Abstract: We analyzed seasonal changes of non-structural carbohydrate (NSC) contents in different organs (leaf, branch and root) and leaf litter of an introduced species Populus alba ×P. berolinensis and a native species Ulmus pumila in Horqin Sandy Land. Carbon allocation and storage strategies of those two species were compared. Results showed that for P. alba × P. berolinensis, contents of soluble sugar and NSC decreased and then increased while starch content gradually decreased in leaves over season; soluble sugar content and ratio of soluble sugar to starch increased and then dropped, starch content decreased and subsequently rose in branches and roots over season. In contrast, for U. pumila, NSC content in branches remained unchanged while contents of soluble sugar, starch and NSC in roots firstly decreased and then increased from spring to autumn. Soluble sugar contents in leaves of P. alba × P. berolinensis were higher than those of U. pumila in spring and summer. Except for branches in autumn, starch contents in all organs of U. pumila were higher than that of P. alba × P. berolinensis, and the ratio of soluble sugar to starch was lower than that in P. alba × P. berolinensis. Contents of soluble sugar, starch, and NSC in leaf litters of U. pumila were higher than those of P. alba × P. berolinensis. Therefore, NSC is mainly used for growth and consumption, implying stronger competition for P. alba × P. berolinensis in the community. NSC is more stored as starch, which may contribute to the stronger stress resistance of U. pumila and facilitate the carbon cycle between plant and soil.

Key words: shelterbelt decline, carbon allocation, introduced tree species, native tree species, adaptive strategy, matching site with tree species