Phosphorus fractions in leaves.

Leaf phosphorus (P) comprises four major fractions; inorganic phosphate (P ), nucleic acids, phospholipids, P-containing metabolites and a residual fraction. In this review paper we investigated whether allocation of P fractions (i) varies among groups of terrestrial vascular plants, and (ii) is indicative of a species' strategy to use P efficiently. We found that as leaf total P concentration increases, the P fraction increases the most, without a plateau, while other fractions plateau. Variability of the concentrations of leaf P fractions is greatest among families>species(family)>regions>plant life forms. The percentage of total P allocated to nucleic acid-P (20-35%) and lipid-P (14-34%) varies less among families/species. High photosynthetic P-use efficiency is associated with low concentrations of all P fractions, and preferential allocation of P to metabolite-P and mesophyll cells. Sequential resorption of P from senescing leaves starts with P , followed by metabolite-P, and then other organic P fractions. Allocation of P to leaf P fractions varies with season. Leaf phytate concentrations vary considerably among species, associated with variation in photosynthesis and defence. Plasticity of P allocation to its fractions is important for acclimation to low soil P availability, and species-specific P-allocation is needed for co-occurrence with other species.