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| 2. |
- Gross, Elisabeth, et al.
(författare)
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Allelochemical interactions among aquatic primary producers
- 2012. - 1
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Ingår i: Chemical Ecology in Aquatic Systems. - Oxford : Oxford University Press. - 9780199583102 ; , s. 196-209
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Bokkapitel (refereegranskat)abstract
- Allelopathy is the study of biochemically-driven organismic interactions among primary producers. One organism affects others by the release of allelochemicals that are transported to the target cells, and cause a negative (or positive) response. Most aquatic allelochemicals are amphiphilic, thus have a sufficient solubility in the water, and at the same time can bind to and penetrate lipophilic cell membranes. Allelopathic interactions are not static but are influenced by variable environmental stressors. Resource availability can both affect the production and release of allelochemicals by the producing organism, but also influence the susceptibility of the target cells. The biosynthesis and excretion of allelochemicals might involve costs for the producing organism, and these costs will only be balanced if a net gain, i.e. better resource availability such as space or nutrients or secondary benefits, e.g. predator deterrence, are achieved. Allelopathic effects against cooccurring organisms might lead to coevolutionary responses, i.e. a lower susceptibility of target cells or to more advanced allelochemicals. Target organisms from different habitats might be more susceptible, especially if they are not acquainted with the allelochemicals. The transfer of laboratory results on allelopathy to realistic field conditions is complex, and might in the long run benefit from advanced analytical and molecular methods identifying specific target cell responses in situ.
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| 3. |
- Ianora, Adrianna, et al.
(författare)
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The Relevance of Marine Chemical Ecology to Plankton and Ecosystem Function : An Emerging Field
- 2011
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Ingår i: Marine Drugs. - : MDPI. - 1660-3397. ; 9:9, s. 1625-1648
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Tidskriftsartikel (refereegranskat)abstract
- Marine chemical ecology comprises the study of the production and interaction of bioactive molecules affecting organism behavior and function. Here we focus on bioactive compounds and interactions associated with phytoplankton, particularly bloom-forming diatoms, prymnesiophytes and dinoflagellates. Planktonic bioactive metabolites are structurally and functionally diverse and some may have multiple simultaneous functions including roles in chemical defense (antipredator, allelopathic and antibacterial compounds), and/or cell-to-cell signaling (e.g., polyunsaturated aldehydes (PUAs) of diatoms). Among inducible chemical defenses in response to grazing, there is high species-specific variability in the effects on grazers, ranging from severe physical incapacitation and/or death to no apparent physiological response, depending on predator susceptibility and detoxification capability. Most bioactive compounds are present in very low concentrations, in both the producing organism and the surrounding aqueous medium. Furthermore, bioactivity may be subject to synergistic interactions with other natural and anthropogenic environmental toxicants. Most, if not all phycotoxins are classic secondary metabolites, but many other bioactive metabolites are simple molecules derived from primary metabolism (e.g., PUAs in diatoms, dimethylsulfoniopropionate (DMSP) in prymnesiophytes). Producing cells do not seem to suffer physiological impact due to their synthesis. Functional genome sequence data and gene expression analysis will provide insights into regulatory and metabolic pathways in producer organisms, as well as identification of mechanisms of action in target organisms. Understanding chemical ecological responses to environmental triggers and chemically-mediated species interactions will help define crucial chemical and molecular processes that help maintain biodiversity and ecosystem functionality.
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| 4. |
- Mitra, Aditee, et al.
(författare)
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Defining Planktonic Protist Functional Groups on Mechanisms for Energy and Nutrient Acquisition : Incorporation of Diverse Mixotrophic Strategies
- 2016
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Ingår i: Protist. - : Elsevier BV. - 1434-4610 .- 1618-0941. ; 167:2, s. 106-120
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Tidskriftsartikel (refereegranskat)abstract
- Arranging organisms into functional groups aids ecological research by grouping organisms (irrespective of phylogenetic origin) that interact with environmental factors in similar ways. Planktonic protists traditionally have been split between photoautotrophic "phytoplankton" and phagotrophic "microzooplankton". However, there is a growing recognition of the importance of mixotrophy in euphotic aquatic systems, where many protists often combine photoautotrophic and phagotrophic modes of nutrition. Such organisms do not align with the traditional dichotomy of phytoplankton and microzooplankton. To reflect this understanding, we propose a new functional grouping of planktonic protists in an ecophysiological context: (i) phagoheterotrophs lacking phototrophic capacity, (ii) photoautotrophs lacking phagotrophic capacity, (iii) constitutive mixotrophs (CMs) as phagotrophs with an inherent capacity for phototrophy, and (iv) non-constitutive mixotrophs (NCMs) that acquire their phototrophic capacity by ingesting specific (SNCM) or general non-specific (GNCM) prey. For the first time, we incorporate these functional groups within a foodweb structure and show, using model outputs, that there is scope for significant changes in trophic dynamics depending on the protist functional type description. Accordingly, to better reflect the role of mixotrophy, we recommend that as important tools for explanatory and predictive research, aquatic food-web and biogeochemical models need to redefine the protist groups within their frameworks. (C) 2016 The Authors. Published by Elsevier GmbH.
