Abstract: High nitrogen (N) efficient varieties (‘Longmu 806’ ‘Zhaodong’) and low N efficiency varieties (‘Gongnong No.1’‘Longdong’) were used to study the genotypic variations in total N uptake and N partition with different nitrogen efficiency and its relation to root morphology at four N levels (2.1,21,210 and 420 mg·L^-1). Plant height,aboveground biomass,root dry weight,total root length,and root volume of high N efficient varieties were greater than that of low N efficiency varieties (P<0.05). The higher N accumulation in root in high N efficient varieties at low N supply (2.1 and 21 mg·L^-1). The higher N accumulation in aboveground in low N efficient varieties at low N supply. There was a significant positive correlation (P<0.05) between root morphological parameters and total nitrogen,and nitrogen uptake was primarily controlled by root dry weight at low N supply,direct path coefficients were 1.230 and 1.102. When N is a limiting factor for plant growth,root morphology became more important in N uptake,and root dry weight was more important.

Key words: Alfalfa, Nitrogen efficiency, Root, Nitrogen uptake

摘要： 以高效型苜蓿（‘龙牧806’‘肇东苜蓿’）和低效型苜蓿（‘公农1号’‘陇东苜蓿’）为试验材料，采用营养液砂培法，在4个供氮量下（2.1，21，210和420 mg·L^-1），研究紫花苜蓿苗期氮素吸收、分配的氮效率型差异及其与根系形态之间的关系。结果表明高效型苜蓿品种的株高、地上生物量、根重、总根长和根体积均显著高于低效型品种（P<0.05）；供氮量较低时（2.1和21 mg·L^-1），高效型向根系分配了较大比例的氮素，而低效型则向地上部分配了较大比例的氮素，根系形态参数与总氮量呈显著正相关（P<0.05），且根重对氮素吸收的直接作用较大，直接通径系数是1.230和1.102。因此，在氮胁迫下，根系形态对氮吸收效率起重要作用，尤其是根系形态中的根重对其影响较大。

关键词: 苜蓿, 氮效率, 根系, 氮素吸收