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Understanding the geochemical basis for soil organic matter storage at the global scale

Active Dates 9/1/2023-8/31/2025
Program Area Environmental Systems Science
Project Description
Much of the carbon assimilated by terrestrial ecosystems ends up shed by plants to become soil organic matter (SOM), the largest carbon reservoir in the terrestrial biosphere. The capacity of soil to retain SOM and stabilize additional carbon is moderated by the activity of soil microbial decomposers—but also by the geochemical environment. Soil minerals transform, dissolve, and interact with organic molecules released and synthesized by microbial decomposers. Soil mineral reactivity hence defines the abiotic environment in which soil biological processes unfold, and is an overarching control on SOM stabilization. Despite its significance in the carbon cycle, soil mineral reactivity is virtually uncharacterized at the scales relevant to Earth system modeling. We will address this knowledge gap by synthesizing a global database of soil geochemical measurements and modeling the global-scale processes that govern soil mineral reactivity and associated SOM storage. Specifically, we will use this database to test the hypothesis that warmer, wetter, more productive biomes tend to host less reactive soil minerals—but mineral reactivity can be amplified by geologic factors: lithology, topography, and depositional history. Consequently, soil mineral reactivity and accompanying soil organic matter storage vary substantially as a function of geologic factors within major biomes. Our analysis will involve harmonizing global geochemical databases and developing approaches to infer soil mineralogical composition from bulk chemical composition. We will then use the harmonized global database to develop gridded maps of soil mineralogy and mineral reactivity, which we will quantify using weathering indices (e.g., the chemical index of alteration). In the final stage of our analysis, we will quantify spatial correlations between soil mineral reactivity and SOM while controlling for confounding environmental variables in a series of regional case studies. The data synthesis and modeling approaches described here will thus provide a scaffolding for the next generation of belowground biogeochemical models. This research will also test our fundamental understanding of how soils develop and function in different ecological and geological contexts.
Award Recipient(s)
  • Yale University (PI: Slessarev, Eric)