Abstract: Phosphorus (P) is essential for photosynthesis and often limits plant productivity in terrestrial ecosystems. Plants allocate foliar P among inorganic phosphate and organic pools, including nucleic acid P, lipid P and metabolite P, with important consequences for photosynthetic capacity and P-use strategies. Here, we synthesize evidence that photosynthetic P-use efficiency (PPUE) depends not only on total foliar P concentration, but also on how P is distributed among functional pools and reconfigured across biological and environmental contexts. Metabolite P directly supports carbon metabolism, RuBP regeneration and carbon export, whereas lipid P and nucleic acid P influence PPUE through membrane investment, phospholipid remodelling, protein synthesis and enzyme turnover. Under P limitation, plants may maintain photosynthetic capacity by mobilizing vacuolar inorganic P, reducing phospholipid P demand and reallocating P towards metabolically active processes. We further show that these allocation patterns are shaped by endogenous factors, such as species traits and ontogeny, and by exogenous drivers, including temperature, water availability, light, and soil nutrient status. These factors interact to determine whether limited foliar P is retained in structural or storage pools, or redirected towards metabolic processes that sustain photosynthesis. However, available evidence indicates that PPUE is shaped by the coordination of different P fractions, with the relative importance of each fraction depending on species traits and environmental context. By integrating these physiological and ecological controls, this review highlights foliar P allocation as a mechanistic basis for understanding variation in photosynthetic P use and plant resilience across species, developmental stages, and nutrient environments.

Key words: Foliar P allocation, Photosynthesis, Nucleic acid P, Phospholipid P, Metabolite P, Soil nutrients