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  • 1
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    N2 fixation in free‐floating filaments of Trichodesmium is higher than in transiently suboxic colony microenvironments (2018)
    WILEY-BLACKWELL PUBLISHING
    In:  EPIC3New Phytologist, WILEY-BLACKWELL PUBLISHING, ISSN: 0028-646X
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    Publication Date: 2019-01-23
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 2
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    Company matters: The presence of other genotypes alters traits and intraspecific selection in an Arctic diatom under climate change (2019)
    WILEY-BLACKWELL PUBLISHING
    In:  EPIC3Global Change Biology, WILEY-BLACKWELL PUBLISHING, ISSN: 1354-1013
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    Publication Date: 2019-07-05
    Description: Arctic phytoplankton and their response to future conditions shape one of the most rapidly changing ecosystems on the planet. We tested how much the phenotypic responses of strains from an Arctic diatom population diverge and whether the physiology and intraspecific composition of multi-strain populations differ from expectations based on single strain traits. To this end, we conducted incubation experiments with the diatom Thalassiosira hyalina under present-day and future temperature and pCO2 treatments. Six fresh isolates from the same Svalbard population were incubated as mono- and multi-strain cultures. For the first time, we were able to closely follow intraspecific selection within an artificial population using microsatellites and allele-specific quantitative PCR. Our results show not only that there is substantial variation in how strains of the same species cope with the tested environments, but also that changes in genotype composition, production rates and cellular quotas in the multi-strain cultures are not predictable from monoculture performance. Nevertheless, the physiological responses as well as strain composition of the artificial populations were highly reproducible within each environment. Interestingly, we only detected significant strain sorting in those populations exposed to the future treatment. This study illustrates that the genetic composition of populations can change on very short timescales through selection from the intraspecific standing stock, indicating the potential for rapid population level adaptation to climate change. We further show that individuals adjust their phenotype not only in response to their physico-chemical, but also to their biological surroundings. Such intraspecific interactions need to be understood in order to realistically predict ecosystem responses to global change.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
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  • 3
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    Acidification, not carbonation, is the major regulator of carbon fluxes in the coccolithophore Emiliania huxleyi (2016)
    WILEY-BLACKWELL PUBLISHING
    In:  EPIC3New Phytologist, WILEY-BLACKWELL PUBLISHING, 211, pp. 126-137, ISSN: 0028-646X
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    Publication Date: 2016-11-16
    Repository Name: EPIC Alfred Wegener Institut
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  • 4
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    Evolutionary potential of marine phytoplankton under ocean acidification (2014)
    WILEY-BLACKWELL PUBLISHING
    In:  EPIC3Evolutionary Applications, WILEY-BLACKWELL PUBLISHING, 7(1), pp. 140-155, ISSN: 1752-4571
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    Publication Date: 2014-11-06
    Description: Marine phytoplankton have many obvious characters, such as rapid cell division rates and large population sizes, that give them the capacity to evolve in response to global change on timescales of weeks, months or decades. However, few studies directly investigate if this adaptive potential is likely to be realized. Because of this, evidence of to whether and how marine phytoplankton may evolve in response to global change is sparse. Here, we review studies that help predict evolutionary responses to global change in marine phytoplankton. We find limited support from experimental evolution that some taxa of marine phytoplankton may adapt to ocean acidification, and strong indications from studies of variation and structure in natural populations that selection on standing genetic variation is likely. Furthermore, we highlight the large body of literature on plastic responses to ocean acidification available, and evolutionary theory that may be used to link plastic and evolutionary responses. Because of the taxonomic breadth spanned by marine phytoplankton, and the diversity of roles they fill in ocean ecosystems and biogeochemical cycles, we stress the necessity of treating taxa or functional groups individually.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev , info:eu-repo/semantics/article
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  • 5
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    Differential effects of ocean acidification on carbon acquisition in two bloom-forming dinoflagellate species (2014)
    WILEY-BLACKWELL PUBLISHING
    In:  EPIC3Physiologia Plantarum, WILEY-BLACKWELL PUBLISHING, 151(4), pp. 468-479, ISSN: 0031-9317
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    Publication Date: 2014-10-10
    Description: Dinoflagellates represent a cosmopolitan group of phytoplankton with the^ability to form harmful algal blooms. Featuring a Ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) with very low CO2 affinities, photosynthesis of this group may be particularly prone to carbon limitation and thusv benefit from rising atmospheric CO2 partial pressure (pCO2) under ocean acidification (OA). Here, we investigated the consequences of OA on two bloom-forming dinoflagellate species, the calcareous Scrippsiella trochoidea and the toxic Alexandrium tamarense. Using dilute batch incubations, we assessed growth characteristics over a range of pCO2 (i.e. 180–1200 atm). To understand the underlying physiology, several aspects of inorganic carbon acquisition were investigated by membrane-inlet mass spectrometry. Our results show that both species kept growth rates constant over the tested pCO2 range, but we observed a number of species-specific responses. For instance, biomass production and cell size decreased in S. trochoidea, while A. tamarense was not responsive to OA in these measures. In terms of oxygen fluxes, rates of photosynthesis and respiration remained unaltered in S. trochoidea whereas respiration increased in A. tamarense under OA. Both species featured efficient carbon concentrating mechanisms (CCMs) with a CO2-dependent contribution of HCO3− uptake. In S. trochoidea, the CCM was further facilitated by exceptionally high and CO2-independent carbonic anhydrase activity. Comparing both species, a general trade-off between maximum rates of photosynthesis and respective affinities is indicated. In conclusion, our results demonstrate effective CCMs in both species, yet very different strategies to adjust their carbon acquisition. This regulation in CCMs enables both species to maintain growth over a wide range of ecologically relevant pCO2.
