Variability in soil microbial community and activity between coastal and riparian wetlands in the Yangtze River estuary - Potential impacts on carbon sequestration

Wetlands are an important part of the global soil organic carbon pool and microorganisms play a pivotal role in carbon exchange between soils and atmosphere. Most wetland carbon studies have focused on boreal freshwater wetlands, especially peatlands. Less attention has been paid on the estuarine wetlands where variation in tide salinity can highly affect microbiology and carbon sequestration ability of the wetland soils. In this study, two representative estuarine wetlands in the Yangtze River estuary were chosen to determine the possible differences in microbial communities and activities between coastal (high salinity) and riparian (low salinity) zones of both wetlands. Over a 4-year period, the mean soil respiration of the coastal zones was significantly lower (P < 0.05) than that of the riparian zones in each wetland. Soil respiration activities measured in laboratory as well as dehydrogenase activity were also lower in the coastal than in the riparian zones of the wetlands. The differences in the microbial activities could be a result of the differences in the microbial community structure. The riparian wetlands had e.g. more beta-Proteobacteria with strong heterotrophic metabolic activity than the coastal wetlands. Soil salinity correlated negatively to the abundance of beta-Proteobacteria and thus respiration. The riparian wetlands received approximately the same organic matter from plant biomass compared with the coastal wetlands but have lower soil carbon content than the coastal wetlands. This could be associated to the higher microbial decomposition capacity in soils with low salinity. (C) 2013 Elsevier Ltd. All rights reserved.