CAREER: Mechanisms of Forest Nitrogen Retention Over Seasons, Sites, and Succession

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Current concepts of ecosystem ecology center on the coupling between nitrogen availability and biotic demand in controlling retention of nitrogen by ecosystems. Increased nitrogen loss is expected from ecosystems when the nutritional demands of plants are low, as in old age or during the dormant season, or when nitrogen availability has increased due to air pollution or fertilizer use. The proposed work confronts these models using three field experiments. In the first, nitrogen retention over the course of forest development in time will be examined through initiation of a long term experiment where nitrogen is added to abandoned agricultural fields of different ages in central New York. This will also enable testing the role of age and nitrogen deposition on forest carbon sequestration. The second derives from the observation that chronic nitrogen pollution has not led to the increases in stream water nitrate as expected. One constraint may be that the excess nitrogen is complexed by dissolved organic carbon produced during recovery that these ecosystems have undergone in recent years as acid rain was reduced. This will be tested by evaluating factors that control dissolved carbon and nitrate losses and by responses of both dissolved carbon and nitrate in experiments in New Hampshire where acidity is manipulated. The third will address the assumed role of plant uptake in controlling seasonal stream nitrate loss through a series of nitrogen additions to a watershed in central New York. This will also enable contrasts of the role of terrestrial versus aquatic nitrogen retention mechanisms and determination of the fate of nitrogen in soil organic matter. All three experiments seek to examine important intersections of forest carbon and nitrogen cycles, while employing new and existing field experiments, new data collections, and stable isotopes to develop a more complex understanding of the plant, soil, microbial and hydrologic factors that affect nitrogen retention. The global nitrogen cycle has been profoundly altered by human activities. Impacts of air pollution on downwind ecosystems depend on the fate of the added nitrogen. Uptake and retention by vegetation may stimulate carbon sequestration, at least for some forests, while losses of nitrate in stream water may acidify soils and surface waters and contribute to downstream eutrophication. Retention of nitrogen in relatively stable forms of soil organic matter could provide a long term sink for added nitrogen. This project will provide a more complete understanding of the effects of nitrogen on forest ecosystems and enable better management of affected forests. Activities as part of an integrated education and outreach program include collaboration with education specialists from the Paleontological Research Institution and Museum of the Earth in Ithaca, New York. This would include public outreach in connection with a visiting exhibit on forests, development of a K-12 teacher professional development workshop on forest ecosystems and impacts from air pollution, and development of a graduate student workshop on skills for partnering with science educators to produce useful education materials. This research would also establish a local watershed as a field site for teaching ecology to undergraduates. Together these partnerships will enable more effective science education and outreach to a much broader audience.