Dynamic carbon flux network of a diverse marine microbial community

The functioning of microbial ecosystems has important consequences from global climate to human health, but quantitative mechanistic understanding remains elusive. The components of microbial ecosystems can now be observed at high resolution, but interactions still have to be inferred e.g., a time-series may show a bloom of bacteria X followed by virus Y suggesting they interact. Existing inference approaches are mostly empirical, like correlation networks, which are not mechanistically constrained and do not provide quantitative mass fluxes, and thus have limited utility. We developed an inference method, where a mechanistic model with hundreds of species and thousands of parameters is calibrated to time series data. The large scale, nonlinearity and feedbacks pose a challenging optimization problem, which is overcome using a novel procedure that mimics natural speciation or diversification e.g., stepwise increase of bacteria species. The method allows for curation using species-level information from e.g., physiological experiments or genome sequences. The product is a mass-balancing, mechanistically-constrained, quantitative representation of the ecosystem. We apply the method to characterize phytoplankton—heterotrophic bacteria interactions via dissolved organic matter in a marine system. The resulting model predicts quantitative fluxes for each interaction and time point (e.g., 0.16 µmolC/L/d of chrysolaminarin to Polaribacter on April 16, 2009). At the system level, the flux network shows a strong correlation between the abundance of bacteria species and their carbon flux during blooms, with copiotrophs being relatively more important than oligotrophs. However, oligotrophs, like SAR11, are unexpectedly high carbon processors for weeks into blooms, due to their higher biomass. The fraction of exudates (vs. grazing/death products) in the DOM pool decreases during blooms, and they are preferentially consumed by oligotrophs. In addition, functional similarity of phytoplankton i.e., what they produce, decouples their association with heterotrophs. The methodology is applicable to other microbial ecosystems, like human microbiome or wastewater treatment plants.DFG, 248198858, GRK 2032: Grenzzonen in urbanen WassersystemenTU Berlin, Open-Access-Mittel – 202

Recovery of lakes and coastal marine ecosystems from eutrophication: A global meta-analysis

In order to inform policies aimed at reducing nutrient emissions to surface waters, it is essential to understand how aquatic ecosystems respond to eutrophication management. Using data from 89 studies worldwide, we examined responses to the reduction or cessation of anthropogenic nutrient inputs relative to baseline conditions. Baseline conditions were pre-disturbance conditions, undisturbed reference sites, restoration targets, or experimental controls. We estimated recovery completeness (% baseline conditions reached) and recovery rate (annual % change relative to baseline conditions) for plant and animal abundance and diversity and for ecosystem functions. Categories were considered fully recovered if the 95% confidence interval (CI) of recovery completeness overlapped 100% and partially recovered if the CI did not overlap either 100% or zero. Cessation of nutrient inputs did not result in more complete or faster recovery than partial nutrient reductions, due likely to insufficient passage of time, nutrients from other sources, or shifting baselines. Together, lakes and coastal marine areas achieved 34% (±16% CI) and 24% (±15% CI) of baseline conditions decades after the cessation or partial reduction of nutrients, respectively. One third of individual response variables showed no change or worsened conditions, suggesting that achieving baseline conditions may not be possible in all cases. Implied recovery times after cessation of nutrient inputs varied widely, from up 1 yr to nearly a century, depending on response. Our results suggest that long-term monitoring is needed to better understand recovery timescales and trajectories and that policy measures must consider the potential for slow and partial recovery. (c) 2016 The Authors Limnology and Oceanography published by Wiley Periodicals, Inc. on behalf of Association for the Sciences of Limnology and OceanographyThis work was supported by the National Socio-Environmental Synthesis Center (SESYNC) under funding received from the National Science Foundation DBI-1052875, by the German Helmholtz Centre for Environmental Research – UFZ, Leipzig (Research Program ‘Terrestrial Environments’), and by sDiv, the Synthesis Centre of the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig (German Research Foundation DFG FZT 118). Funding for MLM was provided by Baltic Eye, the Baltic Sea 2020 Foundation, and the National Academies of Science Research Associateship Programe

Bestimmung der Sensitivitätsfaktoren des Phytoplanktons und Ermittlung neuer Wirkmodi

