Abstract: Although ecologists have made great efforts and produced a large number of hypotheses and models attempting to explain species coexistence and the mechanisms of species diversity maintenance in plant communities, this problem remains unresolved. We investigate relationships between species diversity and the patterns of realized niche distribution of species along five soil resource gradients (C, N, P, K and H2O) in a species-rich Leymus chinensis herb meadow community, on the Songnen Plain of Northeast China. The results showed that despite niche differentiation between species, the degree of niche overlap between species was high. We present a mechanism for coexistence deriving from small-scale pattern competition. However, we must conclude that niche differentiation cannot solely account for maintenance of species diversity in this grassland community, and that greater attention should be paid to the longterm co-evolution of species biological properties.

Key words: Grassland community, Species diversity, Realized niche, Maintaining mechanism