Effects of elevated CO2 on communities of denitrifying bacteria and methanogens in a temperate marsh microcosm

The effects of elevated CO(2) on soil bacterial community with upland vegetation have been widely studied, but limited information is available regarding responses of denitrifier and methanogen communities to elevated CO(2) in wetland ecosystems. Using restriction fragment length polymorphism (RFLP), terminal RFLP analysis, and real-time quantitative PCR, we compared communities of denitrifiers and methanogens in a laboratory-scale wetland system planted with one of three macrophytes, Typha latifolia, Scirpus lacustris, or Juncus effusus, after 110 days of incubation. Our study showed that elevated CO(2) could affect community structures of both denitrifiers and methanogens, each of which had a unique response pattern. In particular, elevated CO(2) shifted nirS-containing community with a unique structure irrespective of vegetation type. mcrA-containing community appeared to shift to community with unique types of hydrogenotrophs under elevated CO(2) conditions. The change of dissolved organic carbon driven by elevated CO(2) appeared to be related with the shift of both denitrifiers and methanogens. Overall, this study indicates that elevated CO(2) could change the community structure of denitrifiers and methanogens temporarily. These results also suggest a presence of stable dominant populations that were not substantially affected by changes in CO(2) concentration.