Eutrophication led to the loss of the macrophyte-dominated clear-water regime and a shift towards a phytoplankton-dominated turbid regime in many shallow lakes. Allelochemicals released by submerged macrophytes can inhibit the growth of phytoplankton and might therefore contribute to the stabilization of the clear-water regime. This thesis aims to determine the ecological relevance of allelopathic effects between macrophytes and the phytoplankton by detecting new modes of actions of allelochemicals (chapter II) and by evaluating factors that influence the sensitivity of the phytoplankton (chapters III-V). The significance of allelopathic effects of macrophytes on phytoplankton at the ecosystem scale is still debated. The currently available detection methods have some drawbacks if used for in situ investigations as they do not allow a clear separation of allelopathy from other mechanisms. A common problem is competition for nutrients between phytoplankton and macrophytes that is assumed to increase with increasing exposure times. In chapter II new modes of action of the common allelochemical tannic acid were evaluated on three algal species by the use of flow cytometry. The inhibition of esterase activity and the production of reactive oxygen species (ROS) were found as new observation variables. An inhibition of the esterase activity was shown after short exposure times (3 h) and at naturally occurring tannic acid concentrations and is thus a promising tool for future studies on allelopathic effects from submerged macrophytes on phytoplankton under in situ conditions (chapter II). The reasons for sensitivity differences of phytoplankton groups and species to allelochemicals are not yet known. Two factors potentially influencing the sensitivity of the phytoplankton to allelochemicals were tested in this thesis by evaluating the influence of algal-associated bacteria (chapter III), and the impact of interactions between two phytoplankton species on their sensitivity (chapter IV). One prerequisite for bacterial involvement in different sensitivities is their species-specific association to the algae. This hypothesis was tested by comparing the algal-associated bacterial communities of the insensitive green alga Desmodesmus armatus and the sensitive diatom Stephanodiscus minutulus after drastic changes to the environmental conditions. Both species, D. armatus as well as S. minutulus, were found to harbor species-specific bacterial communities. However, allelochemical degrading bacteria were associated with both of the tested species, and consequently a bacterial involvement with species-specific sensitivities is not likely (chapter III). The influence of interactions between phytoplankton species on their sensitivity to allelochemicals was investigated using the cyanobacterium Microcystis aeruginosa and the green alga D. armatus (chapter IV). Their interactions significantly altered their sensitivity to allelochemicals. Growth rate inhibition of M. aeruginosa by the allelopathically active macrophyte Myriophyllum spicatum in single-species cultures changed to an enhancement if co-cultured with D. armatus. This finding implies that results of single-species tests may not easily be transferred to the ecosystem level (chapter IV). Algal sensitivities to stressors have been analyzed at the group, genus or species level. However, sensitivities of algae to allelochemicals may also be strain-specific, and these sensitivities may depend on the presence of allelopathically active macrophytes in their original habitat due to potential adaptations. To test this, 13 strains of the green alga Pediastrum duplex were isolated from three different macrophyte-free water bodies, and ten strains from two water bodies containing dense stands of allelopathically active macrophytes. The tested strains exhibited differences of sensitivity to allelochemicals with respect to growth rates and photosynthetic yields of about one order of magnitude. Consequently, future studies on allelochemical sensitivities of algae should also consider strain-specific sensitivities. However, the sensitivities of P. duplex growth rates and photosynthetic yields to allelochemicals were not dependent on the presence of allelopathically active macrophytes in their water bodies of origin. Thus, a local adaptation of the target algae to allelochemicals of submerged macrophytes was not shown.Durch Eutrophierung verloren viele der mitteleuropäischen Flachseen den von Makrophyten dominierten Klarwasser-Zustand und gingen in den Phytoplankton dominierten trüben Zustand über. Allelopathische Substanzen, die von aquatischen Makrophyten exudiert werden, können das Wachstum des Phytoplanktons inhibieren und damit potenziell zu einer Stabilisierung des Klarwasser-Zustandes in eutrophen