Straw returning and night-warming improve grain yield and nitrogen use efficiency of winter wheat under rice–wheat rotation

Global climate warming is characterized by diurnal and seasonal asymmetry, with greater increases at nighttime and in winter and spring. Growing evidence has recognized that night-warming in winter and spring significantly impacts winter wheat production. Pre-crop straw returning is the principal method for straw utilization, but the interactions between straw returning and night-warming on wheat yield and N use efficiency (NUE) remain unclear. Here, a consecutive three-year field experiment with two straw treatments (S0, straw removal; S1, straw returning) and two warming treatments (W0, no warming control; W1, night-warming) found that both S1 and W1 improved wheat grain yield and NUE, with W1 exhibiting more pronounced improvements. Notably, the interaction between S1 and W1 (S1W1) further enhanced yield and NUE by 13.0 and 16.5%, respectively, compared to S0W0 through increasing grain number and 1,000-grain weight (three-year average). Additionally, root growth and topsoil inorganic N content decreased in S1 before jointing, thereby reducing plant dry matter and N accumulation. However, W1 exhibited an opposite trend, thereby mitigating these negative effects. Simultaneously, under S1W1, increased N translocation to grain and post-anthesis dry matter accumulation, driven by greater N distribution to leaves and higher N metabolism enzyme activity, enhanced both yield and NUE. This improvement was supported by better root morphology and biomass, particularly in the 0–40 cm soil layer, boosting plant N absorption. Additionally, elevated soil N-acquiring enzyme activity after jointing increased the net N mineralization rate and microbial biomass N, enhancing soil N-supply capacity. As a result, post-jointing inorganic N content rose in the 0–20 cm layer while decreasing at 20–60 cm, thus reducing the apparent N surplus. Collectively, straw returning, night-warming, and their interactions enhanced root distribution and N-supply capacity after jointing in the topsoil layer, thereby increasing plant N uptake and its translocation to grains, along with post-anthesis dry matter accumulation, ultimately improving grain yield and NUE.