Improving Sustainability of Coniferous Ecosystems across the Southeastern United States Using 15N.

Our primary research objective was to refine our understanding of N dynamics in coniferous ecosystems across the southeastern United States. We used ¹⁵N enriched fertilizers (0.5 atom %) to trace the ecosystem fate and partitioning of applied N in these systems. We also compared the efficacy of two types of N containing fertilizers, urea and urea+NBPT after a winter fertilization. Nine 100 m² circular plots (3 urea, 3 urea+NBPT, 3 control – no fertilization) were installed at each of the three study sites during the winter of 2016-2017. During December 2016-January 2017, 224 kg ha^-1 of total N was applied to each treatment plot. At the end of the first growing season, fertilizer N uptake was determined by sampling a single pine tree from the center of each treated plot. In addition, all primary ecosystem components were analyzed to assess the fate of applied N (understory, litterfall, forest floor, mineral soil, roots). Losses were determined by using a microcosm experiment.