Changes of bacterial communities in restored Phragmites australis wetlands indicate the improvement of soil in the Yellow River Delta

With increasing global awareness of the ecological services that wetlands can provide, an increased emphasis has been placed on the need for wetland restoration projects. Among the types of wetland restoration projects that have been initiated are those that aim to return farmlands back to their previous wetland state to restore wetland vegetation and regain the ecological services that had been lost. However, studies on the changes of belowground bacterial diversities following the conversion of farmlands back to wetlands are rare, especially in coastal areas. In the present study, we examined the soil characteristics and the microbial diversity of the soil and roots across Phragmites australis-dominated coastal marshes within the Yellow River Delta. We sampled two marshes that had been restored 11 and 3 years prior to sampling (11-year site and 3-year site, respectively). We also sampled two additional, undisturbed wetlands-one within the new Yellow River course (NC site), and the other within the abandoned Yellow River course (OC site)-to serve as controls to assess the effectiveness of the wetland restoration project. Specifically, we measured the concentrations of nutrients and organic matter in the soil, the activities of the enzymes urease, sucrase, and alkaline phosphatase in the soil, and the diversity of the microbial communities in the soil and roots. The results showed that the concentrations of soil nutrients and the activities of the soil enzymes were significantly greater in the 11-year site compared to the 3-year site but were similar between the 11-year site and the NC site. Shannon, Simpson, and Pielou indices of diversity among the soil bacteria were positively correlated with the concentrations of soil nutrients and the activities of the soil enzymes, which were generally lowest in the 3-year site compared to the other study sites. The diversity indices among the root bacteria, however, did not exhibit a similar trend. The bacterial community composition of the soil and roots differed between sites. The relative abundance of Firmicutes in the soil and roots was highest in the 3-year site compared to the 11-year, NC, and OC sites. The relative abundance of soil Bacteroidetes was higher in the soils of the NC and OC sites compared to in those of the restoration sites. Overall, the diversity richness of the subsurface bacterial communities increased with the time since the restoration of these wetlands, and after 11 years post-restoration, appeared to resemble those of the natural wetlands of the area. Our results therefore imply that future assessments of coastal wetland restoration projects could be made based in part on soil nutrient concentrations, enzyme activities, and the microbial diversity of the soil and plant roots within these systems.