Responses of soil microbial activity to cadmium pollution and elevated CO2

To address the combined effects of cadmium (Cd) and elevated CO2 on soil microbial communities, DGGE (denaturing gradient gel electrophoresis) profiles, respiration, carbon (C) and nitrogen (N) concentrations, loessial soils were exposed to four levels of Cd, i.e., 0 (Cd-0), 1.5 (Cd-1.5), 3.0 (Cd-3.0) and 6.0 (Cd-6.0) mgCd kg(-1) soil, and two levels of CO2, i.e., 360 (aCO(2)) and 480 (eCO(2)) ppm. Compared to Cd-0, Cd-1.5 increased fungal abundance but decreased bacterial abundance under both CO2 levels, whilst Cd-3.0 and Cd6.0 decreased both fungal and bacterial abundance. Profiles of DGGE revealed alteration of soil microbial communities under eCO(2). Soil respiration decreased with Cd concentrations and was greater under eCO(2) than under aCO(2). Soil total C and N were greater under higher Cd. These results suggest eCO(2) could stimulate, while Cd pollution could restrain microbial reproduction and C decomposition with the restraint effect alleviated by eCO(2).