Abstract: In order to understand the changes of non-structural carbohydrates (NSC) in Populus× xiaozhuanica cv. Zhangwu seedlings under drought stress, we analyzed leaf water potential and contents of NSC, soluble sugar, and starch in different organs (leaf, stem, and root) with intensified drought conditions. The results showed that the contents of NSC and soluble sugar in leaves and roots increased, and starch content and water potential in leaves and soluble sugar content in stems decreased when soil water content dropped from 100% to 84% of field waterholding capacity. NSC contents in leaves and stems decreased and the ratio of soluble sugar to starch in stems and roots increased, while leaf water potential increased at predawn and decreased at midday when soil water content dropped from 84% to 41% of field water holding capacity. Leaf NSC content and water potential, stem NSC content, and root soluble sugar content increased, while leaf and root starch contents decreased when soil water content dropped from 41% to 31% of field water holding capacity. NSC and starch contents in leaves and stems, and leaf soluble sugar content and water potential decreased, whereas root NSC contentincreased when soil water content dropped from 31% to 20% of field water-holding capacity. Contents of NSC, soluble sugar and starch in leaves and stems increased, whereas root NSC content and ratio of soluble sugar to starch, and leaf water potential decreased when soil water content dropped from 20% to 16% of field waterholding capacity. Our results indicated that P. ×xiaozhuanica cv. Zhangwu seedlings would decrease leaf carbon storage but increase root carbon distribution and carbon consumption under natural drought. When hydraulic imbalance limits carbon transport and metabolism, seedlings may die due to root carbon starvation.

Key words: drought-induced mortality, organ difference, hydraulic failure, carbon starvation, staged response.