RUI: Ecosystem responses to atmospheric N deposition in an ombrotrophic bog: vegetation and microclimate feedbacks lead to stronger C sink or source?

工业污染引起的大气氮沉降的增加是北方生态系统中主要关注的问题，北方生态系统通常营养有限。以往的研究假设氮沉降可能通过刺激植物生产力而增加北方生态系统的二氧化碳（CO2）汇潜力。泥炭地，特别是营养有限的沼泽，自冰川消融以来积累了大量的碳(C)，但每年的碳平衡往往是植物生产和土壤分解之间非常小的差异。本研究的主要目的是提高我们对泥炭地生态系统与大气之间复杂反馈的理解，以响应不断增加的大气氮沉降和气候变化。氮沉降会增强还是削弱营养有限的沼泽生态系统的二氧化碳吸收潜力？N沉降对生态系统净CO2交换和气候变化的正反馈和负反馈是什么？植被功能和结构的变化，以及相应的小气候（湿度、温度、截光）变化是如何导致碳平衡变化的？叶片化学、物候和植物功能的变化将如何影响CO2交换的季节性？研究的总体框架包括：(1)氮沉降对全球大气-生物圈相互作用的影响；(2)泥炭地生态系统成为碳源而非长期碳汇的脆弱性。该项目建立在加拿大安大略省渥太华的Mer blue Bog进行的一项长期施肥试验的10年研究和教育基础上，该试验使用不同水平的氮、磷和钾。测量和实验包括几个现场和实验室组成部分：苔藓和维管植物在一定光照水平下的生态系统和叶片水平二氧化碳气体交换，叶片生物化学测试对潜在氮饱和度的胁迫响应，地上和地下植物生产和分解，以及植物冠层和土壤剖面内的小气候。这些数据将有助于建立泥炭地生态系统模型，从而提高我们预测这些全球重要生态系统变化阈值的能力。这个项目更广泛的影响包括培训芒特霍利奥克学院的女本科生，为她们进入研究生院和未来的环境科学职业生涯做好准备。该计划包括一个梯级指导模式，在第一个夏天将学生培养成研究合作者，在第二个夏天指导新的本科生研究助理，最后是科学研究的设计者和荣誉研究论文的作者，最终在国际科学会议上发表演讲，并在同行评议的期刊上发表文章。与加拿大、芬兰和美国主要研究型大学的科学家密切合作对培养本科生至关重要。通过让这些学生参与研究生、博士后和教师组成的充满活力的研究社区，他们将通过跨学科研究有助于我们了解北部泥炭地碳和氮循环的复杂性。

The increase in atmospheric nitrogen (N) deposition from industrial pollution is of major concern in northern ecosystems, which are typically nutrient-limited. Previous studies have hypothesized that N deposition may increase the carbon dioxide (CO2) sink potential of northern ecosystems by stimulating plant productivity. Peatlands, in particular nutrient-limited bogs, have accumulated vast amounts of carbon (C) since deglaciation, yet the annual C balance is often a very small difference between plant production and soil decomposition. The main objective of this research is to improve our understanding of complex feedbacks between peatland ecosystems and the atmosphere in response to increasing atmospheric N deposition and climate change. Will N deposition enhance or diminish the CO2 sink potential of nutrient-limited bog ecosystems? What are the positive and negative feedbacks of N deposition to net ecosystem CO2 exchange and climate change? How do changes in vegetation function and structure, as well as corresponding changes in microclimate (moisture, temperature, light interception), contribute to changes in the carbon balance? How will changes in leaf chemistry, phenology, and plant function affect the seasonality of CO2 exchange? The overall framework for the research addresses 1) the impacts of N deposition on global atmosphere-biosphere interactions, and 2) the vulnerability of peatland ecosystems to become C sources rather than long-term C sinks. The project builds on 10 years of research and education at a long-term fertilization experiment with varying levels of nitrogen, phosphorus, and potassium at Mer Bleue Bog in Ottawa, Ontario, Canada. The measurements and experiments include several field and laboratory components: ecosystem and leaf-level CO2 gas exchange of mosses and vascular plants at a range of light levels, leaf biochemistry to test stress responses to potential N saturation, above and belowground plant production and decomposition, and microclimate within the plant canopy and soil profile. These data will contribute to a peatland ecosystem model that will improve our ability to predict thresholds of change in these globally important ecosystems.The broader impacts of this project include training women undergraduates at Mount Holyoke College, to prepare them for graduate school and future careers in environmental science. The plan includes a cascade mentoring model, which trains students to become research collaborators by following the sequence of trainee during the first summer, mentor to new undergraduate research assistants in the second summer, and finally designers of scientific studies and authors of honors research theses, leading to presentations at international scientific meetings and publication in peer-reviewed journals. Strong collaborations with scientists from major research universities in Canada, Finland and the U.S. are essential for training undergraduates. By involving these students in vibrant research communities of graduate students, postdoctoral fellows and faculty, they will contribute to our understanding of the complexities of carbon and nitrogen cycling in northern peatlands through interdisciplinary research.