Doctoral Dissertation Research: Spatio-Temporal Patterns of Soil Respiration and Age of Respired Carbon from High-Elevation Alpine Tundra

由于与人类有关的二氧化碳排放量和自然二氧化碳排放量以及生物圈和海洋二氧化碳同化速率之间的不平衡，当代大气中的二氧化碳正在增加。这些情况正在加剧自然的温室效应。由此导致的气候变暖与洪水、飓风以及海冰、冰川和永久冻土的丧失有关。高山冻土带在全球环境数据库中是一个代表性不足的生态系统，因为它本身就很偏远，而且在陡峭的山区工作存在困难。最近的研究表明，高山冻土带的二氧化碳排放量可能远远超过之前的估计。为了对高海拔高山冻土带年净碳损失进行基于过程的协调，这项博士论文研究项目将使用一套独特的测量技术并结合放射性碳同位素分析，评估科罗拉多州尼沃特岭的土壤呼吸和净生态系统交换。博士生将使用多尺度方法来(1)通过使用包括小室、梯度和涡流协方差技术在内的独立样本设计来证实先前的数据；(2)调查土壤属性、气候和二氧化碳通量之间的关系；(3)模拟土壤类型对二氧化碳通量的不同响应；以及(4)通过应用放射性碳测年技术来约束大气碳损失的年龄、机制、幅度和趋势。这些方法将被用来检验这一假设，即先前研究提出的不平衡碳循环代表着出人意料的活跃微生物群落对古碳的新陈代谢。证实这一假设将表明，定向气候变化已经开始影响高山地区，同时也提供了未来可能更广泛的碳循环模式的早期指示。该项目旨在将目前的二氧化碳通量测量网络扩展到未被充分研究的生态系统，并将完善高山冻土带二氧化碳通量的大小和时空变异性。通过将自上而下的监测技术与自下而上的机械分析相结合，该项目将调查观察到的高山二氧化碳损失的原因和影响。为了促进将具体结果应用于其他高山系统，将开发概念和经验模型来描述小区尺度和生态系统尺度的通量。这些模型将直接有助于了解全球碳循环。对自然碳循环的全面了解对于准确评估当前二氧化碳排放、政策决策和气候强迫情景的未来后果至关重要。为此，这项工作的结果将有助于限制拟议的政策和法规可能产生的影响。作为博士论文研究改进奖，该奖项还将提供支持，使有前途的学生建立一个强大的独立研究生涯。

Carbon dioxide is increasing in the contemporary atmosphere as a result of an imbalance between the rates of human-related and natural carbon dioxide emission and biospheric and oceanic carbon dioxide assimilation. These circumstances are augmenting the natural greenhouse effect. Resultant climate warming has been linked to flooding, hurricanes, and the loss of sea-ice, glaciers, and permafrost. Alpine tundra is an underrepresented ecosystem in global environmental databases due to its inherently remote nature and the difficulties associated with working in steep, mountainous terrain. Recent research suggests that carbon dioxide emissions from alpine tundra may be far greater than previously estimated. Toward a process-based reconciliation of net annual carbon loss from high-elevation alpine tundra, this doctoral dissertation research project will evaluate soil respiration and net ecosystem exchange through space and time at Niwot Ridge, Colorado, using a distinctive suite of measurement techniques in combination with radiocarbon isotopic analysis. The doctoral student will use a multi scale approach to (1) substantiate previous data through the use of independent sampling designs including chamber, gradient, and eddy covariance techniques; (2) investigate the relationship between soil properties, climate, and carbon dioxide flux; (3) model the differential response of carbon dioxide flux by soil type; and (4) constrain the age, mechanism for, magnitude, and trend of atmospheric carbon loss through the application of radiocarbon dating techniques. These methods will be used to test the hypothesis that an imbalanced carbon cycle suggested by previous research represents metabolism of paleocarbon by an unexpectedly active microbial community. Confirmation of this hypothesis would demonstrate that directional climate change has already begun to affect alpine regions while also providing an early indication of potentially more-widespread carbon cycling patterns in the future.This project addresses expansion of the current network of carbon dioxide flux measurements into understudied ecosystems and will refine the magnitude and spatio-temporal variability of carbon dioxide flux from alpine tundra. By coupling top-down monitoring techniques to bottom-up mechanistic analyses, this project will investigate both the causes and effects of observed alpine carbon dioxide loss. To promote application of specific results to other alpine systems, conceptual and empirical models will be developed to describe both plot- and ecosystem-scale fluxes. These models will directly contribute to knowledge about the global carbon cycle. A comprehensive understanding of the natural carbon cycle is crucial to accurately assess the future ramifications of present-day carbon dioxide emissions, policy decisions, and climate-forcing scenarios. To that end, the results of this work will help constrain the probable effects of proposed policies and regulations. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.