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

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.