Friday, August 6, 2010: 8:40 AM
401-402, David L Lawrence Convention Center
Kelly Sierra Ramirez, School of Global Environmental Sustainability, Colorado State University, Fort Collins, CO, Christian Lauber, Department of Ecology and Evolutionary Biology, University of Colorado at Boulder, Boulder, CO and Noah Fierer, Ecology and Evolutionary Biology and CIRES, University of Colorado, Boulder, CO
Background/Question/Methods Ecosystems worldwide are receiving increasing amounts of reactive nitrogen (N) through anthropogenic activities. Bacteria play critical roles in ecosystem processes and identifying how anthropogenic N impacts bacterial communities may elucidate how critical microbially-mediated ecosystem functions are altered by N additions. Our previous work on experimental N gradients at Cedar Creek, MN and Kellogg Biological Station, MI demonstrated that N fertilization consistently impacts both the phylogenetic and taxonomic structure of soil bacterial community structure in a predictable manner regardless of ecosystem type. These results suggest that bacterial communities across N fertility gradients are structured more by either nitrogen and/or soil carbon availability, rather than by shifts in the plant community or soil pH indirectly associated with the elevated nitrogen inputs. Still, field N additions can have both direct and indirect effects on microbial communities and previous work was unable to fully decouple N and C effects with this study. In an effort to identify the bacterial groups that respond directly to N additions we preformed an in-lab follow up experiment. Four concentrations (10, 50, 200, 500 ug N) of six N types (NH4NO3, Urea, KNO3, NH4Cl, (NH4)2SO4, Ca(NO3)2) were added to three distinct soils. Soil respiration (CO2) was measured and analyzed using an infrared gas analyzer (IRGA) for 45 days.
Results/Conclusions Across all soil types we consistently observed a significant decrease in soil respiration of approximately 60%, indicating that N additions functionally impact the soil bacterial community. Using high-throughput pyrosequencing we are able to identify which bacterial groups respond directly to in-lab N additions. By comparing our in-lab community composition and functional changes to our field results we build a predictive understanding of how N additions impact the structure and function of soil microbial communities.
