MINERALOGY CONTROLS THE MECHANISM AND EXTENT OF MICROBIAL C STABILIZATION (Invited Presentation)

Soils are a vital component of many upcoming global challenges, as increasing soil organic matter (SOM) affords us the opportunity to improve soil health and food security, as well as potentially mitigate climate change. However, the mechanisms controlling the stabilization and destabilization of this large pool of carbon (C) are relatively unknown, although there has been a recent understanding of the importance of microbial activity and microbial-derived C for the formation of stable (i.e. long-lived) and mineral-associated soil OM. But the mechanistic processes underlying this conceptual framework have yet to be established. In particular, visualizing biotic and abiotic stabilization of C on mineral surfaces is difficult using current techniques. We developed Raman microscopy as a tool to probe OM association with mineral surfaces, as it allows for the simultaneous quantification and identification of living microbes, carbon, and minerals in one sample through time. We used Raman microscopy combined with incubation to probe how microbial C becomes stabilized on two contrasting soil minerals (feldspar and amorphous aluminum hydroxide). With these experiments, we found that the type of mineral present had a significant influence on the amount of microbial C retained. Interestingly, the dominant mechanism by which added microbial C was stabilized (i.e. biotic vs abiotic) varied between the two minerals during incubation. We extended our work to examine the destabilization of microbial residues and again found that mineralogy (altered by soil depth) significantly impacted the extent of microbial C destabilization during wetting and drying. In addition to providing important insights into initial OM association with soil minerals, this work also establishes Raman microscopy as a viable method to further probe the mechanisms behind rocks transforming into soil and forming mineral-associated SOM.