Strong phosphorus (P)-zinc (Zn) interactions in a calcareous soil-alfalfa system suggest that rational P fertilization should be considered for Zn biofortification on Zn-deficient soils and phytoremediation of Zn-contaminated soils

Aims: Zinc (Zn) and phosphorus (P) often interact negatively with each other in soil-plant systems. We investigated the effects of P-Zn interaction on Zn and P accumulation and partitioning in alfalfa. Methods: Plants were grown in a calcareous soil supplied with different rates of Zn (0, 200, and 800 mg kg⁻¹) and P (0, 20, and 80 mg kg⁻¹). Plant dry mass, Zn and P concentrations in shoots and roots, bulk soil and rhizosheath pH, rhizosheath carboxylates, and DTPA-extractable Zn concentration in the bulk soil were determined. Results: Phosphorus-Zn interaction significantly affected DTPA-extractable Zn concentration, plant dry mass, accumulation of Zn and P, and partitioning of Zn in alfalfa, but did not affect rhizosheath pH or the amounts of rhizosheath carboxylates. Increasing P rate promoted plant growth at all soil Zn rates and might enhance the plants’ capacity to cope with excessive Zn; it resulted in a lower rhizosheath pH, which likely contributed to greater Zn and P uptake. Zinc deficiency enhanced exudation of citrate, malonate and malate, while the release of tartrate was related with P deficiency. Conclusions: There are strong P-Zn interactions in calcareous soil-plant system, such interactions significantly affect Zn bioavailability, plant growth, accumulation of Zn and P, and partitioning of Zn in alfalfa. Rational P fertilization should be considered for efficient Zn biofortification on Zn-deficient soils and phytoremediation of Zn-contaminated soils.