PLANT GROWTH RESPONSES TO VESICULAR-ARBUSCULAR MYCORRHIZA V. PHOSPHATE UPTAKE BY THREE PLANT SPECIES FROM P-DEFICIENT SOILS LABELLED WITH 32P

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Summary

The uptake of phosphorus from 32P-labelled soil solution by three plant species, with and without mycorrhiza, was measured. All soils contained very little CaCl2- and NaHCO3-soluble phosphorus. In two soils the specific activity of phosphorus taken up by mycorrhizal and non-mycorrhizal Melinis minutiflora was very similar, indicating that even in very P-deficient soils mycorrhizal plants used the same source of phosphate as non-mycorrhizal. In two other soils non-mycorrhizal Paspalum notatum and Centrosema pebescens contained no 32P activity, suggesting that they had not taken up any soil phosphorus, whereas mycorrhizal plants of both species contained 32P activity and grew much better. It is suggested that non-mycorrhizal roots of some plant species do not utilize phosphate present at extremely low concentrations in the soil solution, but that mycorrhizal roots or fungal hyphae do. The implications of this finding for the mechanism of phosphate uptake by VA mycorrhiza are discussed.

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