Soil Carbon (de)Stabilization Under Changing Climate: Scaling from Micropores to Catchments.

Extensive mechanistic research into soil organic matter (SOM) stabilization against microbial degradation indicates that key processes occur at the pore and grain scale that involve reactions of SOM with metal(loid)s, surfaces and enzymes. However, pore and molecular-scale processes and their effectiveness at regulating carbon exchange between land and the atmosphere are expected to vary greatly within the spatial domains employed in climate-land modeling because of variation in a multitude of factors including: climate, lithologic setting, seasonal dynamics, landscape position, and interfacial chemistry and its distribution in hierarchically-aggregated soil media. Therefore, bridging the gap between molecular-scale, mechanistic understanding and landscape-scale manifestations of carbon exchange requires an interdisciplinary approach that recognizes the complex feedbacks that occur between hydrologic flows, autotrophic fixation, microbial degradation, and mineral neogenesis that drive event-based carbon stabilization and release. In the Jemez – Catalina Critical Zone Observatory (CZO), we are combining laboratory-scale experiments with instrumented field measurements and modeling to resolve controls over land-atmosphere and terrestrial-aquatic exchanges of organic and inorganic carbon. By using soils from instrumented field sites in controlled laboratory experiments, and by interrogating both laboratory and field studies with the same set of molecular spectroscopic and routine analytical tools, we are working to unravel the pore-scale mechanistic underpinnings of seasonal catchment-scale responses, and their spatial distribution at the sub-catchment scale. In seasonally snow-covered, montane catchments in New Mexico and Arizona, we observe pulsed uptake and release of carbon in soils that is driven by season and moisture availability. Shifts between plant- and microbe-derived organic matter signatures in streams reflect a fluctuation between predominance of hillslope plant autotrophy during the summer months and soil microbial heterotrophy during the spring snowmelt. The implications of such shifts in labile SOM forms in soil pore waters for pore-scale interfacial reactions will be discussed.