Research progress on carbon sources and sinks of farmland ecosystems

Farmland ecosystems are the most active carbon pool and contribute significantly to the global carbon cycle. Since these ecosystems are influenced by both natural and human factors it is important to study their roles as carbon sources and sinks in order to reach "peak carbon emissions"and "carbon neutrality"goals. This review provides a systematic summary of research in this area and explores the deficiencies in current research approaches by addressing common carbon flux accounting methods and mainstream carbon cycle measurement models. Natural and human factors that affect the functions of farmland ecosystems as sinks and sources of carbon are discussed and prospects for addressing existing problems and suggestions for future directions are presented. The factors affecting carbon sources and sinks in farmland ecosystem have great heterogeneity and complexity due to differences in management practices and natural conditions with the former being more important. However, due to differences in assessment models and accounting methods, there is still great uncertainty in the assessment of carbon sources and sinks in farmland ecosystems. Therefore, more emphasis is needed on the optimization of models and the improvement of accounting methods in the future. This review provides a comprehensive reference for further study on carbon sources and sinks of farmland ecosystems, rational adjustment of farmland management measures, and strategies for the reduction of agricultural non-point source pollution.