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

Abstract:

Tropical dry forests are an intricate ecosystem with special adaptations to periods of drought. Arbuscular mycorrhizal fungi (AMF) are essential for plant survival in all terrestrial ecosystems but might be of even greater importance in dry forests as plant growth is limited due to nutrient and water deficiency during the dry season. Tropical dry forests in Ecuador are highly endangered, but studies about AMF communities are scarce. We investigated the AMF community of a premontane semi-deciduous dry forest in South Ecuador during the dry season. We estimated AMF diversity, distribution, and composition of the study site based on operational taxonomic units (OTUs) and compared the results to those from the tropical montane rainforest and páramo in South Ecuador. OTU delimitation was based on part of the small ribosomal subunit obtained by cloning and Sanger sequencing. Nearly all OTUs were Glomeraceae. The four frequent OTUs were Glomus, and comparison with the MaarjAM database revealed these to be globally distributed with a wide range of ecological adaptations. Several OTUs are shared with virtual taxa from dry forests in Africa. Ordination analysis of AMF communities from the tropical dry and montane rainforests in South Ecuador revealed a unique AMF community in the dry forest with only few overlapping OTUs. Most OTUs that were found in both dry and rainforests and on the two continents were globally distributed Glomus.

Abstract:

Arbuscular mycorrhizal fungi (AMF) are the most prominent mycobionts of plants in the tropics, yet little is known about their diversity, species compositions and factors driving AMF distribution patterns. To investigate whether elevation and associated vegetation type affect species composition, we sampled 646 mycorrhizal samples in locations between 1000 and 4000 m above sea level (masl) in the South of Ecuador. We estimated diversity, distribution and species compositions of AMF by cloning and Sanger sequencing the 18S rDNA (the section between AML1 and AML2) and subsequent derivation of fungal OTUs based on 99% sequence similarity. In addition, we analyzed the phylogenetic structure of the sites by computing the mean pairwise distance (MPD) and the mean nearest taxon difference (MNTD) for each elevation level. It revealed that AMF species compositions at 1000 and 2000 masl differ from 3000 and 4000 masl. Lower elevations (1000 and 2000 masl) were dominated by members of Glomeraceae, whereas Acaulosporaceae were more abundant in higher elevations (3000 and 4000 masl). Ordination of OTUs with respect to study sites revealed a correlation to elevation with a continuous turnover of species from lower to higher elevations. Most of the abundant OTUs are not endemic to South Ecuador. We also found a high proportion of rare OTUs at all elevations: 79–85% of OTUs occurred in less than 5% of the samples. Phylogenetic community analysis indicated clustering and evenness for most elevation levels indicating that both, stochastic processes and habitat filtering are driving factors of AMF community compositions.

Abstract:

Arbuscular mycorrhizae are important for growth and survival of tropical trees. We studied the community of arbuscular mycorrhizal fungi in a tropical mountain rain forest and in neighbouring reforestation plots in the area of Reserva Biológica San Francisco (South Ecuador). The arbuscular mycorrhizal fungi were analysed with molecular methods sequencing part of the 18S rDNA. The sequences were classified as Operational Taxonomic Units (OTUs). We found high fungal species richness with OTUs belonging to Glomerales, Diversisporales and Archaeosporales. Despite intensive sampling, the rarefaction curves are still unsaturated for the pristine forest and the reforestation plots. The communities consisted of few frequent and many rare species. No specific interactions are recognizable. The plant individuals are associated with one to ten arbuscular mycorrhizal fungi and mostly with one to four. The fungal compositions associated with single plant individuals show a great variability and variety within one plant species. Planted and naturally occurring plants show high similarities in their fungal communities. Pristine forest and reforestation plots showed similar richness, similar diversity and a significantly nested structure of plant-AMF community. The results indicate that small-scale fragmentation presently found in this area has not destroyed the natural AMF community, at least yet. Thus, the regeneration potential of natural forest vegetation at the tested sites is not inhibited by a lack of appropriate mycobionts.

Abstract:

Fungi are believed to be diverse in the tropics, but because many groups are only known from their DNA sequences this hampers comparative diversity studies. We investigated mycorrhizal Sebacinales (Basidiomycota) of 67 individuals of Ericaceae and Orchidaceae in a tropical mountain ecosystem in Southern Ecuador to provide a ?rst estimate of whether these fungi are particularly diverse in the Northern Andes. We par- tially sequenced the internal transcribed spacer (ITS) and large subunit (LSU) regions of the nuclear ribosomal DNA and analyzed them together with all Sebacinales sequences available from GenBank. The clustering optimization technique was used to determine clustering parameters that maximize the comparability between molecular operational taxonomic units (MOTUs) obtained from the distinct loci. Sampling effort and species richness were estimated with rarefaction-accumulation curves and non-parametric esti- mation using Chao2 and compared between Southern Ecuador and France. Clustering optimization indicated that a 1% LSU distance threshold corresponds to the commonly used 3% dissimilarity threshold for ITS, and that a clustering algorithm close to single- linkage clustering is optimal. The resulting clusters show that about 8?9% of observed Sebacinales MOTUs occur in the study area and that most of these MOTUs are endemic (74%). The widespread MOTUs from Southern Ecuador were also found in Panama, North America and Europe. The estimation of species richness revealed unsaturated sampling of Sebacinales in general and also in our study area. Our results suggest a high diversity of Sebacinales associated with Ericaceae and Orchidaceae at the study site in Southern Ecuador, but no hotspot of Sebacinales in comparison with other areas.

