What was done
The authors investigated soil microbial diversity in a species-rich calcareous grassland at the foothills of the Swiss Jura Mountains, portions of which had been exposed to ambient air of 365 ppm CO2 and portions of which had been exposed to CO2-enriched air of 600 ppm for six full years via the Screen Aided CO2 Control system of Leadley et al. (1997).  This work was conducted, in their words, "using phospholipid fatty acid (PLFA) profiles and DNA fingerprints obtained by Denaturing Gradient Gel Electrophoresis (DGGE) of 16S rDNA fragments amplified by the Polymerase Chain Reaction (PCR)."

What was learned
Ebersberger et al. report that "diversity and species richness, as estimated by Shannon diversity indices and the number of bands in DNA fingerprints, were not affected by CO2 enrichment," and that only "minor significant changes in bacterial community structure, as shown by PCR-DGGE of 16S rDNA fragments analyzed by ordination techniques" were apparent.  These results, according to them, are in line with the results of most other such CO2-enrichment studies, in support of which conclusion they cite the work of Insam et al. (1999), Wiemken et al. (2001) and Ronn et al. (2002).

What it means
The changes in soil microbial community structure brought about by raising the air's CO2 concentration to 600 ppm for a period of six years in this study was not enough, in the words of Ebsersberger et al., "to profoundly affect soil microbial community structure."

References
Insam, H., Baath, E., Berreck, M., Frostegard, A., Gerzabeck, M.H., Kraft, A., Schinner, F., Schweiger, P. and Tschuggnall, G.  1999.  Responses of the soil microbiota to elevated CO2 in an artificial tropical ecosystem.  Journal of Microbiological Methods 36: 45-54.

Leadley, P.W., Niklaus, P., Stocker, R. and Korner, C.  1997.  Screen-aided CO2 control (SACC): A middle-ground between FACE and open-top chamber.  Acta Oecologia 18: 207-219.

Ronn, R., Gavito, M., Larsen, J., Jakobsen, I., Frederiksen, H. and Christensen, S.  2002.  Response of free-living soil protozoa and microorganisms to elevated atmospheric CO2 and presence of mycorrhiza.  Soil Biology and Biochemistry 34: 923-932.

Wiemken, V., Laczko, E., Ineichen, K. and Boller, T.  2001.  Effects of elevated carbon dioxide and nitrogen fertilization on mycorrhizal fine roots and the soil microbial community in beech-spruce ecosystems on siliceous and calcareous soil.  Microbiological Ecology 42: 126-135.