Root–Canopy Coordination Drives High Yield and Nitrogen Use Efficiency in Dryland Winter Wheat

Improving yield and nitrogen-use efficiency (NUE) is essential for dryland winter wheat. We hypothesized that cultivars classified as high-yield and high-efficiency (HH) achieve superior performance through coordinated root-canopy traits that enhance water and nitrogen acquisition, sustain post-anthesis photosynthesis, and maintain assimilate and nitrogen remobilization. A two-year field experiment was conducted using ten regionally representative cultivars, which were grouped into HH, high-yield and low-efficiency (HL), low-yield and high-efficiency (LH), and low-yield and low-efficiency (LL) types based strictly on grain yield and NUE. Measurements included yield components, grain-filling, dry matter accumulation and partitioning, soil water use, nitrogen uptake and remobilization, and root-canopy structural traits. HH increased yield by 41.5% and water-use efficiency by 24.1% relative to LH, supported by denser shallow roots, moderate deeper-root development, higher leaf area index, and more compact canopies. HH also exhibited stronger post-anthesis dry matter and nitrogen translocation, resulting in a larger grain number per unit area and improved sink capacity. Correlation analyses further demonstrated positive associations among root-canopy traits, water and nitrogen dynamics, and yield formation. These results support the hypothesis that a coordinated root-canopy structure underlies the superior yield and NUE performance of HH cultivars in dryland systems, providing a physiological basis for cultivar improvement.