Greenhouse gases distribution and the modulating role of salinity in coastal wetlands from semiarid region of the eastern south Pacific

Coastal wetlands are ecosystems considered as a source of greenhouse gases (GHG), such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Wetlands hydrodynamics and water balance influence salinity, a potential driven factor of GHGs recycling and the microbial community involved in its production and consumption. In this study, the influence of conductivity on GHG concentration and benthic microbial community composition was determined during winter and summer in wetlands distributed in a latitudinal gradient (33´77´S- 29´82´S) associated with basins with higher aridity and lower anthropogenic influence at north compared to south. Results indicate that wetlands have a temporal and latitudinal variability associated with higher organic matter content at the north and greater nutrient concentration at the south, predominantly during summer and winter, respectively.. In general, wetlands were characterized by positive CO2 and CH4 excess, and a shift of N2O excess from a negative to positive values from north toward the south. Benthic microbial communities were taxonomically diverse with > 60 phyla mainly associated with low frequent taxa. Highly abundant classes were assigned as Gammaproteobacteria, Alphaproteobacteria and Deltaproteobacteria, including key functional groups involved in GHG recycling such as nitrifying and methanotrophic bacteria. Generalized additive model (GAM) indicated that conductivity accounted for the larger variability of CH4 and CO2, but the predictions were improved when other variables were add, i.e., latitude and pH for CH4 and CO2 concentration. Nitrate and nitrite, but not conductivity, were the best independent predictors to explain changes in the N2O distribution. GAM analysis also indicates that conductivity and nutrients accounted for the changes in the relative abundance (n° sequences) of Betaproteobacteria and Methylotenera sp. Our result highlights the combined role of salinity together with other factors in shaping benthic microbial communities and regulating GHG exchange with the atmosphere in coastal wetlands from a semiarid region of central Chile.