Microcosm-based analyses of Scots pine seedling growth, ectomycorrhizal fungal community structure and bacterial carbon utilization profiles in boreal forest humus and underlying illuvial mineral horizons

We report on the identity of indigenous mycorrhiza forming fungi and rhizos phere/mycorrhizosphere bacterial community carbon source utilization profil es of Scots pine (Pinus sylvestris L,) seedlings grown in boreal forest hum us (O) or illuvial (B) mineral horizon containing microcosm growth systems. Based on rDNA (ITS)-RFLP analyses, a total of 10 fungal RFLP taxa were ide ntified from pre-morphotyped mycorrhizas on 7-month-old seedling roots. Hie rarchical cluster analysis, including corresponding RFLPs of known fungal s pecies, confirmed root colonization by eight mycorrhizal species. In the O horizon, roots were colonized by e.g. Suillus bovinus, Suillus variegatus, Cenococcum geophilum, Piloderma croceum, Thelephora terrestris and Russula vinicolor. Mycobiont diversity in the mineral B horizon was lower but inclu ded Piceirhiza bicolorata and both Suillus species which produced extensive extramatrical mycelium. In comparison to noncolonized soils, rhizosphere a nd mycorrhizosphere compartments supported significantly higher numbers of bacteria (mean range 10(8)-10(11) cells g(-1) fresh weight (fw)) Specific r hizosphere/mycorrhizosphere 'niche'-linked bacterial communities were detec ted following multivariate analyses (PCA and CA) of bacterial carbon utiliz ation profiles (Biolog (R) GN microplate). Distinct preferences for amino a nd carboxylic acids were identified in mineral B horizon rhizospheres where as a wider range of carbon sources were utilized in the fungal-dominated my corrhizospheres irrespective of soil types. (C) 2001 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights r eserved.