Microbial response to nitrogen deposition, invasive species presence, and flooding in the Upper Mississippi River floodplain, La Crosse, WI

Floodplain forests are influenced by many environmental changes, including invasive species, nutrient deposition, and changes in flood regimes. These factors may influence soil and microbial processes, with consequences for floodplain ecosystems and nutrient transfer between terrestrial and aquatic systems. Extracellular enzyme activity (EEA) reflects the requirements of the microbial community and can demonstrate how communities respond to environmental changes. I measured the effects of experimental nitrogen deposition, invasive species (Phalaris arundinacea) presence, and flooding on EEA in the Upper Mississippi River floodplain in La Crosse, WI. I measured soil abiotic characteristics (gravimetric water content and NH4+ availability) and analyzed soil for the activity of six enzymes (xylosidase (XYL), α-glucosidase (αGLUC), cellbiohydrolase (CBH), phosphatase (PHOS), N-acetyl-β-D-glucosaminidase (NAG), leucine aminopeptidase (LAP)). I found that seasonality was the main control on carbon- and phosphorus-acquiring enzyme activity (XYL p=0.037, αGLUC p=0.002, CBH p=0.107, PHOS p=0.019) and that soil NH4+ availability was strongly correlated with carbon- and phosphorus-acquiring enzymes (XYL p=0.084, αGLUC p=0.002, CBH p=0.046, PHOS p=0.009). Vegetation (native vs. invasive-dominated) and elevation (a proxy for flood duration) were not major drivers of microbial activity. My results suggest that microbial activity is primarily controlled by nutrient availability rather than flood duration or vegetation characteristics