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Diversity and Ecosystem Functioning: Redundancy and Resilience in Freshwater Bacterial Communities
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Bacteria are immensely diverse and hold key-positions in essentially all biogeochemical cycles. In freshwater ecosystems, bacteria degrade and mineralize organic compounds, linking the pool of dissolved organic matter to higher trophic levels. Aware of the global biodiversity loss, ecologists have started identifying the relationship of diversity and ecosystem functioning. Central to this is the question if species can functionally replace other species, hence being functionally redundant. Functional redundancy might allow communities to maintain functioning when diversity is lost. Due to their large numbers and great diversity, bacterial communities have been suspected to harbor large amounts of redundancy. The central aim of this thesis is to investigate the coupling of diversity and ecosystem functioning of bacterial communities and to understand how environmental perturbation affects this relationship. I manipulated the diversity of complex communities by a dilution technique, and measured the performance of bacterioplankton and biofilm-forming communities at different diversities. Reduction of bacterial diversity differently affected different functions, and that the presence or absence of certain species might be causing this pattern. However, for ecosystems to function, the interplay of multiple functions, i.e. multifunctionality, has to be sustained over long periods of time. In bacterial biofilm communities reduced diversity affected multifunctionality, as reflected by extracellular enzyme activities. A continuous cultivation system was used to address the importance of diversity for resistance and resilience upon environmental perturbation. The analysis of co-occurrence of bacterial taxa showed that the communities form a dense network before the perturbation and that these patterns are disturbed by the environmental perturbation. The final chapter of the thesis presents experimental evidence for the positive effects of temporal and spatial refuges for bacterial communities and the functions they provide. Overall, I found several indications for a lower amount of functional redundancy as previously assumed and it becomes apparent from this thesis that a multifunctional perspective and the consideration of environmental heterogeneity is pivotal.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2011. , 48 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 882
Keyword [en]
biodiversity, ecosystem functioning, bacteria, fresh water, biofilms, multifunctionality, ecological networks, perturbation, fragility
National Category
Ecology Microbiology
Research subject
Biology with specialization in Limnology
Identifiers
URN: urn:nbn:se:uu:diva-160780ISBN: 978-91-554-8223-7 (print)OAI: oai:DiVA.org:uu-160780DiVA: diva2:453381
Public defence
2011-12-16, Friessalen, Evolutionary Biology Centre (EBC), Norbyvägen 18, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2011-11-24 Created: 2011-10-31 Last updated: 2012-01-03
List of papers
1. Function-specific response to depletion of microbial diversity
Open this publication in new window or tab >>Function-specific response to depletion of microbial diversity
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2011 (English)In: The ISME Journal, ISSN 1751-7362, Vol. 5, no 2, 351-361 p.Article in journal (Refereed) Published
Abstract [en]

Recent meta-analyses suggest that ecosystem functioning increases with biodiversity, but contradictory results have been presented for some microbial functions. Moreover, observations of only one function underestimate the functional role of diversity because of species-specific trade-offs in the ability to carry out different functions. We examined multiple functions in batch cultures of natural freshwater bacterial communities with different richness, achieved by a dilution-to-extinction approach. Community composition was assessed by molecular fingerprinting of 16S rRNA and chitinase genes, representing the total community and a trait characteristic for a functional group, respectively. Richness was positively related to abundance and biomass, negatively correlated to cell volumes and unrelated to maximum intrinsic growth rate. The response of chitin and cellulose degradation rates depended on the presence of a single phylotype. We suggest that species identity and community composition rather than richness matters for specific microbial processes.

Keyword
cellulose, chitin, functional diversity, species traits, T-RFLP
National Category
Biological Sciences
Identifiers
urn:nbn:se:uu:diva-131083 (URN)10.1038/ismej.2010.119 (DOI)000290020000018 ()20686511 (PubMedID)
Available from: 2010-09-22 Created: 2010-09-22 Last updated: 2017-11-30Bibliographically approved
2. Multifunctionality and Diversity in Bacterial Biofilms
Open this publication in new window or tab >>Multifunctionality and Diversity in Bacterial Biofilms
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2011 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 6, no 8, e23225- p.Article in journal (Refereed) Published
Abstract [en]

Bacteria are highly diverse and drive a bulk of ecosystem processes. Analysis of relationships between diversity and single specific ecosystem processes neglects the possibility that different species perform multiple functions at the same time. The degradation of dissolved organic carbon (DOC) followed by respiration is a key bacterial function that is modulated by the availability of DOC and the capability to produce extracellular enzymes. In freshwater ecosystems, biofilms are metabolic hotspots and major sites of DOC degradation. We manipulated the diversity of biofilm forming communities which were fed with DOC differing in availability. We characterized community composition using molecular fingerprinting (T-RFLP) and measured functioning as oxygen consumption rates, the conversion of DOC in the medium, bacterial abundance and the activities of five specific enzymes. Based on assays of the extracellular enzyme activity, we calculated how the likelihood of sustaining multiple functions was affected by reduced diversity. Carbon source and biofilm age were strong drivers of community functioning, and we demonstrate how the likelihood of sustaining multifunctionality decreases with decreasing diversity.

National Category
Biological Sciences
Identifiers
urn:nbn:se:uu:diva-158168 (URN)10.1371/journal.pone.0023225 (DOI)000293563300048 ()
Available from: 2011-09-05 Created: 2011-09-01 Last updated: 2017-12-08Bibliographically approved
3. Fragility of aquatic microbial communities exposed to perturbation
Open this publication in new window or tab >>Fragility of aquatic microbial communities exposed to perturbation
(English)In: The ISME Journal, ISSN 1751-7362Article in journal (Refereed) Submitted
National Category
Ecology Microbiology
Identifiers
urn:nbn:se:uu:diva-160773 (URN)
Available from: 2011-10-31 Created: 2011-10-31 Last updated: 2017-11-30Bibliographically approved
4. Resistance and resilience of microbial communities: temporal and spatial insurance against perturbations
Open this publication in new window or tab >>Resistance and resilience of microbial communities: temporal and spatial insurance against perturbations
2012 (English)In: Environmental Microbiology, ISSN 1462-2912, E-ISSN 1462-2920, Vol. 14, no 9, 2283-2292 p.Article in journal (Refereed) Published
Abstract [en]

Bacteria play fundamental roles for many ecosystem processes; however, little empirical evidence is available on how environmental perturbations affect their composition and function. We investigated how spatial and temporal refuges affect the resistance and resilience of a freshwater bacterioplankton community upon a salinity pulse perturbation in continuous cultures. Attachment to a surface avoided the flushing out of cells and enabled re-colonization of the liquid phase after the perturbation, hence serving as a temporal refuge. A spatial refuge was established by introduction of bacteria from an undisturbed reservoir upstream of the continuous culture vessel, acting analogous to a regional species pool in a metacommunity. The salinity pulse affected bacterial community composition and the rates of respiration and the pattern of potential substrate utilization as well as the correlation between composition and function. Compared with the no-refuge treatment, the temporal refuge shortened return to pre-perturbation conditions, indicating enhanced community resilience. Composition and function were less disturbed in the treatment providing a spatial refuge, suggesting higher resistance. Our results highlight that spatial and temporal dynamics in general and refuges in particular need to be considered for conceptual progress in how microbial metacommunities are shaped by perturbations.

National Category
Ecology Microbiology
Identifiers
urn:nbn:se:uu:diva-160777 (URN)10.1111/j.1462-2920.2012.02754.x (DOI)000308300600004 ()
Available from: 2011-10-31 Created: 2011-10-31 Last updated: 2017-12-08Bibliographically approved

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