Abstract: The amount and distribution of non-structural carbohydrates (NSC) is critical for plant growth and survival. Studies on the effects of nitrogen addition and precipitation change on NSC of seedlings will provide basis for revealing the mechanism of seedling death caused by drought and predicting natural regeneration and cultivation of seedlings under the background of climate change. In this study, we measured the contents of NSC and its components in organs of one-yearReaumuria soongorica seedlings under different precipitation conditions \[decreasing precipitation (W-), natural precipitation (W) and increasing precipitation (W+)\] and nitrogen addition levels \[N₀ (0 g N·m^-2·a^-1), N₁ (4.6 g N·m^-2·a^-1), N₂ (9.2 g N·m^-2·a^-1), N₃ (13.8 g N·m^-2·a^-1)\]. The results showed that the content of NSC in organs of R. soongorica seedlings ranged from 28.8 to 71.8 mg·g^-1, with the highest content in leaves and the lowest in stems. Nitrogen addition and precipitation change had significant effects on starch and total NSC contents in leaves and roots, but had no significant effects on starch and total NSC contents in stems. Across all precipitation conditions, nitrogen addition promoted the accumulation of starch and total NSC in leaves of R. soongorica seedlings. The positive effect of nitrogen addition was more significant when precipitation was increased by 30%. The contents of starch and total NSC in leaves under middle and high nitrogen (N₂ and N₃) were significantly higher than that in leaves under low nitrogen (N₁ and N₀). Under the treatment of low nitrogen and precipitation (N₁W^-), the contents of starch and NSC in leaves reached the minimum value, while the roots reached the maximum value, indicating that R. soongorica could adapt to the stress environment through redistributing NSC in different organs under low nitrogen and drought stress. Under natural precipitation and higher precipitation conditions, the contents of starch and NSC in roots decreased with the increasing nitrogen addition level, and the effects of high nitrogen treatments (N₂ and N₃) were significantly lower than that of the control (N₀). Therefore, leaves are the source of NSC of R. soongorica, and nitrogen addition will promote the accumulation of NSC in leaves. Such effect is closely related to water availability, with the effect being more significant when precipitation increased. However, excessive nitrogen can inhibit the accumulation of NSC in roots. Under drought stress and low nitrogen, R. soongorica could transfer NSC from leaves to roots to adapt to stress.

Key words: cotton, fertilizer application mode, residue management, soil organic carbon pool.