Abstract: Plant hydraulic traits maintain water transport and mediate responses to climatic variation, providing insight into water-use strategies and structural adaptation in desert vegetation. However, how desert shrubs coordinate hydraulic function and xylem structure to maintain water transport under extreme aridity remains unclear. We investigated Tamarix ramosissima, a desert shrub native to Northwest China, and quantified sixteen branch-related hydraulic and anatomical traits across eight sites spanning an extreme aridity gradient (mean annual precipitation: 32–160 mm). The main findings were as follows: (1) Sapwood-specific hydraulic conductivity (K_s) and native percentage loss of conductivity (PLC) remained relatively stable across sites, whereas leaf-specific hydraulic conductivity (K_l), embolism resistance (P₅₀), vessel density (VD), cell wall reinforcement (CWR), and wood density (WD) varied significantly. (2) Vessel and pit traits were tightly associated with hydraulic performance: thicker vessel walls, higher wood density, and more circular pit apertures were associated with greater embolism resistance, while larger pit membrane area was associated with higher K_s. No hydraulic efficiency–safety trade-off was detected. (3) Mean annual precipitation (MAP) mainly explained the variation in pit structure and hydraulic efficiency, whereas mean annual temperature (MAT) and mean temperature of the driest quarter (TDQ) primarily influenced vessel traits and hydraulic safety. Structural equation modeling revealed that MAT affected P₅₀ both directly and indirectly through vessel diameter. Overall, T. ramosissima maintains hydraulic stability through coordinated variation in vessel traits, pit characteristics, and wood density, with its hydraulic adaptation jointly shaped by precipitation and temperature.

Key words: Desert shrub, Environment gradient, Hydraulic traits, Xylem structure, Vessel-pit coordination