| As a significant contributor to greenhouse gas emissions,China has an enormous responsibility in dealing with climate change,and has committed to achieve carbon sequestration by 2030 and carbon neutrality by 2060,which urgently necessitates technical measures to decrease sources and increase sinks.Analyses of the spatial and temporal evolution trends and influences of farmland ecosystems,which are essential components of terrestrial ecosystems,will be meaningful for enhancing the carbon sequestration capacity of farmland ecosystems,mitigating climate change and guaranteeing food security.The Study targeted the urban agglomeration in the Middle Reaches of the Yangtze River(MRYR-UA),based on the statistical data of 31 cities from 2003 to 2020,considered carbon input(crop carbon uptake),Carbon Storage(carbon immobilized in farmland soil)and carbon output(agricultural production carbon emission),adopted the carbon emission factor method,NPP method and DNDC model to estimate the carbon source and carbon sink of farmland ecosystem in MRYR-UA more comprehensively,and comparatively analyzed the spatial and temporal evolution trends of carbon sources and carbon sinks in Wuhan Urban Agglomeration,Changsha-Zhuzhou-Xiangtan Urban Agglomeration and Poyang Lake City Cluster.Meanwhile,we applied the LMDI model and sensitivity analysis to evaluate the influences of carbon sources and sinks in farmland ecosystems,appropriated carbon sequestration and emission reduction measures are proposed to provide a scientific basis for the sustainable development of farmland ecosystems in MRYR-UA.The main conclusions are as follows:(1)Carbon emissions from farmland ecosystems in MRYR-UA have significantly increased,displayed a spatially higher northwest and lower southeast trend.Fertilizer was the primary emission source of carbon from farmland ecosystems in MRYR-UA,influenced by the scale of cultivation and agricultural technology level,the intensity of carbon emission tended to decrease,and the spatial pattern was higher in the northwest and lower in the southeast.the level of agricultural economy was the primary reason for the enhancement of carbon emissions in MRYR-UA,while the reduction of carbon productive efficiency,the decrease of labour size,and the optimization of agricultural structure exhibited negative effects on carbon emissions.Among the three urban agglomerations,Wuhan Urban Agglomeration had the maximum carbon emission and was the most dependent on chemical fertilizer,and the carbon emission and its intensity decreased most significantly.The largest increases in carbon emissions and intensity were seen in Changsha-Zhuzhou-Xiangtan Urban Agglomeration.The influence of agricultural economic level and carbon productive efficiency on Wuhan Urban Agglomeration was utmost significant,the accumulated carbon emission effectiveness was 6.86 million tons and-5.54 million tons respectively,the reduction of agricultural labour scale played an essential function in suppressing carbon emission in Poyang Lake City Cluster and Wuhan Urban Agglomeration,the accumulated effectiveness was-1.36 million tons and-1.09 million tons.(2)The carbon absorption of farmland ecosystems in MRYR-UA presented an increasing trend,and its intensity in spatial terms was higher in the south and lower in the north.Rice was the dominant source of carbon absorption,with 67.86% of the aggregate.Agricultural technology level was the primary influencing factor of crop carbon absorption growth in MRYR-UA,accounted for 45.12% of the total carbon absorption effect,agricultural scale and planting structure were next.The carbon absorption of Poyang Lake City Cluster,Changsha-Zhuzhou-Xiangtan Urban Agglomeration and Wuhan Urban Agglomeration were all increasing,accounted for 29.73%,32.29% and 37.98% of the aggregate respectively,and the carbon absorption intensity increased by 38.07%,13.41%and 23.93% respectively,while the carbon absorption of rice accounted for 80.05%,72.48%and 54.39% of each city cluster separately.Technology level had the greatest influence on Poyang Lake City Cluster,with the cumulative carbon absorption effect of 3.92 million tons,and the promotion effect of agricultural scale element on carbon absorption in Wuhan Urban Agglomeration was remarkably greater than other urban agglomerations,the cumulative effect was 2.61 million tons.The influence of agricultural planting structure on carbon absorption in Wuhan Urban Agglomeration and Poyang Lake City Cluster was more significant,the cumulative effect was 2.64 million tons and 2.36 million tons respectively.(3)The soil organic carbon(SOC)content of farmland in MRYR-UA was generally increasing,and SOC growth exhibited a spatially higher trend in the southwest and lower trend in the northeast.The soil organic carbon content in MRYR-UA increased 56.66 million tons in 18 years,and the organic carbon density increased from 79.80 t/ha to 82.63t/ha.The organic fertilizer application was the dominant positive influence on soil carbon storage in MRYR-UA,initial soil organic carbon content and average annual temperature were the majority negative influencing factors.Among the three urban agglomerations,the SOC content of farmland in Wuhan Urban Agglomeration increased highest,whereas the minimum increase was in Changsha-Zhuzhou-Xiangtan Urban Agglomeration.Organic fertilizer application,initial organic carbon content and average annual temperature had the greatest influence on Changsha-Zhuzhou-Xiangtan Urban Agglomeration,while average annual rainfall,p H value,soil capacity,soil clay content,nitrogen fertilizer application and straw return rate had relatively small influences on each urban cluster,but the degree and effects were dissimilar.To analyze the factors influencing carbon sources and sinks in farmland ecosystems in MRYR-UA,we proposed three recommendations to optimize farmland management measures,optimize agricultural productivity structure,and promote the development of agricultural scale and mechanization,which will help enhance the carbon sink capacity of farmland ecosystems in MRYR-UA and facilitate the development of low-carbon agriculture. |
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