A Stable Isotope and Eddy Covariance System for Monitoring Ecosystem Metabolism

北亚利桑那大学获得了一笔资金，用于购买涡动相关塔和稳定同位素比质谱仪。涡旋相关变设备将用于测量西南生态系统与大气之间的碳、水和能量交换。这些通量是生态系统过程的关键调节因子，如分解、养分循环、消费者活动和河岸生态系统的地下水补给。它们还影响区域和全球气候，并日益引起与温室气体管理有关的决策者的兴趣。以往的涡动相关研究强调确定原始生态系统的净通量。该项目的两个主要目标是：1)利用稳定同位素技术确定导致净通量变化的机制（例如，对于二氧化碳，确定林下树与林下草对整个生态系统光合作用和呼吸作用的贡献）；2)利用大规模实验，确定碳、水和能量的通量如何响应干扰和土地利用做法。涡旋相关方差和稳定同位素测量将在两个实验环境中进行。首先，为了减少火灾危险而被砍伐的大片黄松林将与茂密的对照林进行比较，记录所谓的“森林恢复”对碳、水和能量通量的影响。其次，将比较不同放牧管理措施下的草原，以评估哪种土地管理措施在保水和储存碳方面更有效。在这些实验中，塔上的仪器将被用来测量“涡流”（湍流空气运动），这些涡流携带着空气向上、向下和向侧面移动。测量垂直空气运动及其所含的二氧化碳、水蒸气和热量的量，可以计算出这些成分在生态系统和大气之间的净通量。同位素比值质谱仪将用于分析整个冠层空气样本中二氧化碳和水蒸气的稳定同位素组成。碳、氢和氧的稳定同位素提供了生态系统各个组成部分如何对涡动相关方差测量的总体通量做出贡献的特征指纹，因此将这两种技术结合起来将使研究人员能够确定哪些生态系统组成部分负责改变净通量。该设备将用于解决从气候对生态系统功能的影响到大规模森林恢复对区域气候和现场水平衡的影响等研究问题。一旦建立，这个新的通量测量阵列将吸引更多的研究人员从事各种各样的问题，从设计新的范围管理方案到厄尔尼诺和太平洋年代际振荡等全球重要现象的区域影响。来自代表性不足群体的本科生将通过NSF资助的UMEB项目参与拟议的研究。UMEB计划的主题包括与该仪器资助的研究相吻合的具体研究活动（例如，科罗拉多高原生态系统的碳平衡，以及西南草原的牲畜管理，生产力和多样性）。招收到UMEB项目的少数民族学生将与参与通量和同位素研究的导师一起工作，并将参加介绍生态系统实验结果的特殊课程。总而言之，这笔资助的设备将增加在生态学和环境生物学重要问题上培养不同背景的学生的机会

Non-Technical AbstractA grant has been awarded to Northern Arizona University to acquire eddy covariance towers and a stable isotope ratio mass spectrometer. The eddy covariance equipment will be used to measure carbon, water, and energy exchange between southwestern ecosystems and the atmosphere. These fluxes are critical regulators of ecosystem processes, such as decomposition, nutrient cycling, consumer activity, and groundwater recharge to riparian ecosystems. They also influence regional and global climate and are of increasing interest to policy-makers concerned with management of greenhouse gases. Previous eddy covariance studies emphasize determining net fluxes in pristine ecosystems. The two major goals of this project are 1) to use stable isotope techniques to determine the mechanisms responsible for changing net fluxes (e.g., for carbon dioxide, determining how overstory trees versus understory grasses contribute to total ecosystem photosynthesis and respiration), and 2) using large-scale experiments, to determine how fluxes of carbon, water, and energy respond to disturbance and land use practices.Eddy covariance and stable isotope measurements will be conducted in two experimental settings. First, tracts of Ponderosa Pine forest that have been thinned to reduce fire danger will be compared with dense, control forests, documenting the impacts of so-called 'forest restoration' on fluxes of carbon, water, and energy. Second, grasslands under varying grazing management practices will be compared to assess which land management practices, for example, are more effective at conserving water and storing carbon. In these experiments, instruments on towers will be used to measure 'eddies' (turbulent air movements) carrying pockets of air upwards, downwards, and sideways. Measuring vertical air movements and the amount of carbon dioxide, water vapor, and heat they contain enables one to calculate the net fluxes of these constituents between the ecosystem and the atmosphere. The isotope ratio mass spectrometer will be used to analyze the stable isotope composition of carbon dioxide and water vapor in samples of air throughout the canopy. Stable isotopes of carbon, hydrogen and oxygen provide characteristic fingerprints of how individual components of ecosystems contribute to overall fluxes measured by eddy covariance, so coupling these two techniques will enable researchers to determine which ecosystem components are responsible for altering net fluxes.This equipment will be used to address research questions ranging from the effects of climate on ecosystem functioning to the implications of large-scale forest restoration for regional climate and site water balance. Once established, this new flux measurement array will attract additional researchers working on issues as diverse as design of new range management programs to regional influences of globally important phenomena such as El Nino and the Pacific Decadal Oscillation. Undergraduate students from underrepresented groups will be recruited to participate in the proposed research through an NSF funded UMEB program already in place at NAU. The theme of the UMEB program includes specific research activities that dovetail nicely with the research enabled by this instrumentation grant (e.g., Carbon Balance of Colorado Plateau Ecosystems, and Livestock Management, Productivity, and Diversity of Southwestern Grasslands). Minority students recruited into the UMEB program will work with mentors involved with the flux and isotope studies and will attend special classes in which the findings of the ecosystem experiments are presented. In sum, the equipment funded by this grant will increase opportunities for training students of diverse backgrounds at NAU in state-of the-art techniques and research relevant to important issues in ecology and environmental biology