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

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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.