CO2 impacts on microbial communities in different near-surface geosystems

authored by: Simone Gwosdz
supervised by: A. Schippers
Abstract: Anthropogenic CO2 emissions increased during the last ~150 years. Subsequently, the atmospheric CO2 concentration increased with severe effects for the Earth’s climate and the global carbon cycle. Although technical progress in energy efficiency, renewable energy sources and industrial CO2 capture and storage techniques led to decreasing greenhouse gas emissions in many countries, the potential impacts of the still increasing atmospheric CO2 concentrations for the ocean and terrestrial carbon cycle are still poorly understood. Hence, this thesis focussed on geochemical processes and the microbial activity, abundance and community structure potentially altered by high CO2 concentrations in different near-surface geosystems. The main objectives of this thesis were (i) to investigate CO2-induced geochemical alterations, (ii) to identify potential adaptation mechanisms of the microbial community leading to changes in the microbial community structure and metabolic activity and (iii) to identify potential indicator organisms. Therefore, two long-term CO2-adapted geosystems (terrestrial and freshwater) and one artificial short-term CO2 injection facility have been studied. The main findings of the thesis are: (i) Long-term CO2 exposure with high CO2 concentrations led to significant changes in both, plant coverage and community composition as well as geochemistry e.g. the acidification of soil and sediment (pore water), increased soil moisture content and soil weathering. (ii) Long-term CO2 exposure with high CO2 concentrations led to a shift towards anaerobic, acidic tolerant to acidophilic methanogens and autotrophs. The verified predominant archaeal taxa belonged to Methanomicrobia (Euryarchaeota), Thermoprotei (Crenarchaeota) and Pacearchaeota. (iii) Long-term CO2 exposed geosystems with high CO2 concentrations revealed the potential importance of Chloroflexi as potential bacterial indicator species. The very abundant Chloroflexi species are presumably connected to anaerobic organic matter degradation and CO2-fixation. (iv) Short-term CO2 injection over a period of 24 months revealed no significant geochemical and microbiological alterations. The CO2-exposed samples did not show significant changes in microbial CO2 and CH4 turnover rates compared to reference samples. Likewise, no alterations in microbial abundances and community composition were detected. (v) Concerning a possible CO2 threshold for significant i.e. detectable ecosystem changes, the results of all geosystems in summary suggest a CO2 concentration of up to 50 % as critical level. CO2 concentrations below did not lead to significant geochemical and microbiological changes.
Organisation(s): Institute of Microbiology
Type: Doctoral thesis
No. of pages: 100
Publication date: 2018
Publication status: Published
Sustainable Development Goals: SDG 7 - Affordable and Clean Energy, SDG 13 - Climate Action, SDG 15 - Life on Land
Electronic version(s): https://doi.org/10.15488/3466 (Access: Open)