| 1. |
- Flynn, Kevin J, et al.
(författare)
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Misuse of the phytoplankton-zooplankton dichotomy : the need to assign organisms as mixotrophs within plankton functional types
- 2013
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 35:1, s. 3-11
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Tidskriftsartikel (refereegranskat)abstract
- The classic portrayal of plankton is dominated by phytoplanktonic primary producersand zooplanktonic secondary producers. In reality, many if not most planktontraditionally labelled as phytoplankton or microzooplankton should be identifiedas mixotrophs, contributing to both primary and secondary production. Mixotrophicprotists (i.e. single-celled eukaryotes that perform photosynthesis and grazeon particles) do not represent a minor component of the plankton, as some formof inferior representatives of the past evolution of protists; they represent a majorcomponent of the extant protist plankton, and one which could become moredominant with climate change. The implications for this mistaken identification, ofthe incorrect labelling of mixotrophs as “phytoplankton” or “microzooplankton”,are great. It extends from the (mis)use of photopigments as indicators of primaryproduction performed by strict photoautotrophs rather than also (co)locating mixotrophicactivity, through to the inadequacy of plankton functional type descriptionsin models (noting that mixotrophic production in the individual organism is not asimple sum of phototrophy and heterotrophy). We propose that mixotrophy shouldbe recognized as a major contributor to plankton dynamics, with due effortexpended in field and laboratory studies, and should no longer be side-lined inconceptual food webs or in mathematical models.
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| 2. |
- 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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| 3. |
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| 4. |
- Lindehoff, Elin, et al.
(författare)
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Nitrogen uptake kinetics of Prymnesium parvum (Haptophyte)
- 2011
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Ingår i: Harmful Algae. - : Elsevier. - 1568-9883 .- 1878-1470. ; 12, s. 70-76
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Tidskriftsartikel (refereegranskat)abstract
- The uptake rates of different nitrogen (N) forms (NO3-, urea, and the amino acids glycine and glutamicacid) by N-deficient, laboratory-grown cells of the mixotrophic haptophyte, Prymnesium parvum, weremeasured and the preference by the cells for the different forms determined. Cellular N uptake rates(rcell, fmol N cell-1 h-1) were measured using 15N-labeled N substrates. P. parvum showed highpreference for the tested amino acids, in particular glutamic acid, over urea and NO3 under the culturenutrient conditions. However, extrapolating these rates to Baltic Seawater summer conditions, P. parvumwould be expected to show higher uptake rates of NO3- and the amino acids relative to urea because ofthe difference in average concentrations of these substrates. A high uptake rate of glutamic acid at lowsubstrate concentrations suggests that this substrate is likely used through extracellular enzymes.Nitrate, urea and glycine, on the other hand, showed a non-saturating uptake over the tested substrateconcentration (1–40 mM-N for NO3- and urea, 0.5–10 mM-N for glycine), indicating slower membranetransportrates for these substrates
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| 5. |
- Lundgren, Veronica, et al.
(författare)
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Metabolic and physiological changes in Prymnesium parvum when grown under, and grazing on prey of, variable nitrogen:phosphorus stoichiometry
- 2016
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Ingår i: Harmful Algae. - : Elsevier BV. - 1568-9883 .- 1878-1470. ; 55, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- Mixotrophy is found in almost all classes of phytoplankton in a wide range of aquatic habitats ranging from oligotrophic to eutrophic marine and freshwater systems. Few studies have addressed how the nutritional status of the predator and/or the prey affects mixotrophic metabolism despite the realization that mixotrophy is important ecologically. Laboratory experiments were conducted to examine changes in growth rates and physiological states of the toxic haptophyte Prymnesium parvum when fed Rhodomonas sauna of varying nutritional status. Haemolytic activity of P. parvum and prey mortality of R. sauna were also measured. P. parvum cultures grown to be comparatively low in nitrogen (low-N), phosphorus (low-P) or low in both nutrients (low-NP) were mixed with low-NP, low-N, and low-P R. saline in all possible combinations, i.e., a 3 x 3 factorial design. N deficiency was obtained in the low-N cultures, while true P deficiency may not have been obtained in the low-P cultures. Mortality rates of R. salina (both due to ingestion and/or cell rupture as a function of grazing or toxic effects) were higher when R. sauna cells were low-P, N-rich, regardless of the nutritional state of P. parvum. Mortality rates were, however, directly related to the initial prey:predator cell ratios. On the other hand, growth of the predator was a function of nutritional status and a significant positive correlation was observed between growth rates of P. parvum and cell-specific depletion rates of N, whereas no such relationship was found between P. parvum growth rates and depletion rates of P. In addition, the greatest changes in chlorophyll content and stoichiometric ratios of P. parvum were observed in high N:P conditions. Therefore, P. parvum may show enhanced success under conditions of higher inorganic N:P, which are likely favored in the future due to increases in eutrophication and altered nutrient stoichiometry driven by anthropogenic nutrient loads that are increasingly enriched in N relative to P. (C) 2016 Elsevier B.V. All rights reserved.
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| 6. |
- 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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