The factors controlling temporal variations of nitric oxide (NO) and nitrous oxide (N20) production in several systems with distinct wet and dry seasons will be investigated. More specifically, the researchers will examine: 1) biotic and abiotic processes of inorganic-N and N0 production in dry soil; 2) the origin of trace N-gas flushes when dry soils are wetted; 3) dynamics of nitrifying populations under changing soil moisture and substrate availability; 4) origin and control of N0 production by nitrifiers and denitrifiers; and 5) factors affecting escape of N0 and N20 from soil. These studies will be carried out on soils taken from three west-coast ecosystems - the oak-grasslands and coniferous forest ecosystems of California and the deciduous forests of Mexico. State-of-the-art techniques for studying nitrogen cycling in soils and microbial populations will be used. These include 15N isotope dilution techniques in the nitrogen cycling work and fluorescent antibody and micro-autoradiography techniques in the microbial population work. Various aspects of the process-level research will ultimately be integrated through modeling. The significance of this research is that it will help us to understand how changes in soil moisture content affect the production of two important trace gases, N0 and N20. Nitric oxide is of interest because of its involvement in tropospheric reactions which, among other things, create ozone, a major pollutant in the lower atmosphere. Nitrous oxide is of interest because it is a highly efficient greenhouse gas and so is involved in global climate change. Dr. Firestone has a very good record of productivity working in the complex area of soil-N dynamics. The institutional support available to her is superior.
