中文摘要：

放牧对牧草的影响有两种相反的作用,既有降低生长的机制如减少光合面积,同时,也有促进生长的机制。本实验通过对短花针茅荒漠草原在不同放牧强度下植被地上、地下碳密度的研究,探讨放牧强度对短花针茅荒漠草原植被碳密度的影响。结果显示：在决定草地碳密度的两个值（生物量和含碳量）中,放牧主要通过影响草地的生物量来改变草地的碳密度;在对照区和各个放牧区中,植被地上、地下部分含碳量的值差异不显著（P〉0.05）,植被含碳量的值比较稳定,基本不受放牧干扰;轻度放牧可增加植被地上部分生物量,而中度和重度放牧使之减少;轻度、中度、重度放牧都使植被地下部分生物量减小。综合放牧对植被地上部分和地下部分碳密度的影响,得出各个放牧区的植被总碳密度均低于对照区,且随着放牧强度的增加,草地植被碳密度减少。

英文摘要：

The impact of grazing on grassland is often an opposing two sided effect： certain detrimental growth effect（such as reduced photosynthetic area） mingled with some other spontaneous beneficial growth effect.In this experiment,under different grazing intensities,carbon densities of aboveground and underground of desert steppe of Stipa breviflora vegetation were analyzed.The results show： the impacts produced by grazing on the two measurable criteria（biomass and carbon content） that can express carbon density were mostly derived from the changes of grassland biomass.On the controlled and all other grazing spots,the collected data of above and below ground carbon contents of vegetations did not deviate significantly（P 0.05）.The levels of the carbon contents of the vegetations are relatively stable and less likely disturbed by grazing.Light grazing can increase the aboveground biomass of vegetation while the moderate and heavy grazing tends to reduce the biomass.Overwhelmingly,light,moderate and heavy grazing all reduced the below ground biomass of vegetation.Based on the impacts on the aboveground and underground carbon density by different level of grazing,it can be concluded that the total carbon density of vegetation in grazing plots is lower than that in the control.It is very compelling that the vegetation carbon density decreased with the increased grazing intensity.