Dark microbial CO₂ fixation in temperate forest soils increases with CO₂ concentration

Area of Science:

• Soil Science
• Microbiology
• Biogeochemistry

Background:

• Dark, nonphototrophic microbial CO2 fixation is a widespread soil process.
• Its contribution to soil carbon balance and controlling factors remain largely unknown.

Purpose of the Study:

• Quantify dark microbial CO2 fixation in temperate forest soils.
• Determine the relationship between soil CO2 concentration and fixation rates.
• Identify microbial groups responsible for dark CO2 fixation.

Main Methods:

• Utilized a 13C-CO2 labeling experiment.
• Measured CO2 concentrations and fixation rates across soil horizons.
• Employed phospholipid fatty acid analyses to assess microbial community composition.

Main Results:

• Dark microbial CO2 fixation rates positively correlated with soil CO2 concentration.
• Fixation rates were significantly higher in the Ah horizon (up to 320 µg C kg-1 day-1) than in the Bw1 horizon.
• Gram-positive bacteria were identified as the primary microbial group responsible for CO2 fixation.

Conclusions:

• Dark microbial CO2 fixation is influenced by soil CO2 availability in temperate forest soils.
• This process, primarily driven by gram-positive bacteria, contributes to the soil organic matter pool.
• Microbial detritus from CO2 fixation represents a stable component of soil organic matter.