How do Elevated CO₂ and Nitrogen Addition Affect Functional Microbial Community Involved in Greenhouse Gas Flux in...

Salt marshes are unique ecosystem of which a microbial community is expected to be affected by global climate change. In this study, by using T-RFLP analysis, quantitative PCR, and pyrosequencing, we comprehensively analyzed the microbial community structure responding to elevated CO₂ (eCO₂) and N addition in a salt marsh ecosystem subjected to CO₂ manipulation and N addition for about 3 years. We focused on the genes of microbes relevant to N-cycling (denitrification and nitrification), CH₄-flux (methanogens and methanotrophs), and S-cycling (sulfate reduction) considering that they are key functional groups involved in the nutrient cycle of salt marsh system. Overall, this study suggests that (1) eCO₂ and N addition affect functional microbial community involved in greenhouse gas flux in salt marsh system. Specifically, the denitrification process may be facilitated, while the methanogenesis may be impeded due to the outcompeting of sulfate reduction by eCO₂ and N. This implies that future global change may cause a probable change in GHGs flux and positive feedback to global climate change in salt marsh; (2) the effect of eCO₂ and N on functional group seems specific and to contrast with each other, but the effect of single factor would not be compromised but complemented by combination of two factors. (3) The response of functional groups to eCO₂ and/or N may be directly or indirectly related to the plant community and its response to eCO₂ and/or N. This study provides new insights into our understanding of functional microbial community responses to eCO₂ and/or N addition in a C3/C4 plant mixed salt marsh system.