Collaborative Research: Shrub Impacts on Nitrogen Inputs and Turnover in the Arctic, and the Potential Feedbacks to Vegetation and Climate Change

生态系统通过生物与其自然环境的相互作用而发展和变化。植被的变化是生态系统可以经历的最重要的变化之一，因为它可以改变空气、植物和土壤之间的能量（来自阳光）、水和碳、氮等元素的交换。在北极，从苔原到以灌木为主的植被的大范围转变似乎正在发生。这个研究项目将通过复杂的相互作用来确定，北极向灌木丛的转变是否可能导致更多的碳释放到空气中（二氧化碳或甲烷，这两种都是温室气体）。北极和北部土壤中储存着大量的碳，因此北极碳储量的减少可能会影响世界其他地区的天气和气候。本项目将评估不同灌木反馈对碳(C)和氮(N)循环的贡献。现有的雪栅栏将跨越灌木密度和高度的自然梯度来控制积雪深度，并将在桤木中建立新的雪栅栏实验。在一个生态系统中，灌木引起的土壤C的长期变化将在一个18年的物种去除实验中进行检验。将测量灌木生长、初级生产和生物量。通过15N示踪剂试验，测定增雪对生态系统N分配和灌木N吸收的长期影响。将在与灌木相关的桤木种群和苔藓群落中测量固氮作用。评价不同灌丛反馈对植被氮有效性和吸收的相对优势。该项目将改进对北极灌木扩张的后果及其对区域和全球气候的潜在影响的预测。研究结果将有助于培养研究生和本科生、进行公共宣传和培训K-12教师和学生，以及开发基于网络的教育资源。

Ecosystems develop and change through interactions between living organisms and their physical environment. A shift in vegetation is one of the most important changes an ecosystem can experience, because it can alter exchanges of energy (originating from sunlight), water, and elements such as carbon and nitrogen, among air, plants, and soil. In the Arctic, a widespread shift from tundra to shrub-dominated vegetation appears to be occurring. This research project will discern whether, through complex interactions, this transition to shrublands in the Arctic is likely to result in the release of more carbon into the air (as either carbon dioxide or methane, which are both greenhouse gases). Vast amounts of carbon are stored in Arctic and northern soils, so reduced carbon storage in the Arctic may affect weather and climate in other parts of the world. This project will assess the contributions of different shrub feedbacks to carbon (C) and nitrogen (N) cycling. Snow depth will be manipulated with existing snow fences across a natural gradient of shrub density and height, and a new snowfence experiment will be established in alders. Shrub-induced changes in soil C over the longer term in one ecosystem will be examined in an 18-year-old species removal experiment. Shrub growth, primary production, and biomass will be measured. Long-term effects of added snow on ecosystem N partitioning and shrub N uptake will be measured in a 15N tracer experiment. N fixation will be measured in alder populations and moss communities associated with shrubs. The relative strengths of different shrub feedbacks to N availability and uptake by vegetation will be evaluated. This project will improve prediction of the consequences of shrub expansion in the Arctic, and its potential impacts on regional and global climate. Results will contribute to training of graduate and undergraduate students, to public outreach and training of K-12 teachers and students, and to development of a web-based resource for education.