中文摘要：

过度放牧不仅导致草地生产力下降,还会引起植物群落结构的改变,这可能与土壤理化性状和土壤生物组成的变化有关。探索土壤和植物的互反馈现象,对理解草原生态系统的稳定性具有重要意义。本研究选择内蒙古锡林郭勒草原相邻地块中度和过度放牧样地的2种土壤,在灭菌和不灭菌条件下,分别种植中度放牧样地优势物种大针茅（Stipagrandis）和过度放牧样地优势物种冷蒿（Artemisia frigida）2块样地共有物种冰草（Agropyron cristatum）和隐子草（Cleistogenes squarrosa）,测定了植物生物量和水分利用效率。结果表明,中度放牧样地优势物种大针茅表现出显著的负反馈作用,而过度放牧样地优势物种冷蒿,则表现出显著的正反馈作用。与不灭菌处理相比,灭菌后,4个物种地上部生物量与水分利用效率都有增加趋势,其中冰草和隐子草生物量和水分利用效率增加显著。

英文摘要：

Overgrazing resulted in productivity decrease of typical grassland and species composition change of plant community,which might be caused by the change of soil phy-chemial properties and soil microbes.Exploring plant-soil feedback has important implications for understanding the stability of grassland ecosystem.We sampled soil from two adjacent sites which were moderately grazed and overgrazed sites in Xilingol grassland.We used two sterilization treatments,and planted four species,the dominant species of moderately grazed site Stipagrandis,the dominant species of overgrazed site Artemisia frigida and the co-occurrence species Agropyron Cristatum and Cleistogenes squarrosa.Then we estimated shoot biomass and water use efficiency of the four species.Our results indicated that Stipagrandis showed negative feedback,while Artemisia frigida showed positive feedback.Compared with non-sterilized treatments,shoot biomass and water use efficiency of four species increased after sterilization,especially for Agropyron cristatum and Cleistogenes squarrosa,their shoot biomass and water use efficiency increased significantly.