中文摘要：

放牧对草地植物种群遗传与进化产生重要影响，本研究利用 SSR 分子标记对4个不同放牧强度下垂穗披碱草种群遗传多样性进行研究，试验地选择在甘肃省甘南自治州玛曲县的阿孜试验站，利用8对多态性强的 SSR 引物对不同放牧压力下4个居群的800个个体基因组进行检测，每个位点的有效等位基因数在1．2267～1．9976之间。利用 popgene 分析发现不放牧垂穗披碱草种群遗传多样性最高，在3种不同放牧地，中等放牧强度的遗传多样性指数较高，其次为重牧，最后为轻度放牧。在不同放牧干扰下的4个垂穗披碱草种群的遗传分化系数为0．5168，基因流 Nm ＝0．2337，说明4个种群的遗传变异主要发生在种群之间。从种质资源保护角度来讲，不放牧对于垂穗披碱草种质资源的保护是有利的；从草地利用角度，中等放牧强度比较合理。

英文摘要：

Grazing can influence the population genetics and evolution of grassland plant species.To study the relationship between grazing and the potential for evolutionary differentiation and gene flow,we used SSR markers to study the genetic diversity of Elymus nutans .The experiment station investigated is based at Azi, in Maqu County in the Gannan region of Gansu Province.The grazing lands were divided into four levels ac-cording to different grazing intensities.Eight pairs of SSR primers were used to detect genetic diversity among 800 individual plants from the four populations under different grazing pressures.The effective number of al-leles per locus ranged from 1.2267 to 1.9976.We found that materials under moderate grazing intensity had the highest genetic diversity index,followed by the heavy and then light grazing levels.The genetic differentia-tion coefficient under different grazing levels is 0.5168.This suggests that genetic variation of the four popula-tions exists mainly among populations.In conclusion,no grazing or enclosure is effective for the conservation of E .nutans genetic resources.For grassland utilization,however,moderate grazing is relatively optimal.