Kinetics of the respiratory response of the soil and rhizosphere microbial communities in a field experiment with an elevated concentration of atmospheric CO2

The effect of an elevated concentration of atmospheric CO^sub 2^ and the application rate of nitrogen fertilizers on the microbial biomass and maximum specific growth rate of microorganisms in the soil and rhizosphere was studied in a long-term field experiment involving the growing of sugar beets and winter wheat. It was shown that the treatment of field plots with carbon dioxide at a concentration higher than that in the atmosphere (550 ppm) for three-four years resulted in the formation of a microbial community with a higher maximum specific growth rate and a larger share of R-strategy microorganisms as compared to the soil under the control plants. No reliable differences in the total microbial biomass in the soil under the winter wheat were revealed between the treatments with the ambient and elevated CO^sub 2^ concentrations; in the soil under the beet plants, a reliable increase in the total microbial biomass at the elevated CO^sub 2^ concentration was noted only in the close vicinity of the plant roots.[PUBLICATION ABSTRACT]