Abstract:Changes of community structure of Songnen grassland and its relation to soil factors were analyzed based on field experiment in 1996. Variation of species abundance within an alkaline grassland in Northeast China plant community was partitioned into four portions: 40% of environmental variation, 3% of spatial variation, 35% environmental-cross-spatial variation, and 20% of undetennined variation due to biological factors and random factors. A canonical ordination analysis on the species abundance data constrained by environmental variables revealed that alkali and salinity are the determinant factors of ecological processes for the whole growth season. However, the relative importance of nitrogen and soil water varies with time, so that effect of nitrogen is less evident than soil water in dry seasons, but vice verse in wet seasons.