Molecular-level investigation into the release and transformation of iron-bound soil organic carbon during redox reactions
EMSL Project ID
50139
Abstract
This project aims to understand the release and transformation of iron (Fe)-bound soil organic carbon (SOC) during the redox reactions of Fe. SOC, with 1,500 gigaton of organic carbon (C) globally, is one of the largest C reservoirs on the earth surface. Previous studies suggested that the association between Fe minerals and SOC as one of the major factors controlling the stability of C in soil. Various interactions between Fe oxides and SOC, e.g. inner-sphere/outer-sphere complexation, hydrogen bond, and hydrophobic interactions, can protect Fe-bound SOC from degradation depending on the SOC compositions. However, Fe minerals can undergo the redox cycles, which can compromise the stability of Fe-bound SOC. Our recent studies suggested that Fe-bound SOC can be partially released to solution phase during the Fe reduction, possibly increasing the mobility and bioavailability of SOC. In addition, recent studies have highlighted the importance of photochemical reaction in the transformation of SOC. Therefore, we hypothesize that:
During the reduction of Fe, SOC components (such as organic acids) able to form strong binding with Fe are selectively retained in the complexes, when other components loosely bound to Fe are more favorably released to the solution phase. Low-molecular-weight hydrophilic SOC compounds are more selectively degraded during the anaerobic reduction and consequent oxidation.
We will use water-extracted C from litter as representative SOC to synthesize ferrihydrite (Fh)-SOC co-precipitated complex, which will then be abiotically reduced by S2- under anaerobic condition. The reduced samples will then be exposed to aerobic condition for consequent oxidation. Fourier transform ion cyclotron resonance mass spectroscopy (FTICR-MS) will be applied to study the molecular compositions of Fe-bound SOC, SOC released during Fe reduction, and SOC remaining in solution phase after the aerobic incubation. We will also monitor CH4 and CO2 production during the incubation. 57Fe Mossbauer spectroscopy will be used to characterize Fe mineral phases to understand Fh transformation during anaerobic reduction and aerobic oxidation. Electron paramagnetic resonance (EPR) will be used to monitor ?OH radical production during different phases of incubation. The results obtained will provide molecular-level insights into the release and transformation of Fe-bound SOC during the redox cycles, with broader implications on the C cycle.
Project Details
Start Date
2018-01-01
End Date
2020-01-01
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members