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

在北方生态系统中，工业污染导致的大气氮(N)沉积增加是一个主要问题，这些生态系统通常是营养有限的。以前的研究假设，氮沉降可能通过刺激植物生产力来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的很小差异。这项研究的主要目的是提高我们对泥炭地生态系统和大气之间的复杂反馈的理解，以响应不断增加的大气N沉积和气候变化。氮沉积会增加还是减少营养有限的沼泽生态系统的二氧化碳吸收潜力？氮沉降对净生态系统、二氧化碳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小气候(湿度、温度、光截获)的相应变化如何促进碳平衡的变化？叶片化学、物候和植物功能的变化将如何影响二氧化碳交换的季节性？研究的总体框架涉及1)氮沉积对全球大气-生物圈相互作用的影响，以及2)泥炭地生态系统成为碳源而不是长期碳汇的脆弱性。该项目建立在加拿大安大略省渥太华Mer Bleue Bog的一项长期施肥实验的10年研究和教育基础上，该实验使用不同水平的氮、磷和钾。测量和实验包括几个田间和实验室部分：在不同光照水平下苔藓和维管植物的生态系统和叶水平的二氧化碳气体交换，测试对潜在N饱和的胁迫响应的叶片生物化学，地上和地下植物的生产和分解，以及植物冠层和土壤剖面内的小气候。这些数据将有助于泥炭地生态系统模型，该模型将提高我们预测这些全球重要生态系统变化阈值的能力。该项目的更广泛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做准备。该计划包括一种级联指导模式，通过在第一个夏天按照实习生的顺序培训学生成为研究合作者，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师和荣誉研究论文的作者，导致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，对于培养本科生至关重要。通过让这些学生参与由研究生、博士后研究员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帮助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.