Phosphorus efficiency and root exudates in two contrasting tropical maize varieties

Nutrient solution culture and quartz sand amended with or without rock phosphate, were used to compare the short-term responses to phosphorus (P) deficiency of two contrasting maize hybrids, L3x228-3 (P-efficient) and HS 2841x5046 (P-inefficient). In solution-grown seedlings, the rapid P deficiency-induced enhancement of root growth and of the root/shoot ratio was a sign of P deficiency stress rather than of P efficiency. In sand culture, uptake of P from sparingly soluble rock phosphate was higher in P-efficient plants than in P-inefficient maize. In the variety L3-228-3, P efficiency seemed due to enhanced P acquisition rather than to an enhanced P use efficiency. In sand, but not in solution culture, higher citrate concentrations were detected in the rhizosphere of P-efficient than of P-inefficient maize. Quartz sand amended with rock phosphate was a better substrate than nutrient solution for revealing the varietal differences in P acquisition efficiency in short-term experiments.