Aggregation-dependent electron transfer via redox-active biochar particles stimulate microbial ferrihydrite reduction

Area of Science:

• Biogeochemistry
• Environmental Microbiology
• Soil Science

Background:

• Microbial iron reduction is crucial for carbon and iron cycling in soils and sediments.
• Biochar, a soil amendment, is redox-active and can influence microbial iron reduction.
• The impact of biochar particle aggregation on microbial iron reduction remains unclear.

Purpose of the Study:

• To investigate how biochar particle size and biochar/ferrihydrite ratios affect microbial iron reduction.
• To determine the role of aggregation in mediating electron transfer between microbes, biochar, and iron minerals.

Main Methods:

• Studied ferrihydrite reduction rates using Shewanella oneidensis MR-1.
• Utilized different particle sizes of wood-derived biochar (Swiss and KonTiki) at varying biochar/ferrihydrite ratios.
• Observed aggregation of biochar, microbial cells, and ferrihydrite.

Main Results:

• Small biochar particles and high biochar/ferrihydrite ratios promoted close aggregation, stimulating microbial iron reduction.
• Large biochar particles and low ratios inhibited iron reduction due to poor aggregation.
• Effective aggregation facilitated electron transfer via biochar's functional groups and conductive matrix.

Conclusions:

• Biochar particle size and biochar/ferrihydrite ratio are critical for stimulating microbial iron reduction.
• Close aggregation of biochar, cells, and iron minerals enhances electron transfer processes.
• Findings improve understanding of biochar's role in environmental electron transfer and biogeochemical cycling.