中文摘要：

选择苏北沿海5、9和15年生杨树人工林作为实验地，采用随机区组设计，设置了 N0（ CK ）、N1（5 g/（m2·a））、N2（10 g/（m2·a））、N3（15 g/（m2·a））、N4（30 g/（m2·a））共5个不同浓度的氮沉降处理，研究氮沉降对土壤细根糖化学组分的影响。结果表明：（1）3个林龄杨树林地下细根中可溶性糖、淀粉含量，在1 a的观测期内，最大值出现在12月份，其中可溶性糖在1 a中的变化幅度最大，最高值与最低值相差约7倍；而作为结构性碳水化合物的纤维素和木质素在1 a的观测期内相对较为稳定。（2）随着外源氮输入增加，细根中可溶性糖、淀粉含量在N2水平最大，在N4水平则低于对照。而非结构性碳水化合物在氮增加处理的不同水平间差异不显著（p＞0．05）。总之，一定浓度的氮增加，将增加细根中活性代谢物质的碳投入。（3）杨树细根生物量与非结构性碳水化合物存在显著的正相关，杨树细根糖化学组分与土壤C、N以及温湿度没有显著相关性。

英文摘要：

We chose three different ages （5 years, 9 years and 15 years old） of poplar plantations in a coastal area in Dongtai city, Jiangsu province. The experiment used randomized block design with five nitrogen deposition concentration treatments, i.e. N0（CK）, N1 （5 g/（m2·a））, N2 （10 g/（m2·a））, N3 （15 g/（m2·a）, N4 （30 g/（m2·a）） in the field. The results showed that：（1） The manimum content of soluble sugar and starch appeared in December, and solu-ble sugar in one year had the largest change range, the highest and the lowest differed about seven times. While the sea-sonal variation of structural carbohydrates （ cellulose and lignin） was not obvious, and the cellulose and lignin content was relatively stable. （ 2） With the increase of exogenous nitrogen input, soluble sugar, starch and NSC content in the fine roots increased and then decreased, and the largest content at N2, while N4 （ the most nitrogen input） appeared be-low N0（control treatment）. SC had no significant difference （p〉0.05） among of levels of nitrogen increase treatments. （ 3） There were significantly positive correlation between fine root biomass and NSC, and no significant correlation be-tween soil C, N and carbohydrates compositions, as well as temperature and humidity.