JXB Advance Access originally published online on December 15, 2005
Journal of Experimental Botany 2006 57(2):413-423; doi:10.1093/jxb/erj004
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RESEARCH PAPER |
Systemic suppression of cluster-root formation and net P-uptake rates in Grevillea crithmifolia at elevated P supply: a proteacean with resistance for developing symptoms of ‘P toxicity’
School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, Crawley, WA 6009, Australia
* Present address and to whom correspondence should be addressed. Department of Botany, University of Cape Town, Private Bag, Rondebosch, 7701, South Africa. E-mail: mshane{at}cyllene.uwa.edu.au
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.
Key words: Hakea prostrata, net P uptake, phosphorus toxicity, plant growth, proteoid roots, split-root design, systemic regulation
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