Selection of Sphingomonadaceae at the Base of Laccaria proxima and Russula exalbicans Fruiting Bodies

ABSTRACT The dense hyphal network directly underneath the fruiting bodies of ectomycorrhizal fungi might exert strong influences on the bacterial community of soil. Such fruiting bodies might serve as hot spots for bacterial activity, for instance by providing nutrients and colonization sites in soil. Here, we assessed the putative selection of specific members of the Sphingomonadaceae family at the bases of the fruiting bodies of the ectomycorrhizal fungi Laccaria proxima and Russula exalbicans in comparison to the adjacent bulk soil. To do so, we used a previously designed Sphingomonadaceae-specific PCR-denaturing gradient gel electrophoresis (DGGE) system and complemented this with analyses of sequences from a Sphingomonadaceae-specific clone library. The analyses showed clear selective effects of the fruiting bodies of both fungi on the Sphingomonadaceae community structures. The effect was especially prevalent with R. exalbicans. Strikingly, similar fungi sampled approximately 100 m apart showed similar DGGE patterns, while corresponding bulk soil-derived patterns differed from each other. However, the mycospheres of L. proxima and R. exalbicans still revealed divergent community structures, indicating that different fungi select for different members of the Sphingomonadaceae family. Excision of specific bands from the DGGE patterns, as well as analyses of the clone libraries generated from both habitats, revealed fruiting body-specific Sphingomonadaceae types. It further showed that major groups from the mycospheres of R. exalbicans and L. proxima did not cluster with known bacteria from the database, indicating new groups within the family of Sphingomonadaceae present in these environments.

Ectomycorrhizal associations in jack pine stands in northeastern Alberta

Ectomycorrhizae of jack pine occurring in mature stands, on bare roadsides, and in a recently burned area were compared. Fifty-six fungus associates were identified from sporocarp collections. Species of Elaphomyces, Suillus, Cortinarius, Cantharellus, and hydnums were almost exclusively limited to mature stands. Laccaria proxima, Rhizopogon rubescens. Scleroderma macrorhizon, and Astraeus hygrometricus were typically found on disturbed sites. Visual observations and direct isolations from ectomycorrhizae further indicated that the symbionts differed between the burn site and mature jack pine – lichen woodlands. A majority of the ectomycorrhizae in all sites were nondescript and could not be identified by culturing. Unlike the vascular plants, ectomycorrhizal symbionts were very numerous without any single species or small group of species dominating jack pine root systems. Pure culture syntheses confirmed that Tricholoma flavovirens, T. pessundatum, T. zelleri, Suillus flavovirens, S. albidipes, Cenococcum geophilum, Laccaria proxima. Scleroderma macrorhizon, Astraeus hygrometricus, Lactarius paradoxus, Coltrichia perennis, and Bankera fuligineo-alba were ectomycorrhizal associates of jack pine.