Resilience of Amino Acid-Mineral Assemblages
EMSL Project ID
60963
Abstract
The persistence of organic matter (OM)-mineral assemblages in soils relies on their ability to resist chemical change. Association of OM and/or Si within mineral assemblages serves a dual purpose – 1) protection of the mineral from redox-triggered transformations and 2) protection of the OM from degradation. These capabilities depend on the surrounding biogeochemical conditions and chemical characteristics of the assemblage, including mineral properties and OM composition. Certain organic compounds introduce redox-active functionalities that counteract the OM’s shielding effect. For example, OM rich in thiol groups (–SH) can mediate the abiotic reductive dissolution of Fe-(oxy)hydroxides under anoxic conditions (coupled to the oxidation of cysteine to cystine). The impact of such reactions on the resilience of OM-mineral assemblages is largely unknown. Therefore, our objective is to assess the interplay between OM/Si protection and OM induced reactivity to improve understanding of the mechanisms governing OM cycling in soils.
We will study the degree of chemical change of amino acid-ferrihydrite assemblages exposed to anoxia as a function of OM ligand species, OM/Si ratio and surface area coverage. Research on amino acid-Si-ferrihydrite assemblage resilience will be guided by the following questions:
1. What are the chemical and structural features of the modified assemblages?
2. How does the functionality of the redox-active ligand influence abiotic reductive dissolution of the ferrihydrite and its degree of transformation?
3. How does the Si/OM ratio impact assemblage resilience (i.e., the competition between protection and reactivity)?
EMSL resources will support our studies on the micro- and nano-scale characteristics of the amino acid-Si-ferrihydrite assemblages. These will be synthesized via precipitation of ferrihydrite in the presence of silicic acid and select amino acids (at different Si:OM ratios) including cysteine, glutamic acid, arginine, and the tripeptide glutathione. We will analyse and compare the assemblages before and after exposure to anoxia to monitor the chemical change.
The size, structure, and composition of the assemblages will be analysed using S/TEM, coupled with the EDS and EELS features to identify the spatial distribution of elements and examine whether specific Fe(II)/(III) domains exist. Exploration of the oxidation states and mineralogy of iron will be employed using XPS and Mössbauer spectroscopy. Furthermore, we will identify and map the associated organic functional groups using XPS as well as Nano-FTIR. Lastly, thermal stability of the organics will be measured using Pyrolysis-GC-MS to evaluate the strength of the organic-mineral associations.
This comprehensive set of analyses will allow us to visualize structural and compositional modifications in the assemblages, determine which processes are taking place (sorption/desorption, aggregation/disassembly/dissolution, redox-triggered transformations) and quantify their extent and rate. This in turn will advance our mechanistic knowledge of OM-Si-mineral assemblages – their role in OM persistence, in Fe and OM bio(availability) and cycling in soil systems. Our results will be valuable for accurate representations of OM dynamics in predictive Earth System models and align with EMSL’s mission to study the function and role of abiotic processes in environmental settings.
Project Details
Project type
Exploratory Research
Start Date
2024-01-01
End Date
N/A
Status
Active
Released Data Link
Team
Principal Investigator
Co-Investigator(s)