Tuesday, November 14, 2006
187-9
Nitrous Oxide Production and Consumption Processes in Soils: Evidence from Stable Isotope Analyses.
Joost Van Haren, University of Arizona, Tucson, AZ 85721 and Dean Martens, USDA-ARS-SWRC, 2000 E Allen Road, Tucson, AZ 85719-1596.
The global budget of nitrous oxide (N2O), an important greenhouse gas and component in ozone destruction, is still poorly constrained. N2O is mainly produced by nitrifying and denitrifying bacteria and fungi in soils. Subsequently, N2O diffuses out of the microorganism and is transported to the atmosphere. In wet soils N2O is mostly produced by denitrifier bacteria that can reduce N2O to N2 and transport out of the soil is limited. In semi-arid soils (low water content) gas transport is relatively rapid and nitrification produces most N2O. Substantial N2O consumption is expected in tropical, but not semi-arid soils. We will present natural abundance N2O stable isotope and isotopomer data and analyses based on culture experiments (Sutka et al. 2003 and 2006) to distinguish N2O consumption and production processes. Stable isotope analysis is a powerful tool in tracing elements, especially in the N cycle where isotope differences can be large, due to large valence state changes. In a wet (tropical forest Biosphere 2) and semi-arid (Santa Rita Experimental Range) setting, we measured N2O concentration and stable isotope composition of soil gas fluxes and profiles. We will discuss the measured data in light of the endmember values calculated based on the culture studies and soil pool isotope compositions.