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Grevillea crithmifolia R. Br. is a species of Proteaceae that is resistant to developing P-toxicity symptoms at phosphorus supplies in the root environment that induce P-toxicity symptoms in the closely related Hakea prostrata (Proteaceae). It was discovered previously that development of P-toxicity symptoms in H. prostrata is related to its low capacity to down-regulate net P-uptake rates (i.e. its low plasticity). The plasticity of net P-uptake rates and whole-plant growth responses in G. crithmifolia has now been assessed in two separate experiments: (i) a range of P, from 0 to 200 μmol P d−1, was supplied to whole root systems; (ii) using a split-root design, one root half was supplied with 0, 3, 75, or 225 μmol P d−1, while the other root half invariably received 3 μmol P d−1. Fresh mass was significantly greater in G. crithmifolia plants that had received a greater daily P supply during the pretreatments, but symptoms of P toxicity were never observed. Cluster-root growth decreased from about half the total root fresh mass when the leaf [P] was lowest (c. 0.1 mg P g−1 DM) to complete suppression of cluster-root growth when leaf [P] was 1–2 mg P g−1 DM. Split-root studies revealed that cluster-root initiation and growth, and net P-uptake rates by roots were regulated systemically, possibly by shoot P concentration. It is concluded that, in response to higher P supply, G. crithmifolia does not develop symptoms of P toxicity because of (i) greater plasticity of its net P-uptake capacity, and (ii) its greater plasticity for allocating P to growth and P storage in roots. This ecologically important difference in plasticity is most probably related to a slightly higher nutrient availability in the natural habitat of G. crithmifolia when compared with that of H. prostrata. [ABSTRACT FROM PUBLISHER]

Storage of phosphorus (P) in stem tissue is important in Mediterranean Proteaceae, because proteoid root growth and P uptake is greatest during winter, whereas shoot growth occurs mostly in summer. This has prompted the present investigation of the P distribution amongst roots, stems, and leaves of Hakea prostrata R.Br. (Proteaceae) when grown in nutrient solutions at ten P‐supply rates. Glasshouse experiments were carried out during both winter and summer months. For plants grown in the low‐P range (0, 0.3, 1.2, 3.0, or 6.0 µmol d–1) the root [P] was > stem and leaf [P]. In contrast, leaf [P] > stem and root [P] for plants grown in the high‐P range (6.0, 30, 60, 150, or 300 µmol P d–1). At the highest P‐supply rates, the capacity for P storage in stems and roots appears to have been exceeded, and leaf [P] thereafter increased dramatically to approximately 10 mg P g–1 dry mass. This high leaf [P] was coincident with foliar symptoms of P toxicity which were similar to those described for many other species, including non‐Proteaceae. The published values (tissue [P]) at which P toxicity occurs in a range of species are summarized. X‐ray microanalysis of frozen, full‐hydrated leaves revealed that the [P] in vacuoles of epidermal, palisade and bundle‐sheath cells were in the mM range when plants were grown at low P‐supply, even though very low leaf [P] was measured in bulk leaf samples. At higher P‐supply rates, P accumulated in vacuoles of palisade cells which were associated with decreased photosynthetic rates. [ABSTRACT FROM PUBLISHER]