中文摘要：

以低蛋白小麦品种宁麦9号和高蛋白小麦品种淮麦20为材料，研究了冬小麦不同生育时期冠层叶片氮素时空分布特征及其与植株氮含量的关系。结果表明，叶片氮含量在不同叶位间的分布因生育时期而异，拔节期、抽穗期和开花期叶片氮含量都呈现顶1〉顶2〉顶3〉顶4的趋势，而在药隔期及孕穗期，两品种顶2叶氮含量均大于顶1叶。施氮水平对叶片氮含量的影响因品种而异，宁麦9号上3叶氮含量对增施氮肥反应敏感，使顶4叶氮含量与上3叶的差值增大；淮麦20顶部4张叶片氮含量均增加。从时间变化看，两品种不同叶位叶片氮含量在施氮处理下以药隔期最高，之后随生育进程而下降。植株氮含量随施氮水平增加而增加，随生育进程而降低。相关分析表明，不同生育时期叶片氮含量与植株氮含量大都呈显著或极显著正相关，品种间略有差异。叶位叶氮差与植株氮含量的关系随品种和生育期而异，其中拔节期顶4叶与顶1、顶2叶氮含量的差值（LND4-1、LND4-2）与植株氮含量的相关性最佳，且不受品种的影响。因此，利用拔节期LND4-2和LND4-1可以较可靠地预测小麦植株氮素营养状况。

英文摘要：

It is very important to elucidate the plant nitrogen status in nitrogen fertilizer management of wheat, but the distribution characteristics of nitrogen in different organs involving in plant nitrogen status prediction is unclear. Field experiment was conducted using two wheat （ Triticum aestivum L. ） cultivars differing in protein content to investigate the distribution characteristics of leaf nitrogen content affected by different nitrogen application rates and the relationships with plant nitrogen status. The results showed the vertical distribution of leaf nitrogen content in different positions varied with growth stages. Leaf nitrogen content declined as the order of the 1st leaf 〉 2nd leaf〉 3rd leaf 〉 4th leaf from the top at jointing, heading and anthesis stages. At anther connective and booting stages, however, leaf nitrogen content in the 2nd leaf was higher than that in the 1st leaf. Moreover, the effects of nitrogen application rates on leaf nitrogen content varied with cultivars. For Ningmai 9, leaf nitrogen contents in top three leaves were more sensitive to increased nitrogen supply compared with 4th leaf, and the differences of nitrogen content between 4th leaf and top three leaves were enlarged. For Huaimai 20, nitrogen content in top four leaves was enhanced synchronously. Temporal changes of leaf nitrogen content varied with growth processes and nitrogen application rates. Leaf nitrogen content in different leaf positions was the highest at anther connective stage under nitrogen fertilization treatments. Plant nitrogen content increased with increasing nitrogen application rates, but reduced with growth processes. The correlation analysis showed that leaf nitrogen contents in most leaf positions were significantly positively correlated with plant nitrogen content though there were slight differences between two wheat cultivars. The relationships between the leaf nitrogen difference （LND） and plant nitrogen content varied with cultivars and growth stages, but LND4-1 and LND4-2 exhib