| 1. |
- Andersson, Martin, et al.
(author)
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Response and effect interactions between bacterial communities and organic matter
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Other publication (other academic/artistic)abstract
- The interaction between bacteria and dissolved organic matter (DOM) is crucial for the global carbon cycling. Despite decades of research there are, however, few consistent patterns regarding the relationship between bacterial diversity and community composition and DOM. Here we hypothesized that one reason for such inconsistences among studies is that bacterial communities can adapt to a DOM source over time, whereby a change in the functioning of a community can be, at least partly, decoupled from its composition and diversity. To test this idea we performed a reciprocal transplant experiment with medium (i.e. DOM source) and bacterial communities from two boreal lakes. In this experiment the two communities were allowed to adapt to their indigenous and their foreign source of DOM over 42 days. Bacterial community composition (BCC) was measured throughout the experiment. In addition we measured the capacity of the communities to use DOM, in repeated short (5 days) separated bioassays. The results show a response of bacterial community composition to the DOM sources which was influenced by the origin of the community. In contrast, we could not show an effect of BCC on DOM-processing and functional performance. Indeed, communities of different origin processed the two DOM sources equally well even at the beginning of the experiment. This work demonstrates that the DOM pool can be a strong selective force for BCC but not vice versa.
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| 2. |
- Andersson, Martin, et al.
(author)
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The spatial structure of bacterial communities is influenced by historical environmental conditions
- 2014
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In: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 95:5, s. 1134-1140
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Journal article (peer-reviewed)abstract
- The spatial structure of ecological communities, including that of bacteria, is often influenced by species sorting by contemporary environmental conditions. Moreover, historical processes, i.e., ecological and evolutionary events that have occurred at some point in the past, such as dispersal limitation, drift, priority effects, or selection by past environmental conditions, can be important, but are generally investigated much less. Here, we conducted a field study using 16 rock pools, where we specifically compared the importance of past vs. contemporary environmental conditions for bacterial community structure by correlating present differences in bacterial community composition among pools to environmental conditions measured on the same day, as well as to those measured 2, 4, 6, and 8 d earlier. The results prove that selection by past environmental conditions exists, since we were able to show that bacterial communities are, to a greater extent, an imprint of past compared to contemporary environmental conditions. We suggest that this is the result of a combination of different mechanisms, including priority effects that cause rapid adaptation to new environmental conditions of taxa that have been initially selected by past environmental conditions, and slower rates of turnover in community composition compared to environmental conditions.
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| 3. |
- Arnott, Shelley E., et al.
(author)
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Widespread variation in salt tolerance within freshwater zooplankton species reduces the predictability of community-level salt tolerance
- 2023
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In: Limnology and Oceanography Letters. - : John Wiley & Sons. - 2378-2242. ; 8:1, s. 8-18
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Journal article (peer-reviewed)abstract
- The salinization of freshwaters is a global threat to aquatic biodiversity. We quantified variation in chloride (Cl-) tolerance of 19 freshwater zooplankton species in four countries to answer three questions: (1) How much variation in Cl- tolerance is present among populations? (2) What factors predict intraspecific variation in Cl- tolerance? (3) Must we account for intraspecific variation to accurately predict community Cl- tolerance? We conducted field mesocosm experiments at 16 sites and compiled acute LC(50)s from published laboratory studies. We found high variation in LC(50)s for Cl- tolerance in multiple species, which, in the experiment, was only explained by zooplankton community composition. Variation in species-LC50 was high enough that at 45% of lakes, community response was not predictable based on species tolerances measured at other sites. This suggests that water quality guidelines should be based on multiple populations and communities to account for large intraspecific variation in Cl- tolerance.
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| 4. |
- Baker, Kate L., et al.
(author)
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Environmental and spatial characterisation of microbial community composition to inform sampling strategies
- 2009
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In: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 41:11, s. 2292-2298
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Journal article (peer-reviewed)abstract
- Soil physicochemical properties and microbial communities are highly heterogeneous and vary widely over spatial scales, necessitating careful consideration of sampling strategies to provide representative and reproducible soil samples across field sites. To achieve this, the study aimed to establish appropriate sampling methodology and to determine links between the variability of parameters, utilising two sampling strategies. The first (design 1) involved extracting 25 cores from random locations throughout the field and pooling them into five sets of five cores. The second (design 2) involved a further 25 cores within five 1 m2 sub-plots. Sub-samples from each sub-plot were pooled in order to determine between and within sub-plot variability. All samples were analysed independently and as pooled sub-samples. Results indicate that pooling spatially separated samples significantly reduced the variability in pH, compared to individual samples. Pooling samples from a small area resulted in lower within sub-plot variability than between sub-plots for pH and bacterial community composition assessed by terminal-restriction fragment length polymorphism analysis. Following multivariate statistical analysis, a large amount of variation in community composition was explained by soil pH, which is remarkable given the relatively small size of the sampling area and minor differences in pH. Moisture content was also important in determining bacterial communities in the random design (design 1). In the 1 m2 sub-plot design (design 2), the spatial location of the plots explained a large degree of the variation in bacterial community composition between plots, which was due to spatial autocorrelation of pH and possible additional environmental parameters. This study emphasises the importance of sampling design for obtaining representative samples from soil.
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| 5. |
- Berga, Mercè, et al.
(author)
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Combined effects of zooplankton grazing and dispersal on the diversity and assembly mechanisms of bacterial metacommunities
- 2015
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In: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920. ; 17:7, s. 2275-2287
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Journal article (peer-reviewed)abstract
- Effects of dispersal and the presence of predators on diversity, assembly and functioning of bacterial communities are well studied in isolation. In reality, however, dispersal and trophic interactions act simultaneously and can therefore have combined effects, which are poorly investigated. We performed an experiment with aquatic metacommunities consisting of three environmentally different patches and manipulated dispersal rates among them as well as the presence or absence of the keystone species Daphnia magna. Daphnia magnareduced both local and regional diversity, whereas dispersal increased local diversity but decreased beta-diversity having no net effect on regional diversity. Dispersal modified the assembly mechanisms of bacterial communities by increasing the degree of determinism. Additionally, the combination of the D. magna and dispersal increased the importance of deterministic processes, presumably because predator-tolerant taxa were spread in the metacommunity via dispersal. Moreover, the presence of D. magna affected community composition, increased community respiration rates but did not affect bacterial production or abundance, whereas dispersal slightly increased bacterial production. In conclusion, our study suggests that predation by a keystone species such as D. magna and dispersal additively influence bacterial diversity, assembly processes and ecosystem functioning.
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| 6. |
- Berga, Mercé, et al.
