中文摘要：

以扬麦20为材料，研究后期追氮时期对小麦花后LAI、叶绿素含量、光合物质生产与运转及产量的影响。结果表明：基本苗150×10^4、225×10^4苗·hm-2、氮肥运筹5：1：2：2（基肥：壮蘖肥：拔节肥：后期追肥）条件下孕穗期追肥处理产量高于其他处理；在基本苗225×10^4苗·hm^-2、氮肥运筹3：1：3：3条件下剑叶露尖追肥处理产量高于其他处理。剑叶露尖、孕穗期追施氮肥可维持群体花后较高LAI和SPAD值，延缓植株剑叶、倒二叶、倒三叶叶绿素降解速率，提高开花期、花后20d和成熟期干物质积累量，增加花后干物质积累量及其对籽粒的贡献率。

英文摘要：

In 2010--2011, Yangmai 20, with different planting densities [150 × 10^4 seeding · hm -2 （A1） and 225 × 10^4 seeding · hm-2 （A2）] was used, and nitrogen fertilizer was applied with the ratio of basic： tillering： elongation： late topdressing nitrogen[3 ： 1 ： 3 ： 3（C1） and 5 ： 1 ： 2 ： 2（C2）], to investigate the effects of late nitrogen topdressing stages [flag leaves stage（D1）, hooting stage（D2）, heading stage（D3） and anthesis stage（D4）] on post-anthesis leaf area index, chlorophyll content, the productivity and translocation of photosynthates and grain yield. The main results were as follows： The treatments of topdressing nitrogen at booting stage under A1C1, A1C2 and A2C2 could significantly improve grain yield. In addition, topdressing nitrogen at flag leaf stage under A2C1 also could improve grain yield. The treatments of topdressing nitrogen at flag leaf stage or booting stage could maintain high post-anthesis leaf area index, SPAD value, postpone chlorophyll degradation of the top three leaves, improve dry matter accumulation after anthesis and increase post-anthesis dry matter accumulation, which were the main reasons for grain yield increase under topdressing nitrogen at flag leaf stage or booting stage.