Effects of Short and Long-Term Hydrological Regimes on the Composition and Function of Denitrifying Bacteria in Experimental Wetlands

We investigated effects of short-and long-term hydrologic fluctuations on denitrification in constructed wetland basins. N-2 and N2O emission rates, their ratio and a number of physicochemical variables were compared between pulsed (with annual drawdown-flooding cycles) and static (constantly flooded) wetland basins. The abundance and structure of general and denitrifying bacterial communities were compared based on quantitative PCR and terminal restriction fragment polymorphism analyses of 16S rRNA and nosZ genes, respectively. These variables significantly differed among sampling months, but not between the two long-term hydrologic treatments. The same set of variables were measured and compared among samples from different sites of one pulsed basin. The single basin experiment revealed temporal shifts in measured variables, which coincided with short-term hydrological changes. Bank sites, which had larger changes in abiotic conditions, showed greater variability in denitrifying activities than basin sites. Significant difference in N-2 and N2O emission rates, 16S rRNA and nosZ gene abundance and structural composition was also identified between basin and bank sites. Our results suggest that activity and community structure of denitrifying bacteria in wetland soils are insensitive to moderate hydrology change, but can be significantly impacted by large hydrological fluctuation at both short-term and long-term scales.