The coupling mechanism of the dual “supply-buffer” effects of farmland on regional carbon storage in China’s coastal regions

Land use and land cover change (LUCC) has a significant impact on ecosystem stability and carbon storage capacity. However, the specific roles of different land types are still not well understood. This study examined the spatial and temporal patterns of land use changes and their effects on carbon storage in China’s rapidly urbanizing coastal regions from 1980 to 2050, including various future scenarios. The findings showed that over a 40-year period, complex land use changes led to a total loss of carbon storage equivalent to 1.22 × 108 t. Among all land types, built-up land and farmland experienced the most dynamic changes. Built-up land expanded by 59,192 km2, while farmland decreased by 46,653 km2. Farmland emerged as a key driver of land use change, with the conversion between farmland and built-up land accounting for 79.29% of the total expansion of built-up areas. In regions with the largest changes in carbon storage (|∆Carbon storage|> 15,000 t), the conversion between farmland and woodland was particularly pronounced. Future scenario simulations projected a continued decline in carbon storage, with the ecological priority scenario showing the highest projected value of 139,722,841.2 × 104 t by 2050. Differences in carbon storage across scenarios were mainly driven by transitions between farmland and woodland, as well as the extent of farmland being converted into built-up land. These results offer practical guidance for improving land management strategies to enhance carbon storage in coastal regions, highlighting the pivotal “supply-buffer” mechanism of farmland in mediating regional carbon budgets.