Vertically stratified carbon fixation and coupling processes in deep-sea sediment.
Hai Shi1, Xiaotong Zhang1, Liyan Liu1
1Frontiers Science Center for Deep Ocean Multispheres and Earth System, and College of Marine Life Sciences, Ocean University of China, No. 5 Yushan Road, Shinan District, Qingdao 266000, China.
ISME Communications
|January 7, 2026
Summary
Deep-sea microbes fix carbon through diverse pathways, shifting with depth. Dissolved inorganic carbon and ammonium drive these processes, revealing crucial insights into the deep biosphere's carbon cycling.
Area of Science:
- Marine microbiology
- Biogeochemistry
- Deep-sea ecology
Background:
- Deep-sea sediments are vital for global carbon cycling but poorly understood.
- Microbial carbon fixation, its pathways, and drivers in deep-sea environments remain largely unexplored.
Purpose of the Study:
- Investigate microbial carbon fixation and energy metabolism in South China Sea sediments.
- Determine the vertical distribution of carbon fixation pathways and their environmental drivers.
- Characterize microbial communities involved in carbon fixation across sediment depths.
Main Methods:
- Analyzed microbial carbon fixation and associated energy metabolism in sediment cores (0-690 cm).
- Assessed the influence of environmental factors like dissolved inorganic carbon and ammonium.
- Utilized metagenomic analysis to identify carbon fixation pathways, functional genes, and microbial taxa.
Main Results:
- Dissolved inorganic carbon and ammonium concentrations were key drivers of carbon fixation and redox processes.
- Carbon fixation gene diversity increased with depth, while network complexity decreased.
- Observed a vertical succession of pathways: Calvin-Benson-Bassham (CBB) and reductive glycine (rGLY) in surface sediments, Wood-Ljungdahl (WL) in deeper layers.
- Gammaproteobacteria and Methylomirabilia dominated surface sediments; Desulfobacterota, Chloroflexota, and Aerophobota predominated at depth.
- Most identified carbon-fixing microbes exhibited mixotrophic lifestyles.
Conclusions:
- Deep-sea subsurface microbial communities possess significant carbon fixation potential.
- Findings advance understanding of carbon fluxes and microbial metabolic strategies in the deep biosphere.
- Vertical stratification of microbial communities and metabolic pathways is a key feature of deep-sea sediments.
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