Combined effects of temperature and resource availability on organic matter degradation by Antarctic bacterioplankton
Final Report Abstract
The extent of Antarctic sea ice has changed dramatically in the last ~50 years, from relatively gradual increases in the late 1970s to rapid decreases since 2014. Similar to other Antarctic marginal seas, the ice extent in the Weddell Sea decreased markedly during 2015–2018, when our investigations took place. Overall, our results show that phytoplankton and bacteria were tightly coupled during this phase of rapid ice loss, such that bacterial carbon remineralization increased in response to the increased availability of fresh organic matter in the expanding icefree regions along the Weddell Sea shelves. Both field data and experimental results revealed increasing heterotrophic bacterial activity in response to elevated concentrations of natural DOM that was largely driven by ubiquitious marine lineages like Sulfitobacter and Polaribacter, even though seawater temperature was at -1.8°C. The dominance of ubiquitous genera along the Weddell Sea shelves may point to only moderate cold adaptation. An alternative explanation, however, is that the dominating taxa achieve cold adaptation mostly at the species and/or ecotype level. The addition of glucose and its polymer laminarin to natural bacterioplankton induced the growth of various coldadapted genera like Pseudoalteromonas, Pacificibacter and Maribacter with site- and carbohydrate-specific differences. Experimental temperature manipulation revealed that a short-term increase from 0°C to 3°C resulted in significantly higher bacterial production in approximately 40% of the investigted communities. Bacterial production in temperature-sensitive communities increased by a factor of 1.8 on average, a value similar to the change of bacterial growth in experiments with incubation times of 4-5 days (average factorial increase 1.4). The latter experiments, which allowed for adaptation and taxonomic shifts in the communities, demonstrated that temperature effects on bacterial growth had a high potential to interact with the supply of labile organic matter. In three out of four experiments, the combined effect of temperature and the addition of labile substrates on bacterial growth was synergistic, i.e., stronger than the additive effect of the two manipulations. Because climate change-induced warming will be accompanied by an increase in phytoplankton production as sea ice decreases, the amplification of temperature effects on heterotrophic bacterial activity and thus on remineralization of organic matter can be expected. The composition of dissolved organic matter suggests that proteinaceous material is an important labile carbon and nitrogen source for heterotrophic bacterioplankton in the Weddell Sea. The inventory of extracellular peptidases in metagenomes confirmed a broad spectrum and identified bacterial homologues of the metalloendopeptidase neprilysin (MEROPS family M13), the subtilisin family (MEROPS subfamily S08A) and prolyl aminopeptidases (MEROPS family S33) as potentially important in the utilization of proteins produced by blooms of Phaeocystis sp. The Scientific Committee on Antarctic Research (SCAR) identified a better understanding of potential effects of climate change on the biological uptake of CO2 by the Southern Ocean as one of the most pressing tasks in Antarctic research. Overall, our results suggest that enhanced bacterial carbon remineralization is a possible consequence of multiple environmental changes that may increase the production of CO2 by heterotrophic microbial plankton in the Southern Ocean.
Publications
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Organic matter composition and heterotrophic bacterial activity at declining summer sea ice in the central Arctic Ocean. Limnology and Oceanography, 66(S1).
Piontek, Judith; Galgani, Luisa; Nöthig, Eva‐Maria; Peeken, Ilka & Engel, Anja
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Bacterial biomass production measured in water samples of POLARSTERN cruise PS111 (ANT-XXXIII/2). PANGAEA
Piontek, J.; Hassenrück, C. & Jürgens, K.
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Dissolved organic matter, chlorophyll a and bacterial abundance measured in water samples of POLARSTERN cruise PS111 (ANT-XXXIII/2). PANGAEA
Piontek, J.; Hassenrück, C.; Jürgens, K. & Engel, A.
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The significance of organic carbon limitation for heterotrophic bacterioplankton acting at subzero seawater temperature. ASLO Aquatic Sciences Meeting, 17-22 June 2021, virtual (oral presentation)
Piontek, J.; Meeske, C.; Engel, A. & Jürgens, K.
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Organic matter availability drives the spatial variation in the community composition and activity of Antarctic marine bacterioplankton, 28th International Polar Conference, 1 - 5 May 2022, Potsdam (oral presentation)
Piontek, J.; Engel, A.; Hassenrück, C. & Jürgens, K.
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Organic matter availability drives the spatial variation in the community composition and activity of Antarctic marine bacterioplankton. Environmental Microbiology, 24(9), 4030-4048.
Piontek, Judith; Meeske, Christian; Hassenrück, Christiane; Engel, Anja & Jürgens, Klaus
