Diversity of mycorrhizal fungi and carbon nutrition in tropical epiphytic orchids

• Ano de defesa: 2018
• Autor(a) principal: Vieira, Conrado Augusto
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa; Microbiologia Agrícola
• Palavras-chave em Português: Orquídea - Conservação; Isochilus linearis; Mata Atlântica; Micologia
• Link de acesso: https://locus.ufv.br//handle/123456789/31493

Orchids, in the nature, depend on the interaction with mycorrhizal fungi to complete the life cycle. At the center of the interaction, different fungi are involved which promote the exchange of compounds, mainly carbon, with the host orchid. However, the diversity of mycorrhizal fungi, mainly those belong to Tulasnellaceae, the commonest family of orchid mycorrhizal fungus, as well as the carbon flux in tropical epiphytic orchids are still little known. We investigated if there is the occurrence of this fungal family in the root of epiphytic tropical orchids as well as in the phorophyte bark where they occur, and if along the phorophyte there is difference in the carbon flux between the fungus and the orchid. Grids were used for sampling in two phorophytes, with five individuals of Isochilus linearis (Jacq.) R.Br. in each. Samples were collected from all roots of the orchids and also from the bark of the phorophyte just below the orchids roots, as well as from the bark of the phorophytes. After extraction of total DNA, PCR was performed with the primers for fungi in general (ITS86F + ITS4) and specifically for Tulasnellaceae (ITS86F + ITS4-Tul). The amplicons were sequenced by NGS (Next Generation Sequencing) by the Ion TorrentTM platform. The data were analyzed and the sequences identified in the lowest possible taxonomic level. The data were also submitted to ANOVA, and diversity indices and artificial neural networks (ANN) were analyzed. To evaluate the carbon flux, orchid metabolism (C3 or CAM), as well as the strategy of acquiring carbon by the orchid (mycoheterotrophic - MH, autotrophic - AT or mixotrophic - MT), we sampled leaves of orchid, non-orchids species and pelotons present in the roots of the orchids, growing in different height of phorophytes. The samples were dried to constant mass, ground and the 13 C/12C isotopic ratio measured by isotope ratio mass spectrometer. The isotopic signatures data were submitted to ANOVA, cluster analysis and ANN. It was observed the general fungi and also of the family Tulasnellaceae (42.38%) in different types of samples, mainly a species not yet described, Tulasnella sp. 3. Tulasnellaceae has been shown to be the key to diversity in I. linearis, as well as in associated phytophytes. The presence of fungi previously described in associations with lichens (Pectenia plumbea, Biatora ligni-mollis and Bacidia laurocerasi) suggests a “bridge” for the entry of N in the mycorrhizal association. In addition, two fungi with high prevalence (Candida smithsonii and Fusarium buharicum) have been described in intestinal tract of Coleoptera. This fact suggests that herbivory can be a tool for dispersion of these fungi. No patterns of mycorrhizal fungus dependence were observed by the orchid and altimetry gradient, although carbon flow was observed, and 11.11% of the orchids presented CAM. The orchids were MH, AT and MT, with prevalence of 63.64%, 22.72% and 13.64% respectively. Among three MT samples, two received more C from photosynthesis than from the associated mycorrhizal fungus. The climatic characteristics of the collection site, such as the constant presence of fog, may explain the low prevalence of orchids with CAM type, and because it is a dense forest, no difference was observed in the carbon flux, since it was expected that orchids in higher positions, would receive more light and would less dependent on mycorrhizal fungi. This is the first record of Tulasnellaceae in phorophytes bark and the carbon flux in tropical epiphytic orchids. The information generated in this study can provide subsidy for the elaboration of more efficient management plans, in which areas with occurrence of fungi potentially forming orchid mycorrhiza may be able to sustain the permanence of the species.