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

9652581诺比自然生态系统对大气中二氧化碳浓度增加的反应是分析当前和潜在的全球变化影响的一个重要组成部分。到目前为止，了解东部落叶林将如何受到大气中二氧化碳浓度升高的影响的努力，是通过研究森林系统的组成部分(个别小树、具体过程)来解决的，但现在是时候迈出关键一步，以林分一级机制为重点，衡量完整森林生态系统的综合反应。在橡树岭国家环境研究公园组装的自由空气二氧化碳暴露(Face)设备为研究林分水平的反应提供了一种机制。该设施位于封闭式树冠中，11米高，单一种植香胶，将使树木持续暴露在高于周围环境200 ppm的二氧化碳浓度下。科学任务围绕一系列相互关联的假设进行组织，这些假设涉及森林的基本特征，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素年际变化的关系；确定响应的生理机制，包括叶片气体交换、植物水分关系、呼吸和组织生物化学；量化细根密度和周转以及土壤碳循环的其他组成部分；量化氮循环的关键组成部分及其对二氧化碳增加的响应；以及使用基于过程的机械性土壤-植物生态系统模型来制定和完善生态系统对二氧化碳增加的响应假设。这些分析的结果将用于对潜在的全球变化影响进行建模和评估。Oak Ridge 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，他们有兴趣研究与森林对升高的二氧化碳的反应相关的其他问题。

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.