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Introduction
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Enzymes are involved in all biological processes and play an especially important role in nutrient mobilisation and uptake as well as pathogen defence in the mycorrhizosphere. We determined enzymatic activities in soil samples of SFB607-experiments A6, B5, B10, B12 and of Kranzberg Forest with emphasis on changes of enzymatic activities under different experimental szenarios (ozone, carbon dioxide, pathogen).
A newly developed and adapted method allowed detection of enzymatic activities in very small samples allowing to investigate activities of single mycorrhizal tips, soil samples from the mycorrhizosphere and microsuction solutions. All selected enzymes are ecologically relevant in forest soils and litters: N-acetylglucosaminidase (chitin degradation, pathogen defence), ß-glucosidase and cellobiohydrolase (cellulose degradation), phosphatase (mobilisation of organically bound phosphate) and widely distributed.
Continuing the studies on the interaction of soil and rhizosphere microorganisms, the specific influence of mycorrhizal species on composition and cell numbers of bacterial communities was investigated using in situ hybridisation with fluorescence labelled oligonucleotides and DAPI staining of DNA.
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Results
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Influence of ozone on enzymatic activities in the mycorrhizosphere of beech and spruce (GSF-phytotrone experiment of B5)
Activities of all 4 measured enzymes are higher in soil samples from containers under elevated ozone compared to ambient ozone in the first year of ozone treatment.
Except for ß-glucosidase, enzymatic activities are higher in the mycorrhizosphere of spruce compared to beech.
These results confrimour hypothesis, that above ground elevated ozone concentrations change processes in the mycorrhizosphere.
Fig 1: Enzymatic activities in mycorrhizosphere soil samples originating from the GSF-phytotron experiment B5>
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Enzymatic activities of 4 abundant ectomycorrhizal species at Kranzberg Forest (Piloderma croceum, Cortinarius obtusus, Xerocomus cf. chrysenteron, Lactarius subdulcis)
4 ectomycorrhizal species show different enzymatic activities depending on the substrate.
L. subdulcis has clearly higher phosphatase and chitinase activities than the other investigated species.
This diversity has to be taken into account in field studies on enzymatic activities under different environmental conditions.
Fig 2: Enzymatic activities of different ectomycorrhizal species collected at Kranzberg Forest
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Bacterial communities in the mycorrhizosphere
Bacterial colonisation of different ectomycorrhizal species is influenced by the fungal partners. Bacterial communities on surfaces of hyphal mantles exhibit high numbers of active cells compared to other habitats such as bulk soil.
This result again points at the high functional diversity in forest soils influenced by different fungal partners.
The following table shows the cell numbers (in thousands per mm2) counted in hyphal mantle preparates of different field sampled ectomycorrhizal species (DAPI=all cells, EUB=active cells).
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| species | date | DAPI | EUB | DAPI:EUB |
| T. submollis | Nov 02 | 20.2 | 9.1 | 2.2 |
| Mar 03 | 9.2 | 4.2 | 2.2 |
| P. croceum | Nov 02 | 7.1 | 3.5 | 2.0 |
| | Mar 03 | 3.9 | 3.4 | 1.2 |
| | Apr 03 | 20.7 | 14.4 | 1.4 |
| L. subdulcis | Nov 02 | 92.2 | - | - |
| | Apr 03 | 142.8 | 114.4 | 1.3 |
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