三种杓兰根相关真菌多样性和生态功能

Diversity and ecological function of root-associated fungi in three Cypripedium species

摘要:

【背景】除了菌根真菌(Orchid mycorrhizal fungi，OrMF)外，兰科植物根中还有其它内生真菌，称为根相关真菌(Root-associated fungi，RAF)。【目的】采用分离培养的方法获得同一栖息地针叶林和灌木林两种不同生境西藏杓兰、黄花杓兰和无苞杓兰的RAF菌株，研究其真菌谱系、多样性和生态功能结构。【方法】从杓兰根碎屑中分离RAF，通过总DNA提取、PCR扩增及测序得到ITS (Internal transcribed spacer)序列；进行系统发育和多样性分析，并通过NCBI数据库比对得到相似性最高序列的注释信息来分析RAF生态学特性。【结果】共分离得到278株RAF，25种OTU类型，包括23个子囊菌门OTU，2个毛霉菌门OTU。RAF物种丰富度分析发现西藏杓兰的较黄花杓兰高，不同生境没有显著差异；不同杓兰物种较不同生境的RAF群落分化程度高。生态功能分析显示25个OTU包括共生型、腐生型和致病型3种营养型，以及外生菌根菌群、植物病原菌群、内生真菌群、动物病原菌群、真菌寄生菌群、杜鹃花类菌根群、未定义的腐生菌群和不确定型8种共位群。【结论】阐明不同生境采集的不同杓兰中RAF的分布特点和生态功能，为未来研究RAF与杓兰属植物的共生关系奠定基础。

Abstract:

[Background] In addition to orchid mycorrhizal fungi, the roots of orchids harbor plant fungal endophytes termed root-associated fungi. [Objective] Three endangered photosynthetic Cypripedium species distributed in coniferous forest and shrub habitats were screened for root-associated fungi using culture-dependent (isolations from root fragments) techniques. The species richness and the degree of root-associated fungi community differentiation of examined Cypripedium species and two different habitats were determined. Ecological function analysis of root-associated fungi was also estimated. [Methods] RAF were isolated from surface sterilized root fragments of orchids. Total DNA were extracted from isolated root-associated fungi, and internal transcribed spacer (ITS) regions were amplified. The ITS-PCR products were sequenced. Phylogenetic analysis was applied. Species richness and diversity of fungal communities of studied orchid species and collecting sites were estimated. After blasting the ITS sequences of root-associated fungi in NCBI database, the annotation of the closest matched sequences were used to analyse the ecological function. [Results] 278 root-associated fungi isolates, corresponding to 25?operational taxonomic units (otus), were identified, including 23 Ascomycota OTUs and 2?Mucoromycota OTUs. The root-associated fungi species richness of Cypripedium tibeticum was higher than that of Cypripedium flavum. The degree of root-associated fungi community differentiation of different Cypripedium species is bigger than that of different habitats. Fungal taxa in the roots of the three Cypripedium species could be assigned to 3 trophic modes, which were symbiotroph, saprotroph and pathotroph, respectively; and 8 guilds, which were ectomycorrhizal, plant pathogen, endophyte, animal pathogen, fungal parasite, ericoid mycorrhizal, undefined saprotroph and uncertain, respectively. [Conclusion] This study revealed the distribution characteristics and ecological function of RAF in roots of three Cypripedium species sampled from two different habitats, and also laid a foundation for the symbiotic relationship study of root-associated fungi and Cypripedium species in the future.