Accumulation of Soil Microbial Necromass Controlled by Microbe-Mineral Interactions

Area of Science:

• Soil Science
• Biogeochemistry
• Environmental Science

Background:

• Soil organic matter (SOM) is crucial for soil fertility and global carbon cycling.
• Microbial residues are key components of SOM, but mineral interactions are not fully understood.
• Understanding these interactions is vital for managing soil carbon sequestration and greenhouse gas emissions.

Purpose of the Study:

• To investigate how minerals influence the accumulation of microbial residues in soil.
• To trace the fate of microbial carbon using isotopic labeling.
• To identify specific mineral properties and soil characteristics that promote microbial necromass stabilization.

Main Methods:

• Used 13C-labeled glucose to trace microbial residue formation over a year-long incubation.
• Analyzed microbial residue partitioning between mineral-associated organic matter (MAOM) fractions in sandy and silty soils.
• Characterized the mineralogy and chemical composition of different MAOM fractions.

Main Results:

• Approximately 89% of retained microbial 13C was found in the fine (<53 μm) MAOM pool.
• A light MAOM fraction, rich in poorly crystalline iron minerals, stored 4.3 times more 13C than heavy MAOM.
• This light MAOM fraction showed higher N-content, indicating stabilized microbial compounds like proteins.

Conclusions:

• Mineral composition, particularly iron oxides, and soil texture jointly regulate microbial necromass accumulation.
• The light MAOM fraction is a critical reservoir for stabilizing microbial residues and enhancing soil carbon storage.
• Finer-textured soils showed greater microbial residue accumulation, suggesting texture plays a key role.