Shrubs can improve soil structure and the micro-environment during growth, enriching soil nutrients in their vicinity compared to the surrounding areas which is known as soil "fertile island" effect. The formation and development of the "fertile island" effect significantly influence soil ecological stability as well as the structure and function of vegetation ecosystems in arid regions, which play a critical role in mitigating wind-sand hazards and safeguarding oasis ecological security. Tamarix ramosissima Ledeb. and Calligonum caput-medusae Schrenk. are two dominant shelterbelt species in the protective shelterbelt system of desert-oasis transition zone at the southern Tarim Basin, perform pivotal ecological functions including windbreaking and sand fixation, desertification control, climate regulation, and stabilization of regional ecological equilibrium. In present study, we combined field sampling and laboratory experiments to reveal the differences in soil improvement functions between these two species. Soil nutrient content was analyzed at different depths under varying canopy cover densities (30% and 50%) of both shrubs and compared with bare land in order to investigate their "fertile island" effects and associated variations. According to the results (1) Both shrubs demonstrated significant soil "fertile island" effects, but these were species-specific. At the Tamarix site, the amounts of soil organic content (SOC), total nitrogen (TN), and total phosphorus (TP) were 265%, 220%, and 230% higher than those of bare land; at the Calligonum site, they were higher by 195%, 120%, and 185%. The enrichment rates of SOC, TN, and TP at the Tamarix site were 2.17±0.32, 4.80±0.16, and 3.04±0.25, respectively, while those at the Calligonum site were 1.84±0.24, 4.39±0.15, and 2.63±0.18. (2) The strength of the soil "fertile island" effect varied with vegetation coverage. Both the soil SOC, TN, TP contents and their enrichment rates were highest at the Tamarix site with 50% vegetation coverage. (3) The vertical distribution of soil nutrients was also species-specific. At the Tamarix site with 50% coverage, the content and enrichment rate of TP in all soil layers exceeded those of other sites, while the enrichment rates of SOC and TN peaked at lower depths (80-140 cm). In general, Tamarix showed a stronger soil "fertile island" effect than Calligonum. Therefore, Tamarix could be prioritized in species selection for shelterbelt forest construction at the southern margin of the Tarim Basin. These findings were significant for ecological restoration, protection, and sustainable development in arid regions as well as combating against desertification in the southern Taklamakan.