9727056 Davidson One of the most subtle and pervasive aspects of human-induced global change is the chronic deposition of atmospheric nitrogen in the forests of the northeastern United States. The mechanisms by which inputs of inorganic nitrogen are converted to organic nitrogen and retained within the forest litter layer and mineral soil are key to understanding the fate of nitrogen from atmospheric deposition and its effects on carbon storage in forests. Currently, the processes by which inorganic nitrogen from atmospheric deposition is immobilized in soil are not understood. Whether or not organic nitrogen produced in soil is subsequently made available for plant growth or if it is stored in the soil-humus matrix are unknown. The "unknown nitrogen" fraction commonly comprises the largest single fraction of total soil nitrogen in conventional wet chemical analyses. This research will use 15N-nuclear magnetic resonance (NMR) technology to address these questions. Answers to these two fundamental questions are needed to fully comprehend the soil N cycle, and to predict the ultimate impact of chronic N deposition in forest ecosystems. This project will address these two fundamental questions by using existing long-term forest nitrogen addition experiments at Harvard Forest LTER site in Massachusetts, the Bear Brook Watershed in Maine, and the Fernow Experimental Forest in West Virginia.
