Elevated CO2 alters community-level physiological profiles and enzyme activities in alpine grassland

Plots of an alpine grassland in the Swiss Alps were treated with elevated (680 microl l(-1)) and ambient CO2 (355 microl l(-1)) in open top chambers (OTC). Several plots were also treated with NPK-fertilizer. Community level physiological profiles (CLPPs) of the soil bacteria were examined by Biolog GN microplates and enzyme activities were determined through the release of methylumbelliferyl (MUF) and methylcoumarin (MC) from MUF- or MC-labelled substrates. A canonical discriminant analysis (CDA) followed by multivariate analysis of variance showed a significant effect of elevated CO2 on the CLPPs both under fertilized and unfertilized conditions. Further, the installation of the OTCs caused significant shifts in the CLPPs (chamber effect). Of the four enzyme activities tested, the beta-D-cellobiohydrolase (CELase) and N-acetyl-beta-D-glucosaminidase (NAGase) activity were enhanced under elevated CO2. L-Leucin-7-aminopeptidase (APEase) activity decreased, when the plots received fertilizer. Beta-D-glucosidase (GLUase) remained unaffected. The results suggest effects of elevated CO2 on specific microbial activities even under low mineral nutrient conditions and when bulk parameters like microbial biomass or respiration, which have been investigated on the same site, remain unaffected. The observed medium-term changes point at possible long-term consequences for the ecosystem that may not be specified yet.