Rapid response of soil protozoa to elevated CO2

Short-term changes in bacterial and protozoan populations from the soil of plants grown under elevated atmospheric CO2 were quantified. We grew Brassica nigra at either ambient or twice-ambient CO2 levels within open-top chambers in the field for 4 weeks. Plant biomass, above- and belowground, was unaffected by elevated CO2. Direct count bacterial density was unchanged under elevated CO2. Flagellate density tended to increase, whereas amoebal density significantly declined under elevated CO2. This change in protozoan community structure suggests trophic transfer of the elevated CO2 fertilization effect through the soil food chain.