Abstract: Species diversity pattern is a hot topic in the forward field of international biodiversity research. Taking a degraded successional series (six communities distributed in 144 isolated patches) of fragmented Leymus chinensis meadow in Songnen Plain as test objects, this paper studied the spatial patterns of SymbolaA@, β, and γ diversities and related mechanisms. Eighty seven plant species were recorded, but none of them were distributed across all patches. L. chinensis + Kalimeris integrifolia community or L. chinensis community had higher SymbolaA@, β, and γ diversities, with more rare species and endemic species, while Kochia sieversiana community had lower SymbolaA@, β, and γ diversities, with few rare species and no endemic species. The γ diversity showed significant positive correlation with SymbolaA@ 〖KG*2〗diversity, but no correlation with β diversity. There was a significant power function correlation between the α〖KG*2〗diversity and the area of single patch of the six communities, but no correlation between the β diversity (Bray-Curtis similarity index, Sjk) and the area of single patch of the communities except for L. chinensis + K. integrifolia. Both the α and  γ diversity showed significant correlations with the mean patch area and total patch area, but the β diversity did not. The higher the species richness in the communities, the more the rare species and endemic species, the larger the possibility of species depopulation in local patches was. The importance of β diversity for shaping species diversity pattern was related to the degree of
habitat fragmentation.

Key words: Leymus chinensis meadow,  , plant species diversity,  , spatial pattern, plant community patch, Songnen Plain