Organic Matter from Redoximorphic Soils Accelerates and Sustains Microbial Fe(III) Reduction

Area of Science:

• Environmental microbiology
• Geochemistry
• Soil science

Background:

• Microbial reduction of Fe(III) minerals is crucial in redoximorphic soils.
• Organic matter (OM) significantly influences this process.
• Effluent OM (efOM) from anoxic conditions contains microbial-released compounds.

Purpose of the Study:

• To investigate how adsorbed versus coprecipitated OM affects microbial Fe(III) reduction by Geobacter sulfurreducens.
• To understand OM's role in electron uptake and ferrihydrite (Fh) crystallinity changes.
• To assess the impact of efOM on Fe(III) reduction rates and extent.

Main Methods:

• Microbial reduction experiments using Geobacter sulfurreducens.
• Ferrihydrite (Fh) incubated with adsorbed or coprecipitated effluent OM (efOM).
• Mössbauer spectroscopy to analyze Fh structure alterations.

Main Results:

• Coprecipitated efOM accelerated Fe(III) reduction, likely due to Fh structure disruption.
• Adsorbed efOM decelerated Fe(III) reduction by passivating the Fh surface.
• Both adsorbed and coprecipitated efOM led to more sustained Fe(III) reduction.

Conclusions:

• The interaction mode (adsorption vs. coprecipitation) of OM with Fe(III) minerals dictates microbial reduction rates.
• Fe(III)-OM coprecipitates are readily reducible by bacteria in redoximorphic soils.
• OM influences soil biogeochemical cycling by modulating Fe(III) reduction.