9311380 Robertson This proposal will examine the effect of environmental factors and diversity of denitrifying bacteria on the spatial and temporal variability of denitrification in agricultural and grassland ecosystems. Specific questions to be addressed include 1) to what extent, and under what circumstances, is denitrifier community composition different among ecosystems with different nitrous oxide production potentials?, 2) do denitrifiers from different ecosystems produce nitrous oxide at different rates?, and 3) does spatial and temporal variability in nitrous oxide production reflect differences in dominant denitrifier populations as well as differences in environmental controls? These questions will be addressed by sampling soil from ecosystems that differ in chemical conditions that affect nitrous oxide flux rates, incubating to characterize nitrous oxide flux rates, and denitrifier isolation to characterize community structure. %%% Denitrifiers are bacteria that, during anaerobic respiration, convert nitrogen from a form available to plants to gaseous nitrous oxide not available to plants. Thus, denitrifiers have a direct impact on soil fertility and plant production. Denitrification also is important because the nitrous oxide is an important greenhouse gas and a catalyst of statospheric ozone decay. Environmental factors affecting denitrification processes have been examined, but their relative importances and the significance of particular denitrifier species composition is not known. This study will all evaluation of the relative contributions of environmental controls and denitrifier diversity to nitrous oxide flux rates. ***
