| As the basic material for human survival and development,food security has always been an issue of social stability and economic development for all countries in the world.While cultivated land ensures national food security through grain production,it is also an important carbon source.Under the circumstances of global carbon emissions growth,China is the one of main carbon emitters all over the world.As the second largest source of carbon emissions in China,agriculture production is under tremendous pressure to reduce carbon emissions.Especially,there is a unity of opposites between grain production and carbon emission,thus balancing the relationship between them is essential to achieve a win-win situation.Therefore,this paper constructed a theoretical framework of carbon emission from cultivated land use and grain production and clarified the logical relationship and mechanism between them.The study area included 356 prefecture-level cities(regions,autonomous prefectures,leagues,and provinces directly administrating counties)in 31 provinces(autonomous regions and municipalities directly under the central government)in China.Based on the long time series data during 2000-2020,this paper measured the carbon emission from cultivated land use at national,grain function zones,provincial and city scales,analyzed the spatiotemporal evolution characteristics and change patterns of cultivated land use,carbon emission,and grain production,and explored the spatiotemporal coupling characteristics between carbon emission from cultivated land use and grain production and its influencing factors,calculated carbon compensation for cultivated land use in the face of the dual objectives of national food security and reducing carbon emissions and increasing carbon sinks in cultivated land,then conducted"grain-carbon"correlation zoning and proposed regional optimization development strategies.This paper provided a scientific reference for the low-carbon,green and efficient use of China’s cultivated land for realizing and guaranteeing national food security,and could contribute to the achievement of a balance between carbon emission from cultivated land use and grain production.The main conclusions of this paper were as follows:(1)Based on the long time series data during 2000-2020,the spatiotemporal evolution characteristics of cultivated land use and grain production were comprehensively analyzed at multiple scales.1)In terms of the spatiotemporal evolution characteristics of the cultivated land quantity in China during 2000-2020,it showed an overall trend of reduction,decreasing by 243.37×10~4 hm~2 in the past 20 years,and the decline rate was 1.36%.This decline was mainly due to the occupancy of cultivated land by three types of construction land:urban construction land,rural settlements,and other construction lands;and the center of gravity of cultivated land quantity is slightly moved to the northwest of China as a whole.During 2000-2020,the cultivated quantity in the main grain-producing zone and the main grain-marketing zone decreased by 334.24×10~4 hm~2 and 138.21×10~4 hm~2,respectively,while that in the grain production and marketing balance zone increased by 230.62×10~4 hm~2.Most of the provinces and cities showed decreasing trends in cultivated land quantity from 2000 to2020,and there were significant differences in the change of cultivated land area and its dynamic degree in each study period.2)In terms of the spatiotemporal evolution of cultivated land quality in China,it showed a general fluctuating upward trend during2000-2020,with an increase of 1.48%in the past 20 years,mainly due to the large-scale implementation of land consolidation projects by the Chinese government since 1998.During 2000-2020,the quality of cultivated land in the main grain-producing zone and the grain production and marketing balance zone showed an overall upward trend,and the latter showed a higher increasing range than the former,while the main grain-marketing zone showed a decreasing trend.And the quality of cultivated land in most provinces and cities showed increasing trends during 2000-2020.3)In terms of the spatiotemporal evolution characteristics of grain production in China,from 2000 to2020,it showed fluctuating"continuous harvests"on the whole,with an increase of20,306.94×10~4 t in the past 20 years,and the rate was 43.54%.The overall change in the center of grain production gradually moved to the northeast of China.Grain production in the main grain-producing zone showed an upward trend in line with the national trend,and the proportion of grain yield in this zone to national grain production increased significantly.Grain production in the grain production and marketing balance zone was the second largest and showed a slight upward trend,while its proportion to the national scale decreased slightly.Grain production in the main grain-marketing zone was the smallest and showed a slight downward trend,and its proportion to the national scale decreased significantly.In each study period during 2000-2020,most of the provinces and cities showed an increasing trend in grain production,especially in northeastern China,where the rising trend was relatively obvious.(2)The index system of carbon emission calculation was constructed from four dimensions,namely,cultivated land production factors,rice cultivation,returning grain crop straw to cultivated land soil,and burning grain crop straw.The carbon emission of the whole life cycle of major grain crops in the agricultural production process in cultivated land was calculated comprehensively with the fully considering of the regional differences in the correlation coefficients of each dimensional index.During2000-2020,the carbon emission from cultivated land use in China showed a continuously increasing trend,raising by 9,643.79×10~4 t,with a rate of 28.60%.The mean values of carbon emission from rice cultivation and burning grain crop straw accounted for 41.22%and 44.46%,respectively,while the mean values of carbon emission from cultivated land production factors and returning grain crop straw to cultivated land soil only accounted for 11.92%and 2.40%,respectively.The overall change in the gravity center of carbon emission from cultivated land use was similar to that of grain yield,with a gradual movement toward the northeast of China.The proportions of mean values of carbon emissions from cultivated land use in the main grain-producing zone,main grain-marketing zone,and the grain production and marketing balance zone were 73.97%,10.08%,and 15.95%,respectively.In the past 20years,the carbon emissions from cultivated land use in the main grain-producing zone and the grain production and marketing balance zone increased by 47.33%and 10.62%,respectively,while the main grain-marketing zone decreased by 36.28%.In each study period from 2000 to 2020,the carbon emissions from cultivated land use in most provinces and cities showed an increasing trend,mainly showing the characteristic of"strong in the east and weak in the west,low in the south and high in the north",and the changing trend was closely related to the change of grain yield.