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

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烈和最有可能的正反馈之一。永久冻土氮释放有可能稳定碳循环对气候变暖的反应，因为它是一个负的、系统内的反馈。它可以在变暖的北极赋予生态系统-大气相互作用的弹性。该奖项下的研究将通过将这种反馈纳入一个陆地生物圈模型来推进对北极系统的理解，该模型被科学界广泛用于预测北极环境变化及其与地球系统的联系。该项目的合作性质将在生态系统生态学家和分子生物学家之间建立伙伴关系，创造关于植物-真菌相互作用在地球系统反馈循环中的新知识。该项目将支持两名女性北极科学家的博士后或新教员水平的职业发展。它将有助于培养两名生物地球科学、生态学和分子生物学的研究生，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参与生态和环境科学。大约1700毫克的有机碳(C)存在于北极和北方地区的永久冻土土壤和沉积物中。由于这一储量是大气C库的两倍多，因此了解永久冻土生态系统的C平衡如何对观测到的和预测的气候变暖做出反应是相当有兴趣的。随着永久冻土的解冻，被低温保护了数百年至数千年的有机物暴露在微生物分解中，并以温室气体的形式释放到大气中。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)的同步释放，氮是最有可能限制植物生产力的元素。解冻时或解冻后氮的释放可以增加植物氮的有效性，刺激植物碳的吸收，抵消或平衡永久冻土碳的排放。尽管科学家们承认N可能在永久冻土C对气候的反馈中发挥关键作用，但很少有关于在变暖的永久冻土生态系统中控制其命运的因素的实证研究。该项目的目的是开发一个机制的作用，了解永久冻土带下的阿拉斯加冻土带景观的C平衡的永久冻土带N。该项目将重点关注植物对永久冻土N的获取，因为在大多数氮有限的陆地生态系统中，植物吸收是微生物过程释放N的主要命运。植物依赖真菌伙伴获取根系以外的氮，因此本研究还将重点研究植物菌根状况和真菌群落组成，以阐明真菌共生体在植物氮获取中的作用。最后，将探索永久冻土N的其他命运，包括停滞和损失。拟议的研究将探讨三个一般性问题：从融化的永久冻土土壤有机质中释放植物可利用氮的潜力是什么；活性层底部土壤剖面深处释放的氮有多少比例是由菌根和植物获取的，控制获取的关键生物和非生物因素是什么；永久冻土融化和氮释放将如何影响生态系统的净碳平衡和永久冻土融化的净生物地球化学辐射强迫？研究方法包括三个要素：通过对阿拉斯加布鲁克斯山脉北坡高地冻土带生态景观单元的区域调查对植物、真菌和土壤进行观察；在寒冷和温暖的潮湿酸性冻土带中占据密集的研究地点，在长期变暖实验和具有良好特征的自然融化梯度中进行菌根真菌和植物N获取和N损失的测量；利用专门为模拟高纬度系统中碳氮动态而开发的陆地生物圈模式进行建模和区域整合。

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.