Spatial distribution and regulatory mechanism of available soil nutrients is widely considered as an important issue in plant and soil relations in arid areas, in which the impact of interaction between different plant populations on spatial distribution of soil available nutrients has been little reported. According to Liang et al. (2010), soil-plant interactions and sustainability of eco-agriculture in arid region is a crucially important topic to address. Manas River watershed is situated at the areas between northern slope of Tianshan Mountain and south edge of Junggar watershed, where the alluvial fan area of the watershed is a severely saline and alkaline eco-agricultural region in northwest China. In this study, a comparative experiment was conducted to reveal the "fertile island" features of soil available nutrients around the halostachys (Halostashys caspica) shrub under the conditions of single population and companion population with salsola (Salsola collina) in the alluvial fan areas of Manas River watershed. The results showed that soil "fertile island" effect around halostachys shrubs was mainly focused on the soil surface, and tended to be weakened gradually at intervals of 0.6m outward the standing point, and to decrease along the soil depth. Under the condition of solitary halostachys population, there existed a clear enrichment distribution for both soil alkaline nitrogen (AN) and available potassium (AK) along with the standing center. In the surface soil of 3m outward from standing point, the concentrations of these two nutrients were gradually lowered from 2.75 g/kg and 56.67 mg/kg to 1.66 g/kg and 29.0 mg/kg, and decreased significantly along the soil profile (P<0.05), yet were significantly higher than the corresponding values of bare land. For the change in available phosphorus (AP), there was a wholly deficit status in comparison with that of bare land, whose average content of AP was lower by 25.33% than the bare land. This result indicated that the Halostachys population has the ecological function to improve the enrichment of nitrogen and potassium, but lead to the consumption of phosphorus. However, no clear variation trend was observed along with the soil profile. On the other hand, under the symbiotic conditions of Halostachys and Salsola, the concentrations of three available nutrients in either the soil surface or along the soil profile were significantly higher than those of bare land. Furthermore, the soil AN concentrations were in general lower in symbiotic condition than those of solitary condition, but the AP and AK concentrations were greater in the former than those of the latter. Halostachys as a desert plant has a significant effect on the soil fertility, and the symbiotic interaction of Salsola leads to a more extensive and complementary influence on the "fertile island" effect of Halostachys shrub. Importantly, the loss of soil AP components in simplex Halostachys population can be reversed under the symbiotic conditions with Salsola population. This founding provides a theoretical potential for understanding plant and soil relations in arid saline regions, and a new practical approach to manage saline and alkaline soil for scientists and policy makers.