The goal of this proposed research is to understand effects of agricultural conversions on soil inorganic carbon (SIC) cycle. Mitigating rising atmospheric CO2 is a top priority for human and environmental health. Despite their prevalence and increasing pressure from land-use changes, effect of SIC on climate regulation is thought to be insignificant in the short-term, leading to focused efforts and research on other means of carbon sequestration. The proposed research builds on the fellow’s previous NSF-funded project, in which large losses of SIC were observed with the land-use changes, and has potential to transform the current understanding of these issues. In this proposal, soil incubations in a factorial design will simulate land use-induced ecosystem changes (soil water flux, acidification, freeze-thaw cycle) to identify mechanisms of SIC transformations. Incubators customized for the field-observed conditions such as drainage, are used to approximate water-carbonate reactions closely, and periodic measurements of inorganic carbon in gas and water fluxes using stable isotopes will determine the potential rates and pathways of fluxes from SIC. Lab and field conditions will be simulated with coupled geochemistry and hydrology codes and the results compared to those from the lab and field to help improve our understanding of SIC processes. The proposal integrates geochemistry and hydrology with original methodologies involving field, lab, and modeled data for predictive understanding of rate, fate, and mechanisms of SIC transformations with land-use changes. The mentor (Dr. S. Trumbore) and the host institute (Max Planck Institute of Biogeochemistry in Jena, Germany) collectively bring expertise in isotopes and biogeochemical modeling, demonstrate excellent research and training track records, and comprise a research setting uniquely adapted to the project and the fellow.