Abstract: Grazing induces species turnover by livestock foraging and faeces input,which regulates plant diversity in grassland ecosystems. However,little is known about the correlation between species turnover and plant diversity in the grazed grassland ecosystems. We conducted a long-term grazing experiment in a desert steppe in Inner Mongolia and measured plant diversity at four levels by quadrat method. The results showed that:(1) At species level,species number decreased by 28%~52% and species composition significantly altered with the increase of grazing intensity； (2) At Family and plant functional group levels,number of Family and perennial forbs gradually decreased but that of annual plants increased with that increase. At community level,Simpson index and Shannon-Weiner index significantly decreased with increasing of the grazing intensities (P<0.05)； (3) Grazing significantly increased the species loss rate and turnover rate but had no significant effect on species recruitment rate in the grazed desert steppe； (4) Species loss rate and turnover rate were negatively correlated with plant diversity index (P<0.05). This study revealed the underlying mechanism of plant diversity change in the grazed desert steppe from the perspective of species turnover,and provided scientific support for optimizing the management and utilization of desert steppe.

Key words: Species loss, Species turnover, Desert steppe, Plant functional group, Plant diversity

摘要： 放牧引起草原生态系统物种更替，进而调控群落植物多样性。然而，放牧过程中物种更替与植物多样性改变间具有怎样的联系，目前缺乏系统的研究。本试验在内蒙古荒漠草原放牧实验平台进行，对群落植物多样性进行了调查。研究发现：随放牧强度的增加，群落物种总数下降了28%~52%且物种组成发生了明显的分异；随放牧强度的增加，群落科的数目和多年生杂类草的物种数逐渐减少，一年生植物的物种数增加，同时群落Simpson指数和Shannon-Weiner指数等显著降低(P<0.05)；随放牧强度的增加，物种损失率和周转率显著提高(P<0.05)，但物种获得率无显著变化；放牧荒漠草原物种损失率和周转率与植物多样性指数间呈显著负相关关系(P<0.05)。本研究从物种周转的角度揭示了放牧荒漠草原植物多样性降低的驱动机制，为优化荒漠草原管理和利用提供科学支撑。

关键词: 物种损失, 物种更替, 荒漠草原, 植物功能群, 植物多样性