In desert ecosystems of arid regions, water availability is severely limited. Root systems, serving as critical functional organs of plants, exhibit spatial fractal architectures that directly influence plant water acquisition capacity. Populus euphratica Oliv., a typical deciduous tree species in arid zones characterized by well-developed root systems, presents a valuable model for investigating dimorphic root architectural features. Such research provides crucial insights into the adaptive strategies employed by desert vegetation in response to environmental constraints. This study selected naturally occurring, healthy Populus euphratica specimens within the Xinjiang Ebinur Lake Wetland National Nature Reserve as research subjects. Employing TRU tree radar technology integrated with three-dimensional modeling and statistical analyses, we investigated the response patterns of topological fractal characteristics in P. euphratica root systems along water availability gradients, thereby elucidating the adaptive mechanisms governing root system plasticity in response to hydrological variability. Results revealed that: (1) Soil moisture content exhibited a significant decreasing gradient with increasing distance from the riparian zone (declining from 18.36% to 4.58%), while the vertical soil profile demonstrated a contrasting stratification pattern, characterized by a progressive increase from moisture-depleted surface horizons (0-20 cm; 3.78%) to water-enriched deeper soil layers (>200 cm; 11.50%). (2) P. euphratica root density exhibited a non-linear response pattern with increasing distance from the riverbank, initially increasing before subsequently declining across the lateral gradient, with values ranging from a minimum of 1.75 g/cm³ to a maximum of 2.58 g/cm³. Peak root densities were predominantly concentrated in sampling plots located 2-2.5 km from the river. Vertical distribution patterns varied systematically across the riparian-upland gradient: both proximal riparian zones (0-0.5 km) and distal zones (4-4.5 km) displayed unimodal root density distributions, with maximum concentrations occurring in the intermediate soil horizon (50-150 cm). In contrast, the intermediate transition zone (2-2.5 km) exhibited a distinct bimodal distribution pattern, characterized by maximum root density values in the deeper soil strata (>200 cm). (3) The relationship between P. euphratica root density and soil moisture content exhibited significant spatial variation. In both riparian (0-0.5 km) and distal zones (4-4.5 km), root density displayed a unimodal response to increasing soil moisture, initially increasing before subsequently declining. Conversely, in the intermediate zone (2-2.5 km from the river), root density showed a positive correlation with soil moisture content. Vertical analysis revealed that the spatial distribution of P. euphratica root systems exhibited a linear relationship with soil moisture gradients. Specifically, shallow soil horizons (0-20 cm) demonstrated a significant positive correlation, while deeper horizons (100-150 cm) exhibited a significant negative correlation.