Impact of ocean acidification on microbial degradation of organic matter

• Main Author: Endres, Sonja
• Format: Thesis
• Language: English
• Published: 2013
• Subjects: Ocean acidification
• Online Access: https://oceanrep.geomar.de/id/eprint/19384/; https://oceanrep.geomar.de/id/eprint/19384/1/Diss.%202013%20Endres,S.pdf

Marine bacteria play a key role in carbon and nutrient cycles of the ocean. The majority of organic carbon fixed during photosynthesis is rapidly recycled in the upper ocean via microbial degradation. The remaining organic carbon is sequestrated in the deep sea making the ocean a net sink for atmospheric carbon dioxide (CO2). Organic matter in the ocean is a complex mixture of organic compounds and a major portion is continuously transformed chemically from dissolved small molecules to polymers and gels, up to particles and broken back down to small dissolved monomers by microbial activities. Gel particles, in particular, are hotspots of microbial degradation as they provide food and a surface to attach to. Furthermore gel particles accelerate aggregation of particulate organic matter (POM) and play a major role in sedimentation processes in the sea. In order to utilize organic matter, bacteria have to produce extracellular enzymes that operate outside the cell to degrade polymers into smaller compounds. Many enzymes involved in the bacterial hydrolysis of organic matter were shown to be pH-sensitive. As CO2 concentrations in the ocean rise due to anthropogenic CO2 emissions, seawater pH decreases – a process known as ‘ocean acidification’. Since 1750, the ocean’s pH decreased by 0.1 units and a further decrease of around 0.15 - 0.35 units in the surface oceans by the year 2100 is projected. Despite their importance, relatively little is known about in what way marine bacteria may be influenced by ocean acidification. This doctoral thesis addresses the question how microbial degradation of organic matter and organic matter composition may change in the acidifying ocean. The first part of the thesis investigates the response of a natural plankton community to CO2 enrichment during a mesocosm study in a Norwegian fjord. The second part focuses specifically on the filamentous diazotrophic cyanobacterium Nodularia spumigena, which plays an important role in nitrogen and phosphorus cycling in the Baltic Sea. In both ...