heading reached the highest level （above 0.80）. Then, several temporal windows were determined based upon the NDVI variations of different rice cropping systems. （3） With the spatial pattern of paddy rice field and the NDVI threshold within optimum temporal windows, the spatial variation of rice cropping systems was very obvious, with an increased multiple cropping index of rice about 20.2% from 2004 to 2010. The result indicates that agricultural policies have greatly enhanced the food provision services in the PLR, China.
基金the International Partnership Project of Chinese Academy of Sciences (Grant No. CXTD-Z2005-1)National Basic Research Program of China (Grant No. 2002CB412501)NASA Land Cover and Land Use Change (LCLUC) Program (Grant Nos. NAG5-11160, NNG05GH80G)
文摘Carbon fluxes in temperate grassland ecosystems are characterized by large inter-annual variations due to fluctuations in precipitation and land water availability. Since an eddy flux tower has been in operation in the Xilin Gol grassland, which belongs to typical temperate grassland in North China, in this study, observed eddy covariance flux data were used to critically evaluate the biophysical performance of different remote sensing vegetation indices in relation to carbon fluxes. Furthermore, vegetation photosynthesis model (VPM) was introduced to estimate gross primary production (GPP) of the grassland ecosystem for assessing its dependability. As defined by the input variables of VPM, Moderate Resolution Imaging Spectroradimeter (MODIS) and standard data product MOD09A1 were downloaded for calculating enhanced vegetation index (EVI) and land surface water index (LSWI). Measured air temperature (Ta) and photosynthetically active radiation (PAR) data were also included for model simulating. Field CO2 flux data, during the period from May, 2003 to September, 2005, were used to estimate the “observed” GPP (GPP obs) for validation. The seasonal dynamics of GPP predicted from VPM (GPP VPM) was compared quite well (R 2=0.903, N=111, p<0.0001) with the observed GPP. The aggregate GPP VPM for the study period was 641.5 g C·m?2, representing a ～6% over-estimation, compared with GPP obs. Additionally, GPP predicted from other two typical production efficiency model (PEM) represents either higher overestimation or lower underestimation to GPP obs. Results of this study demonstrate that VPM has potential for estimating site-level or regional grassland GPP, and might be an effective tool for scaling-up carbon fluxes.
基金National Key Program for Developing Basic Science, No.2010CB950904National Natural Science Foundation of China, No.41071344+1 种基金Knowledge Innovation Program of CAS, No.KZCX2-EW-306Strategic Priority Research Program of CAS, No.XDA05050602
文摘The changes in cropland quantity and quality due to land use are critical concerns to national food security, particularly for China. Despite the significant ecological effects, the ecological restoration program （ERP）, started from 1999, has evidently altered the spatial patterns of China＇s cropland and agricultural productivity. Based on cropland dynamic data from 2000 to 2008 primarily derived from satellite images with a 30-m resolution and satel- lite-based net primary productivity models, we identified the impacts on agricultural produc- tivity caused by ERP, including ＂Grain for Green＂ Program （GFGP） and ＂Reclaimed Cropland to Lake＂ （RCTL） Program. Our results indicated that the agricultural productivity lost with a rate of 132.67×104 t/a due to ERP, which accounted for 44.01% of the total loss rate caused by land use changes during 2000-2005. During 2005-2008, the loss rate due to ERP de- creased to 77.18×104 t/a, which was equivalent to 58.17% of that in the first five years and 30.22% of the total loss rate caused by land use changes. The agricultural productivity loss from 2000-2008 caused by ERP was more attributed to GFGP （about 70%） than RCTL. Al- though ERP had a certain influence on cropland productivity during 2000-2008, its effect was still much less than that of urbanization; moreover, ERP was already converted from the project implementation phase to the consolidation phase.
基金National Natural Science Foundation of China(41871349)The Strategic Priority Research Program of the Chinese Academy of Sciences(XDA19040301)。
文摘Bangladesh is one of the most vulnerable countries to natural disasters such as droughts in the world.The pre-monsoon Aus rice in Bangladesh depends on rainfall and is threatened by increasing droughts.However,limited information on the changes in Aus rice as well as droughts hamper our understanding of the country’s agricultural resilience and adaption to droughts.Here,we collected all the official statistical data of Aus rice at the district level from 1980 to 2018,and examined the interannual variations of area,yield,and production.The results showed both area and production of Aus rice decreased significantly(61.58×103 ha yr-1 and 17.21×103 M.tons yr-1,respectively),while yield increased significantly(0.03 M.tons ha-1 yr-1).We also found a significantly increasing trend of droughts in 88%of area based on the Palmer Drought Severity Index(PDSI)data,especially in those rainfed agricultural areas.Moreover,we found significant positive correlations between PDSI and Aus rice area(production)in 33(25)out of 64 districts.There is hardly a relationship between PDSI and yield,likely due to the improved management and increasing irrigated areas.Implementing continuous drought monitoring,combined irrigation(surface and groundwater)systems,and conservation and precision agriculture are highly recommended in these drought-prone districts to ensure food security in Bangladesh.