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| 5. |
- Mitra, Aditee, et al.
(författare)
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The role of mixotrophic protists in the biological carbon pump
- 2014
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 11, s. 995-1005
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Tidskriftsartikel (refereegranskat)abstract
- The traditional view of the planktonic foodweb describes consumption of inorganic nutrientsby photo-autotrophic phytoplankton, which in turn supports zooplankton and ultimately higher trophic levels. Pathways centred on bacteria provide mechanisms for nutrient recycling. This structure lies at the foundation of most models used to explore biogeochemical cycling, functioning of the biological pump, and the impact of climate change on these processes. We suggest an alternative paradigm, which sees the bulk of the base of this foodweb supported by protist plankton (phytoplankton and microzooplankton) communities that are mixotrophic – combining phototrophy and phagotrophy within a single cell. The photoautotrophic eukaryotic plankton and their heterotrophic microzooplankton grazers dominate only within immature environments (e.g., spring bloom in temperate systems). With their flexible nutrition, mixotrophic protists dominate in more mature systems (e.g., temperate summer, established eutrophic systems and oligotrophic systems); the more stable water columns suggested under climate change may also be expected to favour these mixotrophs. We explore how such a predominantlymixotrophic structure affects microbial trophic dynamics and the biological pump. The mixotroph dominated structure differs fundamentally in its flow of energy and nutrients, with a shortened and potentially more efficient chain from nutrient regeneration to primary production. Furthermore, mixotrophy enables a direct conduit for the support of primary production from bacterial production. We show how the exclusion of an explicit mixotrophic component in studies of the pelagic microbial communities leads to a failure to capture the true dynamics of the carbon flow. In order to prevent a misinterpretation of the full implications of climate change upon biogeochemical cyclingand the functioning of the biological pump, we recommend inclusion of multi-nutrient mixotroph models within ecosystem studies.
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| 6. |
- Weissbach, Astrid, et al.
(författare)
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Allelopathic potential of the dinoflagellate Alexandrium tamarense on marine microbial communities
- 2010
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Ingår i: Harmful Algae. - : Elsevier. - 1568-9883 .- 1878-1470. ; 10:1, s. 9-18
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Tidskriftsartikel (refereegranskat)abstract
- The impacts of two strains of the dinoflagellate Alexandrium tamarense, differing in lytic activity, on the abundance and the composition of microbial communities (<150 μm) were studied in North Sea water during spring with Phaeocystis globosa as a dominant species. Cell-free suspensions (supernatant) of exponentially growing lytic and non-lytic Alexandrium culture were added at different concentrations to natural microbial communities under nutrient rich conditions. The non-lytic strain had a positive impact on diatoms whereas the lytic strain suppressed phytoplankton growth in comparison to the control. P. globosa, present as single cells in the initial community, increased in abundance and formed colonies in all treatments. However, total abundance and number of colonies was low with lytic Alexandriumadditions, whereas shape of the colonies, but not abundance of cells, was affected by non-lytic Alexandrium additions. During the 4-day experiment, bacterial abundance was constantly higher with high lytic additions (highest concentration equivalent to 1000 cells ml−1) whereas nanoflagellate abundance in the same treatments was found to be lower at the end of the experiment. Initial bacterial community composition differed significantly among lytic Alexandrium, non-lyticAlexandrium and North Sea water. However, neither bacterial activity nor composition was significantly affected by the supernatants after 96 h. Our results indicated that Alexandrium allelochemicals do not inhibit growth and production of bacteria in seawater collected during spring in the North Sea.
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| 7. |
- Weissbach, Astrid, et al.
(författare)
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Phytoplankton allelochemical interactions change microbial food web dynamics
- 2011
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Ingår i: Limnology and Oceanography. - : John Wiley & Sons. - 0024-3590 .- 1939-5590. ; 56:3, s. 899-909
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the effect of filtrates from an allelopathic dinoflagellate, Alexandrium tamarense, onfour microbial food webs that have been manipulated experimentally from natural seawater by modifying theavailability of resources in the form of dissolved organic carbon with additions of peptone, and by altering thegrazing pressure with size fractionation. Bacterial production was generally not affected by allelochemicals, butbacteria showed higher net growth in all food webs when allelochemicals were added, whereas heterotrophicnanoflagellates . 7 mm and ciliates were constrained in all food webs. Allelochemicals had the largest negativeeffects on microbial communities with low grazing pressure. In food webs with high grazing pressure andadditional resources, phytoplankton and small nanoflagellates were positively affected by the addition ofallelochemicals, suggesting that those were interfering with trophic interactions in the microbial communities. Bythe lysis of organisms sensitive towards allelochemicals, resources are made available and grazing pressure oncertain microorganisms is reduced. However, the intensity of these interactions is modulated by both theavailability of resources and the biomass of grazers in the initial food web.
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