JXB Advance Access published online on December 15, 2005
Journal of Experimental Botany, doi:10.1093/jxb/erj004
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1 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
* To whom correspondence should be addressed. 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.
Received May 31, 2005
Accepted September 8, 2005
PHENOTYPIC PLASTICITY AND THE CHANGING ENVIRONMENT SPECIAL ISSUE ARTICLE
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’
Michael W. Shane 1 *
and
Hans Lambers 2
2 School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, Crawley, WA 6009, Australia
Michael W. Shane, E-mail: mshane{at}cyllene.uwa.edu.au
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