中文摘要：

提高氮肥利用率依赖于氮肥优化管理及作物氮素营养效率的遗传改良。本文分析了作物氮高效的定义，并以玉米为例，分析了氮高效的生物学机制，提出了玉米氮高效品种的生物学特征。本文认为，玉米氮高效品种的生物学特征为：（1）在开花前，维持稳定的氮吸收，并将所吸收的氮素高效利用于穗的发育，提高小花结实率，为产量形成过程中的碳、氮积累提供较大的库；根系生长发育能力强，能建成较大的根系，以满足籽粒生长期氮素吸收的要求；有较强的叶片扩展能力，保持较大的叶面积。（2）在开花后，充分利用前期建成的根系，高效吸收土壤中的矿化氮，用于籽粒生长所需，从而减少叶片中氮素的输出，减缓叶片衰老（保绿性强），维持叶片较高的光合效率，为籽粒灌浆提供碳化合物。因此，在氮高效育种中，应注重穗部性状（大穗，结实能力强）、根系性状（发达的根系，功能期长）与叶片性状（保绿性好）的结合。

英文摘要：

Nitrogen （N） fertilizer use efficiency can be improved by two ways, that is, optimized N fertilizer management and genetic improvement of nitrogen use efficiency （NUE） of crops. In this paper, the biological mechanism of NUE is analyzed and the biological characteristic of N-efficient maize genotypes is proposed. It is suggested that, under N limitation conditions, a N-efficient maize genotype should be, （1） before flowering, a steady N uptake should be maintained the N should be utilized efficiently for ear development to enhance floret set and, therefore, a big sink is established for carbon and N accumulation during kernel filling stage. Root growth at this stage should vigorous, a trait essential for N uptake at late stage. Leaf expansion should fast so that a big canopy is established. （2） after flowering, N （especially the mineralized soil N） is taken up efficiently by the pre-established big root system, and is used for kernel growth. By this way, N export from leaves is slowed and leaf photosynthetic rate is maintained. As a result, more photosynthate is available for kernel filling. It is stressed that a big ear, a large root system and stay-green leaves arc most important secondary traits for breeding for N-efficient genotypes.