Changes in soil microbial community structure under elevated tropospheric O3 and CO2

We studied the effects of O3 and CO2 alone and in combination on soil microbial communities by assessing the changes in total PLFA biomass, profiles and specific subgroups. Meadow mesocosms were exposed to slightly elevated O3 (40–50 ppb) and CO2 (+100 ppm) in open-top chambers for three subsequent growing seasons (2002–2004). Decreased total, bacterial, actinobacterial, fungal PLFA biomass values as well as fungal:bacterial PLFA biomass ratio were measured after three growing seasons of fumigations with elevated O3. There were significant differences in the relative proportions of individual PLFAs between the control and elevated O3 treatments. Moreover, enhanced O3 alone and in combination with CO2 modified the structure of the microbial community. The effects of elevated CO2 given alone on PLFA profiles were negligible. Our results show that elevated O3 alone and in combination with CO2 even at moderate levels may cause changes in the biomass and composition of the microbial community in meadow soils, which may lead to functional changes in soil ecosystem processes.