The variability of soil microbial community composition of different types of tidal wetland in Chongming Dongtan and its effect on soil microbial respiration

Previous studies have shown that the soil enzyme activity and microbial respiration intensities varied in two different types of tidal wetland in Chongming Dongtan, the first a sandy soil in a scouring bank with Phragmites australis and the second a saline-alkali clay soil in silting bank with P. australis/Spartina alterniflora/Scirpus mariqueter, resulting in different organic carbon reservation capabilities; however, their microbial biomass did not differ significantly. To clarify the microbial mechanism that explains the variability of soil respiration among different wetland areas, the community structure and abundance of soil microorganisms in different types of wetland were investigated using denaturing gradient gel electrophoresis (DGGE) plus real-time quantitative polymerase chain reaction (PCR) technologies, and the relationship between soil environmental factors and the microbial community structure and the soil respiration intensity was elucidated. The results revealed that the soil microbial diversity and community structure differed between the two typical wetland areas. The common population was uncultured bacterium in both areas, and the most abundant community was α-, β-, γ-Proteobacteria, which play an important role in the cycling of carbon in soil. However, the abundance of α-Proteobacteria in Area A was 18.2% of that in Area B (P <0.05), while the β-Proteobacteria in Area A was 3.23 times higher than that in Area B (P <0.05). In addition, one cellulose-degrading bacteria, uncultured Bacilli, was detected in Area A. PCA (Principal component analysis) revealed that γ-Proteobacteria and β-Proteobacteria had the greatest impact on soil respiration intensity. Both soil water content and salinity depressed the propagation of β-Proteobacteria. Considering the similar microbial biomass and abundance of γ-Proteobacteria between the two areas, the lower level of β-Proteobacteria, uncultured Bacilli bacterium in Area B might be important factors involved in the lower soil respiration, and hence the higher soil organic carbon reservation capability in Area B.