(3)This paper macroscopically grasped the characteristics of the multi-scale correlations and change patterns among cultivated land use,carbon emission,and grain production,evaluated the spatiotemporal coupling characteristics between carbon emission from cultivated land use and grain production at multi-scales,and explored the influencing factors in China with the comparison among different grain production zones.1)The change pattern during 2000-2020 in China as a whole was that the quantity of cultivated land declined,while the quality of cultivated land,carbon emission from cultivated land use and grain production all increased(A↓Q↑E↑G↑),and this pattern of change was also the main trend in each study period.The change pattern in the main grain-producing zone during 2000-2020 was the same as that on the national scale,reflecting that the change pattern at the national level was mainly dominated by this zone.The main grain-marketing zone and the grain production and marketing balance zone showed decreases in the quantity and quality of cultivated land,carbon emission and grain yield(A↓Q↓E↓G↓)and increases in the quantity and quality of cultivated land,carbon emission and grain yield(A↑Q↑E↑G↑)respectively during 2000-2020.Moreover,it was found that the change patterns among provinces and cities in different study periods were in a dynamic and repetitive state with significant differences.2)The spatiotemporal coupling characteristics of carbon emission and grain production in China as a whole during 2000-2020 ideally presented weakly decoupled(VII),while that in each study period mainly showed expansion decoupled(VI)and weakly decoupled(VII).During 2000-2020,the decoupling types in the main grain-producing zone and the grain production and marketing balance zone were the same as the national scale,while the type in the main grain-marketing zone was unsatisfactorily declining decoupled(III).The decoupling types at the provincial and city levels during 2000-2020 mainly presented coupling with the ideal degree,and the decoupling types were in a dynamic fluctuating state at each research stage.3)In China,during 2000-2020,the multiple cropping index,per capita GDP,and precipitation all had positive effects on the spatiotemporal coupling levels between carbon emissions from cultivated land use and grain production,while the rural per capita electricity consumption had a negative effect.In each study period,the quantity of cultivated land and the multiple cropping index had positive impacts,and the degree of agricultural chemicalization per land unit had a negative effect.Based on comparative analysis,this paper found that the influencing factors of spatiotemporal coupling levels in the three grain function zones during 2000-2020 showed significant differences.Specifically,the multiple cropping index and irrigation status were the core factors influencing the spatiotemporal coupling levels in the grain production and marketing balance zone with positive effects;while in the main grain-producing zone and the main grain-marketing zone,the proportion of employees in the primary industry and the degree of agricultural chemicalization per land unit were the core factors,the former had positive impacts on both types of zones,and the latter negatively and positively influenced the two zones respectively.(4)To realize the dual objective of China’s grain production and reducing carbon emissions and increasing carbon sinks in cultivated land,this paper calculated carbon compensation,delineated zones according to“grain-carbon”correlation characteristics,and put forward regional optimization development measures.1)According to the calculated results,the amount of carbon compensation for cultivated land use in China showed a continuously increasing trend,with an increase rate of 307.72%in the past 20years,indicating the need for carbon compensation for agricultural and grain production industry in China.The carbon compensation amount and its changing trend of cultivated land use in the main grain-producing zone were similar to those at national scales,with an increase rate of 200.73%,and that in the grain production and marketing balance zone increased with a rate of 104.59%.However,the amount in the main grain-marketing zone changed from-2,846.98×10~4 t in 2000 to-1,957.52×10~4 t in 2020,indicating the decreasing trend of carbon compensation in this zone.The amounts of carbon compensation for cultivated land use at provincial and city levels varied significantly and fluctuated in each study period,and the overall spatial distribution pattern was"equivalent in the east and west,weak in the south and strong in the north",and most of the grain production zones needed to be compensated.2)The coupling zoning of"grain-carbon"was carried out based on the ideal degree of spatiotemporal coupling between carbon emission from cultivated land use and food production with the consideration of carbon compensation results for cultivated land use,and then this paper proposed the regional optimization development strategies.The results indicated that,as the most ideal"grain-carbon"coupling model for cultivated land use,it was necessary to establish a carbon compensation mechanism for high grain yield and low carbon emission in the"grain-carbon"coordinated development zone,meanwhile,it was also required to strictly protect the quantity of cultivated land,improve the quality of cultivated land,and protect its ecological environment.The"grain-carbon"coordinated optimization zone was the main type in the study area,the relationship between optimizing grain production and reducing carbon emissions from cultivated land use in this zone could be realized by optimizing grain production methods,developing intensive production models,and establishing systematic thinking.In the"grain-carbon"trade-off and grain yield increase zone,the quantity of cultivated land should be insured,and the grain yield could be increased by establishing a mechanism for controlling the utilization of cultivated land and increasing investment in agricultural production technology on existing cultivated land,and it was also significant to minimize carbon emission as much as possible.In terms of the"grain-carbon"trade-off and carbon reduction zone,which was regarded as the least ideal zone,it was recommended to promote the"grain-carbon"development of grain production through deepening technological innovation. |
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