Abstract: Aims In-depth research on the hydraulic traits of plant xylem and leaf functional traits would be helpful to reveal their adaptation strategies to the environment, providing a theoretical basis for vegetation management and restoration. Methods This study focuses on three typical shrub species in the mixed Pine-Quercus forests of Beijing mountains areas: Vitex negundo, Grewia biloba, and Morus mongolica. Leaf functional traits (e.g., leaf area, net photosynthetic rate, leaf water potential, etc.) are determined through outdoor measurements and indoor experiments, while the xylem anatomical structure of the roots, stems, and branches of the three shrub species (e.g., vessel diameter, vessel density, etc.) is observed through sectioning, and hydraulic traits (e.g., specific hydraulic conductivity, hydraulic vulnerability index) are calculated, so as to understand the plant hydraulic structure and leaf functions and to reveal the adaptation strategies of these three shrub species to the shaded understory environment. Important findings (1) Significant differences in leaf morphology, hydraulics, and functional traits are observed among the three shrubs; Vitex negundo has smaller leaf area but greater specific leaf mass, with the highest specific leaf mass and net photosynthetic rate; Grewia biloba has the largest vein volume but the lowest net photosynthesis and transpiration rates; Morus mongolica has the largest leaf area and midday leaf water potential. (2) Notable differences are found in the xylem vessel characteristics and hydraulic traits of the roots, stems, and branches of the three shrubs; Vitex negundo’s aboveground water transport efficiency exceeds that of its underground part; Grewia biloba maintains a balanced water transport efficiency across all xylem parts, with the strongest resistance to embolism; Morus mongolica maintains high water transport efficiency in all parts, with the weakest resistance to embolism. (3) Correlation analysis indicates that the xylem hydraulic traits of the three shrubs influence most of the variations in leaf structural traits and hydraulic traits. (4) Principal component analysis reveals that Grewia biloba tends towards a conservative slow strategy, Morus mongolica leans towards a water-consuming fast strategy, and Vitex negundo’s adaptation strategy lies between the former two.

Key words: shrub, hydraulic structure, xylem, water transport, vessels, leaf functional traits, adaptation strategies