Effects of nitrogen management on root morphology and zinc translocation from root to shoot of winter wheat in the field

• Effects of nitrogen (N) management on root morphology and zinc (Zn) translocation in winter wheat were studied.
• Increasing N supply improved root length density, surface area and root dry weight, resulting in an increased root Zn uptake.
• Improved ratios of shoot to root Zn concentration and shoot to total Zn content indicate higher N supply promotes root to shoot Zn translocation.
• Combination of optimum N management and a better root system could be a promising approach to improve grain Zn accumulation for human nutrition.

Nitrogen (N) nutrition is a critical factor in root uptake and deposition of zinc (Zn) into wheat grain. However, little is known about how the root system in the soil profile responds to various N supplies under field conditions. A two-year field experiment was conducted to investigate the temporal and spatial distributions of winter wheat roots and relationships between root morphological traits and root Zn uptake with different N supplies. Results showed that an increasing N supply improved root length density (RL), surface area (RSA) and root dry weight (DW), thereafter, resulting in an increased root Zn uptake. For example, root Zn uptake significantly and positively correlated with RL, RSA and root DW at jointing (r = 0.608*, 0.540* and 0.785***, respectively) and flowering (r = 0.611*, 0.602* and 0.876***, respectively) stages. Furthermore, substantial root DW (80–92%) and root Zn uptake (85–96%) were mainly recovered from the upper 30 cm of soil layer irrespective of N supply, showing a good spatial matching. The increased ratios of shoot-to-root Zn concentration and shoot-to-total Zn content with the increasing N supply indicate improving N supply promotes the root-to-shoot Zn transport and increases shoot Zn nutrition. Shoot Zn content was positively correlated with final grain yield and grain Zn concentration. Thus, a combination of optimum N supply with breeding for a better root system could be a promising approach to improve root uptake and accumulation of Zn in grain to maintain relatively higher grain Zn for human nutrition.