Changes in soil N2O and CH4 emissions and related microbial functional groups in an artificial CO2 gassing experiment

Abstract

Potential CO2 leakage is a major concern for carbon capture and storage (CCS). The effects of high soil CO2 concentration on microbes is a major element of impact assessments of CO2 leakage on terrestrial ecosystems. We conducted a field experiment to investigate the responses of microbial functional groups of ammoniaoxidizers, methanogens, and methanotrophs in high soil CO2 conditions. A single-point injection gassing plot (2.5 m x 2.5 m in size), which had 52.2% CO2 in the center (radius = 0.5 m) and 5.5% in the edge (radius = 1.7 m) at 10 cm depth, was employed. N2O and CH4 emissions increased after I day of injection because injected CO2 was instantly utilized by nitrifiers and methanogens. This suggests that the activities of the selected microbes could be stimulated by high soil CO(2 )concentrations. Prolonged CO2 injection has toxic effects on aerobic nitrifiers, but may favor anaerobic methanogens. However, the early stimulatory effects of high soil CO2 on N2O and CH4 production did not last to the end of injection. These results imply that increased N2O and CH4 emissions could be the minor side effects of high soil CO2. Microbes responded faster than plants to high soil CO2, with responses observed as late as 7 days after injection. The inhibition of plant absorption of soil water and nutrients by high soil CO2 concentrations may also influence microbial responses. Moreover, high soil water content could retard underground CO2 diffusion, which would magnify CO2 impacts on plants and microbes. Our results suggest that microbial response could be used as an early indicator of the impact assessments of CO2 leakage on soil ecosystems. An understanding of the interaction among soils, plants, and microbes would be helpful in assessing the biological risks of potential CO(2 )leakage. (C) 2019 Published by Elsevier B.V.