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Coupling between bacterial community composition and allochthonous organic matter in a sub-arctic estuary
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
(UMR 42 CARRTEL (Centre Alpin de Recherche sur les Réseaux Trophiques des Ecosystèmes Limniques), INRA Thonon-les-bains. France)
(Center for Microbial Oceanography Research and Education., University of Hawaií at Mānoa, Honolulu. United States)
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Climate change is expected to cause increased precipitation in boreal and subarctic zones, leading to increased runoff of allochthonous dissolved organic matter (ADOM) from land to the sea. ADOM has been shown to be a major driver of bacterioplankton production in a sub-arctic estuary in the northern Baltic Sea, the Råne estuary. By using a network approach we here analyzed how the bacterial community is affected by ADOM and other environmental factors in the same estuary. β-proteobacteria were observed to be dominant in spring when the river runoff and the ADOM concentrations were high. Planctomycetes and Verrucomicrobia become more abundant later during the summer when the ADOM discharge was low. The diversity and evenness in the bacterioplankton community increased as the runoff decreased during the summer. During this period Verrucomicrobia, β-proteobacteria, Bacteriodetes, γ-proteobacteria and Planctomycetes became more abundant. Overall more complex population interactions were established in summer than in spring. β-proteobacteria and Bacteriodetes formed clusters, showing similar responses to different environmental factors, which suggest a functional connection between these groups. The bacterial community consisted of as much as ~60% of generalists, which reflected the large variation of the environmental conditions in the estuary.

Keyword [en]
Bacterial community structure; allochthonous organic matter; bacterioplankton ecological function; bacterial diversity; bacterial network; environmental changes; Baltic Sea estuary.
National Category
Ecology
Research subject
Earth Sciences with Specialization Environmental Analysis; Microbiology
Identifiers
URN: urn:nbn:se:umu:diva-117976OAI: oai:DiVA.org:umu-117976DiVA: diva2:910229
Funder
Ecosystem dynamics in the Baltic Sea in a changing climate perspective - ECOCHANGE
Available from: 2016-03-08 Created: 2016-03-08 Last updated: 2016-03-10
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.
Keyword
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
Ecology
Research subject
biology, Environmental Science
Identifiers
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)
Opponent
Supervisors
Funder
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, DanielaRowe, OwenPaczkowska, JoannaAndersson, Agneta
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