Abstract: Field sampling and laboratory analysis were conducted to study the morphometric changes in branches, leaves and flower buds, along with the diameter at breast height (DBH) of Populus euphratica under the same site conditions. The results showed that with the increase of DBH, leaf index, shoot length, and the number of leaves on each branch decreased, while leaf area and perimeter, petiole length, diameter of branches, number of flower buds on each branch, flower bud length and diameter increased. Correlation analysis showed that DBH had very significant negative or positive correlations with the morphological and quantitative parameters of branches, leaves and flower buds as indicated above, suggesting a gradual phase changes as the trees grow. ANOVA analysis showed that the branches length and number of leaves on each branch had significantly reduced in 4th diameter level. The branch diameter and number of flower bud on each  branch,  flower bud length and width synchronization began to stepwise increase significantly in 10th diameter level. Meanwhile leaf index and petiole length also started to significant changes in 10th diameter. The number and morphology in branch, leaf and flower bud showed significant difference on stages, and  was closely related to phase change of P. euphratica.

Key words: seedling, natural regeneration, water use efficiency, chlorophyll content, photosynthetic characteristics