Optimizing photoassimilate synthesis, metabolism, and loading in cotton’s “source-sink-flow” system by boron fertilizer management to increase boll weight

The objective of this study was to identify a boron (B) application strategy maximizing cotton yield. In a two-year experiment across two soil types with three B application rates, B availability significantly regulated boll biomass accumulation rate in a 12–19-d post-anthesis window; B concentrations of 41–74 mg B kg⁻¹ in leaves subtending bolls maximized boll weight; and moderate B application increased source–sink carbon flux by increasing net photosynthetic rate, sucrose biosynthesis, and phloem loading efficiency. Integrating these three findings will increase photoassimilate partitioning to reproductive sinks, boosting cotton yield and B-use efficiency.