Objective This study aims to investigate the characteristics and influencing factors of leaf functional traits of Populus euphratica at different tree ages. Additionally, it aims to explore the intraspecific variation and adaptation characteristics of leaf functional tarits. The findings of this study aim to establish a theoretical basis for protection and management of P. euphratica.

Method In this study, P. euphratica trees of different tree ages were selected as research object, and the changes in leaf morphology, photosynthetic physiology, nutrient traits and their responses to tree age and soil factors were studied by means of correlation analysis and variance decomposition.

Result With the increase of tree age, leaf dry matter content, chlorophyll a content, chlorophyll b content, total chlorophyll content, leaf carbon content, leaf nitrogen content, and leaf phosphorus content increased, while specific leaf area and leaf thickness decreased. There was a certain correlation between the leaf functional traits, in which chlorophyll a content, chlorophyll b content and total chlorophyll content were significantly positively correlated with leaf dry matter content, leaf carbon content, leaf nitrogen content, and leaf phosphorus content, negatively correlated with specific leaf area and leaf thickness, and the relationship between traits was regulated by tree age. The specific leaf area, leaf dry matter content, chlorophyll a content, chlorophyll b content, leaf carbon content, leaf nitrogen content and leaf phosphorus content were mainly affected by tree age and soil pH, and leaf thickness and total chlorophyll content were mainly affected by tree age and soil total nitrogen content. It showed that tree age, soil pH and soil total nitrogen content were the main influencing factors of leaf functional traits, and compared with soil factors, tree age had a higher explanation rate for the variation of leaf functional traits, which could explain 15.1%−38.1% of the variation.

Conclusion With the increase of tree age, P. euphratica adapts to environmental changes through certain trait variations and trait combinations, and the influencing factors of leaf functional traits are different. Among them, tree age and soil factors jointly regulate the change of leaf functional traits, and tree age may play a more critical role in determining the variation of leaf functional traits in P. euphratica.