Effects of Elevated CO ₂ 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.