Photoassimilate allocation in soybean: influence of source-sink spatial relationships

Carbon allocation from source leaves to sink organs is a key determinant of plant growth and yield. Spatial patterns of photoassimilate transport in soybean were quantified during reproductive and vegetative stages using 14 C-labeled CO 2 and sucrose. Both labeling approaches revealed comparable spatial patterns, with preferential carbon delivery to sink organs formed on the same stem node as the labelled source leaf and distributions varying according to the vertical position of the source leaf. These findings reveal pronounced spatial heterogeneity in source–sink relationships and provide mechanistic insight into positional regulation of carbon partitioning in crop plants.