Gewässern führen. Die vorliegende Arbeit trägt zur Aufklärung der ökologischen Relevanz dieser allelopathischen Effekte der Makrophyten auf das Phytoplankton bei, indem die Wirkmechanismen allelopathischer Substanzen (Kapitel II) und Faktoren, die die Sensitivität des Phytoplanktons beeinflussen (Kapitel III-V), erörtert werden. Die Signifikanz allelopathischer Effekte von Makrophyten gegenüber dem Phytoplankton auf Ökosystemebene ist umstritten. Einen Hauptgrund hierfür stellen die bisher etablierten Nachweismethoden dar, welche Einschränkungen für die Messung allelopathischer Effekte in situ aufweisen. Daher gelang es bisher nicht, Allelopathie aquatischer Makrophyten unter in situ Bedingungen zweifelsfrei von anderen Effekten zu separieren. Problematisch ist insbesondere der Ausschluss einer Nährstoffkonkurrenz zwischen Makrophyten und Phytoplankton, die mit zunehmender Expositionszeit zu erwarten ist. In Kapitel II wurden neue Wirkmechanismen einer typischen polyphenolischen Allelochemikalie (Tanninsäure) mittels Durchflusszytometrie mit Fluoreszenzmarkern an drei Algenarten evaluiert. Hierbei konnten die Inhibition des Enzymes Esterase und die Produktion reaktiver Sauerstoff- Radikale als neue Anzeiger für allelopathische Effekte detektiert werden. Die nach kurzer Expositionszeit (3 h) und unter natürlich vorkommenden Tanninsäure-Konzentrationen nachgewiesene Inhibition der Esterase-Aktivität stellt eine vielversprechende neue Methodik zur Untersuchung allelopathischer Effekte submerser Makrophyten auf Phytoplankton unter in situ Bedingungen dar (Kapitel II). Die Gründe für unterschiedliche Sensitivitäten verschiedener Phytoplankton-Gruppen und -Arten gegenüber Allelochemikalien sind bisher unbekannt. In der vorliegenden Arbeit wurden der Einfluss Algen-assoziierter Bakterien (Kapitel III) und der Einfluss von Interaktionen zwischen verschiedenen Phytoplanktonarten (Kapitel IV) als potentielle Einflussfaktoren untersucht. Eine Voraussetzung für die Beteiligung assoziierter Bakterien an unterschiedlichen Sensitivitäten ist eine Algenart-spezifische Assoziation. Diese Hypothese wurde durch Vergleiche der Algen-assoziierten Bakteriengemeinschaften vor und nach drastischen Umweltveränderungen der gegenüber Allelochemikalien unsensitiven Grünalge Desmodesmus armatus und der sensitiven Kieselalge Stephanodiscus minutulus getestet (Kapitel III). Sowohl für D. armatus als auch für S. minutulus wurden artspezifische Bakteriengemeinschaften nachgewiesen (Kapitel III). Allelochemikalien abbauende Bakterien fanden sich jedoch in Assoziation mit beiden Algenarten, so dass deren signifikante Beteiligung an artspezifischen Sensitivitätsunterschieden nicht wahrscheinlich ist (Kapitel III). In Kapitel IV wurde der Einfluss von Interaktionen zwischen Phytoplanktonarten auf deren Sensitivität gegenüber Allelochemikalien am Beispiel der Cyanobakterie Microcystis aeruginosa und der Grünalge D. armatus untersucht. Hierbei veränderte die Interaktion der beiden Phytoplanktonarten deren Sensitivität gegenüber Allelochemikalien signifikant. Die in einartlichen Kulturen von M. aeruginosa nachgewiesene Inhibition der Wachstumsraten durch die allelopathisch aktive Makrophytenart Myriophyllum spicatum wandelte sich in Mischkulturen mit D. armatus in eine Förderung. Dieses Ergebnis verdeutlicht, dass Resultate aus Experimenten mit einartlichen Kulturen nur bedingt auf die Freilandsituation übertragbar sind (Kapitel IV). Ein Vergleich der Sensitivitäten des Phytoplanktons gegenüber Allelochemikalien erfolgte bisher nur auf Gruppen-, Gattungs- oder Artniveau. In Kapitel V wurde getestet, ob auch stammspezifische Unterschiede in der Sensitivität auftreten, und ob diese Sensitivitäten aufgrund von Adaption von der Anwesenheit allelopathisch aktiver Makrophyten im Herkunftsgewässer der Stämme abhängen. Um dies zu überprüfen wurden 13 Stämme der Grünalge Pediastrum duplex aus drei verschiedenen Makrophyten-freien Gewässern und 10 Stämme aus zwei Gewässern mit allelopathisch aktiven Makrophyten isoliert. Anschließend wurden die Wachstumsraten und die photosynthetische Aktivität aller Stämme unter Einfluss von Allelochemikalien gemessen. Die getesteten Stämme wiesen Unterschiede in der Inhibition ihrer Wachstumsraten und photosynthetischen Aktivität von ca. einer Größenordnung auf. Zukünftige Sensitivitätstests sollten also stammspezifische Unterschiede berücksichtigen, da das Artniveau nicht ausreichend trennscharf bezüglich der Empfindlichkeit gegenüber Allelochemikalien ist. Eine Korrelation von niedrigen Sensitivitäten mit der Herkunft aus Makrophyten-dominierten Gewässern wurde allerdings weder für die Wachstumsraten noch für die photosynthetische Aktivität festgestellt. Somit konnte keine lokale Adaption der Algen an Allelochemikalien nachgewiesen werden

