ESS Ph.D. Defense: Soil Carbon Cycling Constrained by Oxygen-Dependent Enzyme by Hannah Naughton
- Tuesday, Sep 22, 2020 1:00 PM
- Zoom (https://stanford.zoom.us/j/96032877040?pwd=TncrclB5OUlTZWJ5dXhpOHJxSHBWQT09)
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- ESS Ph.D. Defense: Soil Carbon Cycling Constrained by Oxygen-Dependent Enzyme b…
- Faculty/Staff, Students, Alumni/Friends
- Department of Earth System Science
I use both laboratory soil reactors and a floodplain field site as soil environments with spatially or temporally varying oxygen availability to test for enzymatic and thermodynamic limitations on SOC degradation and accompanying greenhouse gas production. Soil redox environment altered dissolved organic carbon (DOC) composition and chemistry over short times in the reactor setup and over short spatial scales in field soils. Oxygen-limited soils had more reduced organic C corresponding to lower thermodynamic favorability as a microbial substrate in anaerobic metabolisms. The reactors had a stark increase in relative abundance of lignin-like carbon going from aerobic to anaerobic environments, indicative of enzymatic limitations, but field soils indicated plant inputs counteract this often depth-related pattern. Aeration of soils resulted in equivalent respiration when normalized to SOC content, regardless of original microbial community or SOC composition, even in methanogenic soils lacking saprotrophic communities. This finding prompted exploration of the potential for abiotic, metal-catalyzed processes to depolymerize SOC in redox-heterogeneous floodplain soils. Ferrous iron better corresponded to phenol oxidation potential than any microbial or carbon-related predictors, highlighting the potential for rapid oxidative SOC depolymerization upon aeration of permanently or temporarily saturated soils containing reduced transition metals. Altogether, this work highlights the rapidity with which novel redox status of soils alters SOC composition, favorability as a microbial substrate, and potential for unexpected greenhouse gas release. Terrestrial carbon models are unlikely to accurately predict future stocks and fluxes of SOC if they do not account for the influence of heterogeneity of oxygen availability and ensuing effects on carbon lability.