Optimization of nitrogen allocation and remobilization improves nitrogen use efficiency of winter wheat in the North China Plain

Understanding the allocation and remobilization of nitrogen within canopy during grain filling is crucial for improving nitrogen use efficiency in wheat. How nitrogen fertilizer management in the North China Plain (NCP) determines nitrogen use efficiency by impacting the allocation and remobilization of nitrogen at the individual organs scales remains unclear. To address this, a two-year field study quantified organ-specific nitrogen allocation and remobilization dynamics across canopy hierarchies under varying nitrogen doses (0–330 kg ha⁻¹). Results demonstrated a quadratic response of grain yield to nitrogen doses, peaking at 241 kg N ha⁻¹ (8.23 Mg ha⁻¹), and nitrogen doses of 180–220 kg ha⁻¹ synchronized nitrogen supply with grain nitrogen-sink development, maximizing remobilization. Nitrogen remobilization efficiency (NRE) was positively associated with nitrogen efficiency parameters and grains spike⁻¹. Organ-level analysis revealed that upper-canopy organs (flag leaf, first internode) maintained stable NRE (75–85 %) across nitrogen regimes, while lower-canopy organs (3rd/4th leaves/internodes) exhibited significant plasticity (NRE: 57–79 %), with reduced nitrogen supply increasing NRE of lower-canopy organs. Reduced nitrogen supply elevated nitrogen allocation to spikes at anthesis by 20.0 %, concurrently enhancing spike NRE by 9.7 %. These dynamics demonstrate that strategic nitrogen reduction simultaneously preserves photosynthetic capacity in the upper canopy, exploits lower-canopy plasticity for efficient remobilization, and prioritizes spike development as a high-efficiency nitrogen sink. To reconcile productivity and sustainability, we propose to exploit NRE plasticity in lower canopy organs through precision nitrogen placement, combined with nitrogen-sink enhancement via either breeding or growth regulators to increase grains per spike.