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Transplant experiments uncover Baltic Sea basin-specific responses in bacterioplankton community composition and metabolic activities
Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF). Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
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2015 (English)In: Frontiers in Microbiology, ISSN 1664-302X, Vol. 6, 223Article in journal (Refereed) Published
Abstract [en]

Anthropogenically induced changes in precipitation are projected to generate increased river runoff to semi enclosed seas, increasing loads of terrestrial dissolved organic matter and decreasing salinity. To determine how bacterial community structure and functioning adjust to such changes, we designed microcosm transplant experiments with Baltic Proper (salinity 7.2) and Bothnian Sea (salinity 3.6) water. Baltic Proper bacteria generally reached higher abundances than Bothnian Sea bacteria in both Baltic Proper and Bothnian Sea water, indicating higher adaptability. Moreover, Baltic Proper bacteria growing in Bothnian Sea water consistently showed highest bacterial production and beta-glucosidase activity. These metabolic responses were accompanied by basin specific changes in bacterial community structure. For example, Baltic Proper Pseudomonas and Limnobacter populations increased markedly in relative abundance in Bothnian Sea water, indicating a replacement effect. In contrast, Roseobacter and Rheinheknera populations were stable or increased in abundance when challenged by either of the waters, indicating an adjustment effect. Transplants to Bothnian Sea water triggered the initial emergence of particular Burkholderiaceae populations, and transplants to Baltic Proper water triggered Alteromonadaceae populations. Notably, in the subsequent re transplant experiment, a priming effect resulted in further increases to dominance of these populations. Correlated changes in community composition and metabolic activity were observed only in the transplant experiment and only at relatively high phylogenetic resolution. This suggested an importance of successional progression for interpreting relationships between bacterial community composition and functioning. We infer that priming effects on bacterial community structure by natural episodic events or climate change induced forcing could translate into long-term changes in bacterial ecosystem process rates.

Place, publisher, year, edition, pages
2015. Vol. 6, 223
Keyword [en]
bacterial community functioning, salinity, DOM, terrigenous carbon, climate change, marine bacteria, bacterial diversity
National Category
URN: urn:nbn:se:umu:diva-103544DOI: 10.3389/fmicb.2015.00223ISI: 000352541600001PubMedID: 25883589OAI: diva2:813929
Available from: 2015-05-25 Created: 2015-05-21 Last updated: 2016-03-10Bibliographically approved
In thesis
1. Bacterioplankton in the Baltic Sea: influence of allochthonous organic matter and salinity
Open this publication in new window or tab >>Bacterioplankton in the Baltic Sea: influence of allochthonous organic matter and salinity
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Climate change is expected to increase the precipitation ~30% in higher latitudes during the next century, increasing the land runoff via rivers to aquatic ecosystems. The Baltic Sea will receive higher river discharges, accompanied by larger input of allochthonous dissolved organic matter (DOM) from terrestrial ecosystems. The salinity will decrease due to freshwater dilution. The allochthonous DOM constitute a potential growth substrate for microscopic bacterioplankton and phytoplankton, which together make up the basal trophic level in the sea. The aim of my thesis is to elucidate the bacterial processing of allochthonous DOM and to evaluate possible consequences of increased runoff on the basal level of the food web in the Baltic Sea. I performed field studies, microcosm experiments and a theoretical modeling study.

Results from the field studies showed that allochthonous DOM input via river load promotes the heterotrophic bacterial production and influences the bacterial community composition in the northern Baltic Sea. In a northerly estuary ~60% of bacterial production was estimated to be sustained by terrestrial sources, and allochthonous DOM was a strong structuring factor for the bacterial community composition. Network analysis showed that during spring the diversity and the interactions between the bacteria were relatively low, while later during summer other environmental factors regulate the community, allowing a higher diversity and more interactions between different bacterial groups. The influence of the river inflow on the bacterial community allowed “generalists” bacteria to be more abundant than “specialists” bacteria.   

Results from a transplantation experiment, where bacteria were transplanted from the northern Baltic Sea to the seawater from the southern Baltic Sea and vice versa, showed that salinity, as well as the DOM composition affect the bacterial community composition and their enzymatic activity. The results showed that α-proteobacteria in general were favoured by high salinity, β-proteobacteria by low salinity and terrestrial DOM compounds and γ-proteobacteria by the enclosure itself. However, effects on the community composition and enzymatic activity were not consistent when the bacterial community was retransplanted, indicating a functional redundancy of the bacterial communities. 

Results of ecosystem modeling showed that climate change is likely to have quite different effect on the north and the south of the Baltic Sea. In the south, higher temperature and internal nutrient load will increase the cyanobacterial blooms and expand the anoxic or suboxic areas. In the north, climate induced increase in riverine inputs of allochthonous DOM is likely to promote bacterioplankton production, while phytoplankton primary production will be hampered due to increased light attenuation in the water. This, in turn, can decrease the production at higher trophic levels, since bacteria-based food webs in general are less efficient than food webs based on phytoplankton. However, complex environmental influences on the bacterial community structure and the large redundancy of metabolic functions limit the possibility of predicting how the bacterial community composition will change under climate change disturbances.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2016. 23 p.
Bacterioplankton production; bacterial community structure; allochthonous organic matter; carbon utilization; dissolved organic carbon composition; bacterioplankton ecological function; bacterial diversity; bacterial network; Baltic Sea estuary; food web; climate change.
National Category
Research subject
biology, Environmental Science
urn:nbn:se:umu:diva-117977 (URN)978-91-7601-412-7 (ISBN)
Public defence
2016-04-01, KB3B1, Linnaeus väg 6 (Chemical Biological Center, KBC), Umeå, 10:00 (English)
Ecosystem dynamics in the Baltic Sea in a changing climate perspective - ECOCHANGE
Available from: 2016-03-11 Created: 2016-03-08 Last updated: 2016-03-10Bibliographically approved

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Figueroa, DanielaAndersson, Agneta
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