Abstract:

Neotropical Vaccinioideae (Ericaceae) are evolutionary rather young and presumably of Northern Hemisphere origin. Vaccinioideae are highly dependent on their mycorrhizal symbionts and Sebacinales (basidiomycetes) were previously found to be the dominant mycobionts of Andean Clade Vaccinioideae (Neotropical Vaccinieae). We were interested to see whether the North American Vaccinioideae reached the Neotropics with their mycobionts or whether they acquired new, local Sebacinales. We investigated Sebacinales of 58 individuals of Vaccinioideae from Ecuador, Panama and North America to examine whether mycobionts of each region are distantly or closely related. We isolated the ITS of the ribosomal nuclear DNA in order to infer a molecular phylogeny of Sebacinales and to determine Molecular Operational Taxonomic Units (MOTUs). MOTU delimitation was based on a 3% threshold of ITS variability and conducted with complete linkage clustering. The analyses revealed that most Sebacinales from Ecuador, Panama and North America are closely related and that two MOTUs out of 33 have a distribution ranging from the Neotropics to the Pacific Northwest of North America. The data suggest that Neotropical and temperate Vaccinioideae of North America share their Sebacinales communities and that plants and fungi migrated together.

Abstract:

Mycorrhizas of vascular plants and mycorrhiza-like associations of liverworts are integral parts of terrestrial ecosystems, but have rarely been studied in tropical mountain rain forests. Our lightand electron microscopical studies at the RBSF revealed that the roots of nearly all tree species were well colonized by structurally diverse arbuscular mycorrhizal Glomeromycota (Haug et al. 2004, Beck et al. 2005), a few tree species by ectomycorrhizal Ascoand Basidiomycota (Haug et al. 2005), and that epiphytic, pleurothallid orchids formed mycorrhizas with Tulasnella species and members of the Sebacinales (Basidiomycota) (Suárez et al. 2006, Kottke et al. 2007). Species of Sebacinales also occurred in mycorrhizas of hemiepiphytic ericads (Setaro et al. 2006) and Tulasnella species were found in liverworts belonging to the Aneuraceae (Kottke et al. 2007). Traditionally, studies on biodiversity and host specificity have been based on morphologically defined species. No such approach was feasible in the case of the mycobionts in our study as the fungi did not display sufficient structural differences in the mycorrhizas for delimitation of morphospecies. The identification of the mycorrhiza-forming fungi in the forest could be done neither by spore nor by fruiting-body sampling, as both methods would have yielded only a very narrow spectrum of the fungal communities (Husband et al. 2002, Sanders 2004a). Instead, direct sequencing of the associated fungi from the plant material was carried out (Kottke et al. 2007). Given our present stage of knowledge, the sequence types (ribosomal genotypes) can rarely be precisely related to either morphological or biological species. However, the amount of information derived from the sequences of the ribosomal genes appeared to be meaningful in previous ecological studies on arbuscular mycorrhizas (Helgason et al. 2002, Husband et al. 2002, Sanders 2004b) as well as on mycorrhiza-forming Basidiomycota (Bidartondo et al. 2003, Bidartondo et al. 2004). However, analysis of biodiversity and specificity of the mycobionts from field samples using DNA sequences also poses problems. Firstly, results are limited by the available primers. Secondly, problems resulted from the observation that the ribosomal genes can show intraspecific variation, especially in the case of the multinucleate Glomeromycota (Sanders et al. 1995, Lloyd-Macgilp et al. 1996, Clapp et al. 2001, Sanders 2004b). These facts pose general, unresolved challenges to a species concept based on meaningful levels of genetic diversity. Thus the list of fungal sequences presented here is far from being complete and far from being a species list.

Abstract:

Mycorrhizal fungi, because of their obligate symbiotic interaction with plant roots, may either promote or restrict plant diversity depending on broad or narrow plant-fungus relationships. It was challenging to investigate these relationships in a hotspot of plant diversity, the tropical mountain rain forest of Southern Ecuador. Inventories, based on morphotyping and DNA sequencing, were carried out on the mycorrhizal fungi associated with 115 tree species belonging to 40 families, 20 ericad species and 4 epiphytic orchid species in an area of about 12 ha in the Reserva Biológica San Francisco at 1 850 to 2 300 m. Results indicated that diverse Glomeromycota with broad host range may promote high tree diversity, while diverse but plant-family restricted Sebacinales likely support closely related Andean ericads, and diverse, orchidrestricted Tulasnellales and Sebacinales closely related epiphytic orchids. Ectomycorrhizal fungi were found specifically associated with three Nyctaginacean trees and with one member of Melastomataceae. We conclude that the extraordinary high plant diversity of the tropical Andean forest is predominantly promoted by a broad range of mycorrhizal fungi but selected trees are supported by specific fungi.

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.