(author)
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Effects of Disturbance Intensity and Frequency on Bacterial Community Composition and Function
- 2012
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In: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 7:5, s. e36959-
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Journal article (peer-reviewed)abstract
- Disturbances influence community structure and ecosystem functioning. Bacteria are key players in ecosystems and it is therefore crucial to understand the effect of disturbances on bacterial communities and how they respond to them, both compositionally and functionally. The main aim of this study was to test the effect of differences in disturbance strength on bacterial communities. For this, we implemented two independent short-term experiments with dialysis bags containing natural bacterial communities, which were transplanted between ambient and 'disturbed' incubation tanks, manipulating either the intensity or the frequency of a salinity disturbance. We followed changes in community composition by terminal restriction fragment analysis (T-RFLP) and measured various community functions (bacterial production, carbon substrate utilization profiles and rates) directly after and after a short period of recovery under ambient conditions. Increases in disturbance strength resulted in gradually stronger changes in bacterial community composition and functions. In the disturbance intensity experiment, the sensitivity to the disturbance and the ability of recovery differed between different functions. In the disturbance frequency experiment, effects on the different functions were more consistent and recovery was not observed. Moreover, in case of the intensity experiment, there was also a time lag in the responses of community composition and functions, with functional responses being faster than compositional ones. To summarize, our study shows that disturbance strength has the potential to change the functional performance and composition of bacterial communities. It further highlights that the overall effects, rates of recovery and the degree of congruence in the response patterns of community composition and functioning along disturbance gradients depend on the type of function and the character of the disturbance.
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| 7. |
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| 8. |
- Berga, Mercè, et al.
(author)
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Functional and Compositional Stability of Bacterial Metacommunities in Response to Salinity Changes
- 2017
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In: Frontiers in Microbiology. - : Frontiers Media SA. - 1664-302X. ; 8
-
Journal article (peer-reviewed)abstract
- Disturbances and environmental change are important factors determining the diversity,composition, and functioning of communities. However, knowledge about how naturalbacterial communities are affected by such perturbations is still sparse. We performeda whole ecosystem manipulation experiment with freshwater rock pools where weapplied salinity disturbances of different intensities. The aim was to test how thecompositional and functional resistance and resilience of bacterial communities,alpha- and beta-diversity and the relative importance of stochastic and deterministiccommunity assembly processes changed along a disturbance intensity gradient.We found that bacterial communities were functionally resistant to all salinity levels (3, 6, and 12 psu) and compositionally resistant to a salinity increase to 3 psu andresilient to increases of 6 and 12 psu. Increasing salinities had no effect on local richnessand evenness, beta-diversity and the proportion of deterministically vs. stochasticallyassembled communities. Our results show a high functional and compositional stabilityof bacterial communities to salinity changes of different intensities both at localand regional scales, which possibly reflects long-term adaptation to environmentalconditions in the study system.
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| 9. |
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| 10. |
- Berga Quintana, Mercè
(author)
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Assembly Mechanisms in Aquatic Bacterial Communities : The Role of Disturbances, Dispersal and History
- 2013
-
Doctoral thesis (other academic/artistic)abstract
- Environmental conditions, biotic interactions, dispersal and history have been suggested to be important processes influencing the spatial distribution of organisms and thus to affect community assembly. Understanding how these processes influence community assembly is important, particularly because community diversity and composition are suggested to be relevant for ecosystem functioning. Moreover, bacteria are strongly contributing to nutrient and carbon cycle. Bacteria are highly abundant and ubiquitous, and thus it is relevant to study how they are assembled. This thesis aims to gain insight on the role of these processes on aquatic bacterial community assembly, diversity and functioning. The studies included in this thesis involve transplant and microcosm experiments performed in the lab as well as manipulation experiments and field surveys in a natural rock pool systems. Bacterial community composition was addressed by analysis of 16S rRNA gene and community functioning by measuring bacterial production, community respiration and the ability to use different carbon substrates. This thesis highlights that species sorting is a very important assembly mechanism for bacterial communities, but also finds that other processes such as dispersal and history contribute to the patterns observed. Dispersal caused rescuing effects compensating for losses of diversity; at the same time it increased the similarity between communities. Moreover, bacteria have shown a high level of functional plasticity when colonizing a new locality. Interestingly, past environmental conditions explained the structure of bacterial communities better than present-day environmental conditions. Disturbances and biotic interactions are also important in the assembly of communities. Disturbance caused temporary shifts in bacterial function and changes in composition, the magnitude of which depended on the intensity and the frequency of the disturbance. However, natural aquatic bacterial communities showed quite high resilience capacities. Competition can shift the proportion of generalists and specialists species whereas predation or trophic interactions have been found to decrease diversity and to modify the importance of stochasticity. Both caused alterations of community functioning. Finally, this thesis shows that the diversity-functioning relationship is context dependent. Further research should be directed to understanding the intensity and direction of changes in composition and how this affects the functionality of bacterial communities
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| 11. |
- Besemer, Katharina, et al.
(author)
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Unraveling assembly of stream biofilm communities
- 2012
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In: The ISME Journal: multidisciplinary journal of microbial ecology. - : Springer Science and Business Media LLC. - 1751-7362. ; 6:8, s. 1459-1468
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Journal article (peer-reviewed)abstract
- Microbial biofilms assemble from cells that attach to a surface, where they develop into matrix-enclosed communities. Mechanistic insights into community assembly are crucial to better understand the functioning of natural biofilms, which drive key ecosystem processes in numerous aquatic habitats. We studied the role of the suspended microbial community as the source of the biofilm community in three streams using terminal-restriction fragment length polymorphism and 454 pyrosequencing of the 16S ribosomal RNA (rRNA) and the 16S rRNA gene (as a measure for the active and the bulk community, respectively). Diversity was consistently lower in the biofilm communities than in the suspended stream water communities. We propose that the higher diversity in the suspended communities is supported by continuous inflow from various sources within the catchment. Community composition clearly differed between biofilms and suspended communities, whereas biofilm communities were similar in all three streams. This suggests that biofilm assembly did not simply reflect differences in the source communities, but that certain microbial groups from the source community proliferate in the biofilm. We compared the biofilm communities with random samples of the respective community suspended in the stream water. This analysis confirmed that stochastic dispersal from the source community was unlikely to shape the observed community composition of the biofilms, in support of species sorting as a major biofilm assembly mechanism. Bulk and active populations generated comparable patterns of community composition in the biofilms and the suspended communities, which suggests similar assembly controls on these populations.
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| 12. |
- Bier, Raven L., et al.
(author)
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Effects of ecosystem size-induced environmental fluctuations on the temporal dynamics of community assembly mechanisms
- 2022
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In: The ISME Journal. - : Springer Nature. - 1751-7362 .- 1751-7370. ; 16:12, s. 2635-2643
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Journal article (peer-reviewed)abstract
- Understanding processes that determine community membership and abundance is important for many fields from theoretical community ecology to conservation. However, spatial community studies are often conducted only at a single timepoint despite the known influence of temporal variability on community assembly processes. Here we used a spatiotemporal study to determine how environmental fluctuation differences induced by mesocosm volumes (larger volumes were more stable) influence assembly processes of aquatic bacterial metacommunities along a press disturbance gradient. By combining path analysis and network approaches, we found mesocosm size categories had distinct relative influences of assembly process and environmental factors that determined spatiotemporal bacterial community composition, including dispersal and species sorting by conductivity. These processes depended on, but were not affected proportionately by, mesocosm size. Low fluctuation, large mesocosms primarily developed through the interplay of species sorting that became more important over time and transient priority effects as evidenced by more time-delayed associations. High fluctuation, small mesocosms had regular disruptions to species sorting and greater importance of ecological drift and dispersal limitation indicated by lower richness and higher taxa replacement. Together, these results emphasize that environmental fluctuations influence ecosystems over time and its impacts are modified by biotic properties intrinsic to ecosystem size.
