Biochemical phosphorus allocation is linked to photosynthetic phosphorus-use efficiency in a phosphorus-impoverished environment.

Highly efficient phosphorus (P)-use strategies have evolved in plants, allowing them to thrive in severely P-impoverished environments. However, it remains unclear how allocating leaf P to biochemical fractions, including specific P-containing metabolites, contributes to instantaneous photosynthetic P-use efficiency (iPPUE) and the position of species along the leaf economics spectrum (LES). We measured LES-associated traits (leaf mass per area, light-saturated photosynthetic rate, and P and nitrogen concentrations) and iPPUE in 12 coexisting Proteaceae, Fabaceae, Myrtaceae and Ericaceae from two severely P-impoverished soils. We characterised patterns of P allocation into lipids, nucleic acids, metabolites, a residual fraction and inorganic P, and identified P-containing metabolites within the metabolite-P fraction. We identified multiple P-utilisation strategies that were both species-dependent and soil context-dependent. The iPPUE and LES scores, representing leaf-level resource-use strategies, were positively associated with P concentrations in nucleic acids and the residual P fraction. Concentrations of key P-containing metabolites of the Calvin-Benson cycle, ribulose-1,5-bisphosphate and 3-phosphoglycerate, were positively correlated with and served as strong predictors of iPPUE and resource-use strategies within the LES. Species in severely P-impoverished habitats exhibited species-dependent and soil context-dependent P-allocation patterns and maintained specific P-containing metabolite concentrations. These trait combinations underpin high iPPUE and enable multiple resource-use strategies.