The impact of long-term CO2 enrichment and moisture levels on soil microbial community structure and enzyme activities

Soil organic matter is the most important reservoir of terrestrial organic C and minor changes in the balance may have a significant impact on the climate. However, the response of microbial decomposers of soil C to global changes is not fully apprehended. This is particularly the case with regard to the interactive effects of the various climatic changes. Here, we present data from the Giessen Free Air CO2 Experiment (Gi-FACE, University of Giessen, Germany) in which the CO2 concentration at a grassland site was increased by 20% relative to atmospheric levels during a period of 10 years. The site included a slope that resulted in differences in average soil moisture. The effects of CO2 and soil moisture on soil microbial community structure, measured by Denaturing Gradient Gel Electrophoresis (DGGE), PhosphoLipid Fatty Acids (PLFA) and enzyme activity profiles were determined. Total carbon, nitrogen and phosphorous contents were also determined. Soil moisture explained a large part of the variance in the microbial community structure data, by affecting fungi and bacteria. Furthermore, the CO2 treatment had no significant effect on either overall PLFA or DGGE profiles, despite the fact that the fungal:bacterial PLFA ratio was altered. Overall enzyme activity profiles were also only affected by soil moisture levels, although the CO2 treatment induced a significant increase of the acid phosphatase activity. Finally, neither soil moisture nor elevated CO2 induced changes in the soil C stock.

► Ten years of moderate CO2 enrichment did not increase the soil C stocks.
► Soil moisture had greater impact PLFA profile patterns than elevated CO2.
► Enzyme activities were lowest in dry sites and highest in sites with intermediate moisture levels.
► A significant increase in acid phosphatase activity under elevated CO2 was observed.