Bridging the nitrogen–carbon divide: a multi-scale synthesis of source–sink dynamics for yield optimization in annual crops (1970–2026)

Abstract

Crop productivity in annual cropping systems is governed by coordinated interactions among assimilate production, transport, and utilization within the source–sink framework. This review synthesizes classical concepts and recent advances, with emphasis on physiological processes and nitrogen mediated regulation of yield formation. A structured literature survey (1970 to 2026) examined assimilate partitioning, developmental transitions between source and sink states, and the role of nitrogen management in modulating these processes. Nitrogen acts as a central regulatory factor linking canopy development, photosynthesis, and reproductive sink establishment, thereby coordinating carbon assimilation with biomass allocation. Temporal coordination, particularly during grain filling, remains critical for final yield formation. Despite significant progress, gaps remain in understanding molecular regulation of sink strength, integrating environmental variability into predictive models, and scaling physiological insights to field level applications. Future research should adopt interdisciplinary approaches combining plant physiology, genomics, and systems modeling to improve nitrogen efficient strategies and optimize source sink balance under changing climatic conditions.