Spatiotemporal evolution and driving factors of carbon sources and sinks on cultivated land in the main grain producing areas in the Middle Reaches of the Yangtze River

Cultivated land has been the main source of carbon emissions during agricultural production. Especially, the function of carbon absorption by crops also has posed the dual impacts of carbon source or sink in major grain-producing areas. Therefore, the cultivated land can play an important role in the low-carbon transformation of agriculture. It is crucial to recognize the balance and driving factors of carbon sources and sinks in the cultivated land, in order to promote low-carbon production and food security. In this study, the internal and external carbon cycle of cultivated land was considered to measure the net carbon sink of cultivated land in the middle reaches of the Yangtze River from 2005 to 2021. A theoretical framework was proposed, according to the dual perspective of carbon sources and sinks. Spatial autocorrelation and kernel density estimation were applied to investigate the spatial and temporal evolution in different regions. Then, GeoDetector was applied to analyze the influence of the driving factors on carbon sequestration and emission reduction. The results show that: 1) The total net carbon sink of cultivated land increased from 26.7409 million tons in 2005 to 37.5758 million tons in 2021, with an average annual increase of 2.22%. There was a much more prominent function of the carbon sink. The net carbon sink of cultivated land was less than 1.5 million tons in most of the cities. In terms of spatial pattern, there was a significant variation in the net carbon sink of cultivated land in different cities, indicating "low-value point-like dispersion, high-value piece-like agglomeration". (2) The spatial correlation of net carbon sinks in the cultivated land was alternated into the "positive-negative-positive agglomeration". There was a diffusion pattern in the net carbon sinks of cultivated land in each province and the region as a whole. The regional differences were enhanced to deteriorate the spatial non-equilibrium. (3) The spatial and temporal pattern of the net carbon sink in the cultivated land was dominated by the cultivated land use and agricultural economic factors. Among them, the key dominant factors were the size of cultivated land and the level of agricultural mechanization. The influence of the driving factors shared the outstanding regional heterogeneity. A theoretical basis can be offered to promote the core and key areas of carbon sequestration and emission reduction in the cultivated land. (4) Some recommendations were proposed to promote the size and mechanization of cultivated land, the scientific quantification of material inputs, as well as the quality cultivation of producers, in order to realize carbon sequestration and emission reduction. The carbon cycle can also be determined to measure the carbon sources and sinks in the cultivated land, in order to improve the economic and ecological benefits of cultivated land use. The findings can provide decision-making references for pollution reduction, carbon sequestration, and sink enhancement in the cultivated land.