关键词: 玉米, 施氮方式, 施氮量, 花后高温胁迫, 光合特性, 抗氧化特性, 产量

Abstract: From 2023 to 2024，a field experiment was conducted for two consecutive years to study the effects of nitrogen application methods［split root application（S1），root‐leaf coordination（S2））］and nitrogen application rates［180 kg/ha（N1），240 kg/h（N2），and 300 kg/ha（N3）］on the photosynthetic characters，antioxidant properties and yield of maize under natural temperature（NT）and post‐flowering high temperature（HT） conditions. The aim was to select high‐temperature‐tolerant nitrogen fertilizer management mode in dryland farming area of North China. The results showed that under post‐flowering high temperature stress，the leaves SPAD values，net photosynthetic rate（Pn），and ascorbic acid（AsA）content of maize all decreased，while the activities of superoxide dismutase（SOD），peroxidase（POD），and malondialdehyde（MDA）content all increased，and the grains number per ear and 1 000‐grain weight all decreased，resulting in a decrease of yield. Comparisons among different nitrogen application methods showed that，the SPAD value，Pn，AsA content，SOD activity，POD activity，grains number per ear，1 000‐grain weight，and yield of S2 treatment were significantly higher than those of S1 treatment，and MDA content was significantly lower than that of S1 treatment in 2 a，among which the yield increased by 10.73% and 10.21% under HT，respectively.Comparisons among different nitrogen application rates showed that，the SPAD values，Pn，AsA contents，SOD activities，POD activities，grains number per ear，1 000‐grain weight，and yields of N2 and N3 treatments were higher than those of N1 treatment，and MDA contents were lower than that of N1 treatment in 2 a.The N2 treatment reached a significant level.Among them，the yields of N2 treatment significantly increased by 29.05% and 28.77% compared with N1 treatment under HT，respectively.The linear fitting of nitrogen application rate and yield showed that the theoretical optimal nitrogen application rate was 240.16—243.53 kg/ha under NT，and 257.47—260.36 kg/ha under HT.Overall，the optimal nitrogen application rate of S2 treatment was higher than that of S1 treatment，and the theoretical optimal yield of S2 treatment was higher than that of S1 treatment. Correlation analysis revealed that under HT，yield was significantly positively correlated with SPAD value，Pn，AsA content，grains number per ear and 1 000‐grain weight，and significantly negatively correlated with MDA content. In conclusion，it is recommended to promote the nitrogen application method of root‐leaf coordination in the dryland farming area of North China. Nitrogen application amount of 240 kg/ha should be adopted under natural temperature years，and 260 kg/ha under post‐flowering high temperature years to effectively alleviate high temperature stress and achieve high and stable yield of maize.

Key words: Maize, Nitrogen application method, Nitrogen application rate, High temperature stress after flowering, Photosynthetic characteristics, Antioxidant properties, Yield