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

非技术性的释放冻土(冻土)中冻结的碳已被确认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。永久冻土层的氮素释放有可能稳定碳循环对气候变暖的反应，因为它是系统内的负反馈。它可以在变暖的北极地区赋予生态系统-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陆地生物圈模型来促进对北极系统的了解，该模型被该社区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-真菌互惠关系在地球系统反馈周期中的作用的新知识。该项目将支持两名北极女科学家在博士后或新教师级别的职业发展。它将有助于培养两名生物地理学、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不足的群体对生态和环境科学的参与。技术上，北极和北方地区的永冻土和沉积物中约有1700pg的有机碳(C)。由于这一储量是大气碳库的两倍多，人们有相当大的兴趣了解永久冻土生态系统的碳平衡将如何应对观测到的和预测的气候变暖。随着永久冻土的融化，被低温保护了数百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。一个可能强烈影响这些生态系统碳平衡的关键因素是氮(N)的同时释放，这是最有可能限制植物生产力的元素。在解冻时或解冻后释放氮素可以增加植物氮素的有效性，刺激植物对碳的吸收，抵消或平衡永久冻土的碳排放。尽管科学家们承认氮可能在永久冻土C对气候的反馈中发挥关键作用，但对于控制其在变暖的永久冻土生态系统中的命运的因素，鲜有实证研究。该项目的目的是从机制上理解冻土N在阿拉斯加冻土地貌碳平衡中的作用。该项目将重点放在植物对永冻土N的获取上，因为在大多数N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。植物依赖真菌伙伴来获取超出根部的氮，因此本研究还将重点研究植物的菌根状况和真菌群落组成，以阐明真菌共生体在植物氮素获取中的作用。最后，还将探讨永冻层N的其他命运，包括停滞和损失。拟议的研究将探索三个一般性问题：融化的永久冻土有机质释放植物有效氮的潜力是什么；在土壤剖面深处，活跃层的底部，有多大比例的N被菌根和植物获取，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N的释放将如何影响当地和区域尺度上永久冻土融化的净生态系统碳平衡和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丘陵和苔原生态景观单元的区域调查，对植物、真菌和土壤进行观察；将在寒冷和温暖的潮湿酸性冻土带占据密集的研究地点，在那里将通过长期变暖实验和具有良好特征的自然融化梯度来测量菌根真菌和植物氮的获取和损失；利用专门为模拟高纬度系统中的碳和氮动态而开发的陆地生物圈模型进行建模和区域一体化。

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.