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Phosphorus utilization in contrasting pasture legumes

Richard H. Chisholm and Graeme J. Blair

Department of Agronomy and Soil Science, University of New England, Armidale. N.S.W. 3351.

As part of a programme to determine reasons for differences in the efficiency of use of P by plants, a solution culture study of P use by Stylo (S. hamata cv. Verano) and White Clover (T. repens cv. Ladino) was conducted.

Incorporation of 32P using a pulse chase technique was measured over five P levels and five harvests. P was extracted from plant material (Bieleski 1968) to determine the relative size and turnover characteristics of soluble, lipid (membrane) and residue (RNA/DNA/P Protein) pools. Results for two harvests and two P levels are presented in Table l.

TABLE l. Dry weights and P pool dynamics for Verano Stylo and Ladino white clover.

Between 37 and 343 hours yields of tops and roots increased at a greater rate in Stylo than in Clover at low P. In White Clover root soluble and residue pools increased over this time whereas the size of the root lipid pool (membranes) remained static (i.e. its concentration decreased). Whilst a smaller decrease at low P also occurred in the lipid P concentration of Stylo, 32p/31p ratios at 243 hours show that little net export of P (vs cell expansion) occurred. This was not the case in Clover. With data from other P levels and harvests this indicates an association of reduced growth rate with P export from membranes.

At high P, Stylo was unable to produce as much total dry weight as Clover because of a smaller P allocation to structural (L + R) pools relative to the soluble pool.

Bieleski, R.L. (1968). P1. Physiol. 43: 1309-16.

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