The goal of this research is to develop techniques which can be used for in situ measurements of nitrogen cycling processes in saltmarsh ecosystems. Techniques which can be used to measure rates of nitrification by autotrophic and heterotrophic nitrifiers, rates of denitrification by heterotrophic denitrifiers as well as by autotrophic and heterotrophic nitrifiers, and rates of dissimulator nitrate reduction will be developed. The percentage of the products of these nitrogen cycling processes that may be lost from an ecosystem as N20, NO, and N2 will be determined. Initially laboratory studies will be conducted using pure cultures of representative autotrophic nitrifiers, heterotrophic nitrifiers, denitrifiers, and dissimulator nitrate reducers. Emphasis will be place on using a variety of inhibitors to determine which nitrogen metabolizing processes operate under a given set of conditions (pO2, electron donor or substrate availability, pH). Preliminary studies with 14C- and 15N- labelled substrates in conjunction with inhibitors will be performed. Promising techniques will then be tested on soil cores held in a gas-recirculation system. Cores for study will be taken from the Long Term Ecological Research Site, located within the Virginia Coast Reserve. Soil core experiments will be designed to determine which inhibitor and/or labelling technique is most useful for assessing the relative importance of particular nitrogen cycling processes in saltmarsh soil. Finally, exploratory studies will be initiated at the LTER site to determine whether selected inhibitor techniques can be performed effectively under in situ conditions. This team of investigators is very well qualified. Institutional accommodations are appropriate to the work. The association with the Long-Term Ecological Research project at the Virginia Coast Reserve is an added strength. Outputs from this type of research will be of importance not only to the fundament process-level understanding of saltmarsh wetlands but will also provide estimates for the role played by such systems in the biological import of nitrogenous gases to the atmosphere.
