Zinc uptake and accumulation in winter wheat relative to changes in root morphology and mycorrhizal colonization following varying phosphorus application on calcareous soil

Although phosphorus (P) is known to reduce zinc (Zn) uptake by roots and root-to-shoot translocation, how this interaction is affected by changes in root morphology and arbuscular mycorrhizae (AM) are poorly understood. The current study determined the effects of P application rate (0, 25, 50, 100, 200, and 400 kg P ha−1) on Zn uptake by roots and root-to-shoot translocation in a high-yielding winter wheat system on calcareous soil. Root dry weight (RDW), root length density (RLD), and root surface area (RSA) significantly increased as P application increased from 0 to 50 kg ha−1 but were unaffected by rates >50 kg ha−1. Zn accumulation (mg m−2 or μg m−2) by roots at flowering increased with application of 25 and 50 kg P ha−1 but slightly decreased with application of 100-400 kg P ha−1. Zn accumulation in roots and in shoots at flowering and grain yield at maturity were positively correlated with RDW, RLD, and RSA. Root Zn accumulation was increasing with increased AM colonization from low AM (<10%) to 30% AM colonization. Whereas, continuously increasing AM colonization induced root Zn accumulation decrease, which may be mainly due to the decrease of root dry weight affected by P deficiency. P application rate did not significantly affect the ratio of Zn concentrations in roots vs. shoots or the ratio of Zn accumulation in roots vs. total Zn accumulation in the plant, indicating that Zn translocation from roots to shoots is not the primary factor limiting Zn concentrations in grain. These results indicate 1) that P application affects the Zn accumulation of wheat by affecting Zn uptake by roots and 2) that the changes in Zn uptake by roots and Zn accumulation following P application reflect changes in root morphology and AM colonization of roots.