Phosphate availability shapes source–sink dynamics and nitrogen balance in dual-purpose hemp (Cannabis sativa L.): Insights from physiological and transcriptomic analyses

Cannabis sativa L., one of the earliest domesticated crops, was selectively bred into drug-type (high phytocannabinoid yield) and hemp-type (fibre, hurd, and seed production) varieties, leading to divergent physiological and agronomic traits, including nutrient requirements. To address the limited molecular understanding of the regulation of nutrient use in Cannabis, this study investigated the response of a dual-purpose hemp cultivar to varying phosphate availability. Physiological and transcriptomic profiling across source and sink organs revealed that biomass partitioning to flowers was sustained unless phosphate was completely withdrawn, indicating a strong prioritization of reproductive growth. Expression analyses of phosphate-responsive genes highlighted the importance of early senescence in older leaves for nutrient remobilization through the release of phosphate from organic pools and phosphate-saving glycolytic bypass reactions. This sustained phospholipid biosynthesis and other phosphate-dependent metabolic pathways in sink organs despite overall low plant P status. Furthermore, our data suggest that hemp, unlike most other crop species, did not suppress phosphate uptake or root-to-shoot translocation under surplus supply. The elevated phosphate led to a depletion of vacuolar nitrate pools, particularly in source leaves, with the lack of positive feedback on root nitrate acquisition ultimately restricting growth and flower yield. Collectively, our findings reveal both conserved and hemp-specific strategies for nutrient cross-talk, providing new insight into how hemp maintains reproductive growth and nutrient balance under fluctuating phosphate supply. The identified traits support productivity in low-input and sustainably managed protected cropping systems and serve as selection targets for optimizing nutrient efficiency and resilience across diverse crop species. • Hemp flowers are effectively shielded from phosphate deficiency. • Efficient phosphate remobilization and recycling safeguards reproductive sinks. • Optimal phosphate supply is 0.25 mM (8 ppm), excess depletes nitrogen reserves. • Unlike most crop plants, hemp prioritizes phosphate over nitrate acquisition. • Identification of marker genes for P and N status in sink and source organs.