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

Summary 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.