Dynamics of source-sink relationships in crops under marginal environments

In semi-arid environments, crop production is heavily impacted by drought, salinity, and low nutrient availability. These marginal environmental conditions disrupt photosynthetic efficiency, translocation, and assimilate partitioning, all of which lead to yield reductions. As a result, maximizing crop productivity under marginal environments requires plants to effectively balance assimilate production (source strength) with use or storage (sink strength). Understanding the relative trade-offs between resources devoted to plant sources and sinks is critical to the development of resilient, productive crops. This review synthesizes research identifying physiological, morphological, and developmental traits that improve source and sink strength under stress conditions in semi-arid regions. Key source-related traits include intrinsic water-use efficiency, sustained photosynthetic capacity under stress, the stay-green phenotype, and favorable leaf area and canopy architecture. Sink traits such as stable reproductive organ development, phenotypic plasticity, root-shoot balance, and optimized phenological timing are highlighted as critical to maintaining sink strength under limiting conditions. We also assess the potential of advanced genetic, biotechnological, and ''omics'' approaches to develop climate-resilient crops, while addressing inherent trade-offs. Finally, we discuss emerging tools and conceptual frameworks that hold promise for improving selection and management of source–sink traits in climate-resilient cropping systems. This review provides a framework for integrating physiological, morphological, and developmental traits into breeding programs aimed at improving source-sink dynamics and advancing sustainable crop production in semi-arid and other marginal environments.