The Fish Fauna of the Cordillera of Bogota

Volume: 10Start Page: 460End Page: 46

Sensitivity of the green alga Pediastrum duplex Meyen to allelochemicals is strain-specific and not related to co-occurrence with allelopathic macrophytes.

Interspecific differences in the response of microalgae to stress have numerous ecological implications. However, little is known of intraspecific sensitivities and the potential role of local genetic adaptation of populations. We compared the allelochemical sensitivity of 23 Pediastrum duplex Meyen strains, a common component of the freshwater phytoplankton. In order to test for local genetic adaptation, strains were isolated from water bodies with and without the allelopathically-active submerged macrophyte Myriophyllum. Strains were assigned to P. duplex on the basis of cell shape and colony morphology and only P. duplex strains that belonged to the same lineage in an ITS rDNA phylogeny were used. Inhibition of strain growth rates and maximum quantum yields of photosystem II were measured after exposure to tannic acid (TA) and co-culture with Myriophyllum spicatum. Growth rate inhibition varied over one order of magnitude between the P. duplex strains. There was no correlation between the presence of Myriophyllum in the source location and the sensitivity of the strains to TA or the presence of Myriophyllum, suggesting that at least strong unidirectional local adaptation to Myriophyllum had not taken place in the studied water bodies. The maximum quantum yield of photosystem II of TA exposed algae decreased, whereas the yield of algae exposed to M. spicatum was slightly higher than that of the controls. The ranking of P. duplex strain sensitivities differed between the types of exposure (single additions of TA versus co-existence with M. spicatum) and the parameter measured (growth rate versus maximum quantum yield), emphasizing the importance of measuring multiple traits when analysing strain-specific sensitivities towards allelochemicals. The observation that sensitivities to allelochemicals vary widely among strains of a single freshwater algal species should be taken into account if evaluating ecological consequences of allelopathic interactions

Niche separation of Baltic Sea cyanobacteria during bloom events by species interactions and autecological preferences

Cyanobacterial blooms regularly occur in the Baltic Sea during the summer months, with filamentous, heterocystous Nodularia spumigena and Dolichospermum sp. and the coccoid picocyanobacterium Synechococcus spp. as important species. Under calm conditions, N. spumigena accumulate at the surface, whereas Dolichospermum sp. and Synechococcus sp. remain at the subsurface, in the upper water layer. This vertical separation allows co-occurring species to compete for the same resources. The factors that determine the vertical distribution within blooms, however, are mostly unknown. The present study examined the growth rates of these three cyanobacterial species in a two-factorial experiment, with temperature (16 and 24 °C) and radiation (38 and 150 μmol photons m−2 s−1) conditions mimicking those at the water surface and directly below. To determine whether interactions between the three species influenced their growth rates (and therewith also their vertical distribution), paired and multi-species cultures were established. In the single-species cultures, the autecological preferences of the species matched the assumed natural occurrence in bloom events: N. spumigena grew best under high and Dolichospermum sp. and Synechococcus sp. under low light conditions (maximum growth rates at the preferred conditions: μ = 0.48 ± 0.017, 0.88 ± 0.092, and 0.67 ± 0.012, respectively). High temperatures were tolerated by N. spumigena, but inhibited the growth of Dolichospermum sp. and Synechococcus sp. These results suggested that the factors resulting in the vertical separation of species within a bloom are species-specific: N. spumigena responded predominantly to irradiance and only slightly to temperature, Dolichospermum sp. was intensely affected by temperature and less by irradiance, and Synechococcus sp. responded more strongly to irradiance than to temperature. The interactions in paired and multi-species cultures revealed beneficial and detrimental effects, depending on species composition and abiotic conditions. Under the environmental conditions in which the three species occur, however, similar interactions resulted in no or only slight inhibition. Our observations demonstrate how autecological preferences together with the avoidance of negative interactions determine the vertical distribution of cyanobacteria during bloom events in the Baltic Sea