Soil carbon cycling constrained by oxygen-dependent enzyme activity and microbial energetics
Abstract/Contents
- Abstract
- Soils contain up to three times as much dynamic carbon as the atmosphere, making them a critical carbon sink. Soil organic carbon (SOC) performs ecosystem services such as atmospheric carbon sequestration, retention of nutrients and water, promotion of good soil structure, and fueling microbial activity that leads to soil fertility. However, future climate and land use change endanger soil carbon stocks. An incomplete understanding of the mechanisms behind SOC degradation hinders our ability to model carbon cycling, particularly considering temporally and spatially heterogeneous soils. One key factor is the role oxygen availability plays in microbial energetics and enzyme activity, information critical to providing mechanistic predictions of SOC decay. My research explores how oxygen limitations and ensuing redox heterogeneity in soils control both the energetics of respiration, which ultimately controls greenhouse gas production of soils, and microbial access to organic substrates via oxidative enzyme depolymerization. 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.
Description
| Type of resource | text |
|---|---|
| Form | electronic resource; remote; computer; online resource |
| Extent | 1 online resource. |
| Place | California |
| Place | [Stanford, California] |
| Publisher | [Stanford University] |
| Copyright date | 2020; ©2020 |
| Publication date | 2020; 2020 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Author | Naughton, Hannah Rose |
|---|---|
| Degree committee member | Dekas, Anne |
| Degree committee member | Fendorf, Scott |
| Degree committee member | Francis, Christopher |
| Degree committee member | Keiluweit, Marco |
| Thesis advisor | Dekas, Anne |
| Thesis advisor | Fendorf, Scott |
| Thesis advisor | Francis, Christopher |
| Thesis advisor | Keiluweit, Marco |
| Associated with | Stanford University, Department of Environmental Earth System Science |
Subjects
| Genre | Theses |
|---|---|
| Genre | Text |
Bibliographic information
| Statement of responsibility | Hannah Rose Naughton. |
|---|---|
| Note | Submitted to the Department of Environmental Earth System Science. |
| Thesis | Thesis Ph.D. Stanford University 2020. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2020 by Hannah Rose Naughton
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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