Wetlands are often regarded as expendable ecosystems; however, the functional biology of these habitats is difficult to mimic and restore. Of particular importance in restoration efforts is a greater appreciation of the complex relationship that exists between wetland hydrology (e.g., soil saturation and redox), vegetation, and the soil microbial community. Although substantial progress has been made in understanding microbially-mediated processes, there is still a tremendous amount to learn about their interactions in wetlands. The present study characterized this relationship using long-term field manipulations and a nested experimental design. Specifically, plots were established in three hydrologically-distinct regimes (wet, intermediate, and dry) within a non-tidal freshwater wetland along the James River (Virginia). Inside each main plot, ten subplots were cleared of all aboveground plant material; five plots were left to re-grow (“vegetated” controls), while the remaining five were weeded each week to maintain bare soil (“non-vegetated”). Manipulations were started at the beginning of the growing season, and sampling continued until the following winter. Every eight weeks, soil cores (30 cm) were collected , divided into two depth increments, and analyzed for a for a variety of soil properties (e.g., pH, OM, C:N, redox), microbial community structure (16S-rDNA-based T-RFLP), and extracellular enzyme activity.
Results/Conclusions
Data indicate that there are unique physio-chemical properties and differences in plant species composition and biomass across the three hydrological regimes. Analysis of the microbial communities revealed similar patterns, particularly for the extracellular enzyme activity. Similar enzyme activity was observed between dry and wet sites, while responses in the intermediate site correlated to slight changes in saturation. Within a given hydrological regime, depth did not appear to be a significant factor; similarly, there have only been small differences characterized between vegetated and non-vegetated treatment plots. Drastic differences have been seen between the three hydrology conditions indicating that saturation is a more significant variable in soil development in an emerging wetland, while the physical and functional response to vegetation is slow to develop. Differences in microbial community properties tend to best follow differences in soil physicochemical parameters, and to be less strongly related to the presence or type of vegetation. In older marshes, the environmental feedbacks are likely quite different, and the influence of vegetation and plant diversity may have a greater impact on microbial diversity and thus ecosystem function.
