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.

Late sowing is a critical factor that hinders achieving high-yield, good-quality wheat under rice–wheat rotation.  Understanding the physiological basis and regulatory pathways that lead to high yield and sound quality late-sown wheat is crucial for developing effective cultivation strategies.  A 2-year field experiment was conducted to investigate the effects of sowing date, nitrogen (N) application rate, and planting density on wheat yield, grain quality, population characteristics, and the underlying physiological factors.  The results revealed significant interactions among the sowing date, planting density, and N application in regulating both yield and quality.  Late sowing reduced grain yield primarily by reducing the number of spikes and kernels.  However, the latter was improved by increasing N application and the planting density, thus mitigating the yield losses caused by late sowing.  Moreover, the grain protein content (GPC) and wet gluten content (WGC) increased with delayed sowing dates and higher N rates but decreased with increased planting densities.  For wheat yields over 9,000 or 7,500 kg ha^–1, the latest sowing date should not be later than Nov. 4 or 15, respectively.  In addition, specific criteria should be met, including a maximum of 1.5 and 1.0 million stems and tillers ha^–1, a maximum leaf area index of 6.7 and 5.5, and a dry matter accumulation (DMA) at anthesis of 14,000 and 12,000 kg ha^–1, respectively.  For high-yield, good-quality late-sown wheat, the optimal combination is a 25% increase in the N rate (300 kg N ha^–1) and a planting density of 2.25 million (N300D225) or 3.75 million (N300D375) plants ha^–1 for 10- or 20-day delays in sowing, respectively.  These combinations result in a higher leaf net photosynthetic rate, higher activities of leaf nitrate reductase, glutamine synthetase, grain glutamic pyruvic transaminase, and a lower sugar-N ratio during post-anthesis.

Increasing spike number is essential for achieving high wheat yield under dense planting conditions. However, dense planting reduces the ratio of red to far-red light (R/FR) in the canopy, which inhibits productive tiller formation and spike development. Sufficient assimilate supply is essential for spike differentiation and seed setting, but the mechanism of low R/FR affects spike development remains unclear. In this study, a pot experiment was conducted with supplemental FR light from wheat stem elongation to heading to simulate a low R/FR environment and to analyze its impact on young spike differentiation and the physiology of leaves and stems. The results showed that low R/FR significantly reduced wheat yield, primarily due to a decrease in both spike number and grains per spike. The developmental failure of high-position tillers (tiller III) contributed to over 65% of the total yield loss. Under low R/FR, stem elongation and spike differentiation of tiller III were synchronously arrested, with most tillers aborting during the stamen and pistil primordium stage. Low R/FR treatment significantly reduced the net photosynthetic rate (P_n) of the fully expanded top leaves of the main stem and tillers, thereby decreasing the overall supply of assimilates. Furthermore, low R/FR inhibited the export of carbohydrates from leaves to stems, leading to a significant increase in soluble sugar content in leaves and a marked decline in stems. The limited assimilate supply intensifies nutrient competition among tillers, causing more carbohydrates to be allocated to low-position tillers and ultimately leading to the developmental failure of tiller III spikes. Hormonal analysis revealed that low R/FR significantly reduced cytokinin (CTK) levels in young spikes of tiller III by inhibiting its synthesis and promoting degradation, while simultaneously inducing abscisic acid (ABA) synthesis, thereby directly inhibiting the developmental progression of young spikes. In summary, low R/FR signaling alters the hormonal balance of CTK and ABA in the young spikes of high-position tillers, coordinately regulating the export and allocation of carbohydrates, ultimately leading to the termination of spike development in high-position tillers.