Environmental changes in biodiversity hotspot ecosystems of
South Ecuador: RESPonse and feedback effECTs (FOR2730)

Abstract:

Mycorrhizas of vascular plants and mycorrhiza-like associations of liverworts and hornworts are integral parts of terrestrial ecosystems, but have rarely been studied in tropical mountain rain forests. The tropical mountain rain forest area of the Reserva Biológica San Francisco in South Ecuador situated on the eastern slope of the Cordillera El Consuelo is exceptionally rich in tree species, ericads and orchids, but also in liverworts. Previous light and electron microscopical studies revealed that tree roots are well colonized by structurally diverse Glomeromycota, and that epiphytic, pleurothallid orchids form mycorrhizas with members of the Tulasnellales and the Sebacinales (Basidiomycota). Sebacinales also occurred in mycorrhizas of hemiepiphytic ericads and Tulasnellas were found in liverworts belonging to the Aneuraceae. On the basis of these findings we hypothesized that symbiotic fungi with a broad host range created shared guilds or even fungal networks between different plant species and plant families. To test this hypothesis, molecular phylogenetic studies of the fungi associated with roots and thalli were carried out using sequences of the nuclear rDNA coding for the small subunit rRNA (nucSSU) of Glomeromycota and the large subunit rRNA (nucLSU) of Basidiomycota. Sequence analyses showed that Sebacinales and Tulasnellas were only shared within but not between ericads and orchids or between liverworts and orchids, respectively. Regarding arbuscular mycorrhiza forming trees, however, 18 out of 33 Glomus sequence types were shared by two to four tree species belonging to distinct families. Nearly all investigated trees shared one sequence type with another tree individual. Host range and potential shared guilds appeared to be restricted to the plant family level for Basidiomycota, but were covering diverse plant families in case of Glomeromycota. Given that the sequence types as defined here correspond to fungal species, our findings indicate potential fungal networks between trees.

Abstract:

The vast majority of the highly diverse trees in the tropical mountain rain forest of South Ecuador form arbuscular mycorrhizas and previous molecular investigations revealed a high diversity of fungi. Here we present a first trial to link fungal DNA-sequences with defined morphotypes characterized on the basis of partly new mycelial features obtained from field material of one tree species, Alzatea verticillata. Fine roots were halved lengthwise to study the mycelium anatomy on one half and to obtain fungal nuclear rDNA coding for the small subunit rRNA (nucSSU) of Glomeromycota from the other half. Light microscopy revealed conspicuously large amounts of mycelium attaching to the surface of the rootlets. The mycelium formed fine or large branched appressoria-like plates, vesicles of regular or irregular shape, and very fine, multi-branched hyphal systems ensheathed by septate hyphae. These previously undescribed features of the supraradical mycelia combined with intraradical mycelium structures were used for distinguishing of four main morphogroups and subordinate 14 morphotypes. DNA sequences of Glomus-group A, Acaulospora and Gigaspora were obtained and linked to three morphogroups. Two sequence types within Glomus-group A could be tentatively associated to subordinate morphotypes.