Microbial community changes at a terrestrial volcanic CO₂vent induced by soil acidification and anaerobic microhabitats within the soil column

Abstract

CO2 capture and storage (CCS) in deep geological formations is one option currently evaluated to reduce greenhouse gas emissions. Consequently, the impact of a possible CO2 leakage from a storage site into surface environments has to be evaluated. During such a hypothetical leakage event, the CO2 migrates upwards along fractures entering surface soils, a scenario similar to naturally occurring CO2 vents. Therefore, such a natural analogue site at the Laacher See was chosen for an ecosystem study on the effects of high CO2 concentrations on soil chemistry and microbiology. The microbial activities revealed differences in their spatial distribution and temporal variability for CO2 -rich and reference soils. Furthermore, the abundance of several functional and group-specific gene markers revealed further differences, for example, a decrease in Geobacteraceae and an increase in sulphate-reducing prokaryotes in the vent centre. Molecular-biological fingerprinting of the microbial communities with DGGE indicated a shift in the environmental conditions within the Laacher See soil column leading to anaerobic and potentially acidic microenvironments. Furthermore, the distribution and phylogenetic affiliation of the archaeal 16S rRNA genes, the presence of ammonia-oxidizing Archaea and the biomarker analysis revealed a predominance of Thaumarchaeota as possible indicator organisms for elevated CO2 concentrations in soils.

Long-term CO2injection and its impact on near-surface soil microbiology

“…Higher values were detected for Crenarchaeota with 10 7 -10 9 16S rDNA gene copy numbers gdw -1 in CO 2 -exposed and 10 8 -10 9 gene copy numbers gdw -1 in reference samples (Table 2). Similar values for both mcrA and crenarchaeal gene copies were detected in previous studies for different soil types (Oppermann et al 2010;Angel et al 2012;Frerichs et al 2013;Dubey et al 2014). …”

“…Both bacterial and archaeal 16S rDNA gene copy numbers ranged from 10 7 to 10 10 gdw -1 of soil (Figure 3a and 3b) without significant CO 2 -induced differences between CO 2 -exposed and reference samples (ANOVA, P > 0.05; Supplementary Table 6a). Similar results were detected for the CO 2 injection site PISCO 2 as well as for some natural CO 2 vents (Beaubien et al 2008;Frerichs et al 2013;Beulig et al 2015;Fernández-Montiel et al 2015). In contrast, decreasing microbial gene copy numbers by up to two orders of magnitude with increasing CO 2 at natural CO 2 vents were previously detected (Oppermann et al 2010;.…”

“…Oppermann et al 2010;Frerichs et al 2013;Fernández-Montiel et al 2015). However, CO 2 -induced differences in aerobic and anaerobic CO 2 production rates as described in these studies, could not be detected for the ASGARD site (Oppermann et al 2010;Frerichs et al 2013). In addition, no significant CO 2 impact over time was detected for the CH 4 production and oxidation (Figure 2c and 2d).…”

“…However, contrary results were detected especially for natural CO 2 vents with both increasing and decreasing numbers of mcrA genes with increasing CO 2 concentration (Oppermann et al 2010;Frerichs et al 2013). Gene copy numbers of ammonia-oxidizing Bacteria (AOB) in May samples ranged between 10 6 -10 8 for both CO 2 -exposed and reference samples.…”

“…Previous investigations of AOB and AOA gene copy numbers in CO 2 -unaffected agricultural soil and pasture showed similar numbers between 10 4 -10 9 gene copies gdw -1 (Nicol et al 2008;Daebeler et al 2014). Unfortunately, the potential stimulation or inhibition of AOA and AOB by increasing CO 2 concentrations remains unclear (Frerichs et al 2013;Holben 2013, 2014).…”