The cycling of carbon through soils is one of the least understood components of the global carbon cycle and hence represents a key uncertainty in the prediction of land-surface response to global climate change. Therefore, there is an urgent need for advanced characterization of soil organic carbon (SOC) to develop and evaluate a new generation of soil carbon models. Here we present a novel strategy that uses Fourier transform infrared spectroscopy (FT-IR) and bulk carbon X-ray absorption spectroscopy (XAS) to identify SOC functional groups and elemental analysis (EA) to constrain the amount of SOC. This method helps us study SOC more quantitatively and allows us to compare SOC variations across a subalpine catchment at East River, a shale-dominated watershed near Crested Butte, CO. Differences in SOC distribution across the catchment may be explained by different local plant input and variations in decomposition activities due to moisture and temperature at different elevations. At all sites, polysaccharide, traditionally considered to be labile to microbial decomposition, makes up a significant portion of SOC while aromatic carbon, usually categorized as recalcitrant, is presented in a very small amount. To further study this counterintuitive observation, scanning transmission X-ray microscope (STXM) was used to image small particles in soil samples to understand the spatial distribution of different SOC species. We found that at all sites and depths, aromatic carbon is mostly concentrated on the edge of soil particles, which could make it easier to access and decompose by soil microbes. On the other hand, polysaccharide, amide, and aliphatic carbons are spread out through the soil particles, and this difference in distribution could possibly explain why polysaccharide was observed in more significant quantity in SOC in spite of its labile chemical structure. In the future, our results will be compared to field-measured CO<sub>2</sub>-fluxes, soil moisture, and radiocarbon data to assess the factors that control SOC turnover rates in different environments across the subalpine catchment and enhance the development of new carbon cycle models.

Molecular investigation of soil organic carbon composition, spatial variability, and depth distribution across a subalpine catchment

253rd National Meeting (2017)

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