This study was conducted in the temperate steppe of Ningxia Luoshan Nature Reserve. The dominant plant species at different altitudes were selected as research objects： Carex aridula at 2374 m， Stipa grandis at 2132 m and 1823 m， and Stipa breviflora at 1566 m. Xylem water from the dominant plants， precipitation， and soil water from the 0-100 cm layer were collected. The stable hydrogen （δD） and oxygen （δ¹⁸O） isotopic compositions were determined. The MixSIAR mixing model was employed to quantitatively analyze the utilization ratios of plants to potential water sources. The results showed that： （1） Soil water δ¹⁸O exhibited significant spatial heterogeneity， generally decreasing with increasing altitude， with significantly lower isotopic values in soil water at high altitudes compared to low altitudes. （2） The water use patterns of dominant plants at different altitudes showed significant differences during the growing season （June-July）. Carex aridula at high altitude shifted its main water absorption source from the 40-60 cm soil layer （23.8%） in June to the 0–20 cm layer （26.9%） in July. Stipa grandis at mid-altitude changed from absorbing water from all soil layers （0-100 cm） with proportions ranging between 15.9% and 22.3% in June to concentrating water uptake in the 0-40 cm layer in July. Stipa breviflora at low altitude stably utilized water from the 0-20 cm shallow soil layer， with a utilization proportion between 27.8% and 32.4%. This study provides an important scientific basis for understanding the water use strategies of dominant species and the water balance in the Luoshan temperate steppe ecosystem.

Temperate mountainous grassland  /  Altitude  /  Dominant plant  /  Hydrogen isotope  /  Water sources