Microbial Activity in a Temperate Forest Soil as Affected by Elevated Atmospheric CO 2

Abstract

Microorganisms play a key role in the response of soil ecosystems to the rising atmospheric carbon dioxide (CO 2) as they mineralize organic matter and drive nutrient cycling. To assess the effects of elevated CO 2 on soil microbial C and N immobilization and on soil enzyme activities, in years 8 (2006) and 9 (2007) of an open-top chamber experiment that begun in spring of 1999, soil was sampled in summer, and microbial biomass and enzyme activity related to the carbon(C), nitrogen (N) and phosphorus (P) cycling were measured. Although no effects on microbial biomass C were detected, changes in microbial biomass N and metabolic activity involving C, N and P were observed under elevated CO 2. Invertase and dehydrogenase activities were significantly enhanced by different degrees of elevated CO 2. Nitrifying enzyme activity was significantly ( P < 0.01) increased in the August 2006 samples that received the elevated CO 2 treatment, as compared to the samples that received the ambient treatment. Denitrifying enzyme activity was significantly ( P < 0.04) decreased by elevated CO 2 treatments in the August 2006 and June 2007 ( P < 0.09) samples. β-N-acetylglucosaminidase activity was increased under elevated CO 2 by 7% and 25% in June and August 2006, respectively, compared to those under ambient CO 2. The results of June 2006 samples showed that acid phosphatase activity was significantly enhanced under elevated CO 2. Overall, these results suggested that elevated CO 2 might cause changes in the belowground C, N and P cycling in temperate forest soils.