Carbon utilization patterns of bacterial communities in forest humus and oil-contaminated soils and in Scots pine rhizospheres/mycorrhizospheres developed on these soil types.

Heinonsalo, Jussi¹, Kirsten S. Jørgensen² Kielo Haahtela¹ & Robin Sen¹.

¹Department of Biosciences, Division of General Microbiology, P.O.Box 56, 00014 University of Helsinki, Finland. ²Finnish Environment Institute, P.O.Box 140, 00251 Helsinki, Finland.

Duddridge-type petridish microcosms each containing natural forest humus (H) with or without cores of oil-contaminated soil (OS) (non-planted controls) and individual Scots pine seedlings were analysed. After eleven-months-growth, root/shoot ratio was higher in OS microcosms although mycorrhizal morphotype diversity remained unaffected. Bacteria were extracted from different compartments: bulk H and OS from control and planted microcosms, and pine root surfaces and mycorrhizas/external mycelium (mycorrhizospheres) developed on H and OS. Compared to bulk H and OS from non-planted controls, bacterial numbers (gram^-1 f. wt.) were significantly higher in rhizosphere and mycorrhizosphere compartments developed on these soils types. The bacterial communities from the different compartments were distinguished following principal component analysis (PCA) of Biolog® carbon source utilization profiles. Differential carbon source utilization patterns were clearly detected in comparisons of non-planted OS and H with other rhizosphere/mycorrhizosphere and adjacent 'bulk soil' compartments. Specific carbon sources utilized in these compartments were also identified and grouped in the PCA analysis. The host plant and ectomycorrhizas/external mycelium was found to be important in maintaining numbers and activities of bacterial communities in these soil types.