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| 13. |
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| 14. |
- Coll, Claudia, et al.
(author)
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Association between Aquatic Micropollutant Dissipation and River Sediment Bacterial Communities
- 2020
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In: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 54:22, s. 14380-14392
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Journal article (peer-reviewed)abstract
- Assessment of micropollutant biodegradation is essential to determine the persistence of potentially hazardous chemicals in aquatic ecosystems. We studied the dissipation half-lives of 10 micropollutants in sediment–water incubations (based on the OECD 308 standard) with sediment from two European rivers sampled upstream and downstream of wastewater treatment plant (WWTP) discharge. Dissipation half-lives (DT50s) were highly variable between the tested compounds, ranging from 1.5 to 772 days. Sediment from one river sampled downstream from the WWTP showed the fastest dissipation of all micropollutants after sediment RNA normalization. By characterizing sediment bacteria using 16S rRNA sequences, bacterial community composition of a sediment was associated with its capacity for dissipating micropollutants. Bacterial amplicon sequence variants of the genera Ralstonia, Pseudomonas, Hyphomicrobium, and Novosphingobium, which are known degraders of contaminants, were significantly more abundant in the sediment incubations where fast dissipation was observed. Our study illuminates the limitations of the OECD 308 standard to account for variation of dissipation rates of micropollutants due to differences in bacterial community composition. This limitation is problematic particularly for those compounds with DT50s close to regulatory persistence criteria. Thus, it is essential to consider bacterial community composition as a source of variability in regulatory biodegradation and persistence assessments.
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| 15. |
- Comte, Jerome, et al.
(author)
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Can marine bacteria be recruited from freshwater sources and the air?
- 2014
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In: The ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 8:12, s. 2423-2430
-
Journal article (peer-reviewed)abstract
- There is now clear evidence that microorganisms present biogeographic patterns, yet the processes that create and maintain them are still not well understood. In particular, the contribution of dispersal and its exact impact on local community composition is still unclear. For example, dispersing cells may not thrive in recipient environments, but may still remain part of the local species pool. Here, we experimentally tested if marine bacteria can be retrieved from freshwater communities (pelagic and sediment) and the atmosphere by exposing bacteria from three lakes, that differ in their proximity to the Norwegian Sea, to marine conditions. We found that the percentage of freshwater taxa decreased with increasing salinities, whereas marine taxa increased along the same gradient. Our results further showed that this increase was stronger for lake and sediment compared with air communities. Further, significant increases in the average niche breadth of taxa were found for all sources, and in particular lake water and sediment communities, at higher salinities. Our results therefore suggests that marine taxa can readily grow from freshwater sources, but that the response was likely driven by the growth of habitat generalists that are typically found in marine systems. Finally, there was a greater proportion of marine taxa found in communities originating from the lake closest to the Norwegian Sea. In summary, this study shows that the interplay between bacterial dispersal limitation and dispersal from internal and external sources may have an important role for community recovery in response to environmental change.
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| 16. |
- Comte, Jérôme, et al.
(author)
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Contribution of different dispersal sources to the metabolic response of lake bacterioplankton following a salinity change
- 2017
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In: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920. ; 19:1, s. 251-260
-
Journal article (peer-reviewed)abstract
- Dispersal can modify how bacterial community composition (BCC) changes in response to environmental perturbations, yet knowledge about the functional consequences of dispersal is limited. Here we hypothesize that changes in bacterial community production in response to a salinity disturbance depend on the possibility to recruit cells from different dispersal sources. To investigate this, we conducted an in situ mesocosm experiment where bacterial communities of an oligotrophic lake were exposed to different salinities (0, 18, 36 psu) for two weeks and subjected to dispersal of cells originating from sediments, air (mesocosms open to air deposition), both or none. BCC was determined using 454 pyrosequencing of the 16S rRNA gene and bacterial production was measured by 3H leucine uptake. Bacterial production differed significantly among salinity treatments and dispersal treatments, being highest at high salinity. These changes were associated with changes in BCC and it was found that the identity of the main functional contributors differed at different salinities. Our results further showed that after a salinity perturbation, the response of bacterial communities depended on the recruitment of taxa, including marine representatives (e.g. Alphaproteobacteria Loktanella, Erythrobacter and the Gammaproteobacterium Rheiheimera) from dispersal sources, in which atmospheric deposition appeared to play a major role.
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| 17. |
- Cunillera-Montcusí, David, et al.
(author)
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Freshwater salinisation : a research agenda for a saltier world
- 2022
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In: Trends in Ecology and Evolution. - : Elsevier BV. - 0169-5347 .- 1872-8383. ; 37:5, s. 440-453
-
Research review (peer-reviewed)abstract
- The widespread salinisation of freshwater ecosystems poses a major threat to the biodiversity, functioning, and services that they provide. Human activities promote freshwater salinisation through multiple drivers (e.g., agriculture, resource extraction, urbanisation) that are amplified by climate change. Due to its complexity, we are still far from fully understanding the ecological and evolutionary consequences of freshwater salinisation. Here, we assess current research gaps and present a research agenda to guide future studies. We identified different gaps in taxonomic groups, levels of biological organisation, and geographic regions. We suggest focusing on global- and landscape-scale processes, functional approaches, genetic and molecular levels, and eco-evolutionary dynamics as key future avenues to predict the consequences of freshwater salinisation for ecosystems and human societies.
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| 18. |
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| 19. |
- Freixa, Anna, et al.
(author)
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River biofilms adapted to anthropogenic disturbances are more resistant to WWTP inputs
- 2020
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In: FEMS Microbiology Ecology. - : OXFORD UNIV PRESS. - 0168-6496 .- 1574-6941. ; 96:9
-
Journal article (peer-reviewed)abstract
- The sensitivity and spatial recovery of river sediment biofilms along 1 km after the input of two wastewater treatment plants (WWTPs) located in two river reaches with different degrees of anthropogenic influence were investigated. First, at the upper reach, we observed an inhibition of some microbial functions (microbial respiration and extracellular enzyme activities) and strong shifts in bacterial community composition (16S rRNA gene), whereas an increase in microbial biomass and activity and less pronounced effect on microbial diversity and community composition were seen at the lower reach. Second, at the lower reach we observed a quick spatial recovery (around 200 m downstream of the effluent) as most of the functions and community composition were similar to those from reference sites. On the other hand, bacterial community composition and water quality at the upper reach was still altered 1 km from the WWTP effluent. Our results indicate that biofilms in the upstream sites were more sensitive to the effect of WWTPs due to a lower degree of tolerance after a disturbance than communities located in more anthropogenically impacted sites.
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| 20. |
- Gerhard, Miriam, et al.
