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 infuencing microbial activity and the carbon pool. In this 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 atmospheric CO₂ concentration (380 ppm) or elevated CO₂ concentration (760 ppm) conditions. Additionally, the community structure of 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 fat in May 2005, and placed in small pots (diameter 6 cm, height 10 cm). The pots were incubated for 60 days in a growth chamber under two different CO₂ concentration conditions. Sediment samples for all measurements were subdivided into two parts: surface (0-2 cm) and rhizome (4-6 cm) soils. No signifcant differences were detected in EEA with different CO₂ treatments in the surface and rhizome soils. However, the ratio of β-glucosidase activity to N-acetylglucosaminidase activity in rhizome soil was signifcantly lower (P < 0.01) at 760 ppm CO₂ than at 380 ppm CO₂, thereby suggesting that the contribution of fungi to the decomposition of soil organic matter might in some cases prove larger than that of bacteria. Community structures of SRB were separated according to different CO₂ treatments, suggesting that elevated CO₂ may affect the carbon and sulfur cycle in salt marshes.