Increased N₂O emission by inhibited plant growth in the CO₂ leaked soil environment: Simulation of CO₂ leakage from carbon capture and storage (CCS) site

Atmospheric carbon dioxide (CO₂) concentrations is continuing to increase due to anthropogenic activity, and geological CO₂ storage via carbon capture and storage (CCS) technology can be an effective way to mitigate global warming due to CO₂ emission. However, the possibility of CO₂ leakage from reservoirs and pipelines exists, and such leakage could negatively affect organisms in the soil environment. Therefore, to determine the impacts of geological CO₂ leakage on plant and soil processes, we conducted a greenhouse study in which plants and soils were exposed to high levels of soil CO₂. Cabbage, which has been reported to be vulnerable to high soil CO₂, was grown under BI (no injection), NI (99.99% N₂ injection), and CI (99.99% CO₂ injection). Mean soil CO₂ concentration for CI was 66.8–76.9% and the mean O₂ concentrations in NI and CI were 6.6–12.7%, which could be observed in the CO₂ leaked soil from the pipelines connected to the CCS sites. The soil N₂O emission was increased by 286% in the CI, where NO₃⁻-N concentration was 160% higher compared to that in the control. This indicates that higher N₂O emission from CO₂ leakage could be due to enhanced nitrification process. Higher NO₃⁻-N content in soil was related to inhibited plant metabolism. In the CI treatment, chlorophyll content decreased and chlorosis appeared after 8th day of injection. Due to the inhibited root growth, leaf water and nitrogen contents were consistently lowered by 15% under CI treatment. Our results imply that N₂O emission could be increased by the secondary effects of CO₂ leakage on plant metabolism. Hence, monitoring the environmental changes in rhizosphere would be very useful for impact assessment of CCS technology.