中文摘要：

氮（N）沉降正在对全球森林生态系统产生显著影响。目前关于氮沉降如何通过影响树木不同径级细根碳水化合物含量，进而影响树木生理特征及生长的机制尚不清楚。本文以2年生油松（Pinus tabuliformis）幼苗细根为对象，研究了短期（2年）氮添加（0、3、6、9 g N·m-2·a-1，分别记为N0、N3、N6、N9）对不同径级（0～0.5、0.5～1和1～2 mm）细根中非结构性碳水化合物（NSC）和结构性碳水化合物（SC）含量的影响。结果表明：（1）0～0.5 mm细根中碳水化合物含量（512.97 mg·g-1）显著低于1～2 mm细根中碳水化合物含量（638.83 mg·g-1）。0～0.5 mm细根中NSC、可溶性糖和淀粉含量显著低于0.5～1及1～2 mm；（2）随着细根径级的增加，SC含量和纤维素含量呈增加趋势，而木质素含量呈降低趋势。N添加对3个径级细根中不同碳水化合物组分的影响不同。N添加对0～0.5和0.5～1 mm细根中NSC、可溶性糖和淀粉含量均无显著影响，但N9处理显著降低了1～2 mm细根中NSC和可溶性糖含量（16.20%和29.90%），对淀粉含量无显著影响。此外，N3处理显著增加了0～0.5 mm 细根中可溶性糖含量（69.65%）；（3）N添加对细根中SC、木质素含量没有显著影响，但N3处理显著增加了最细两级根（0～0.5和0.5～1 mm）纤维素含量（35.3%和57.0%），N9处理显著降低了1～2 mm细根中纤维素含量（30.39%）；（4）N3处理显著增加了0～0.5 mm细根中NSC/SC，而对另两级根系中该比率无显著影响。结果表明，N添加可能通过影响最细两级根（0～0.5和0.5～1 mm）中NSC、可溶性糖含量及NSC/SC影响植物细根的生理功能和生长。

英文摘要：

Increasing nitrogen （N） deposition significantly affects global forest ecosystems. It is not clear how N deposition affects carbohydrate contents of different diameter fine roots, which limits the understanding on the mechanism of plant physiology and growth affected by N deposition. We set up a N addition experiment with 2-year-old Pinus tabuliformis seedlings to examine the effects of different N addition levels on nonstructural carbohydrate （NSC） and structural carbohydrate （SC） contents in different diameter fine roots. Four N treatments were designed, including N0, N3, N6 and N9 （0, 3, 6 and 9 g N·m-2·a-1, respectively）. The results showed that： （1） the carbohydrate contents （512.97 mg·g-1） in fine roots with 0-0.5 mm diameter were significantly lower than those （638.83 mg·g-1） in fine roots with 1-2 mm diameter. The NSC, soluble sugar and starch contents in the fine roots with 0-0.5 mm diameter were significantly lower than those in fine roots with 0.5-1 and 1-2 mm diameter; （2） The SC and the cellulose contents had an increasing trend with the increase of fine root diameter, while lignin content showed a decreasing trend. Different responses of carbohydrate components in different diameter fine roots to N addition were observed in this study. N addition had no significant influence on the NSC, soluble sugar and starch contents in the 0-0.5 and 0.5-1 mm fine roots, except that N9 treatment significantly reduced the NSC and soluble sugar contents in 1-2 mm fine roots （by 16.20% and 29.90%, respectively） and N3 treatment significantly increased the soluble sugar content in the 0-0.5 mm fine roots （69.65%）; （3） Nitrogen addition had no significant influence on the SC and lignin contents. N3 treatment significantly increased the cellulose content in 0-0.5 and 0.5-1 mm fine roots （35.3% and 57.0%, respectively）, while N9 treatment significantly reduced the cellulose content in 1-2 mm fine roots （30.39%）; （4） N3 treatment significa