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| Split-root system was used to investigate whether the external or internal P concentration controls root cluster formation and citrate exudation in white lupin (Lupinus albus L.) grown under the controlled conditions. In spite of low P concentration in shoot and root of the -P plant, its dry weight was not reduced, compared with the +P plant. Supplying external P (0.25 mmol/L) to one root half resulted in increase in P concentration not only in the shoot, but also in the P deprived root half, indicating P cycling within the plants. P omitting from both split-root pots stimulated root cluster formation in both root halves. While P supply to one root half stimulated root cluster formation at the beginning of the treatment. However, neither P supply to just one root half continuously nor re-supply of P to one root half after 19 d of P starvation could inhibited root cluster formation in the P deprived side, although the P concentration in this root half and shoot increased markedly. The results indicated that root cluster formation in Lupinus albus was controlled by both shoot and root P concentration. The rates of citrate exudation by both root halves with P-deficiency were higher than that of one root half supplied with P only. In the treatment with one root half supplied with P, the rates of citrate exudation by either the P-supplied or deprived root halves were almost same regardless of P concentration in the roots. The results suggested that internal P concentration controlled root cluster formation and citrate exudation in white lupin, but they might be regulated by different mechanisms. |
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| Keywords:citrate exudation; P cycling; root clusters; split-root system; white lupin |
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