Abstract: [Objective] To explore the influence of tree species on rhizosphere-associated fungal community in an agroforestry ecosystem, and to provide new insights into agroforestry practice, the fungal community structure in rhizosphere and bulk soil in Melia azedarach-Triticum aestivum agroforestry ecosystem was investigated by 18S rDNA PCR-DGGE.[Method] After the fungal DNA was extracted from extraction of nonrhizosphere and rhizosphere-associated soil, and the targeted fungal 18S rDNA was amplified using universal primers GC-FR1 and FF390. And then the amplified DNA fragments were analyzed by density gradient gel electrophoresis (DGGE). Similarity among different groups was analyzed using the UPGMA (unweighted pair group method with arithmetic averages) method, and the fungal diversity was evaluated with species richness (S), Shannon-Wiener index (H) and the equitability index (E). Finally, dominant DGGE bands were excised, sequenced and a phylogenetic tree was constructed. [Result] Results showed that the structure and diversity of rhizosphere-associated fungi community were much more complex than that of the bulk soil, and more dominant bands were observed in DGGE profiles of rhizosphere soil samples. The DGGE profiles were further investigated by cluster analysis using the UPGAMA method, revealing that the similarity among the three replicates of each treatment was more than 70% except for the rhizosphere soil of M. azedarach. In clustering diagram, all the samples were grouped into three clusters with a similarity of 51%. The highest similarity (72%) was found between the rhizosphere-associated fungal community from wheat and wheat grown under M. azedarach, which indicated that M. azedarach had minor influence on the rhizosphere-associated fungal community of wheat. In addition, only 51% similarity was noticed between the rhizosphere-associated fungal community of M. azedarach and the other groups. The principal-component analysis (PCA) also demonstrated that all the treatments was divided into three groups. There were no obvious differences in species richness among rhizosphere-associated fungal communities and nonrhizosphere fungal communities. However, the species richness of rhizosphere-associated fungal community from wheat grown under M. azedarach and M. azedarach were higher than nonrhizosphere fungal community. There were significant differences in Shannon-Wiener indexes among rhizosphere-associated fungal communities, while the difference was not significant among nonrhizosphere fungal communities. Additionally, no significant differences were present in equitability index among rhizosphere-associated fungal communities or nonrhizosphere fungal communities, whereas, the equitability index between rhizosphere-associated and nonrhizosphere fungal community of wheat grown under M. azedarach was significantly different, and the same as M. azedarach. Finally, sequencing of eleven dominant DGGE bands showed that 3 of the 11 sequences were uncultured fungi and the rest 8 sequences belonged to Glomeromycota, Basidiomycota, Ascomycota or Deuteromycota. [Conclusion] The species richness, Shannon-Wiener index and equitability index of rhizosphere-associated fungi from wheat grown under M. azedarach were higher than that of monocultured wheat, which indicated that diversity of rhizosphere-associated fungal community of wheat was enriched by trees grown in this agroforestry ecosystem. Our results may provide new reference for agroforestry practice.

Key words: agroforestry ecosystem, fungal community, PCR-DGGE