Abstract: Community phylogenetic information is one of the primary contents in biodiversity research. Slope position is an important topographic factor affecting species composition of plant community. It is important to examine the relationships between slope position and community phylogenetic diversity and structure for improving our understanding of distribution patterns of community phylogenetic diversity and assembly mechanisms. Here, we examined the distribution patterns of the community phylogenetic diversity and phylogenetic structure of alpine shrubs in the northeastern QinghaiTibet Plateau (Qinghai Province) along slope position at the herbaceousplant community level, woodyplant community level, and all-plant community level. We found that the phylogenetic diversity of the herbaceousplant and all-plant communities presented a unimodal pattern with the decreasing slope position with highest diversity on the middle slope. Neither the phylogenetic diversity of woodyplant communities nor the phylogenetic structure of the communities (herbalplant community, woodyplant community and allplant community) showed variation along slope position. Soil physicochemical factors (soil total nitrogen, total phosphorus, soil water content and pH) had higher ability to interpret phylogenetic diversity than phylogenetic structure. Especially, soil water content had significant effects on the phylogenetic diversity of herbaceousplant community and all-plant community. In conclusion, the slope position affected the phylogenetic diversity of the shrub community by changing species composition of the herbaceousplant communities rather than the woodyplant communities and had no significant effects on community phylogenetic structure.

Key words: methyl bromide, concentration distribution, seatoair flux, sources and sinks.