Collaborative Research: The roles of plant roots, mycorrhizal fungi and uptake of deep nitrogen in the permafrost carbon feedback to warming climate

永久冻土（冻土）中冻结的碳的释放已被确定为生物圈和气候变暖之间最强和最有可能的正反馈之一。冻土氮释放具有稳定碳循环对气候变暖的响应的潜力，因为它是一种负的系统内反馈。它可以在变暖的北极赋予生态系统-大气相互作用的恢复力。该奖项下的研究将通过将这种反馈纳入社区广泛使用的陆地生物圈模型来预测北极环境变化及其与地球系统的联系，从而促进对北极系统的理解。该项目的合作性质将建立生态系统生态学家和分子生物学家之间的伙伴关系，创造关于植物-真菌互惠共生在地球系统反馈循环中的作用的新知识。该项目将支持两名女性北极科学家在博士后或新教师一级的职业发展。它将有助于培养两名生物科学，生态学和分子生物学研究生，并为大约20名本科生提供真实的实地或实验室研究经验。该项目将有助于扩大代表性不足的群体对生态和环境科学的参与。技术北极和北方地区的永久冻土和沉积物中约有1，700 Pg的有机碳（C）。由于这一存量是大气碳库的两倍多，因此人们对了解永久冻土生态系统的碳平衡如何对观测和预测的气候变暖作出反应非常感兴趣。随着永冻土融化，被低温保护了数百至数千年的有机物暴露于微生物分解，并作为温室气体释放到大气中。在这些生态系统中，可能强烈影响碳平衡的一个关键因素是氮（N）的同时释放，这是最有可能限制植物生产力的元素。解冻时或解冻后的氮释放可以增加植物氮的有效性，刺激植物碳吸收，抵消或平衡冻土碳排放。尽管科学家们承认N可能在永冻层C对气候的反馈中发挥关键作用，但很少有关于控制其在变暖永冻层生态系统中命运的因素的实证研究。本项目的目标是发展一个机制的理解永冻层N的作用在阿拉斯加冻原景观下的C平衡的永冻层soil.The项目将集中在植物收购永冻层N，因为在大多数N有限的陆地生态系统，植物吸收的主要命运的N释放的微生物过程。植物依赖于真菌的合作伙伴，以获得N超出了根，所以这项研究也将集中在植物菌根状态和真菌群落组成，以阐明真菌共生体在植物N的收购中发挥的作用。最后，其他命运的永冻土N将被探讨，包括停滞和损失。拟议的研究将探讨三个一般性问题：从融化的永冻土土壤有机质中释放植物有效氮的潜力是什么;在土壤剖面深处，在活动层的底部，真菌和植物获得的氮的比例是多少，以及控制获得的关键生物和非生物因素是什么;在局部和区域尺度上，冻土融化和氮释放将如何影响生态系统的净碳平衡和冻土融化的净地球化学辐射强迫？该研究方法包括三个要素：在阿拉斯加布鲁克斯山脉北坡的高地冻原生态景观单元的区域调查中观察植物、真菌和土壤;在寒冷和温暖潮湿的酸性冻原中占据密集的研究地点，在长期变暖实验和良好表征的自然解冻梯度中测量菌根真菌和植物氮的获得和损失;和建模和区域一体化的陆地生物圈模式专门开发模拟高纬度系统中的C和N动态。

NontechnicalRelease of carbon frozen in permafrost (frozen ground) has been identified as one of the strongest and most likely positive feedbacks between the biosphere and the warming climate. Permafrost nitrogen release has the potential to stabilize the response of the carbon cycle to climate warming because it is a negative, within-system feedback. It could confer resilience to ecosystem-atmosphere interactions in a warming Arctic. The research under this award will advance understanding of the arctic system by incorporating this feedback into a terrestrial biosphere model used extensively by the community for forecasting arctic environmental change and its links to the Earth system.The collaborative nature of the project will build partnerships between ecosystem ecologists and molecular biologists, creating new knowledge about the role of plant-fungal mutualisms in Earth system feedback cycles. The project will support career development of two female arctic scientists at the postdoctoral or new faculty level. It will contribute to the training of two graduate students in biogeosciences, ecology, and molecular biology, and provide an authentic field or laboratory research experience for about twenty undergraduate students. The project will contribute to broadening participation of under-represented groups in ecological and environmental sciences.TechnicalAbout 1,700 Pg of organic carbon (C) reside in the permafrost soils and sediments of Arctic and Boreal regions. Because this stock is more than twice the size of the atmospheric C pool, there is considerable interest in understanding how the C balance of permafrost ecosystems will respond to observed and predicted climate warming. As permafrost soils thaw, organic matter that has been cryogenically protected for hundreds to thousands of years is exposed to microbial decomposition and released to the atmosphere as greenhouse gases. One key factor that may strongly influence C balance in these ecosystems is the concurrent release of nitrogen (N), the element most likely to limit plant productivity. Release of N at or after thaw could increase plant N availability, stimulate plant C uptake and offset or balance permafrost C emissions. Although scientists acknowledge the key role N is likely to play in the permafrost C feedback to climate, there have been few empirical studies of the factors that control its fate in warming permafrost ecosystems. The objective of this project is to develop a mechanistic understanding of the role of permafrost N in the C balance of Alaskan tundra landscapes underlain by permafrost soils.The project will focus on plant acquisition of permafrost N because in most N-limited terrestrial ecosystems, plant uptake is the dominant fate of N released by microbial processes. Plants depend on fungal partners to access N beyond the reach of roots, so this research will also focus on plant mycorrhizal status and fungal community composition to elucidate the role fungal symbionts play in plant N acquisition. Finally, other fates of permafrost N will be explored, including stasis and loss. Proposed research will explore three general questions: What is the potential for release of plant-available nitrogen from thawing permafrost soil organic matter; what proportion of N released deep in the soil profile, at the base of the active layer, is acquired by mycorrhizae and plants and what are the key biotic and abiotic factors that control acquisition; and how will permafrost thaw and N release affect net ecosystem carbon balance and net biogeochemical radiative forcing from permafrost thaw at local and regional scales?The research approach includes three elements: observations of plants, fungi and soils across a regional survey of upland tundra ecological landscape units on the North Slope of the Brooks Range, Alaska; occupying intensive research sites in cold and warm moist acidic tundra, where measurements of mycorrhizal fungi and plant N acquisition and N loss will be made within long-term warming experiments and well-characterized natural thaw gradients; and modeling and regional integration with a terrestrial biosphere model specifically developed to simulate C and N dynamics in high latitude systems.