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Aluminium (Al) toxicity or phosphorus (P) deficiency can induce exudation of organic acids from the roots of some plants, which is believed to be a tolerance mechanism against Al toxicity or P deficiency. In the present study, the effect of P deficiency on Al‐induced citrate exudation was investigated in three soybean varieties differing in low‐P tolerance. P starvation alone failed to induce secretion of organic acids from all three soybean varieties. However, P deficiency altered Al‐induced citrate exudation over time, showing a complex interaction. Short × term P starvation (4 days) produced up to 50% increase in Al‐induced citrate secretion, while longer‐term (10 days) starvation reduced Al‐induced citrate secretion to trace amounts. However, after a further 1 day in complete nutrient solution for recovery, Al‐induced citrate exudation from the recovered roots was approximately 6 times higher than that from the continuously P‐starved plants, but still approximately 3.6 times lower than that from the P‐sufficient control. With increasing P or Al supply, Al‐induced citrate exudation increased, while Al accumulation in soybean roots decreased in parallel with the decrease of P supply. The photosynthetic rate, stomatal conductance and transpiration were decreased by P deficiency, whereas the intracellular CO 2 concentration was increased. These findings indicate that P nutrition has a significant effect on Al‐induced citrate exudation and Al accumulation in soybean root apices.
Nian et al. (Sat,) studied this question.