Abstract: With three typical saline-alkaline grassland soils in Songnen Plain as test objects, this paper measured their electrical conductivity, iron composition, and organic carbon, and compared the nitrogenfixing Cyanophyta comunities on the soils. The results showed that the physicochemical propertie of test soils and the Cyanophyta communities had their own characteristics. There were seven genera of nitrogen-fixing Cyanophyta, with filamentous cyanobacterium as the dominant. The Cyanophyta had a slightly different distribution on the three saline-alkaline soils, with the richest species on moderate saline-alkaline soil, and different species had different selection of habitats. Songnen Plain is a kind of fragile ecosystem, and its soil physicochemical characteristics and algal distribution are relatively special. Therefore, its ecoprotection and management should be enhanced.

Key words: Megranate orchard, Arthropod community, Dynamics