(author)
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Environmental variability in aquatic ecosystems : Avenues for future multifactorial experiments
- 2023
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In: Limnology and Oceanography Letters. - : John Wiley & Sons. - 2378-2242. ; 8:2, s. 247-266
-
Journal article (peer-reviewed)abstract
- The relevance of considering environmental variability for understanding and predicting biological responses to environmental changes has resulted in a recent surge in variability-focused ecological research. However, integration of findings that emerge across studies and identification of remaining knowledge gaps in aquatic ecosystems remain critical. Here, we address these aspects by: (1) summarizing relevant terms of variability research including the components (characteristics) of variability and key interactions when considering multiple environmental factors; (2) identifying conceptual frameworks for understanding the consequences of environmental variability in single and multifactorial scenarios; (3) highlighting challenges for bridging theoretical and experimental studies involving transitioning from simple to more complex scenarios; (4) proposing improved approaches to overcome current mismatches between theoretical predictions and experimental observations; and (5) providing a guide for designing integrated experiments across multiple scales, degrees of control, and complexity in light of their specific strengths and limitations.
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| 21. |
- Guzman, Laura Melissa, et al.
(author)
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Accounting for temporal change in multiple biodiversity patterns improves the inference of metacommunity processes
- 2022
-
In: Ecology. - : John Wiley & Sons. - 0012-9658 .- 1939-9170. ; 103:6
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Journal article (peer-reviewed)abstract
- In metacommunity ecology, a major focus has been on combining observational and analytical approaches to identify the role of critical assembly processes, such as dispersal limitation and environmental filtering, but this work has largely ignored temporal community dynamics. Here, we develop a "virtual ecologist" approach to evaluate assembly processes by simulating metacommunities varying in three main processes: density-independent responses to abiotic conditions, density-dependent biotic interactions, and dispersal. We then calculate a number of commonly used summary statistics of community structure in space and time and use random forests to evaluate their utility for inferring the strength of these three processes. We find that (i) both spatial and temporal data are necessary to disentangle metacommunity processes based on the summary statistics we test, and including statistics that are measured through time increases the explanatory power of random forests by up to 59% compared to cases where only spatial variation is considered; (ii) the three studied processes can be distinguished with different descriptors; and (iii) each summary statistic is differently sensitive to temporal and spatial sampling effort. Including repeated observations of metacommunities over time was essential for inferring the metacommunity processes, particularly dispersal. Some of the most useful statistics include the coefficient of variation of species abundances through time and metrics that incorporate variation in the relative abundances (evenness) of species. We conclude that a combination of methods and summary statistics is probably necessary to understand the processes that underlie metacommunity assembly through space and time, but we recognize that these results will be modified when other processes or summary statistics are used.
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| 22. |
- Hebert, Marie-Pier, et al.
(author)
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Lake salinization drives consistent losses of zooplankton abundance and diversity across coordinated mesocosm experiments
- 2023
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In: Limnology and Oceanography Letters. - : John Wiley & Sons. - 2378-2242. ; 8:1, s. 19-29
-
Journal article (peer-reviewed)abstract
- Human-induced salinization increasingly threatens inland waters; yet we know little about the multifaceted response of lake communities to salt contamination. By conducting a coordinated mesocosm experiment of lake salinization across 16 sites in North America and Europe, we quantified the response of zooplankton abundance and (taxonomic and functional) community structure to a broad gradient of environmentally relevant chloride concentrations, ranging from 4 to ca. 1400 mg Cl- L-1. We found that crustaceans were distinctly more sensitive to elevated chloride than rotifers; yet, rotifers did not show compensatory abundance increases in response to crustacean declines. For crustaceans, our among-site comparisons indicate: (1) highly consistent decreases in abundance and taxon richness with salinity; (2) widespread chloride sensitivity across major taxonomic groups (Cladocera, Cyclopoida, and Calanoida); and (3) weaker loss of functional than taxonomic diversity. Overall, our study demonstrates that aggregate properties of zooplankton communities can be adversely affected at chloride concentrations relevant to anthropogenic salinization in lakes.
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| 23. |
- Hillebrand, Helmut, et al.
(author)
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Decomposing multiple dimensions of stability in global change experiments
- 2018
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In: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 21:1, s. 21-30
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Journal article (peer-reviewed)abstract
- Ecological stability is the central framework to understand an ecosystem's ability to absorb or recover from environmental change. Recent modelling and conceptual work suggests that stability is a multidimensional construct comprising different response aspects. Using two freshwater mesocosm experiments as case studies, we show how the response to single perturbations can be decomposed in different stability aspects (resistance, resilience, recovery, temporal stability) for both ecosystem functions and community composition. We find that extended community recovery is tightly connected to a nearly complete recovery of the function (biomass production), whereas systems with incomplete recovery of the species composition ranged widely in their biomass compared to controls. Moreover, recovery was most complete when either resistance or resilience was high, the latter associated with low temporal stability around the recovery trend. In summary, no single aspect of stability was sufficient to reflect the overall stability of the system.
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| 24. |
- Hintz, William D., et al.
(author)
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Current water quality guidelines across North America and Europe do not protect lakes from salinization
- 2022
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In: Proceedings of the National Academy of Sciences of the United States of America. - : National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 119:9
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Journal article (peer-reviewed)abstract
- Human-induced salinization caused by the use of road deicing salts, agricultural practices, mining operations, and climate change is a major threat to the biodiversity and functioning of freshwater ecosystems. Yet, it is unclear if freshwater ecosystems are protected from salinization by current water quality guidelines. Leveraging an experimental network of land-based and in-lake mesocosms across North America and Europe, we tested how salinization—indicated as elevated chloride (Cl−) concentration—will affect lake food webs and if two of the lowest Cl− thresholds found globally are sufficient to protect these food webs. Our results indicated that salinization will cause substantial zooplankton mortality at the lowest Cl− thresholds established in Canada (120 mg Cl−/L) and the United States (230 mg Cl−/L) and throughout Europe where Cl− thresholds are generally higher. For instance, at 73% of our study sites, Cl− concentrations that caused a ≥50% reduction in cladoceran abundance were at or below Cl− thresholds in Canada, in the United States, and throughout Europe. Similar trends occurred for copepod and rotifer zooplankton. The loss of zooplankton triggered a cascading effect causing an increase in phytoplankton biomass at 47% of study sites. Such changes in lake food webs could alter nutrient cycling and water clarity and trigger declines in fish production. Current Cl− thresholds across North America and Europe clearly do not adequately protect lake food webs. Water quality guidelines should be developed where they do not exist, and there is an urgent need to reassess existing guidelines to protect lake ecosystems from human-induced salinization.
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| 25. |
- Jezberova, Jitka, et al.
