Phosphorus Tolerance and Sensitivity of Soybeans as Related to Uptake and Translocation

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Abstract
P nutrition of soybean varieties tolerant (Chief) and sensitive (Lincoln) to high P was studied during the period of toxicity symptom development. Increasing the P supply stimulated P uptake by the sensitive variety more than by the tolerant, and the varietal difference was evident during the first 6 hours of high- P treatment. Characteristic symptoms of toxicity occurred when P content of the cotyledons reached 0.45 mg/ plant (1.2% dry wt.). The sensitive variety attained this level on an external concentration of about 1.6 m[image]; the tolerant variety required 16 m[image]. When tops of the tolerant variety were grafted to roots of the sensitive variety, the tolerant variety developed P toxicity symptoms on a nutrient solution P concentration of 1.6 m[image]. Conversely, the tops of the sensitive variety accumulated less P and did not develop toxicity symptoms when grafted to roots of the tolerant variety. The critical genotypic difference in P nutrition thus appears to reside in the roots. The tolerance of the tolerant variety is due primarily to reduced P accumulation.

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