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

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。当前生态系统生态学的概念集中在氮有效性和生物需求之间的耦合，以控制生态系统对氮的保留。当植物的营养需求较低时，如在老年或休眠季节，或由于空气污染或肥料使用而使氮可用性增加时，预计生态系统的氮损失会增加。提出的工作通过三个现场实验来面对这些模型。首先，将通过开始一项长期实验，在纽约中部不同年龄的废弃农田中添加氮，及时检查森林发展过程中的氮保留情况。这也将能够测试年龄和氮沉降对森林碳固存的作用。第二，长期氮污染并没有像预期的那样导致水体硝酸盐含量的增加。一个限制因素可能是，近年来随着酸雨的减少，这些生态系统在恢复过程中产生的溶解有机碳使过量的氮变得复杂。这将通过评估控制溶解碳和硝酸盐损失的因素以及在新罕布什尔州进行的酸度控制实验中溶解碳和硝酸盐的反应来检验。第三部分将通过向纽约中部的分水岭添加一系列氮来解决植物吸收在控制季节性溪流硝酸盐损失中的假设作用。这也将使陆地和水生氮保持机制的作用的对比和土壤有机质中氮的命运的确定成为可能。所有三个实验都试图研究森林碳和氮循环的重要交叉点，同时采用新的和现有的实地实验、新的数据收集和稳定同位素，对影响氮保留的植物、土壤、微生物和水文因素有更复杂的了解。人类活动已经深刻地改变了全球氮循环。空气污染对顺风生态系统的影响取决于增加的氮的命运。至少对某些森林来说，植被的吸收和保持可能刺激碳固存，而溪流中硝酸盐的损失可能使土壤和地表水酸化，并有助于下游富营养化。在相对稳定的土壤有机质形式中氮的保留可以为添加的氮提供长期的汇。该项目将使人们更全面地了解氮对森林生态系统的影响，从而更好地管理受影响的森林。作为综合教育和推广计划的一部分，活动包括与纽约伊萨卡古生物研究所和地球博物馆的教育专家合作。这将包括与森林参观展览有关的公共宣传，发展一个关于森林生态系统和空气污染影响的K-12教师专业发展讲习班，以及发展一个关于与科学教育工作者合作制作有用教育材料的技能的研究生讲习班。本研究还将建立一个当地的分水岭，作为本科生生态学教学的现场。这些伙伴关系将使科学教育更加有效，并使更广泛的受众受益。

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.