(author)
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Ubiquity of Polynucleobacter necessarius ssp asymbioticus in lentic freshwater habitats of a heterogenous 2000 km2 area
- 2010
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In: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920. ; 12:3, s. 658-669
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Journal article (peer-reviewed)abstract
- We present a survey on the distribution and habitat range of Polynucleobacter necessarius ssp. asymbioticus (PnecC), a numerically and functionally important taxon in the plankton of freshwater systems. We systematically sampled stagnant freshwater habitats in a heterogeneous 2000 km2 area, together with ecologically different habitats outside this area. In total, 137 lakes, ponds and puddles were investigated, which represent an enormous diversity of habitats differing, e.g. in depth (< 10 cm - 171 m) and pH (3.9-8.5). PnecC bacteria were detected by cultivation-independent methods in all investigated habitats, and their presence was confirmed by cultivation of strains from selected habitats representing the whole studied ecological range. The determined relative abundance of the subspecies ranged from values close to the detection limit of FISH (0.2%) to 67% (average 14.5%), and the highest observed absolute abundance was 5.3 x 106 cells ml-1. Statistical analyses revealed that the abundance of PnecC bacteria was partially controlled by factors linked to concentrations of humic substances, which support the hypothesis that these bacteria utilize photodegradation products of humic substances. Based on the revealed statistical relationships, an average relative abundance of this subspecies of 20% in global freshwater habitats was extrapolated. Our study provides important implications for the current debate on ubiquity and biogeography in microorganisms.
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| 26. |
- Kritzberg, Emma S., et al.
(author)
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Influence of dissolved organic matter source on lake bacterioplankton community structure and function : implications for seasonal dynamics of community structure.
- 2006
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In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 0168-6496 .- 1574-6941. ; 56:3, s. 406-417
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Journal article (peer-reviewed)abstract
- It has been suggested that autochthonous (internally produced) organic carbon and allochthonous (externally produced) organic carbon are utilized by phylogenetically different bacterioplankton. We examined the relationship between the source of organic matter and the structure and function of lake bacterial communities. Differences and seasonal changes in bacterial community composition in two lakes differing in their source of organic matter were followed in relation to environmental variables. We also performed batch culture experiments with amendments of various organic substrates, namely fulvic acids, leachates from algae, and birch and maple leaves. Differences in bacterial community composition between the lakes, analysed by terminal restriction fragment length polymorphism, correlated with variables related to the relative loading of autochthonous and allochthonous carbon (water colour, dissolved organic carbon, nutrients, and pH). Seasonal changes correlated with temperature, chlorophyll and dissolved organic carbon in both lakes. The substrate amendments led to differences in both structure and function, i.e. production, respiration and growth yield, of the bacterial community. In conclusion, our results suggest that the source of organic matter influences community composition both within and among lakes and that there may be a coupling between the structure and function of the bacterial community.
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| 27. |
- Langenheder, Silke, et al.
(author)
-
Bacterial biodiversity-ecosystem function relations are modified by environmental complexity
- 2010
-
In: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 5:5, s. e10834-
-
Journal article (peer-reviewed)abstract
- BackgroundWith the recognition that environmental change resulting from anthropogenic activities is causing a global decline in biodiversity, much attention has been devoted to understanding how changes in biodiversity may alter levels of ecosystem functioning. Although environmental complexity has long been recognised as a major driving force in evolutionary processes, it has only recently been incorporated into biodiversity-ecosystem functioning investigations. Environmental complexity is expected to strengthen the positive effect of species richness on ecosystem functioning, mainly because it leads to stronger complementarity effects, such as resource partitioning and facilitative interactions among species when the number of available resource increases.Methodology/Principal FindingsHere we implemented an experiment to test the combined effect of species richness and environmental complexity, more specifically, resource richness on ecosystem functioning over time. We show, using all possible combinations of species within a bacterial community consisting of six species, and all possible combinations of three substrates, that diversity-functioning (metabolic activity) relationships change over time from linear to saturated. This was probably caused by a combination of limited complementarity effects and negative interactions among competing species as the experiment progressed. Even though species richness and resource richness both enhanced ecosystem functioning, they did so independently from each other. Instead there were complex interactions between particular species and substrate combinations.Conclusions/SignificanceOur study shows clearly that both species richness and environmental complexity increase ecosystem functioning. The finding that there was no direct interaction between these two factors, but that instead rather complex interactions between combinations of certain species and resources underlie positive biodiversity ecosystem functioning relationships, suggests that detailed knowledge of how individual species interact with complex natural environments will be required in order to make reliable predictions about how altered levels of biodiversity will most likely affect ecosystem functioning.
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| 28. |
- Langenheder, Silke, et al.
(author)
-
Bacterial metacommunity organization in a highly connected aquatic system
- 2017
-
In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 0168-6496 .- 1574-6941. ; 93:4
-
Journal article (peer-reviewed)abstract
- The spatial structure and underlying assembly mechanisms of bacterial communities have been studied widely across aquatic systems, focusing primarily on isolated sites, such as different lakes, ponds and streams. Here, our main aim was to determine the underlying mechanisms for bacterial biofilm assembly within a large, highly connected lake system in Northern Finland using associative methods based on taxonomic and phylogenetic alpha- and beta-diversity and a large number of abiotic and biotic variables. Furthermore, null model approaches were used to quantify the relative importance of different community assembly processes. We found that spatial variation in bacterial communities within the lake was structured by different assembly processes, including stochasticity, species sorting and potentially even dispersal limitation. Species sorting by abiotic environmental conditions explained more of the taxonomic and particularly phylogenetic turnover in community composition compared with that by biotic variables. Finally, we observed clear differences in alpha diversity (species richness and phylogenetic diversity), which were to a stronger extent determined by abiotic compared with biotic factors, but also by dispersal effects. In summary, our study shows that the biodiversity of bacterial biofilm communities within a lake ecosystem is driven by within-habitat gradients in abiotic conditions and by stochastic and deterministic dispersal processes.
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| 29. |
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| 30. |
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| 31. |
- Langenheder, Silke, et al.
(author)
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Factors influencing aquatic and terrestrial bacterial community assembly
- 2019
-
In: Environmental Microbiology Reports. - : Wiley. - 1758-2229. ; 11:3, s. 306-315
-
Research review (peer-reviewed)abstract
- During recent years, many studies have shown that different processes including drift, environmental selection and dispersal can be important for the assembly of bacterial communities in aquatic and terrestrial ecosystems. However, we lack a conceptual overview about the ecological context and factors that influence the relative importance of the different assembly mechanisms and determine their dynamics in time and space. Focusing on free-living, i.e., nonhost associated, bacterial communities, this minireview, therefore, summarizes and conceptualizes findings from empirical studies about how (i) environmental factors, such as environmental heterogeneity, disturbances, productivity and trophic interactions; (ii) connectivity and dispersal rates (iii) spatial scale, (iv) community properties and traits and (v) the use of taxonomic/phylogenetic or functional metrics influence the relative importance of different community assembly processes. We find that there is to-date little consistency among studies and suggest that future studies should now address how (i)-(v) differ between habitats and organisms and how this, in turn, influences the temporal and spatial-scale dependency of community assembly processes in microorganisms.
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| 32. |
- Langenheder, Silke, et al.
