中文摘要：

以水曲柳人工林1级根为研究对象,通过施氮肥处理,对不同季节和不同土壤深度根系取样,研究施用氮肥对根尖内生菌根真菌侵染率和形态与土壤N有效性、季节和土壤深度的关系。结果表明：1）施N肥处理导致水曲柳人工林1级根的菌根真菌侵染率显著降低11%,季节和土壤深度对1级根的侵染率影响显著,其中春季〉夏季〉秋季,土壤表层高于亚表层;2）施N肥导致1级根长度显著降低,季节和处理之间的交互作用影响1级根的直径和根长,季节、土层和处理3者的交互作用影响根长和比根长;3）与未侵染菌根真菌的1级根形态相比,菌根真菌侵染导致1级根平均直径未发生变化,长度略有降低,而比根长则显著减小。这种根系形态变化规律在不同处理、不同季节和不同土壤深度上表现一致。

英文摘要：

In order to detect the relationship between VA mycorrhizal fungi and Fraxinus mandshurica roots under fertilization condition,mycorrhizal colonization and root tip morphology,such as root diameter,length and specific root length（SRL） of the first order roots were examined at different soil depth and seasons.This study was conducted at a site of Maoershan Forest Research Station in 2005.The results showed that VA mycorrhizal fungal infection rate in the first order roots was generally reduced 10% under soil N addition,which varied with soil depths and seasons.The infection rate in spring was the highest,followed by that in summer and autumn.The infection rate in 0-10 cm lager of the soil was significant higher compared to the 10-20 cm of the soil.In comparison with non-mycorrhizal roots,VA mycorrhizal infection did not alter root diameter and length,but significantly decreased SRL.Those changes of root tip morphology were consistent in different treatments,soil depths and seasons.The findings suggested that the degree of colonization by VA mycorrhizal fungi in the first order roots of Fraxinus mandshurica was dependent upon the N availability,soil depths and seasons,and the root morphology was changed by VA mycorrhizal fungal colonization,which all useful knowledge to were in understanding principle of fine root longevity and turnover in this forest ecosystem.