Abstract:

Wheat grains obtain nitrogen continuously through decomposition and assimilation of nitrogen compounds from vegetative organs after anthesis. The ability of grains obtaining nitrogen is an important factor to improve the yield and quality of wheat. To assess the ability differences, the field experiments were conducted under different nitrogen application rates using two wheat cultivars, Yumai 47 (grain protein content 15.5%) and Yumai 50 (grain protein content 12.4%). The results showed that Grain of Yumai47 had greater ability of obtaining nitrogen from its vegetative organs than that of Yumai 50. To reveal the physiological mechanism causing the difference between the two cultivars, investigation was carried out for the dynamic changes of three nitrogen forms as assimilable nitrogen (AN), functional nitrogen (FN) and structural nitrogen (SN) in wheat plants in responses to varied nitrogen rates. The data showed that AN, FN, and SN were affected more significantly by cultivars than by nitrogen rates, especially after anthesis. AN content in stems and leaves of low grain protein genotype Yumai 50 declined continuously after anthesis, while that of high grain protein genotype Yumai 47 increased. In grains, AN content in Yumai 50 decreased slowly from 1.98–2.35 mg g–1 to 1.38–1.70 mg g^–1 after flowering. However, in Yumai 47 it declined sharply from 5.51–5.70 mg g^–1 to 1.15–1.38 mg g^–1 at 17 days after anthesis, and then increased from 1.15–1.38 mg g^–1 to 3.01–3.29 mg g^–1 under different nitrogen rates at maturity. The continuous increase of AN content in the stems and leaves from jointing to filling was closely related to the demand of grain protein formation in high protein genotype Yumai 47. FN content, which participated in absorption and assimilation within leaves, was not significantly different in two different genotypes. In addition to a sharper decrease of SN content in Yumai 47 than Yumai 50 after anthesis, SN content in stems and leaves showed a similar trend over development stages. They all increased with a peak at anthesis, and then exhibited a decreasing trend. In grains, changes of SN contents in two cultivars showed a similar trend, decreasing from anthesis to maturity, although Yumai 47 had a much higher SN content (3.70%–4.28%) at anthesis than Yumai 50(1.38%–1.74%). The results suggest that the higher SN content in grains at anthesis is the key factor caused greater nitrogen gain from the vegetative organs in Yumai 47. SN synthesis determines the direction of nitrogen flow, and the decomposition of SN in leaves and stems provided the key source for nitrogen translocation into grain.

Key words: Wheat, Assimilable nitrogen, Functional nitrogen, Structural nitrogen