Spatially resolved denitrification coupled with methane and arsenite oxidation at the millimeter-scale straw-soil...

Area of Science:

• Soil Science
• Microbial Ecology
• Biogeochemistry

Background:

• Straw return significantly impacts paddy soil biogeochemistry, altering microbial transformations of key elements.
• Understanding the integration of these processes within millimeter-scale soil heterogeneity is crucial but remains unclear.

Purpose of the Study:

• To investigate the impact of straw addition on depth-dependent biogeochemical dynamics and microbial stratification in paddy soils.
• To elucidate the coupled microbial processes occurring at millimeter scales under straw incorporation.

Main Methods:

• Combines high-resolution geochemical profiling with multiomics (metagenomics, metatranscriptomics).
• Analyzes gene abundances and co-occurrence patterns (mcrA, nifH, pmoA, aioA/arxA, denitrification genes).
• Examines transcriptional activity in different soil layers using metagenome-assembled genomes.

Main Results:

• Straw addition induced a three-layer microbial stratification based on organic matter content and redox conditions.
• Identified distinct microbial functions in each layer: methanogenesis/nitrogen fixation (OM-rich), methane oxidation/denitrification (upper), and arsenite oxidation/denitrification (lower).
• Revealed significant positive correlations and co-occurrence between specific functional genes, indicating coupled biogeochemical processes.

Conclusions:

• Straw incorporation establishes dynamic soil redox zones and restructures microbial networks at the millimeter scale.
• Demonstrated coupled denitrification with arsenite or methane oxidation, and methanogenesis with nitrogen fixation.
• Provides a mechanistic basis for optimizing straw placement and nitrogen application to enhance soil functions and mitigate environmental risks.