Abstract: The purpose of this study was to explore the ion distribution in organs of Populus euphratica adapting to saline environment and to reveal the physiological mechanism of salt-tolerance of P. euphratica. We measured the contents of Na⁺, K⁺, Ca²⁺, and Cl^- in root, trunk, old branch, young branch, and leaf of P. euphratica in high and low-salt habitats, and analyzed the differences in absorption, transport and distribution characteristics of various ions and their relationships with soil factors. The results showed that: (1) Foliar Na⁺ and Cl^- contents in high-salt environment were significantly lower than those in low-salt environment, while foliar K⁺ content was significantly higher than that of low-salt environment. However, no significant differences in contents of the ions in other organs were observed between those two habitats. The K⁺/Na⁺ of old branches, young branches, and leaves of P. euphratica in high-salt environment was significantly higher than that in low-salt environment, but the difference of Ca²⁺/Na⁺ was not significant. While the ability of roots to selectively absorb K⁺ in high-salt environment was significantly weaker than that in the low-salt environment, the ability to absorb Ca²⁺ was stronger, and the ability of other organs to selectively transport Ca²⁺ and K⁺ upward was also stronger in high-salt environment. (2) In low-salt environment, Na⁺, K⁺, and Cl^- were mainly distributed in leaves, and Ca²⁺ was mainly distributed in roots. The ability of trunk to selectively transport K⁺ and Ca²⁺ to young and old branches was stronger in low-salt environment than that in high-salt environment. In high-salt environment, Na⁺ and Ca²⁺ were mainly distributed in roots, and K⁺ and Cl^- were mainly distributed in roots and leaves. Roots had stronger ability to transport K⁺ and Ca²⁺ to old branches and young branches. (3) Na⁺ content in the roots and K⁺ content in aboveground organs of P. euphratica were significantly positively correlated with most soil factors. Root K⁺ content was negatively correlated with Na⁺ content in aboveground parts and most soil factors. The content of Ca²⁺ in trunk was negatively correlated with soil total salt content, electrical conductivity, and Na⁺ content. The content of Cl^- in young branches and trunks was significantly correlated with soil HCO₃^- and SO₄^2- contents. Soil water content was positively correlated with root Na⁺ content, and negatively correlated with root K⁺ content. Our results suggested that P. euphratica adapted to different saline environments mainly by regulating the allocation of salt ions in different organs, the separation and restriction of roots and leaves, and the ions regulation by branches, thus ensuring the ion balance and normal physiological metabolism in P. euphratica.

Key words: saline environment, Populus euphratica, ion absorption, ion transport