中文摘要：

【目的】陕西小叶杨主要分布在生态环境差异显著的陕北和秦岭北麓地区。研究小叶杨叶内生真菌群体特征,明确影响小叶杨生态分布的生态因素。【方法】通过对2种生境下小叶杨林分代表植株叶片定点、定时采集,在严格的表面消毒下,进行PDA和纸培养,结合形态学和分子系统学技术对分离真菌进行鉴别,并用SASS软件对内生真菌群体进行统计分析。【结果】宝鸡和榆林的小叶杨内生真菌相似系数较高（0.444 5）,优势种群相似。交链孢属、单隔孢属、茎点霉属真菌相对分离率分别为23.1%,22.5%,28.44%,皆为优势菌群,呈现明显的暗色有隔菌群特点,这可能与小叶杨树种旱生发育型相关。地区内的内生真菌群体相似系数大于地区间的相似系数,尤以陕北榆林地区3个采集点内生真菌相似系数大（0.666 7～0.689 7）。地区间树龄接近、林下植被类似,则相似系数大。榆林地区内生真菌群体的菌株数量、相对分离率和定植率高于宝鸡地区,多样性指数却呈现相反的趋势。在6个不同的采集地点中,小叶杨叶片内生真菌群体多样性指数为1.53～2.62,多样性指数按凤南〉桃川〉鹦鸽〉青云〉红山〉无定河依次递减,但相互间无显著差异。小叶杨叶片内生真菌的组成在春季和秋季存在差异。内生真菌的菌株数量、相对分离率表现为秋季高于春季,定植率和多样性指数呈相反的趋势。【结论】小叶杨叶片内生真菌群体表现出较高的寄主选择性。林下植被类型、树龄影响内生真菌的群体结构,但气候特征对内生真菌群体多样性差异的影响不大。

英文摘要：

【Objective】Populus simonii in Shaanxi mainly distributes in northern Shaanxi and in the north Qinling Mt.,which are significant differences in geology and ecology. In this study,we carried out a basic research on population characteristics of the endophytic fungi in P. simonii in the two regions to further understand the influence of ecological factors on the geo-ecological distribution of P. simonii. 【Method 】The leaf samples were regularly collected from the targeted trees at the two different ecological regions,and strictly sterilized on the surfaces before culture. PDA medium and paper culture were implemented to isolate the endophytic fungi from the poplar leaves. The isolated fungi were identified by combinations with the morphology and molecular phylogenic technologies. The population diversity and structure of those endophytic fungi in the poplar leaves were analyzed with the SASS software. 【Result 】No significant difference of fungal community structure was found between the two distinct sampling regions,Baoji（ BJ） and Yulin（ YL） with high similar coefficient of 0. 444 5,and with similar dominant species of dark septal endophytic（ DSE） fungi groups,which can be ascribed to the xerotolerant auxology of their host P. simonii. The dominant DSE fungi included Alternaria（ RF = 23. 1%）（ relative frequency,RF）,Ulocladium（ RF = 22. 5%）,Phoma（ RF = 28. 44%）. However,the intra-regional similarity coefficients was higher than the inter-regions between BJ and YL,especially in the 3 sampling sites in YL region,whose similarity coefficients was high,ranging from 0. 666 7 to 0. 689 7; Inter-region similarity was higher among sites if they had similar host age and understory vegetation,such as Qingyun（ QY） site and Yingge（ YG）site. The amount,colonized frequency（ CF）,and RF of endophytic fungal communities in YL region were higher thanthose in BJ region,however,the Shannon-weiner index（ H＇） of diversity of endophytic fungal communities was reversed.In the all six