Abstract In eucalypts the reduction in CO 2 assimilation and total leaf area at low phosphorus (P) supply is not associated with lower leaf total P concentrations. We tested the hypothesis that the leaf concentration of inorganic phosphorus ([P i]) may be a better indicator of P nutrition status in Eucalyptus grandis W. Hill ex Maiden by growing seedlings in P deficient soil supplemented with P supplies ranging from 3 to1000 mg kg −1. Height, biomass accumulation, gas exchange, chlorophyll fluorescence and concentrations of total P ([P t]), organic P ([P o]) and [P i] of the last fully expanded leaves were measured when harvested at 19 weeks. All parameters of growth increased with larger applications of soil P with most becoming saturated at additions of 500 mg P kg −1 soil. Soil P supply had larger effects on biomass and canopy leaf area, by both increased in leaf initiation and expansion, than on CO 2 assimilation ( A). Leaf [P t] and [P o] concentrations were largely invariant to soil P supply and were not correlated with any of the measured growth and photosynthetic parameters. By contrast, leaf [P i] increased from 171 to 398 mg kg −1 with increasing soil P supply. Furthermore, number of leaves, total leaf area and seedling biomass increased exponentially with leaf [P i], while individual leaf area and A increased linearly with leaf [P i], and quantum yield of photosystem II similarly increased, and non-photochemical quenching decreased, with increasing leaf [P i]. The response of A to internal CO 2 concentration ( C i) indicated that at lower P supplies A became increasingly restricted by limitations associated with Rubisco and RuBP regeneration. Stomatal limitation may in part be masking the full effect of P supply on A as C i declined with either increasing soil P or leaf [P i] supply. We conclude that leaf [P i] was a potentially better indicator than [P t] or [P o] for correlating the effects of soil P supply on growth and photosynthesis of E. grandis. Furthermore, as A achieved at saturating C a increased with increasing P supply leaf [P i], these findings suggest that a greatly increased rate of canopy assimilation could be achieved at higher P supply in response to the expected increase in global CO 2 levels.