Effects of Postponing Nitrogen Fertilizer Application on Flag Leaf Physiological Characteristics and Yield of Spring Wheat Under High Temperature Stress

The effects of postponing nitrogen fertilizer on membrane lipid peroxidation, antioxidant enzyme activity, osmotic adjustment substance content in flag leaves and yield of spring wheat (Triticum aestivum L.) under high temperature stress were investigated, and the scientific fertilization methods to alleviate high temperature premature senescence of spring wheat after anthesis were screened.

From 2022 to 2023, Ning 3015 was used as the test material, and the test was carried out in the test base of the sixth team of Pingjipu Agricultural Reclamation in Ningxia. The split-plot experiment design was adopted. The main plot was temperature, with (25±2)℃ (normal temperature, RT) and (35±2)℃ (high temperature, HT), and the sub-plot was nitrogen fertilizer operation. The total amount of nitrogen application was constant, with 300 kg·N·hm^-2: in 2022, G1 (30% of nitrogen application at tillering stage), G2 (30% of nitrogen application at jointing stage), G3 (30% of nitrogen application at booting stage), G4 (20% of nitrogen application at heading stage) and G5 (20% of nitrogen application at filling stage) were set up; in 2023, a total of three fertilization methods, including G1, G3 and G5, were selected from the previous year 's test results. Samples were taken every 5 days from the flowering stage to determine the indexes of membrane lipid peroxidation, antioxidant enzyme activity and osmotic adjustment substances in flag leaves.

Superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) activities, proline (Pro) content in flag leaves and yield in two consecutive years of Nitrogen Fertilizer Transportation Experiment (NFTO) reached the highest under the G5 treatment, while malondialdehyde (MDA) and membrane permeability were the lowest under the G5 treatment, which were significantly different from the G1 treatment (P<0.01). According to Pearson's (Pearson) correlation analysis, it was shown that spring wheat grain yield was significantly positively correlated (P<0.05) with SOD, POD, CAT activities and proline content, while it was significantly negatively correlated (P<0.05) with MDA content and membrane permeability. Comprehensive evaluation showed that the ordering of the principal component scores of nitrogen fertilizer transport in 2022 and 2023 was G5>G3>G4>G2>G1 and G5>G3>G1, respectively, and the trend of the results of the two-year test was consistent.

Appropriate nitrogen fertilizer postponing could reduce the membrane lipid peroxidation of spring wheat flag leaves under high temperature stress, increase the activity of antioxidant enzymes and the content of osmotic adjustment substances, and then increase the yield. In this experiment, the treatment of 20% total nitrogen application at filling stage was more suitable.