Effects of shading at different filling stages on nitrogen accumulation and translocation in wheat at different nitrogen rates

Effects of shading at different filling stages on nitrogen (N) accumulation and translocation in wheat at different N rates was studied in the field experiments, which were carried out on high fertility soil with organic matter 12.94 g/kg, total N 0.78 g/kg, alkali-hydrolysable N 84 mg/kg, available P 11.84 mg/kg and available K 83 mg/kg in Zhongcun village, Longkou city, Shandong province, China, using the cultivar “Jimai 20” that has high yield and strong gluten potential. Three N fertilizer rates were used: 0, 168 and 276 kg/ha. Four shading treatments were designed: NS (no shading), SE (shading at early filling stage, from 1 day after anthesis to 12 days after anthesis), SM (shading at middle filling stage, from 13 days after anthesis to 24 days after anthesis ), and SL (shading at later filling stage, from 25 days after anthesis to 36 days after anthesis). The shading environment was created by using black polypropylene fabric with 40% light penetration. Each treatment had three replicates, and the plot area was 3 m×8 m. The seedling density was 150 plant/m2. The results indicated that the activities of nitrate reductase (NR) and endopeptidase (EP) in flag leaves decreased during shading at early filling stage, but after shading, the NR activities of 0 kg ha treatment (N0) and 168 kg/ha treatment (N1) were not significantly different from no shading condition, the NR activity of 276 kg/hm2 treatment (N2) was lower significantly than no shading condition. The EP activities of N2 increased, which improved protein degradation. N translocation accelerated at middle filling stage, so the amount of N transferred from vegetative organs and N translocation efficiency increased. However, the nitrogen assimilation amount after anthesis and kernel yield and protein yield of N2 were lower significantly than that of N1. Shading and after shading at middle filling stage decreased the activities of nitrate reductase (NR) and endopeptidase (EP) in flag leaves, and increased the EP activities of all N treatments compared with no shading condition, and the EP activities of N2 were higher significantly than that of N1.Shading at later filling stage decreased the NR activities of all N treatments, the EP activities of N0 and N1, but increased the EP activity of N2, as compared with no shading condition. In comparison with N1, the amount of N transferred from vegetative organs, N translocation efficiency and the contribution proportion for kernel N increased in N2, but the NR activity and N assimilation amount after anthesis and protein yield did not change significantly. The amount of N transferred from vegetative organs, N translocation efficiency and the contribution proportion for kernel N were the highest under shading at early filling stage, and the lowest under shading at later filling stage. The N assimilation amount after anthesis, kernel yield and protein yield were the highest under shading at later filling stage, and the lowest under shading at early filling stage, whether 0, 168 or 276 kg/ha N was supplied.