    Repository Name: EPIC Alfred Wegener Institut
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  • 6
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    Combined effects of different CO2 levels and N sources on the diazotrophic cyanobacterium Trichodesmium (2014)
    WILEY-BLACKWELL PUBLISHING
    In:  EPIC3Physiologia Plantarum, WILEY-BLACKWELL PUBLISHING, 152, pp. 316-330, ISSN: 0031-9317
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    Publication Date: 2014-11-06
    Description: To predict effects of climate change and possible feedbacks, it is crucial to understand the mechanisms behind pCO2 responses of biogeochemically relevant phytoplankton species. Previous experiments on the abundant N2-fixer Trichodesmium demonstrated strong pCO2 responses, which were attributed to an energy reallocation between its carbon and nitrogen acquisition. Pursuing this hypothesis, we manipulated the cellular energy budget by growing Trichodesmium erythraeum IMS101 under different pCO2 levels (180, 380, 980 and 1400 µatm) and nitrogen sources (N2 and NO3–). Subsequently, biomass production and the main energy-generating processes (photosynthesis and respiration) and energy-consuming processes (N2-fixation and carbon acquisition) were measured. While oxygen fluxes and chlorophyll fluorescence indicated that energy generation and its diurnal cycle was neither affected by pCO2 nor nitrogen source, cells differed in production rates and composition. Elevated pCO2 increased N2-fixation and organic carbon and nitrogen contents. The degree of stimulation was higher for nitrogenase activity than for cell contents, indicating a pCO2 effect on the transfer efficiency from N2 to biomass. pCO2-dependent changes in the diurnal cycle of N2-fixation correlated well with carbon affinities, confirming the interactions between nitrogen and carbon acquisition. Regarding effects of the nitrogen source, production rates were enhanced in NO3– grown cells, which we attribute to the higher N retention and lower ATP demand compared to N2-fixation. pCO2 effects on carbon affinity were less pronounced in NO3– users than N2-fixers. Our study illustrates the necessity to understand energy budgets and fluxes under different environmental conditions for explaining indirect effects of rising pCO2.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev , info:eu-repo/semantics/article
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  • 7
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    Ocean acidification decreases the light-use efficiency in an Antarctic diatom under dynamic but not constant light (2015)
    WILEY-BLACKWELL PUBLISHING
    In:  EPIC3New Phytologist, WILEY-BLACKWELL PUBLISHING, ISSN: 0028-646X
    Details
    Publication Date: 2015-02-27
    Description: - There is increasing evidence that different light intensities strongly modulate the effects of ocean acidification (OA) on marine phytoplankton. The aim of the present study was to investigate interactive effects of OA and dynamic light, mimicking natural mixing regimes. - The Antarctic diatom Chaetoceros debilis was grown under two pCO2 (390 and 1000 latm) and light conditions (constant and dynamic), the latter yielding the same integrated irradiance over the day. To characterize interactive effects between treatments, growth, elemental composition, primary production and photophysiology were investigated. - Dynamic light reduced growth and strongly altered the effects of OA on primary production, being unaffected by elevated pCO2 under constant light, yet significantly reduced under dynamic light. Interactive effects between OA and light were also observed for Chl production and particulate organic carbon quotas. - Response patterns can be explained by changes in the cellular energetic balance. While the energy transfer efficiency from photochemistry to biomass production (Φe,C) was not affected by OA under constant light, it was drastically reduced under dynamic light. Contrasting responses under different light conditions need to be considered when making predictions regarding a more stratified and acidified future ocean.
    Repository Name: EPIC Alfred Wegener Institut
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  • 8
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    Higher sensitivity towards light stress and ocean acidification in an Arctic sea‐ice‐associated diatom compared to a pelagic diatom (2020)
    WILEY-BLACKWELL PUBLISHING
    In:  EPIC3New Phytologist, WILEY-BLACKWELL PUBLISHING, ISSN: 0028-646X
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    Publication Date: 2020-04-15
    Description: Thalassiosira hyalina and Nitzschia frigida are important members of Arctic pelagic and sympagic (sea‐ice‐associated) diatom communities. We investigated the effects of light stress (shift from 20 to 380 µmol photons m−2 s−1, resembling upwelling or ice break‐up) under contemporary and future pCO2 (400 vs 1000 µatm). The responses in growth, elemental composition, pigmentation and photophysiology were followed over 120 h and are discussed together with underlying gene expression patterns. Stress response and subsequent re-acclimation were efficiently facilitated by T. hyalina, which showed only moderate changes in photophysiology and elemental composition, and thrived under high light after 120 h. In N. frigida, photochemical damage and oxidative stress appeared to outweigh cellular defenses, causing dysfunctional photophysiology and reduced growth. pCO2 alone did not specifically influence gene expression, but amplified the transcriptomic reactions to light stress, indicating that pCO2 affects metabolic equilibria rather than sensitive genes. Large differences in acclimation capacities towards high light and high pCO2 between T. hyalina and N. frigida indicate species‐specific mechanisms in coping with the two stressors, which may reflect their respective ecological niches. This could potentially alter the balance between sympagic and pelagic primary production in a future Arctic.
    Repository Name: EPIC Alfred Wegener Institut
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