LAUSR

The potential environmental impacts of CO2 leakage from carbon capture and storage (CCS) sites remain a critical concern for the long‐term viability of CCS technologies. Soil microbial communities, which regulate essential biogeochemical processes, are particularly sensitive to changes in soil CO2 concentrations. In this study, controlled CO2 release experiments at two depths, 2.5 m (shallow subsurface) and 0.5 m (near‐surface) in a field setting in Eumseong, South Korea, were conducted in 2016 and 2017, respectively, to evaluate soil microbial and biogeochemical responses to elevated CO2 exposure. In the 2.5‐m depth experiment, despite substantial CO2 enrichment at 60‐cm soil depth (peaking at 21.2%), minimal CO2 accumulation occurred at the surface (15‐cm depth: <2.6%), and no significant changes were observed in microbial enzyme activities, inorganic nitrogen concentrations, or microbial biomass carbon. These results suggest that seasonal factors such as rainfall exerted stronger influence than the CO2 exposure. In contrast, the 0.5‐m depth experiment produced highly localized CO2 accumulation at the surface (center: 52.2%), resulting in hypoxic conditions (O2: 10.5%). Under these conditions, N‐acetyl‐glucosaminidase activity declined significantly, and ammonium and nitrate concentrations showed spatial and temporal shifts likely driven by inhibited plant uptake and altered microbial nitrogen cycling. These findings demonstrate that microbial responses to CO2 leakage are highly depth‐ and exposure‐dependent. Monitoring microbial functional indicators, particularly N‐acetyl‐glucosaminidase activity and nitrogen metrics, along with gas flux measurements, can improve early detection strategies for the assessment of CCS site integrity.