Water Source Partitioning and Hydrological Niche Differentiation of Riparian Vegetation Across Arid Inland River Corridors in Northwest China

ABSTRACT

Water scarcity in arid and semi‐arid inland river corridors constrains riparian vegetation and can influence community assembly through variation in water‐use strategies among coexisting species. We quantified plant water sources and hydrological niche differentiation (HND) among dominant riparian species across 10 representative corridors in Qinghai, Gansu and Xinjiang, Northwest China. We measured δ ² H and δ ¹⁸ O of xylem water, soil water (0–100 cm) and groundwater. To minimize potential cryogenic vacuum extraction artefacts, we conducted rewatering calibration experiments and corrected field xylem isotope signatures using established correction equations. A Bayesian isotope mixing model (MixSIAR) was then used to estimate the proportional contributions of shallow (0–40 cm) and deep (40–100 cm) soil water. Plant water uptake exhibited pronounced spatial and species variability. Tamarix chinensis exhibited strong plasticity in water‐source use across different habitats. Shallow soil water was the dominant source at the Heihe corridor (74.6% ± 8.3%), whereas deeper soil water became the predominant source at the Wulasitaihe corridor (64.9% ± 31.6%). In contrast, coexisting species in other corridors showed varying degrees of similarity and contrast in water‐source use, suggesting context‐dependent water acquisition strategies. Furthermore, spatial variation in water uptake patterns was associated with a pronounced hydrothermal gradient, with greater reliance on deeper water sources at sites with lower elevation and precipitation, and increased use of shallow water sources at sites with higher elevation and precipitation. Overall, HND in arid riparian zones appeared to be context dependent and may reflect interactions among species traits and local hydrological and edaphic conditions. These findings provide process‐based insights to inform ecological water allocation and restoration planning in Northwest China's inland river basins.