(author)
-
Growth dynamics within bacterial communities in riverine and estuarine batch cultures
- 2004
-
In: Aquatic Microbial Ecology. - : Inter-Research Science Center. - 0948-3055 .- 1616-1564. ; 37, s. 137-148
-
Journal article (peer-reviewed)abstract
- We investigated temporal changes in community composition of bacteria growing on riverine dissolved organic carbon. Batch cultures were adjusted to riverine or estuarine salinity levels and inoculated with bacteria from these 2 environments to test whether growth patterns of bacterial taxa are influenced by salinity and/or the source of the inoculum. Changes in bacterial community composition at different stages of the growth phase were studied by 16S rDNA denaturing gradient gel electrophoresis (DGGE). Furthermore, the growth dynamics of 7 bacteria previously isolated from the estuary were followed by quantitative DNA-DNA hybridization. Growth dynamics within bacterial communities were significantly influenced by the source of the inoculum but not by salinity, suggesting that slight changes in salinity, to which riverine bacteria are exposed when discharged into the Northern Baltic Sea, are not a major regulating factor of community dynamics. Additionally, our results indicated only minor differences in the appearance and growth of bacteria when examined by quantitative DNA-DNA hybridization, whereas DGGE banding patterns suggested that there were fast- and slow-growing types of bacteria.
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| 33. |
- Langenheder, Silke, 1974-
(author)
-
Links Between Structure and Function of Heterotrophic Aquatic Bacterial Communities
- 2005
-
Doctoral thesis (other academic/artistic)abstract
- Heterotrophic bacteria utilize dissolved organic matter, and the carbon flow through an ecosystem depends on the fractions of the utilized carbon that is either respired or transferred to higher trophic levels. The major aim this thesis is to investigate 1) the relationship between composition and functioning in heterotrophic bacterioplankton communities and 2) the influence of environmental conditions on both parameters. I set up several batch culture experiments, where lake water filtrates containing bacteria but no grazers were inoculated into sterile freshwater medium to investigate the importance of the origin of the source community (the inoculum) versus the environmental conditions (the medium) for the composition and functional performance of bacterial communities. In some experiments the medium was manipulated to simulate changes in salinity, pH and dissolved organic matter quantity and quality. Functional parameters (biomass yield, respiration, growth efficiency and enzyme activities) and the genetic composition of the emerging bacterial communities were determined.When bacterial inocula obtained from different habitats were re-grown under identical conditions, differently composed communities emerged. This indicates that the history and distribution of taxa within the inoculum was an important regulating factor of community composition. The coupling between community composition and functioning was not very tight, and there was functional equivalency with respect to aggregated functions important at the ecosystem scale (e.g., biomass production and respiration). The functional performance of bacterial communities could to a large extent be predicted from the medium alone, except when it deviated strongly from the ambient settings. When bacterial communities were exposed to dilution, a strong change in pH or an increase in salinity, growth of structurally and functionally distinct communities occurred. I therefore suggest that it depends on the disturbance regime how bacterial community structure and function are related to each other.
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| 34. |
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| 35. |
- Langenheder, Silke, et al.
(author)
-
Remnants of marine bacterial communities can be retrieved from deep sediments in lakes of marine origin
- 2016
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In: Environmental Microbiology Reports. - : Wiley. - 1758-2229. ; 8:4, s. 479-485
-
Journal article (peer-reviewed)abstract
- Some bacteria can be preserved over time in deep sediments where they persist either in dormant or slow-growing vegetative stages. Here, we hypothesized that such cells can be revived when exposed to environmental conditions similar to those before they were buried in the sediments. To test this hypothesis, we collected bacteria from sediment samples of different ages (140–8500 calibrated years before present, cal BP) from three lakes that differed in the timing of their physical isolation from the Baltic Sea following postglacial uplift. After these bacterial communities were grown in sterile water from the Baltic Sea, we determined the proportion of 16S rRNA sequence reads associated with marine habitats by extracting the environment descriptive terms of homologous sequences retrieved from public databases. We found that the proportion of reads associated with marine descriptive term was significantly higher in cultures inoculated with sediment layers formed under Baltic conditions and where salinities were expected to be similar to current levels. Moreover, a similar pattern was found in the original sediment layers. Our study, therefore, suggests that remnants of marine bacterial communities can be preserved in sediments over thousands of years and can be revived from deep sediments in lakes of marine origin.
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| 36. |
- Langenheder, Silke, et al.
(author)
-
Resource availability influences the diversity of a functional group of heterotrophic soil bacteria.
- 2008
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In: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920. ; 10:9, s. 2245-2256
-
Journal article (peer-reviewed)abstract
- Resource availability is a key factor regulating biodiversity and ecosystem functioning, but the relationship between resource availability and diversity has only been rarely investigated in microbial communities. The aim of this study was to determine how diversity and community structure of a functional group of soil bacteria are influenced by resource concentration. To achieve this, we used soil microcosms to investigate degradation of benzoate, which served as a model compound, by soil bacterial communities. Microcosms were supplied with 13C-labelled benzoate at four concentrations and RNA-stable isotope probing followed by molecular fingerprinting analysis of 16S rRNA genes was employed to identify bacteria able to assimilate benzoate at different concentrations. The composition of the benzoate degrader community differed at different concentrations and there was a significant decrease in taxa evenness at the highest substrate concentration. Active organisms could be grouped into generalists, occurring at all substrate concentrations, specialists, active at one particular benzoate concentration only, and taxa that were active at either the two lowest or two highest concentrations. The study comprises the first explicit demonstration that resource availability has an effect on the diversity of a functional group of heterotrophic soil bacteria.
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| 37. |
- Langenheder, Silke, et al.
(author)
-
Role of functionally dominant species in varying environmental regimes : evidence for the performance-enhancing effect of biodiversity
- 2012
-
In: BMC Ecology. - : Springer Science and Business Media LLC. - 1472-6785. ; 12, s. 14-
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Journal article (peer-reviewed)abstract
- Background: Theory suggests that biodiversity can act as a buffer against disturbances and environmental variability via two major mechanisms: Firstly, a stabilising effect by decreasing the temporal variance in ecosystem functioning due to compensatory processes; and secondly, a performance enhancing effect by raising the level of community response through the selection of better performing species. Empirical evidence for the stabilizing effect of biodiversity is readily available, whereas experimental confirmation of the performance-enhancing effect of biodiversity is sparse. Results: Here, we test the effect of different environmental regimes (constant versus fluctuating temperature) on bacterial biodiversity-ecosystem functioning relations. We show that positive effects of species richness on ecosystem functioning are enhanced by stronger temperature fluctuations due to the increased performance of individual species. Conclusions: Our results provide evidence for the performance enhancing effect and suggest that selection towards functionally dominant species is likely to benefit the maintenance of ecosystem functioning under more variable conditions.
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| 38. |
- Langenheder, Silke, et al.
