Experimental evaluation of CO2 percolation effects on subsurface soil microbiota

Carbon dioxide is an increasing greenhouse gas; its capture and sequestration seems a promising alternative to mitigate global warming, providing all physical, chemical and biological aspects of subsurface gas sequestration are understood. Possible leaks may change soil balance, impacting ecosystems and, consequently, human and animal health. Few data are available on the effects of augmented CO2 concentrations in soil and studies are required to define the role of biological systems and response mechanisms, and to identify CO2 bioindicators for post-injection monitoring. This study was conducted with soil from the Atlantic forest zone, in two scales: unstructured soil batch experiments, in aerobic and CO2 atmosphere, and column microcosms with unstructured and structured soil under CO2 percolation. Microbial metabolic profiles, protein synthesis and degradation activity, soils moisture, available carbon and pH were assessed. In all assays, microbial activity tended to drop with prolonged exposure to CO2. In batch and structured soils, augmented activity, biomass, species richness, besides altered metabolic profiles, all seemed linked to increased CO2. In unstructured column soil a slower pace of response was explained by low initial activity. No significant change in soil moisture was detected and stable pH indicated absence of carbonate precipitation. In conclusion, augmented CO2 changes microbiota composition, enhancing the activity of favoured anaerobic species, which could change ecosystem functions.