Effect of uneven root allocation on shoot Zn uptake by crop plants growing on soil with heterogeneous P and Zn distribution

• Zn uptake affected by soil P patchiness in wheat and cucumber, not in lupin.
• All three plants showed a shift in root allocation to P-enriched soil.
• Shoot Zn uptake was associated with root length growth in wheat and cucumber.
• No effect of preferential cluster root allocation on shoot Zn uptake in lupin.
• Application of P fertilizer increased soil DTPA-extractable Zn.

Many plants are known to preferentially allocate root growth to soil patches with elevated availability of growth-limiting nutrients. Little is known about how this influences the uptake of other nutrients such as trace metals. Here we investigated zinc (Zn) uptake by different crop plants in soil with heterogeneous phosphorus (P) and Zn distribution. Triticum aestivum L. (spring wheat), Cucumis sativus L. (cucumber) and Lupin albus L. (white lupin) were grown in rhizoboxes on low-P soil treated with local P and Zn amendments. A treatment with homogeneous P amendment was used as control. Root system development was monitored over 55 days using neutron radiography and Winrhizo. The treatments had no effect on total root and shoot biomass, but root growth responded positively to local soil P enrichment but not to local Zn enrichment in all three plants. Wheat and cucumber responded with preferential allocation of root length, while in white lupin cluster root (CR) allocation was shifted to the P-enriched soil patches. Shoot Zn uptake was increased in wheat and cucumber when Zn- and P-enrichment were co-located and decreased when they were disjunct, indicating that shoot Zn uptake was related to root length growth in these two plants. In contrast, preferential CR allocation in lupin was not associated with a treatment effect on shoot Zn uptake.