Collaborative Research: Vulnerability of carbon in buried soils to climate change and landscape disturbance

更好地了解土壤中储存的碳量及其在大气中积累的风险对于改善对未来气候变化的预测至关重要，以便我们的社会和农业能够最好地适应不断变化的环境。在地质时间尺度上，土壤中储存和释放的碳量影响了大气中二氧化碳的浓度和全球气候。在较短的时间尺度上，估计土壤中植物碳的储存抵消了人类活动产生的一部分碳排放。为了预测土壤碳对景观干扰的脆弱性，该项目旨在确定导致古土壤中古老碳的持久性或损失的过程，并量化先前受保护的碳在应对不断变化的环境条件时释放到大气中的速度。古土壤，或埋藏的土壤，代表以前的景观表面，可以储存更多的碳比预期的地下深处，并提供了独特的机会，询问有关的问题，现代和未来的预测之间的相互作用碳，干扰和气候。这项拟议的研究将为土壤碳对美国中部大平原两个现实气候变化影响的预测提供信息。更频繁的极端降雨事件可能导致侵蚀，并使以前被掩埋的土壤更多地暴露在现代地表条件下。为应对干旱和变暖的气候而扩大灌溉的努力可能会引发古土壤中的微生物活动，将古老的碳释放到大气中。该项目将为三名研究生和至少四名本科生提供研究和职业培训，并促进具有地球化学，土壤科学，微生物生态学和地貌学专业知识的多元化团队之间的新合作。PI在培训来自地球科学历史上代表性不足的群体的学生方面取得了成功，并将为早期职业研究人员提供专业发展。研究的传播将包括传统的场所，如会议介绍和同行评审的出版物，以及宣传土壤对我们气候的重要性的外联活动，形式是为学童进行实验室演示和参加科学节，免费向公众开放。拟议的研究将测试深埋土壤有机物成为碳源的潜力，气候或土地利用的变化影响了地下土壤与大气的连通性。该研究旨在了解（1）土壤埋藏如何有助于碳以土壤有机质的形式持续存在，以及（2）暴露于地表条件是否会引发古代碳的分解。拟议的研究地点位于美国大平原，在晚更新世和全新世期间，气候驱动的黄土沉积导致厚黄土沉积物中的埋藏土壤序列。将使用一套先进的光谱方法和高分辨率质谱法，对埋藏土壤或古土壤以及上覆的现代表层土壤中的分子组成、氧化状态、微生物处理程度和有机物的潜在来源进行鉴定。将测量土壤的物理、化学和微生物学特性，以研究有助于古土壤中碳持久性的机制的相对有效性。将以两种方式衡量古有机物对不断变化的环境条件的脆弱性。首先，有机质的年龄，成分和生物利用度的变化将被量化沿着侵蚀和沉积领域的地形序列，古土壤存在于不同程度的隔离现代景观表面。第二，实验室操作将测量碳基质，氮的可用性和微生物组成对古有机质分解和动员的气体和溶解形式的影响。本研究将古气候重建的地貌方法与先进的地球化学、光谱学和宏基因组学技术相结合，以产生关于碳地球化学环境控制的新知识。

A greater understanding of the amount of carbon stored in soils and the risk of its accumulation in the atmosphere is fundamental for improving predictions of future changes in climate so that our society and agriculture can best adapt to a changing environment. Over geologic time scales, the amount of carbon stored and released from soils has influenced atmospheric carbon dioxide concentrations and global climate. On shorter time scales, the storage of plant carbon in soils is estimated to have offset a fraction of carbon emissions from human activities. To predict the vulnerability of soil carbon to landscape disturbance, this project aims to identify the processes contributing to the persistence or loss of ancient carbon from paleosols and quantify how quickly previously protected carbon can be released to the atmosphere in response to changing environmental conditions. Paleosols, or buried soils that represent former landscape surfaces, can store more carbon than expected deep underground and provide unique opportunities for asking questions relevant for modern and future projections of interactions among carbon, disturbance and climate. The proposed research will inform predictions of the response of soil carbon to two realistic climate change impacts in the U.S. central Great Plains. More frequent extreme rainfall events can lead to erosion and increase exposure of formerly buried soils to modern surface conditions. Efforts to extend irrigation in response to a drying and warming climate could trigger microbial activity in the paleosol, releasing ancient carbon to the atmosphere. The project will provide research and career training to three graduate students and at least four undergraduates and foster new collaborations among a diverse team with expertise in biogeochemistry, soil science, microbial ecology and geomorphology. The PIs have a successful record of training students from historically underrepresented groups in the geosciences and will provide professional development for early-career researchers. Dissemination of the research will include traditional venues, such as conference presentations and peer-reviewed publications, as well as outreach activities to communicate the importance of soils to our climate, in the form of a lab demonstration for schoolchildren and participation in a science festival, free and open to the public.The proposed research will test the potential for deep buried soil organic matter to become a carbon source in response to changes in climate or land use that affect the connectivity of buried soils to the atmosphere. The research aims to understand (1) how soil burial contributes to the persistence of carbon in the form of soil organic matter and (2) whether exposure to surface conditions can trigger the decomposition of ancient carbon. The proposed study site is located in the U.S. Great Plains, where climate-driven loess deposition during the late Pleistocene and Holocene resulted in sequences of buried soils in thick loess deposits. The molecular composition, state of oxidation, degree of microbial processing and potential sources of organic matter in a buried soil, or paleosol, and in the overlying modern surface soil will be characterized using a suite of advanced spectroscopic methods and high-resolution mass spectrometry. Soil physical, chemical and microbiological properties will be measured to investigate the relative effectiveness of the mechanisms that contribute to carbon persistence in the paleosol. The vulnerability of ancient organic matter to changing environmental conditions will be measured in two ways. First, changes in organic matter age, composition and bioavailability will be quantified along eroding and depositional field toposequences, where the paleosol exists at varying degrees of isolation from the modern landscape surface. Second, laboratory manipulations will measure the effects of carbon substrates, nitrogen availability, and microbial composition on ancient organic matter decomposition and mobilization in gaseous and dissolved forms. This study combines a geomorphic approach drawing from paleoclimatic reconstructions with advanced geochemical, spectroscopic and metagenomic techniques to generate new knowledge on environmental controls on carbon biogeochemistry.This project is jointly supported by the Ecosystem Science Program in the Biological Sciences Directorate and the Geobiology and Low-Temperature Geochemistry Program in the Geosciences Directorate.