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Bacterioplankton in the Baltic Sea: influence of allochthonous organic matter and salinity
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (EcoChange)
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 [en]
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: urn:nbn:se:umu:diva-117977ISBN: 978-91-7601-412-7 (print)OAI: oai:DiVA.org:umu-117977DiVA: diva2:910259
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: 2017-09-01Bibliographically approved
List of papers
1. Allochthonous Carbon - a major driver of bacterioplankton production in the subarctic Northern Baltic Sea
Open this publication in new window or tab >>Allochthonous Carbon - a major driver of bacterioplankton production in the subarctic Northern Baltic Sea
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2016 (English)In: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 71, no 4, 789-801 p.Article in journal (Refereed) Published
Abstract [en]

Heterotrophic bacteria are, in many aquatic systems, reliant on autochthonous organic carbon as their energy source. One exception is low-productive humic lakes, where allochthonous dissolved organic matter (ADOM) is the major driver. We hypothesized that bacterial production (BP) is similarly regulated in subarctic estuaries that receive large amounts of riverine material. BP and potential explanatory factors were measured during May–August 2011 in the subarctic Råne Estuary, northern Sweden. The highest BP was observed in spring, concomitant with the spring river-flush and the lowest rates occurred during summer when primary production (PP) peaked. PLS correlations showed that ∼60 % of the BP variation was explained by different ADOM components, measured as humic substances, dissolved organic carbon (DOC) and coloured dissolved organic matter (CDOM). On average, BP was threefold higher than PP. The bioavailability of allochthonous dissolved organic carbon (ADOC) exhibited large spatial and temporal variation; however, the average value was low, ∼2 %. Bioassay analysis showed that BP in the near-shore area was potentially carbon limited early in the season, while BP at seaward stations was more commonly limited by nitrogen-phosphorus. Nevertheless, the bioassay indicated that ADOC could contribute significantly to the in situ BP, ∼60 %. We conclude that ADOM is a regulator of BP in the studied estuary. Thus, projected climate-induced increases in river discharge suggest that BP will increase in subarctic coastal areas during the coming century.

Place, publisher, year, edition, pages
Springer, 2016
Keyword
Allochthonous organic matter, carbon utilization, bacterioplankton production, Sub-arctic estuary, Baltic Sea
National Category
Ecology
Research subject
Earth Sciences with Specialization Environmental Analysis
Identifiers
urn:nbn:se:umu:diva-117966 (URN)10.1007/s00248-015-0714-4 (DOI)000373683000001 ()
Funder
Ecosystem dynamics in the Baltic Sea in a changing climate perspective - ECOCHANGE
Available from: 2016-03-08 Created: 2016-03-08 Last updated: 2017-10-24Bibliographically approved
2. Transplant experiments uncover Baltic Sea basin-specific responses in bacterioplankton community composition and metabolic activities
Open this publication in new window or tab >>Transplant experiments uncover Baltic Sea basin-specific responses in bacterioplankton community composition and metabolic activities
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2015 (English)In: Frontiers in Microbiology, ISSN 1664-302X, E-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.

Keyword
bacterial community functioning, salinity, DOM, terrigenous carbon, climate change, marine bacteria, bacterial diversity
National Category
Microbiology
Identifiers
urn:nbn:se:umu:diva-103544 (URN)10.3389/fmicb.2015.00223 (DOI)000352541600001 ()25883589 (PubMedID)
Available from: 2015-05-25 Created: 2015-05-21 Last updated: 2017-12-04Bibliographically approved
3. Selective degradation of different dissolved organic matter compounds by regionally transplanted bacteria.
Open this publication in new window or tab >>Selective degradation of different dissolved organic matter compounds by regionally transplanted bacteria.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Climate change projections indicate that precipitation will increase by ~30% in the Baltic Sea within the next hundred years. This will lead to lowered salinity and increased inputs of dissolved organic matter (DOM) to the sea. The interactive effects of these changes on bacterial communities and DOM degradation are virtually unknown. We studied the selective degradation of different DOM compounds by regionally transplanted bacterial communities. Bacteria from the northern Baltic Sea were transplanted and re-transplanted to the southern Baltic Sea and vice versa. Three fractions of DOM were identified; two allochthonous fractions, originating from terrestrial systems and one autochthononous constituting the protein building blocks tryptophan/tyrosine. The largest decrease of dissolved organic carbon was observed in seawater from the Bothnian Sea (northern Baltic Sea), and the bacteria performing this degradation were those transplanted from the Baltic Proper (southern Baltic Sea). The native bacteria from the Bothnian Sea degraded both allochthonous and autochthonous DOM, while, bacteria from the Baltic Proper consumed mainly the autochthonous part of the DOM. Both autochthonous and allochthonous components of the DOM were found to shape the bacterioplankton community, Cyanobacteria and γ-proteobacteria were favored by all three DOM components, while α-proteobacteria and Bacteroidetes were favored by autochthonous DOM and β-proteobacteria by terrestrial DOM. However, no clear connection between different DOM components, specific bacterial groups and metabolic processes could be identified. Our study thus indicates that climate change can cause unforeseen adjustments of the bacterial community composition and function, governed by complex interactions between bacteria and their chemical environment.

Keyword
Dissolved organic matter composition; selective degradation; regionally transplanted bacteria, bacterioplankton community changes; Baltic Sea.
National Category
Ecology
Research subject
Earth Sciences with Specialization Environmental Analysis
Identifiers
urn:nbn:se:umu:diva-117974 (URN)
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
4. Coupling between bacterial community composition and allochthonous organic matter in a sub-arctic estuary
Open this publication in new window or tab >>Coupling between bacterial community composition and allochthonous organic matter in a sub-arctic estuary
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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
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:nbn:se:umu:diva-117976 (URN)
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
5. Projected future climate change and Baltic Sea ecosystem management
Open this publication in new window or tab >>Projected future climate change and Baltic Sea ecosystem management
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2015 (English)In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 44, no Suppl 3, S345-S356 p.Article in journal (Refereed) Published
Abstract [en]

Climate change is likely to have large effectson the Baltic Sea ecosystem. Simulations indicate 2–4 Cwarming and 50–80 % decrease in ice cover by 2100.Precipitation may increase *30 % in the north, causingincreased land runoff of allochthonous organic matter(AOM) and organic pollutants and decreased salinity.Coupled physical–biogeochemical models indicate that, inthe south, bottom-water anoxia may spread, reducing codrecruitment and increasing sediment phosphorus release,thus promoting cyanobacterial blooms. In the north,heterotrophic bacteria will be favored by AOM, whilephytoplankton production may be reduced. Extra trophiclevels in the food web may increase energy losses andconsequently reduce fish production. Future managementof the Baltic Sea must consider the effects of climatechange on the ecosystem dynamics and functions, as wellas the effects of anthropogenic nutrient and pollutant load.Monitoring should have a holistic approach, encompassingboth autotrophic (phytoplankton) and heterotrophic (e.g.,bacterial) processes.

Place, publisher, year, edition, pages
Springer, 2015
Keyword
Climate change, Allochthonous organic matter, Primary production, Bacterial production, Food web, Monitoring
National Category
Chemical Sciences Environmental Sciences
Identifiers
urn:nbn:se:umu:diva-98932 (URN)10.1007/s13280-015-0654-8 (DOI)000362290800003 ()26022318 (PubMedID)
Note

Supplement: 3 Special Issue: SI

Available from: 2015-01-28 Created: 2015-01-28 Last updated: 2017-10-24Bibliographically approved

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Figueroa, Daniela

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