(author)
-
Salinity as a structuring factor for the composition and performance of bacterioplankton degrading riverine DOC
- 2003
-
In: FEMS Microbiology Ecology. - 0168-6496 .- 1574-6941. ; 45:2, s. 189-202
-
Journal article (peer-reviewed)abstract
- The impact of salinity on the composition and functional performance (biomass production, growth efficiency and growth rates) of bacterial communities was investigated using batch cultures growing on dissolved organic carbon from a river draining into the Northern Baltic Sea. The cultures were adjusted to riverine or estuarine salinity levels and inoculated with bacteria from these two environments. Bacterial growth efficiencies differed in response to salinity and the origin of the inoculum. When salinity was adjusted to correspond to the salinity at the site where the inoculum was retrieved, growth efficiency was relatively high (11.5 +/- 2.6%). However, when bacteria were confronted with a shift in salinity, growth efficiency was lower (7.5 +/- 2.0%) and more of the utilized carbon was respired. In contrast, growth rates were higher when bacteria were exposed to a change in salinity. The composition of the bacterial communities developing in the batch cultures differed, as shown by 16S rDNA DGGE, depending on the origin of the inoculum and salinity. Reverse and direct DNA-DNA hybridization revealed salinity optima in the growth of specific bacterial strains as well as broader phylogenetic groups. Strains belonging to the alpha- and beta-Proteobacteria, Actinobacteria and gamma-Proteobacteria other than the genus Pseudomonas showed higher relative abundance under freshwater conditions, whereas strains of the genus Pseudomonas and the Cytophaga-Flavobacterium-Bacteroides group were favored by estuarine conditions. Generally, our results demonstrate functional changes associated with changes in community composition. We suggest that even moderate changes in salinity affect bacterial community composition, which subsequently leads to altered growth characteristics. (C) 2003 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.
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| 39. |
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| 40. |
- Langenheder, Silke, et al.
(author)
-
Species sorting and neutral processes are both important during the initial assembly of bacterial communities
- 2011
-
In: The ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 5:7, s. 1086-1094
-
Journal article (peer-reviewed)abstract
- Many studies have shown that species sorting, that is, the selection by local environmental conditions is important for the composition and assembly of bacterial communities. On the other hand, there are other studies that could show that bacterial communities are neutrally assembled. In this study, we implemented a microcosm experiment with the aim to determine, at the same time, the importance of species sorting and neutral processes for bacterial community assembly during the colonisation of new, that is, sterile, habitats, by atmospheric bacteria. For this we used outdoor microcosms, which contained sterile medium from three different rock pools representing different environmental conditions, which were seeded by rainwater bacteria. We found some evidence for neutral assembly processes, as almost every 4th taxon growing in the microcosms was also detectable in the rainwater sample irrespective of the medium. Most of these taxa belonged to widespread families with opportunistic growth strategies, such as the Pseudomonadaceae and Comamonadaceae, indicating that neutrally assembled taxa may primarily be generalists. On the other hand, we also found evidence for species sorting, as one out of three media selected a differently composed bacterial community. Species sorting effects were relatively weak and established themselves via differences in relative abundance of generalists among the different media, as well as media-specific occurrences of a few specific taxa. In summary, our results suggest that neutral and species sorting processes interact during the assembly of bacterial communities and that their importance may differ depending on how many generalists and specialists are present in a community.
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| 41. |
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| 42. |
- Langenheder, Silke, et al.
(author)
-
Temporal variation of beta-diversity and assembly mechanisms in a bacterial metacommunity
- 2012
-
In: The ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 6:6, s. 1107-1114
-
Journal article (peer-reviewed)abstract
- The turnover of community composition across space, beta-diversity, is influenced by different assembly mechanisms, which place varying weight on local habitat factors, such as environmental conditions and species interactions, and regional factors such as dispersal and history. Several assembly mechanisms may function simultaneously; however, little is known about how their importance changes over time and why. Here, we implemented a field survey where we sampled a bacterial metacommunity consisting of 17 rock pools located at the Swedish Baltic Sea coast at 11 occasions during 1 year. We determined to which extent communities were structured by different assembly mechanisms using variation partitioning and studied changes in beta-diversity across environmental gradients over time. beta-Diversity was highest at times of high overall productivity and environmental heterogeneity in the metacommunity, at least partly due to species sorting, that is, selection of taxa by the prevailing environmental conditions. In contrast, dispersal-driven assembly mechanisms were primarily detected at times when beta-diversity was relatively low. There were no indications for strong and persistent differences in community composition or beta-diversity between permanent and temporary pools, indicating that the physical disturbance regime is of relatively minor importance. In summary, our study clearly suggests that there are temporal differences in the relative importance of different assembly mechanisms related to abiotic factors and shows that the temporal variability of those factors is important for a more complete understanding of bacterial metacommunity dynamics.
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| 43. |
- Langenheder, Silke, et al.
(author)
-
The role of environmental and spatial factors for the composition of aquatic bacterial communities
- 2007
-
In: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 88:9, s. 2154-2161
-
Journal article (peer-reviewed)abstract
- This study investigates the importance of local vs. spatial factors on bacterial community composition of 35 rock pools at the Baltic Sea coast. The pools were located in five distinct spatial clusters over a total scale of <500 m and differed widely in terms of water chemistry. To determine the fractions of the variance in bacterial community composition (BCC) between rock pools that are explained by local environmental vs. spatial factors, a variance partitioning procedure using partial canonical correspondence analysis was performed. Three environmental variables (salinity, chlorophyll a concentration, and water color) had a significant effect on BCC, irrespective of the spatial location of the pools. Vice versa, there was a significant effect of spatial factors on BCC irrespective of any of the environmental factors included in this study. Hence, the patchy spatial distribution of the pools was partly reflected in the composition of the bacterial communities in the pools, which might be caused by congruent colonization events of adjacent pools, such as simultaneous sea-spray inputs or direct exchange of bacteria via connecting rivulets. This study shows that the composition of planktonic bacteria can show provincialism at small spatial scales, which is likely to be caused by -environmental conditions as well as historical events.
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| 44. |
- Langenheder, Silke, et al.
(author)
-
Weak coupling between community composition and functioning of aquatic bacteria
- 2005
-
In: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 50:3, s. 957-967
-
Journal article (peer-reviewed)abstract
- We performed a batch culture experiment with a factorial design in which sterile water from four lakes and bacterial assemblages (size-fractionated lake water) from the same lakes were set up in all possible combinations. The functional performance (biomass yield, respiration, growth rates, and growth efficiency) of bacterial communities growing in the cultures depended primarily on the type of the medium and to a much lesser extent on the origin of the bacterial assemblage. Functional changes were only partly paralleled by changes in community composition, as indicated by terminal restriction fragment length polymorphism analysis. Similar bacterial communities developed in different cultures as a result of receiving either the same medium or the same inoculum, indicating that bacterial communities are comprised of populations of generalists that can grow under most conditions as well as populations with the life strategy of specialists. However, bacteria originating from a slightly acidic polyhumic lake failed to grow, grew unsteadily, or exhibited an extended lag phase when exposed to media originating from other lakes, indicating that the bacterial community in the polyhumic lake was not able to adapt rapidly to changes in environmental conditions.
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| 45. |
- Lebret, Karen, et al.
(author)
-
High abundances of the nuisance raphidophyte Gonyostomum semen in brown water lakes are associated with high concentrations of iron
- 2018
-
In: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 8
-
Journal article (peer-reviewed)abstract
- Algal blooms occur frequently in lakes and oceans and the causes and consequences of those are often studied. In this study, we focus on a less well known type of algal bloom by the freshwater raphidophyte Gonyostomum semen. This species' abundance and occurrence is increasing, especially in brown water lakes, the most abundant lake type in the boreal zone. The aim of the study was to investigate which environmental factors are associated with G. semen by statistical evaluation of field data of 95 Swedish lakes over five years. Although we found G. semen to be associated with dark waters it was, contrary to our expectations, mainly high concentrations of iron, and only to a lesser extent high TOC (total organic carbon) concentrations, that were associated with blooms of G. semen. In addition, high phosphorus concentrations and low pH also appear to facilitate G. semen blooms. We suggest that browning of lakes caused by increased iron concentrations may decrease net heterotrophy by fostering heavy algal blooms, i.e. the opposite to commonly assumed effects of increased DOM (dissolved organic matter).
