Elevated CO2 and nitrogen addition affect the microbial abundance but not the community structure in salt marsh ecosystem

With unique and important characteristics, salt marsh ecosystems are expected to be affected by elevated CO2 and N enrichment. Although various studies have assessed the effects of those changes on the vegetation of salt marshes, little information is available about their impact on microbes. In this study, we comprehensively analyzed the microbial community structure of soils responding to elevated CO2 (eCO2) and N addition (N) over 3 years in salt marsh ecosystem. We employed pyrosequencing, T-RFLP analysis, and quantitative PCR to study the bacterial, archaeal, and fungal communities. The overall results indicated that 1) eCO2 and N affected the microbial abundance but not community structure significantly in salt marsh system, 2) due to their different ecophysiology, the responses of the three different microbial communities to eCO2 and/or N addition varied with each group, 3) the composition (C3/C4 or diversity) of the plant community was important in structuring the microbial community of salt marsh ecosystems, which generally have low plant diversity, 4) the archaeal and fungal communities responded more strongly to eCO2 and/or N addition than the bacterial community. This study represents the first comprehensive report of the effects of eCO2 and/or N addition on the diverse microbial community structures of tidal marsh systems. It suggests that single or combined effect of eCO2 and N on microbial abundance in salt marsh was obvious, and that the key groups playing an important role in the biogeochemical process can be shifted.