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| Influence of elevated carbon dioxide and ozone on the soil microflora under spruce and beech and molecular approaches to characterize the soil microflora and mycorrhiza-associated bacterial community |
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Anton Hartmann, Melanie Kliesch, Bernhard Mogge, Michael Schloter, and Jean Charles Munch
GSF-Research Center for Environment and Health, Institute of Soil Ecology, Neuherberg, Germany
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The effect of atmospheric treatment of spruce and beech with elevated carbon dioxide and ozone levels on soil microbial activity and biomass was investigated using microcalorimetric measurements. Spruce and beech plants either in mixed or pure stands were incubated in the GSF-climatic chamber at ambient or ambient plus 300 ppm C02 and ambient or twice increased 03-concentrations for two years (see Grams et al., this workshop). Soil samples were taken in fall of 1999 and 2000 and the basal microbial activity and the soil microbial biomass were determined. Ozone treatment resulted in reduced soil microbial activity and biomass in beech planted soil, but caused increased microbial activity and biomass in spruce planted soil. Carbon dioxide stimulated the soil microflora in both cases and over-compensated the inhibitory effect of ozone. These results reflect the increased allocation of assimilates into the root system (as measured also by increased root biomass) at elevated C02-levels. They also indicate an inhibitory effect of 03. Probably due to a much higher standing biomass of the spruce root system, the ozone treatment may have caused a deleterius effect on the roots causing increased microbial root decomposition and thus higher microbial activity and biomass in this case.
To be able to characterise in detail the consequences of this differential effects of atmospheric stressors for the root associated and soil microflora, which is nurished by the plant derived carbon substrates, we investigated the population structure and activity of the microflora in the soil with physiological and molecular techniques. Since most of the soil microorganisms usually does not readlly respond to cultivation, molecular genetic means to investigate the diversity of microbial population structure and functions were applied. On the basis of the obtained 16S rDNA- and 18S rDNAsequences for bacteria and fungi respectively, a microarry chip can be developed. Furthermore, the obtained sequence data can be used for in situ bacterial population analysis by fluorescence labelled oligonucleotide probes. After hybridisation of ectomycorrhizal hyphae and mantle structures with fluorescence labelled oligonucleotide probes for the major bacterial groups, the bacteria community could be characterised in situ using confocal laser scanning microscopy (Mogge et al., 2000). Interestingly, mostly beta- and alpha-proteobacteria were found to be tightly colonizing the mantle surface. A subpopulation of these bacteria may have potential to stimulate mycorrhizal formation and functions.
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Mogge, B., Loferer, C., Agerer, R., Hutzler, P., Hartmann, A. (2000)
Bacterial community structure and colonization patterns of Fagussylavatica L. ectomycorrhizospheres as determined by fluorescence in situ hybridization and confocal laser scanning microscopy. Mycorrhiza 9, 271-278
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