Introduction
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The acquisition and uptake of essential nutrients and water from the soil are dependent on the development of the root system and the establishment of a supportive symbiotic or associative rhizosphere microflora. The rhizosphere microflora is recruited from the pool of soil microbes and is strongly dependent on the supply of carbon sources by the roots and other specific conditions of the rhizosphere habitat.
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Methods
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Microbial activity parameters
- Measuring microbial biomass using microcalorimetry
- Determining functional characteristics with BIOLOG
Analyses of microbial populations
- Sequence analyses of ribsomal DNA of bacteria and fungi in forest soil
- Fluorescence in situ hybridisation (FISH) of mycorrhizas-associated bacteria
For the molecular genetic analysis of the microbial community and the mycorrhiza-associated bacteria, the so-called "cyclic rRNA approach" was used. Either the bacteria are directly identified with group-specific probes and FISH or characterized by 16S rDNA swquences retrieved from environmental DNA.
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Results
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Microcalorimetric measurements
Microbial activity in beech soil was inhibited under elevated Ozon concentrations while it was stimulated in spruce soil.
Microbial biomass and activity was stimulated under elevated CO2-concentrations in both soils, under spruce and under beech.
Elevated concentrations of both, Ozon and CO2, compensated the negative effects of elevated Ozon on microbial biomass and acktivity.
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Functional characteristics of the microflora
Using carbon source utilisation tests (BIOLOG), complex carbon sources and amino acids were more readily metabolised by the microbial populations of forest soils as compared to a meadow community. Organic acids and sugars were less readily metabolized by the forest soil microflora.
FISH with group specific 16S rRNA-directed olinucleotide probes
LSM-micrographs of bacteria colonising the hyphal mantle of Lactarius vellereus - ectomycorrhiza
bar 10 µm
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xy-scan, probe: Bet42a-Fluos
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xy-scan, probes: Eub338-Fluos, GAM42a-TRITC, Bet42a-Cy5
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xy-scan, probe: Eub338-Cy5
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Phylogenetic analyses of a 16S rDNA genebank of forest soil bacteria
an example of Bacillus group
bold: clones from forest soil
italic: reference sequences
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