Abstract: Understanding the physiological mechanisms that trees employ to cope with drought-induced mortality is crucial for predicting their responses to a changing climate. Salix species exhibit distinct habit distributions, with Salix babylonica growing in wet habitats and Salix matsudana growing in relatively dry habitats. The objective of this study was to compare hydraulic and gas-exchange traits between these two closely related Salix species with contrasting natural habitats. S. matsudana had lower photosynthesis (A_max), lower stomatal conductance (g_s) and lower stem and leaf hydraulic conductance, but it exhibited higher water use efficiency (WUE_i), higher hydraulic safety and wider leaf-to-stem vulnerability segmentation as well as narrower, shorter and denser conduits and a lower ratio of leaf area to sapwood area than S. babylonica. These findings suggest that variations in hydraulic vulnerability and gas-exchange traits enable closely related Salix species to adapt to different habitats.

Key words: drought, Salix species, hydraulic vulnerability, gas exchange, water use effciency