Soil Emissions of Nitrogen Trace Gases: Leveraging the Decommissioning of the Desert FACE Site

陆地生态系统是全球碳循环的重要组成部分，因此有可能影响气候变化的速度。 大约十年来，美国能源部 (DOE) 一直支持一系列自由空气二氧化碳富集 (FACE) 实验，以评估大气二氧化碳 (CO2) 浓度升高对陆地生态系统的影响。 其中一项实验是位于莫哈韦沙漠的内华达沙漠 FACE 设施 (NDFF)。 没有其他实验能够持续将升高的二氧化碳排放到沙漠生态系统中。 美国能源部正在终止其 FACE 实验。 这一退役过程提供了一个独特的机会，可以对沙漠生态系统在二氧化碳浓度升高的情况下如何发挥作用进行全面分析。 在关闭期间，能源部将仅支持生态系统碳储存的研究。 美国国家科学基金会的这项研究将利用能源部的支持来调查二氧化碳浓度升高对沙漠氮循环的影响。该研究将：1）检查整个生态系统中氮的数量和同位素特征，2）测量氮在土壤内如何循环和转化，以及在去除额外的二氧化碳后氮的变化如何，3）测量去除高浓度二氧化碳处理后生态系统排放的氮气的量级和同位素组成。除了影响生态系统对高浓度二氧化碳的总体响应外，生态系统氮循环的变化还有可能影响区域空气质量、降水酸化、粮食生产和人类健康。 在干旱的西南部尤其如此，因为它是美国增长最快的地区之一。 对氮气排放控制的深入了解将有助于为未来的政策和补救决策提供信息。 该研究的其他更广泛的影响包括：（1）本科生和研究生的教学和培训，（2）代表性不足群体的参与，以及（3）向非学术受众传播结果。

Terrestrial ecosystems are an important component of the global carbon cycle and as a consequence have the potential to influence the rate of climate change. For approximately 10 years, The U.S. Department of Energy (DOE) has been supporting a series of Free Air CO2 Enrichment (FACE) experiments to evaluate the effects of elevated atmospheric carbon dioxide (CO2) concentration on terrestrial ecosystems. One such experiment is the Nevada Desert FACE Facility (NDFF) in the Mojave Desert. No other experiment has continuously applied elevated CO2 to a desert ecosystem. The DOE is in the process of terminating its FACE experiments. This decommissioning process represents a unique opportunity to complete a comprehensive analysis of how a desert ecosystem functions under elevated CO2. During the shut down, DOE will only support research on ecosystem carbon storage. This NSF research will leverage the DOE support to enable investigations of the effects of elevated CO2 on desert nitrogen cycling. The research will: 1) examine the amount and the isotopic signature of nitrogen throughout the ecosystem, 2) measure how nitrogen cycles and transforms within the soil and how this changes after the additional carbon dioxide is removed, and 3) measure the magnitude and isotopic composition of nitrogen gases emitted from the ecosystem following the removal of the elevated CO2 treatment.In addition to influencing the overall response of the ecosystem to elevated CO2, changes in ecosystem nitrogen cycling have the potential to influence regional air quality, acidification of precipitation, food production, and human health. This is especially true in the arid southwest because it is among the fastest growing regions in the US. A firm understanding of the controls on emissions of nitrogen gases will help inform future policy and remediation decisions. Other broader impacts of the research include: (1) teaching and training of undergraduate and graduate students, (2) participation of underrepresented groups, and (3) dissemination of results to non-academic audiences.