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| 46. |
- Lebret, Karen, et al.
(author)
-
Increased water colour affects freshwater plankton communities in a mesocosm study
- 2018
-
In: Aquatic Microbial Ecology. - : Inter-Research Science Center. - 0948-3055 .- 1616-1564. ; 81:1, s. 1-17
-
Journal article (peer-reviewed)abstract
- Increases in water colour (brownification) have been observed in aquatic systems in the Northern Hemisphere, partly caused by increased loading of organic carbon from terrestrial origins. We investigated the effect of increase in water colour on the composition, structure and function of lake plankton communities (bacteria, phytoplankton and zooplankton) conducting a mesocosm experiment in 3 medium-coloured lakes (average absorbance at 420 nm: 0.034 cm(-1)), with different nutrient concentrations and phytoplankton community composition. To simulate an increase in water colour, we added humic substances (HuminFeed) at 3 different concentrations. The additions significantly affected the water colour of the mesocosms, but had no measurable effect on total organic carbon concentration, thus change in light conditions was the main effect of our treatment on the plankton communities. The increase in water colour did not significantly affect the measured functions (productivity, respiration) and biomass of the plankton communities (bacteria, phytoplankton and zooplankton), but led to changes in the relative abundance of some phytoplankton taxa and, to a lesser extent, the bacterial community (differences in relative abundance). The treatments had no significant effect on zooplankton biomass or composition. Our study suggests that increases in water colour favour low-light-adapted phytoplankton species, which in turn also can affect bacterial composition, whereas the change in light climate had no clear impact on the functioning of plankton communities in weakly humic lakes.
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| 47. |
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| 48. |
- Lindström, Eva S., et al.
(author)
-
Local and regional factors influencing bacterial community assembly
- 2012
-
In: Environmental Microbiology Reports. - : Wiley. - 1758-2229. ; 4:1, s. 1-9
-
Research review (peer-reviewed)abstract
- The classical view states that microbial biogeography is not affected by dispersal barriers or historical events, but only influenced by the local contemporary habitat conditions (species sorting). This has been challenged during recent years by studies suggesting that also regional factors such as mass effect, dispersal limitation and neutral assembly are important for the composition of local bacterial communities. Here we summarize results from biogeography studies in different environments, i.e. in marine, freshwater and soil as well in human hosts. Species sorting appears to be the most important mechanism. However, this result might be biased since this is the mechanism that is easiest to measure, detect and interpret. Hence, the importance of regional factors may have been underestimated. Moreover, our survey indicates that different assembly mechanisms might be important for different parts of the total community, differing, for example, between generalists and specialists, and between taxa of different dispersal ability and motility. We conclude that there is a clear need for experimental studies, first, to clearly separate regional and local factors in order to study their relative importance, and second, to test whether there are differences in assembly mechanisms depending on different taxonomic or functional groups.
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| 49. |
- Logares, Ramiro, et al.
(author)
-
Biogeography of bacterial communities exposed to progressive long-term environmental change
- 2013
-
In: The ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 7:5, s. 937-948
-
Journal article (peer-reviewed)abstract
- The response of microbial communities to long-term environmental change is poorly understood. Here, we study bacterioplankton communities in a unique system of coastal Antarctic lakes that were exposed to progressive long-term environmental change, using 454 pyrosequencing of the 16S rDNA gene (V3-V4 regions). At the time of formation, most of the studied lakes harbored marine-coastal microbial communities, as they were connected to the sea. During the past 20 000 years, most lakes isolated from the sea, and subsequently they experienced a gradual, but strong, salinity change that eventually developed into a gradient ranging from freshwater (salinity 0) to hypersaline (salinity 100). Our results indicated that present bacterioplankton community composition was strongly correlated with salinity and weakly correlated with geographical distance between lakes. A few abundant taxa were shared between some lakes and coastal marine communities. Nevertheless, lakes contained a large number of taxa that were not detected in the adjacent sea. Abundant and rare taxa within saline communities presented similar biogeography, suggesting that these groups have comparable environmental sensitivity. Habitat specialists and generalists were detected among abundant and rare taxa, with specialists being relatively more abundant at the extremes of the salinity gradient. Altogether, progressive long-term salinity change appears to have promoted the diversification of bacterioplankton communities by modifying the composition of ancestral communities and by allowing the establishment of new taxa. The ISME Journal (2013) 7, 937-948; doi:10.1038/ismej.2012.168; published online 20 December 2012
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| 50. |
- Logue, Jürg Brendan
(author)
-
Factors influencing the biogeography of bacteria in fresh waters - a metacommunity approach
- 2010
-
Doctoral thesis (other academic/artistic)abstract
- One of ecology’s primary goals is to comprehend biodiversity and its patterns of distribution over space and time. Since microorganisms play a pivotal role in key ecological processes, the diversity of microbial communities may have important implications for the stability and functioning of Earth’s ecosystems. Thus, it is of utmost importance to develop a theoretical foundation but also a conceptual understanding for the mechanisms that generate and maintain microbial diversity. The aim of this thesis is to investigate to what extent local freshwater bacterioplankton diversity, i.e. richness and community composition, is structured by local environmental interactions and/or regional processes. The key objective is to identify ecological linkages between lake bacterioplankton and bacterial communities in connected streams and the surrounding terrestrial landscape, thereby applying a metacommunity approach. To do so, I studied several natural lake bacterioplankton assemblies within different regions of Sweden and assessed both local environmental properties and regional parameters (e.g. dispersal, landscape position). The genetic composition of freshwater bacterioplankton diversity was determined by means of terminal-restriction fragment length polymorphism or 454 pyrosequencing. From the review on the biogeography of bacterioplankton in inland waters it became clear that microbial diversity and its spatial distribution are governed by a complex interplay of both local and regional drivers. In one case, freshwater bacterioplankton communities were structured by local environmental conditions rather than by regional dispersal processes. These local environmental conditions seemed to be equally important in controlling both the total bacterioplankton community and its active fraction. In a study of bacterioplankton communities from five different regions, locally abundant aquatic bacteria were shown to be also regionally widespread, a pattern predicted by neutral theory. Yet, this degree of similarity decreased with increasing environmental heterogeneity. In another study, bacterioplankton richness was controlled mostly by nutrient content, indicating that productivity exerted influence on bacterioplankton richness. However, landscape position and productivity covaried, suggesting that the landscape dictates environmental properties, which then directly structure local bacterioplankton richness. Finally, a review synthesising results from empirical metacommunity approaches and comparing these to theory showed that yet a gap between empirics and theory exists. To conclude, local bacterioplankton diversity appeared to be mainly structured by local environmental properties. However, signatures of neutral processes driving local bacterioplankton community assembly were also recorded.
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