Microbial response over time to hydrologic and fertilization treatments in a simulated wet prairie

Naturally occurring wetlands are often threatened by runoff from urban areas, while constructed wetlands are increasingly used to filter sediments and nutrients from urban runoff. To analyze the potential effects of urban runoff on wetland soil microbial activity and composition, we combined phospholipid fatty acid analysis (PLFA) with assays of enzyme activities and nitrification potential (indicators of microbial function) in constructed wetland mesocosms. Mesocosm treatments included nutrient addition treatments (high, low, and none) and hydologic regimes (constant flood, early season flood, and intermittent flood) in a full factorial design. We found that changes in hydrologic regime affected both structural (membrane lipid) and functional (enzyme activities and nitrification potentials) aspects of the microbial community to a greater degree than did nutrient additions. For example, the arbuscular mycorrhizal fungal (AMF) lipid indicator appeared to be highly sensitive to constant flooding. Although hydologic treatments were the dominant factor affecting microbial community structure and function, nutrient additions did appear to alter fungal lipid biomarkers (both mycorrhizal and saprotrophic) and nitrification potentials. In addition, samples taken between June and September indicated a seasonal/temporal progression; for example the effect of the early season flood treatment subsided after flooding ended. Finally, correlation between structure and function data indicate that the study of microbial community structure, in addition to function, may be important for understanding wetland ecosystem function.