Abstract: Saline-alkaline soil is one of the common habitat types in desert steppe zone. Studying species niche and interspecific association is important for scientific management of salinealkaline ecosystems and vegetation recovery. Here, we analyzed interspecific association and niche among 26 dominant species along the gradient of soil moisture and salinity near the Huamachi saline lake in desert steppe zone in Dingbian County, Shaanxi Province. We discussed the relationship between niche overlaps and interspecific association. Methods used in this study included niche breadth, niche overlap, variance ratio method, χ² test and Ochiai index based on a 2×2 contingency table. The results showed that: (1) Across the soil moisture and salinity gradient, Kalidium gracile, Kalidium cuspidatum and Suaeda glaucahad the higher niche breadths than other species. Thus, those species were the constructive species in saline-alkaline soil of desert steppe zone. (2) The species with lower niche breadth had larger niche overlap, and competed the limited resources. The species with higher niche breadth had relatively larger niche overlap. Some species, such asSalicornia europaea and Suaeda salsa, had relatively higher niche breadth, but had lower niche overlap with a few species, indicating weak competitionbetween them. (3) Macro association was significantly positively correlated among 26 dominant species, whereas species pairs with Ochiai index greater than 0.6 only accounted for 17.85% of total species pairs. This result indicated that the plant community was in a relatively stablesuccession status, and that interspecific association degree was not close. (4) Ochiai index was significantly positively correlated with niche overlap along the soil moisture and salinity gradients, with a stronger correlation existed between Ochiai index and niche overlap along the salinity gradient. However, it was difficult to  reveal completely the inherent mechanism of interspecific association through the regression relationship between niche overlap and Ochiaiindex.

Key words: saline-alkaline soil, soil moisture, soil salinity, niche overlap, interspecific association.