Study On The Relationship Between Plant Growth Forms And Mycorrhizal Fungi

Orchidaceae are typical mycorrhizal plants. Most orchid species are dependent on mycorrhizal fungi for seed germination and growth during seedling stage even grown stage of some orchid species. It is well-known that Orchidaceae have different life forms (terrestial、epiphytic and lithophytic), however the reason why this exists haven’t been paid much attention. Is epiphytic an evolution for plants to get away from soil? Or the choice made by inheritance? Or the mycorrhizal community composition affect the choosing process? These questions still have no clear answers. In consideration of the natural mycorrhizal symbiosis, this paper ecologically analyzes the relationship between orchid plants of three different life forms in Xishuangbanna of Yunnan and their mycorrhizal fungi, in orther to provide a perspective for reference to explain this phenomenon. On the other hand, this ecological research of interaction between orchid and mycorrhizal fungi will lay a foundation for unclosing the mechanism of the symbiosis, meanwh(?)e the resuns w(?) be of nign scient(?)c value for protection of orcnia species ana restoration of their wild populations. The main contents are as follows:1) Ribosomal DNA internal transcribed spacer (rDNA-ITS) sequences of mycorrhizal fungi were amplified, cloned, sequenced. DNA clone libraries constructing and other molecular biology methods were used to analysis the mycorrhizal diversity, all in all, we identified 87 OTUs in 44 orchid species, of which 53 OTUs were species of "Rhizoctonia":39 OTUs were species of Tulasnellaceae, accounting for 80.4% of the total sequences, ranked the main dominant species; 11 OTUs were species of Ceratobasidiaceae, accounting for 4.8% of the total sequences; 3 OTUs were species of Sebacinaceae, accounting for 2.1% of the total sequences.2) Analysis the mycorrhizal variety and diversity index of three life forms separately, epiphytic>terrestial> lithophytic was found, which shows difference between different life forms; Analysis the richness,25 OTUs were detected in Terrestial Orchids of 13species(9 genuses),50 OTUs were detected in Epiphytic Orchids of 25species(16 genuses),24 OTUs were detected of Lithophytic Orchids of 14species(10 genuses), which shows no significant difference in quantity;3) The effect of life form on fungal community composition as the only environment factor was tested with ANOVA、PERMANOVA、PCoA and other statistical analysis approachs. The results shows significant difference(p<0.05) in the community composition;4) Tulasnellaceae ranked the main dominant species in the three life forms, analysis the difference from the angle of phylogeny, which found significant difference between epiphytic and lithophytic. lithophytic and terrestial、terrestial and epiphytic;5) Build Orchid-Mycorrhizal fungi interaction network structure, analysis the statistical significance of nestedness of the overall network structure and the sub-network structure, we found a highly nestedness(p<0.05) in the overall network and Epiphytic Orchids sub-network structure, while the other two life forms not.