Abstract: The effect of nitrogen fertilizer application rate on the characteristics of individual plant and population of Leymus chinensis (Trin.) Tzvel.,the dominant species,was studied by a field trial on natural grassland in Taipusi Banner,Inner Mongolia Autonomous Region from May 2007 to September 2008.The results show that nitrogen fertilizer significantly improved the growth of L.chinensis.However the response of both individual plant and population to fertilizer application rate was not linear,and reached to a maximum at 50kg urea穐m^-2.At this fertilizer rate,the leaf width increased by 17.0% in the first year and 10.3% in the second year,plant height increased by 74.0% and 46.5%,total plant internode length increased by 361.6% and 81.6%,population density increased by 155.6% and 54.3%,and aboveground biomass increased by 633% and 229%,respectively.It was also observed that there was a remarkable between-year variation in the characteristics of both individual plant and population in the control as affected by the fluctuation of rainfall.

Key words: Nitrogen fertilizer, Leymus chinensis(Trin.) Tzvel., Individual plant characteristics, Population density, Aboveground Biomass

摘要： 在内蒙古太仆寺旗的天然草地上,于2007年5月至2008年9月连续2年研究了不同氮肥施用量对草地建群种羊草(Leymus chinensis(Trin.)Tzvel.)的个体生长特征、种群密度及种群地上生物量的影响.结果表明,施用氮肥可显著促进羊草的生长,但施肥效果并未随氮肥用量的增加呈直线上升,而是在50 kg尿素/hm²时达到最高水平,施用效果最为显著(P<0.05),与对照相比叶宽两年增幅分别为17.0%和10.3%、株高分别增加74.0%和46.5%,茎节总长分别增加361.6%和81.6%,种群密度分别增加155.6%和54.3%,种群地上生物量分别增加633%和229%.对照区羊草个体和种群特征受降水量波动影响出现显著的年际变化.

关键词: 氮肥, 羊草, 个体特征, 种群密度,地上生物量