Effects of elevated CO2 on organic matter decomposition capacities and community structure of sulfate-reducing bacteria in salt marsh sediment

Increasing atmospheric CO2 affects the soil carbon cycle by influencing microbial activity and the carbon pool. Inthis study, the effects of elevated CO2 on extracellular enzyme activities (EEA; β-glucosidase, N-acetylglucosaminidase,aminopeptidase) in salt marsh sediment vegetated with Suaeda japonica were assessed under ambient atmosphericCO2 concentration (380 ppm) or elevated CO2 concentration (760 ppm) conditions. Additionally, the community structureof sulfate-reducing bacteria (SRB) was analyzed via terminal restriction fragments length polymorphism (T-RFLP).Sediment with S. japonica samples were collected from the Hwangsando intertidal flat in May 2005, and placed in smallpots (diameter 6 cm, height 10 cm). The pots were incubated for 60 days in a growth chamber under two different CO2concentration conditions. Sediment samples for all measurements were subdivided into two parts: surface (0-2 cm)and rhizome (4-6 cm) soils. No significant differences were detected in EEA with different CO2 treatments in the surfaceand rhizome soils. However, the ratio of β-glucosidase activity to N-acetylglucosaminidase activity in rhizome soil wassignificantly lower (P < 0.01) at 760 ppm CO2 than at 380 ppm CO2, thereby suggesting that the contribution of fungi tothe decomposition of soil organic matter might in some cases prove larger than that of bacteria. Community structuresof SRB were separated according to different CO2 treatments, suggesting that elevated CO2 may affect the carbon andsulfur cycle in salt marshes.