Plant litter amendments in restored wetland soils altered microbial communities more than clay additions

Wetland restoration efforts aim to enhance the structure and function of degraded and damaged wetlands. Unfortunately, restoration techniques often alter a site's soil habitat and plant community structure, which affect the activity and composition of microbial communities. Microbial community structure and activity, as a function of soil texture and plant inputs, were studied in soils collected from a restored and a natural tidal freshwater wetland for a period of nine weeks. We expected that increasing the clay content of restored soils from 13% to 20% and 30% would increase soil C retention via sorption and reduce the carbon dioxide (CO2) and methane (CH4) emissions. To elucidate the role of plant inputs in shaping the microbial community and function, plant litter with contrasting C-to-nitrogen (N) ratios were added to test the hypothesis that a greater portion of plant leaf-C from the nutrient-poor plant, Phragmites australis, would be mineralized to CO2 and CH4 than the nutrient-rich plant, Peltandra virginica. We also expected P. virginica would support a more abundant and diverse microbial community than P. australis. Unexpectedly, we found that increasing the clay content of restored soils caused a marginal reduction in the total amount of C partitioned as CO2 and CH4, while the nutrient-rich plant, P. virginica, emitted more CO2 and CH4 than the nutrient-poor plant, P. australis. Furthermore, clay and plant leaf litter amendments had a greater impact on the size, diversity, and composition of the microbial population in restored than natural wetland soils. Overall, we found that increasing clay content in a restored wetland had a limited effect on soil C retention. We also discovered that plant litter significantly altered the underlying structure of the microbial community in restored wetland soils, suggesting greater plant diversity may lead to a more stable, resilient microbial community.