Free-Air CO2 Enrichment of a Closed-Canopy Deciduous Forest

9652581 Norby自然生态系统对大气中二氧化碳浓度增加的响应是分析全球变化当前和潜在影响的关键组成部分。在了解东部落叶森林如何受到大气中二氧化碳的影响方面，迄今为止一直是通过研究森林系统的组成部分（单个小树、特定过程）来解决的，但现在是时候迈出关键的一步，以测量完整森林生态系统的综合响应，重点关注林分水平的机制。橡树岭国家环境研究公园正在组装一个自由空气二氧化碳暴露（FACE）设施，为研究林分水平的响应提供了一种机制。该设施位于封闭的树冠中，11米高的桉树单一栽培将使树木持续暴露在二氧化碳浓度高于环境浓度200 PPM的环境中。科学任务是围绕一组相互关联的假设来组织的，这些假设涉及森林林分的基本特征以及这些特征如何影响对二氧化碳的反应。这些任务的目标是描述地上树木生长和叶面积与二氧化碳浓度和其他环境因子年际变化的关系；确定生理反应机制，包括叶面气体交换、植物水分关系、呼吸和组织生化；量化细根密度和土壤周转量等土壤碳循环组分；量化氮循环的关键组分及其对CO2富集的响应；并使用一个机械的、基于过程的土壤-植物生态系统模型来发展和完善生态系统对二氧化碳升高的反应的假设。这些分析的结果将用于模拟和评估潜在的全球变化影响。橡树岭FACE设施将是一个用户设施，向来自大学和其他研究实验室的研究人员开放，他们对森林对二氧化碳升高的反应感兴趣。

9652581 Norby The response of natural ecosystems to an increasing concentration of CO2 in the atmosphere is a key component of analyses of the current and potential impact of global change. Efforts to understand how eastern deciduous forests will be affected by CO2 enrichment of the atmosphere have heretofore been addressed by studying components of the forest system (individual small trees, specific processes), but it is now time to take the critical leap to measuring the integrated response of an intact forest ecosystem with a focus on stand-level mechanisms. A free-air CO2 exposure (FACE) facility being assembled on the Oak Ridge National Environmental Research Park provides a mechanism for studying stand-level responses. The facility in a closed-canopy, 11m tall sweetgum monoculture will expose trees continuously to CO2 concentrations 200 PPM above ambient. The scientific tasks are organized around an interconnected set of hypotheses that address the essential features of a forest stand and how these features could influence responses to CO2. The objectives of these tasks are to characterize aboveground tree growth and leaf area in relation to CO2 concentration and interannual variation in other environmental factors; determine physiological mechanisms of response, including foliar gas exchange, plant water relations, respiration and tissue biochemistry; quantify fine root density and turnover and other components of soil carbon cycling; quantify the critical components of the nitrogen cycle and their response to CO2 enrichment; and use a mechanistic, process-based, soil-plant ecosystem model to develop and refine hypotheses of ecosystem response to elevated CO2. The results of these analyses will be used for modeling and assessment of potential global change impacts. The Oak Ridge FACE facility will be a user facility, open to researchers from universities and other research laboratories who are interested in pursuing other questions relevant to forest response to elevated C O2.