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CO2 Impacts on Microbial Communities in Different Near-Surface Geosystems

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CO2 Impacts on Microbial Communities in Different Near-Surface Geosystems CO2 impacts on Microbial Communities in different Near-Surface Geosystems Von der Naturwissenschaftlichen Fakultät der Gottfried Wilhelm Leibniz Universität Hannover zur Erlangung des Grades Doktorin der Naturwissenschaften (Dr. rer. nat.) genehmigte Dissertation von Dipl.-Biol. Simone Gwosdz 2018 Referent: apl. Professor Dr. rer. nat. Axel Schippers Korreferent: Professor Dr. rer. nat. Thomas Brüser Tag der Promotion: 20. April 2018 Diese Arbeit ist mir selbst gewidmet. In Erinnerung an das was möglich ist… Summary 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. Keywords: CO2, geochemistry, methanogens, autotrophs i Zusammenfassung Anthropogene CO2 Emissionen sind während der vergangenen ~150 Jahre angestiegen. Dies führte zu einem Anstieg der CO2 Konzentration in der Atmosphäre und folglich zu schwerwiegenden Auswirkungen auf das weltweite Klima und den globalen Kohlenstoffkreislauf. Obgleich der technische Fortschritt im Bereich der Energieeffizienz, der erneuerbaren Energiequellen und Techniken der industriellen CO2 Abscheidung und Speicherung zu einer Verringerung von Treibhausgas Emissionen führte, die möglichen Auswirkungen der auch weiterhin ansteigenden CO2 Konzentrationen in der Atmosphäre auf den Kohlenstoffkreislauf an Land und im Meer sind auch weiterhin wenig verstanden. Die vorliegende Arbeit konzentrierte sich daher auf mögliche Veränderungen in den geochemischen Prozessen sowie in der mikrobiellen Aktivität, Abundanz und Gemeinschaftsstruktur oberflächennaher Geosysteme durch hohe CO2 Konzentrationen. Die Hauptziele dieser Arbeit waren (i) die Untersuchung CO2 induzierter Veränderungen in den geochemischen Prozessen, (ii) die Identifizierung mikrobieller Anpassungsmechanismen die zu Veränderungen in der mikrobiellen Gemeinschaft und ihrer Aktivität führen und (iii) die Identifikation möglicher Indikatorspezies. Hierfür wurden zwei dauerhafte, CO2 adaptierte Geosysteme untersucht (terrestrisch wie limnisch) sowie eine künstliche Anlage, in welcher CO2 kurzzeitig injiziert wurde. Die wichtigsten Ergebnisse dieser Arbeit sind: (i) Der Nachweis, dass eine langfristige CO2 Exposition zu signifikanten Veränderung im Pflanzenbestand und -Wuchs sowie in den geochemischen Prozessen führte. Dies beinhaltete u.a. die Versauerung des Bodens/Sediments (bzw. Porenwassers), einen Anstieg der Bodenfeuchte sowie die Verwitterung des Bodens. (ii) Das eine langfristige Exposition mit hohen CO2 Konzentrationen zu einer Verschiebung hin zu anaeroben, säuretoleranten bis säureliebenden Methanogenen und Autotrophen führt. Die vorherrschenden Taxa der Archaea wurden hierbei den Methanomicrobia (Euryarchaeota), Thermoprotei (Crenarchaeota) und Pacearchaeota zugeordnet. (iii) Geosysteme, die langfristig hohen CO2 Konzentrationen ausgesetzt waren machten die Bedeutung von Chloroflexi als mögliche bakterielle Indikatorspezies deutlich. Diese besonders abundanten Chloroflexi Spezies sind mit hoher Wahrscheinlichkeit am anaeroben Abbau organischen Materials sowie an der CO2 Fixierung beteiligt. (iv) Eine kurzzeitige CO2 Injektion über einen Zeitraum von 24 Monaten zeigte keine signifikanten geochemischen oder mikrobiologischen Veränderungen. Es wurden keine signifikanten Veränderungen in den mikrobiellen CO2 und CH4 Umsatzraten zwischen CO2 exponierten Proben und Referenzproben festgestellt. Auch die mikrobielle Abundanz und Gemeinschaftsstruktur blieb unverändert. (v) Einen möglichen CO2 Schwellenwert für signifikante d.h. nachweisbare Veränderungen im Ökosystem betreffend, legen die Ergebnisse aller untersuchten Geosysteme nahe, dass eine CO2 Konzentration ab 50% als kritisch eingestuft werden kann. Konzentrationen darunter führten in der vorliegenden Arbeit zu keinen signifikanten geochemischen und mikrobiologischen Veränderungen. Schlagworte: CO2, Geochemie, methanogene und autotrophe Mikroorganismen ii Table of Contents Abbreviations ........................................................................................................................................................ 1 1. General Introduction ........................................................................................................................................ 3 1.1. Climate Change ........................................................................................................................................... 4 1.2. Carbon dioxide and Carbon Cycle ............................................................................................................... 4 1.2.1. Ocean Carbon Cycle ............................................................................................................................. 5 1.2.2. Terrestrial Carbon Cycle ...................................................................................................................... 6 1.3. Sources and Mitigation of Anthropogenic Carbon Dioxide ........................................................................ 7 1.3.1. Carbon Dioxide Capture and Storage (CCS) ........................................................................................ 7 1.4. Potential Impacts of Carbon Dioxide on Near-Surface Ecosystems ............................................................ 9 1.4.1. Potential Impacts of Carbon Dioxide on Plants .................................................................................... 9 1.4.2. Potential Impacts of Carbon Dioxide on Soil Geochemistry ................................................................ 9 1.4.3. Potential Impacts of Carbon Dioxide on Microbial Processes ........................................................... 10 1.5. Scope and Objectives of the Thesis ........................................................................................................... 13 1.6. Description of Geosystems ........................................................................................................................ 14 1.6.1. The ASGARD (Artificial Soil Gassing and Response Detection) Field Site ..................................... 14 1.6.2. The Florina Basin ............................................................................................................................... 15 1.6.3. The Laacher See ................................................................................................................................. 16 2. Results and Discussion .................................................................................................................................... 18 2.1. Long-term CO2 Exposure Induces Changes in Geochemistry and Plant Coverage ................................... 19 2.1.1. The Florina CO2 Vent ......................................................................................................................... 19 2.1.2. The Laacher See High CO2-influenced Sediment Core ...................................................................... 19 2.2. Long-term CO2 Exposure
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