Optimizing nitrogen fertilization to enhance wheat productivity by regulating canopy-root traits and photosynthesis under elevated atmospheric ammonia concentration

The response of crop growth and yield formation to nitrogen (N) application under elevated atmospheric ammonia (NH₃) concentrations remains unclear. We hypothesize that elevated NH₃ concentrations combined with different N application rates would affect wheat productivity through regulating canopy-root traits and photosynthetic capacity. Therefore, a three-year field experiment was conducted to clarify the effects of different NH₃ concentrations (atmospheric NH₃: 0.03 ± 0.01 mg m⁻³, ANH₃; elevated NH₃: 0.30 ± 0.05 mg m⁻³, ENH₃) and nitrogen application rates (0, 150 and 225 kg N ha⁻¹, denoted as N0, N1 and N2, respectively) on canopy and root growth, photosynthetic capacity, and winter wheat productivity. The results indicated that compared to the ANH₃ treatment: (1) ENH₃ treatment (EN1, 150 kg N ha⁻¹) effectively regulated both above- and below-ground growth of winter wheat. This resulted in a lower root-canopy (R/C) ratio, stimulating aboveground biomass and nitrogen accumulation, which ultimately increasing grain yield by 4.2 −6.5 % and partial productivity of nitrogen fertilizer (NPFP) by 3.3 −7.5 %; (2) ENH₃ treatment increased leaf area index (LAI) by 3.2 −5.3 %, net photosynthetic rate (Pn) by 3.1 −5.8 % and relative chlorophyll content (SPAD) by 3.6 −8.1 %, which helped maintain higher source activity in winter wheat. ENH₃ treatment increased source capacity by 5.4 −8.4 % and source-sink ratio by 3.2 −4.7 %. Compared to the EN1 treatment, EN2 treatment increased the R/C ratio by 2.8 −4.5 %, and both kernel number/leaf ratio (KNL) and kernel weight/leaf ratio (KWL) decreased by 8.1 −10.7 % and 4.7 −7.2 %, ultimately decreasing grain yield by 11.8 −14.4 %. Overall, N rate of 150 kg N ha⁻¹ under elevated NH₃ environment improved wheat yield by regulating canopy-root trait and establishing new source-sink balance. This study provides valuable scientific insights into the potential reduction of chemical N use for wheat production in future elevated NH₃ environment.