Search

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 FROM AUTHOR]

Abstract  Biotic interactions affect the impact of potential plant growth promoting microorganisms in the rhizosphere, but their magnitude and fundamentals are often hardly known. In a pot experiment, two physiologically different strains of the ectomycorrhizal fungus Paxillus involutus (GUL and FRA) were tested separately and in combination with associated bacteria (Sphingomonas paucimobilis 1 L, Ralstonia pickettii 16 B, Sphingomonas sp. 23 L) on their effects on the growth of willows (Salix viminalis). Both P. involutus strains significantly increased the growth of the willows compared with non-inoculated plants, but the magnitude of this effect was significantly affected by the fungal strain. The P. involutus strain GUL with higher synthesis of auxin-like substances, acid phosphatases, siderophores and faster utilisation of yeast extract in vitro increased the willow growth in situ more effectively than strain FRA. Additionally, dual inoculation with the P. involutus strains GUL and FRA in combination with the associated bacteria promoted the willow growth, especially the combination with S. paucimobilis 1 L. This bacterial strain used effectively C sources which are common components of plant root exudates, e.g. glucose, sucrose, maltose and mannose as well as compounds synthesized by fungi, e.g. trehalose in vitro. We conclude that the analyses of fungal metabolites and of C source use of associated bacteria can successfully contribute to accelerate the selection of capable plant growth promoting combinations. [ABSTRACT FROM AUTHOR]

Abstract: The goat willow (Salix caprea) belongs to the typical pioneer vegetation at former ore mining sites in Middle Europe as a result of its high metal-tolerance. Ectomycorrhizal (EM) fungi are known to contribute essentially to the tolerance of plants against abiotic stress. We investigated the EM associations of S. caprea at three former silver-mining sites around Freiberg (Saxonia, Germany) after 33years of revegetation. The EM colonisation ranged from 3 to 36% of the fine root tips. We found 14 different EM types and characterised them morphologically as well as anatomically. The fungal partners were identified using LSU and ITS sequences. They belonged to four families: Thelephoraceae, Cortinariaceae, Tricholomataceae and Tuberaceae. Thelephoraceae, with 53–91%, comprised the largest portion of the total EM colonisation at all test sites and sampling dates. Thelephoraceae produced mainly contact exploration types of ectomycorrhiza. Tricholoma cingulatum was the only EM fungus which was found as ectomycorrhiza and sporocarp. We suppose that the low exploration of the majority of EM associations of S. caprea, in combination with high portions of metal-chelating organic acids containing fungal partners, contributes essentially to the high tolerance of this tree species against high metal concentrations in the soil. [Copyright &y& Elsevier]

Copyright of Basic & Applied Ecology is the property of Urban & Fischer Verlag and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Graffenrieda emarginata (Ruiz & Pav.) Triana (Melastomataceae) was found to be the most frequent tree on the nutrient-poor organic soil in a species-rich tropical mountain rain forest of southern Ecuador. Our studies revealed that the rootlets are symbiotically associated with arbuscular mycorrhizal fungi and simultaneously form ectomy corrhizas displaying a superficial Hartig net but no hyphal mantle. Molecular phylogeny revealed a multitude of previously unknown glomeromycete sequence types. Ultrastructure of the ectomycorrhiza-forming fungus indicated an ascomycete, and molecular phylogenetic studies identified the fungal symbiont as a new taxon within the Hymenoscy phus ericae (Read) Korf & Kernan aggregate (Ascomycota). The mycorrhizal state of G. emarginata is considered crucial for its competitiveness and abundance in these sites. [ABSTRACT FROM AUTHOR]