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To fully explore the effects of N on enhancing photosynthesis, grain quality, and yield of wheat (Ningmai 13), experiments with four nitrogen levels 0 (N0), 120 (N1), 180 (N2), and 240 (N3) kg N ha−1 and four ratios of basal to topdressing R0 (0:0), R1 (7:3), R2 (6:4), and R3 (5:5) were conducted. The basal N was applied to soil before sowing and the topdressing N was applied at jointing stage. The effect of N topdressing ratio on improving leaf area of photosynthetic efficiency was insignificant under the same N level. The effect of N fertilization level on increasing chlorophyll content was more significant than that of N topdressing ratio. Within the same N level, the canopy photosynthetically active radiation in R2 was higher than that in R1 and R3, and increasing N by 60 kg ha−1 significantly enhanced canopy photosynthetically active radiation. The effect of N topdressing ratio on photosynthetic rate, stomatal conductance, and transpiration rate were consistently R2 > R3 > R1; compared to N1, N3 could significantly increase photosynthetic rate. Increasing 120 kg N ha−1 significantly enhanced grain protein content, wet gluten, and sedimentation value, while the effect of N topdressing ratio was insignificant. Increasing N dose from 120 kg ha−1 to 180 kg ha−1 significantly enhanced yield, and the yields and harvest indexes in 2019, 2020, and 2021 were consistently R2 > R3 > R1. The findings suggested that the effect of increasing N dose (60 kg ha−1) was more considerable than that of N topdressing ratio, N3R2 (within the range of N application in this experiment) was more conducive to improving canopy photosynthesis, yield, and harvest index, and R3 was more conducive to increasing grain protein content, wet gluten, and sedimentation value. [ABSTRACT FROM AUTHOR]

(Aims) To clarify the mechanisms though which dense planting could alleviate the negative effect of the reducing N rate on yield, (Methods) an experiment with four nitrogen levels—0 (N0), 120 (N1), 180 (N2) and 240 (N3) kg N ha−1—and three plant densities—180 (D1), 240 (D2) and 300 (D3) × 104 basic seedlings ha−1—was conducted. (Results) Increasing plant density decreased the root length, root volume, root surface area and root tips of individual plant while it enhanced the aforementioned root traits in population. The chlorophyll content, photosynthetic rate, stomatal conductance and transpiration rate of the individual plants were decreased with the increase in plant density and enhanced with the increase in N level. The increasing density and N application rate enhanced the leaf area index, photosynthetic high-efficiency leaf area and canopy photosynthetically active radiation of population. N accumulation per plant was decreased with increasing density and was enhanced with an increasing N application level. Within the same N level, the N accumulation in the population, N production efficiency and N recovery efficiency were consistently D3 > D2 > D1. A high N application rate with high density was not conducive to improving the NR (nitrate reductase), GS (glutamine synthetase) and GOGAT (glutamate synthase) activities. The yield could be maintained as stable or improved if decreasing by 60 kg N ha−1 with increasing 60 × 104 basic seedlings ha−1 within the range of N application in this experiment. (Conclusions) These results indicated that the yield of wheat could be improved with less N application by adjusting the compensatory effects from the plant density in populations. [ABSTRACT FROM AUTHOR]

A better understanding of wheat cultivar impact on field N 2 O emissions could provide important information for cultivar improvement and selection to meet food security and greenhouse gas (GHG) mitigation. A 2-year field experiment was carried out from 2015 to 2017 on 12 leading cultivars released in the major winter wheat cropping regions of China since the 1940s. Field N 2 O emissions, wheat growth, and plant nitrogen uptake were determined. The results showed that both the cumulative and yield-scaled N 2 O emissions differed significantly among cultivars, varying on average from 1.64 to 2.10 kg N 2 O–N ha−1 and 232.65–529.37 mg N 2 O–N kg−1, respectively. As the wheat cultivar renewal progressed, the cumulative and yield-scaled N 2 O emissions declined significantly at the relative decrease rates of 0.2% yr−1 and 0.9% yr−1, respectively. In addition to wheat grain yield and biomass, amount of plant N uptake has been enhanced significantly over the past sixty years. The spike number per unit area, leaf dry matter, net photosynthesis rate, and transpiration rate also all increased, whereas wheat plant height decreased over the decades. Our findings demonstrate that lower N 2 O emissions can primarily be attributed to the greater N uptake of the newly high-yielding wheat cultivars, suggesting a great chance of ensuring food security and GHG mitigation simultaneously through cultivar selection and improvement. [Display omitted] • Both the cumulative and yield-scaled N 2 O emissions were lower with new wheat cultivars compared to old ones. • The reduction effects of yield-scaled N 2 O emissions with the cultivar improvement overperformed the cumulative N 2 O emissions. • Wheat yield and N uptake increased significantly along with the cultivar improvement. • Lower N 2 O emissions with new cultivars was associated with higher productivity and N uptake, and lower soil N availability. [ABSTRACT FROM AUTHOR]