Effect of Zinc Deficiency on Growth, Phosphorus Concentration, and Phosphorus Toxicity of Wheat Plants
- Michael J. Webb and
- Jack F. Loneragan
In some previous experiments, Zn deficiency has enhanced P accumulation in old leaves to toxic concentrations by enhancing the rate of P absorption. This research was undertaken to examine the relationship of Zn deficiency to P accumulation and toxicity in young wheat plants (Triticum aestivum L. ‘Gamenya’) grown in a complete nutrient solution with 1000 µM phosphate and either with or without 2.5 µM Zn. Mild Zn deficiency depressed shoot but enhanced root DM and this change was almost paralleled by P distribution. Severe Zn deficiency enhanced P concentration to 3 to 4% in old leaves and the marked necrotic symptoms were attributed to combined Zn deficiency and P toxicity. It depressed whole plant dry matter (DM) by 40% but P content by only 10%. It severely depressed DM distribution but enhanced P distribution to shoots thus doubling shoot P concentration. Short term and long term estimates indicate that mild Zn deficiency had only a transient effect in enhancing Pi absorption rate as severe Zn deficiency substantially depressed it. Thus, Zn deficiency enhanced P concentrations to toxic levels in old leaves through the cumulative effects of responses at three tiers of structural organization: (i) in the whole plant, it depressed DM more strongly than P content, (ii) between roots and shoots, it depressed that proportion of total DM which was present in shoots while increasing that of total P, (iii) within shoots, it concentrated P in old leaves by depressing new growth.
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