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Organized Oral Session

Session: : Enhancing a Molecular Understanding of Soil Biogeochemistry from Local to Continental Scales

OOS 29-3 - Molecular-scale mechanisms inform continental-scale patterns in soil carbon persistence and climate vulnerability

Tuesday, August 8, 2023
4:00 PM – 4:15 PM PDT
Location: 256
Application of high spatial and chemical-resolution analytical tools to soil systems has greatly advanced our fundamental understanding of how interactions among soil organic carbon (SOC), minerals, and microbes drive SOC cycling. However, it is unknown to what degree emerging concepts of molecular-scale SOC-mineral-microbial processes are transferable to measurable differences in ecosystem behavior, especially across wide spatial scales. In this work, we integrated data on SOC turnover (via radiocarbon measurements), climate sensitivity (via incubation studies), and SOC molecular composition (fluorescence EEMS, X-ray absorption spectroscopy, and X-ray EEMS) with a suite of soil mineralogical and chemical analyses to link presumed mechanisms of molecular-scale SOC stabilization to large-scale predictors and patterns. Overall, we propose that understanding of molecular controls on SOC cycling should account for large-scale divergence in climate regime, specifically moisture regime. We showed that soil mineralogy – which varies across a gradient from humid to arid systems – was the best predictor of SOC sensitivity elevated temperature or moisture, a response we hypothesize is tied to differences in the reversibility of SOC-mineral surface interactions. Furthermore, we used differences in the chemical characteristics of soluble SOC to show that the timing and abundance of SOC supply for microbial transformations at depth is a fundamental control on differences in SOC turnover between humid and arid systems. In future work, we aim to integrate the concept of climate-driven subsystem behavior into large-scale SOC models that emphasize this microbial-mineral SOC stabilization pathway.