Abstract: With the wide application of molecular biology technique in ecology,the study on phylogenetic diversity and maintenance mechanism of plant community has become as the research hotspots. In this study,a case study was carried out in the Xilingol typical steppe so as to reveal the phylogenetic diversity and difference of plant community as well as the driving factors of community construction at different slope positions in a typical steppe in Inner Mongolia.In our study,the phylogenetic tree of all species in the region was constructed based on the online APGⅢ system,and the phylogenetic diversity and structure of plant community at different slope positions were quantified by phylogenetic diversity index and net relatedness index. Moreover,the soil samples were collected,the soil nutrient content,water content,pH value and mechanical composition were detected,and their effects on the phylogenetic diversity were analyzed.The results are as follows:① The phylogenetic diversity of plant community was significantly decreased with the increase of slope position,and the coarse powder content was the dominant factor in soil mechanical composition; ② The aggregation level of phylogenetic structure of plant community was increased with the increase of slope position,and the available phosphorus content in soil was the dominant factor; ③ The net relationship index at all the slope positions was higher than zero,which indicated that the habitat filtering was the dominant factor of plant community construction.

Key words: phylogenetic diversity, phylogenetic structure, slope position, habitat filtering, typical steppe, Xilingol, Inner Mongolia