Reactive magnesium oxide-driven soil carbonation: evidence from CO2 fluxes, inorganic carbon dynamics, and microbial community shifts

Reactive magnesium oxide (MgO), characterized by its high reactivity, large specific surface area, and mesoporous structure, can rapidly sequester CO 2 through hydration-carbonation reactions. Hence, MgO is a promising material for carbon sequestration. However, the effects of MgO on soil CO₂ fluxes and carbon storage dynamics remain unveiled. In this study, a 180-day incubation experiment was conducted to assess the effects of MgO with different effective contents (92%, 95%, 99%) applied at 3% w/w on soil CO 2 flux, soil inorganic carbon (SIC), organic carbon (SOC) pools, and soil microbial communities. The MgO addition led to a net CO 2 uptake and increased soil pH from 6.9 to above 9.3. Higher effective MgO content induced greater cumulative CO 2 absorption, but resulted in slower carbonation rates due to lower reactivity. Among the tested materials, the MgO with 95% effective content achieved a balance between the carbonation rate and SIC accumulation. The δ¹³C signatures of SIC confirmed that most newly sequestered SIC originated from atmospheric CO 2 . In addition, the MgO with 99% effective content significantly reduced bacterial diversity but enhanced fungal richness and diversity. These findings highlight the critical role of MgO reactivity and effective content in regulating carbonation kinetics and provide insights into the environmental implications of MgO-based soil carbon sequestration.