Abstract: To elucidate the response of non-structural carbohydrates (NSC) of Ulmus pumila seedlings to nitrogen deposition and increasing precipitation, we analyzed concentrations of soluble sugar, starch, and NSC in different organs (leaf, branch, stem, coarse root and fine root) under a full-factorial experiment, i.e., four levels of nitrogen deposition (0, 5, 10, and 15 g N·m^-2·a^-1) and three precipitation levels (natural precipitation, 50% and 100% increase in precipitation) with randomized block design. The results showed that increased precipitation caused the decrease of soluble sugar concentrations in branches, stems, coarse roots and fine roots, but did not affect leaf soluble sugar concentration under treatment without nitrogen addition. With increasing nitrogen deposition, under natural precipitation, soluble sugar concentrations increased in leaves, branches and stems but decreased in fine roots. There were pronounced interactions between nitrogen deposition and increased precipitation on NSC concentrations in each organ of U. pumila seedlings. Under 15 g N·m^-2·a^-1 nitrogen addition treatment, compared to natural precipitation, starch concentrations in each organ decreased under 50% increase in precipitation, while soluble sugar, starch and NSC concentrations in branches, stems and coarse roots decreased under 100% increase in precipitation. Therefore, nitrogen deposition would increase NSC storage of U. pumila seedlings, and 50% increase in precipitation is conducive to promote seedling growth.

Key words: water and nitrogen coupling, carbon allocation, soluble sugar, starch, climatic change