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Organic vs. inorganic nitrogen as promoting nutrient in aquatic microplankton food webs
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF). Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.ORCID iD: 0000-0003-0107-9374
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In aquatic microplankton food webs, the relative availability of dissolved inorganic nitrogen (DIN) and organic nitrogen (DON) can shape trophic interactions, food web structure and the stoichiometry of the organisms. To evaluate the importance of nitrogen forms, i.e., whether microplankton have access to organic or inorganic forms of nitrogen, we performed a short-term microcosm study of a coastal microplankton food web (organism size < 50 µm). In this experiment, the microplankton community was exposed to two different carbon (C) and nitrogen (N) sources: C and N were either associated in a single organic molecule or dissociated in two different molecules. The results showed that the different nitrogen forms had a strong impact on the food web composition, which resulted in different nitrogen food web use efficiency. The entire microplankton food web benefited from the association of C and N in a single DON molecule. The association or dissociation of C and N input had marked effects on all trophic levels, most probably through its effect on bacteria-phytoplankton interaction, which switched from mutualism to competition. Hence, the degree of association between N and C is an important factor to be considered in microplanktonic food web dynamics, at least for the short-term food web response.

Keywords [en]
organic nitrogen, inorganic nitrogen, microplankton food web, ecological stoichiometry, bacteria-phytoplankton interaction, food web resource use efficiency
National Category
Earth and Related Environmental Sciences
Research subject
environmental science
Identifiers
URN: urn:nbn:se:umu:diva-167425OAI: oai:DiVA.org:umu-167425DiVA, id: diva2:1387023
Available from: 2020-01-20 Created: 2020-01-20 Last updated: 2020-02-04
In thesis
1. Consequences of consumer-resource stoichiometric imbalance in planktonic food webs
Open this publication in new window or tab >>Consequences of consumer-resource stoichiometric imbalance in planktonic food webs
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Resource imbalance between consumers and their resources can come from inadequate resource quantity or quality. The ecological stoichiometry theory focuses on understanding the consequences of imbalance in elemental composition.  In this thesis, I have used both resource quality (e.g., inorganic vs organic forms of nutrients) and resource quantity (e.g., terrestrial and freshwater nutrient loading to natural coastal systems) to address the consequences of consumer-resource imbalance in planktonic food webs. First, I provided a framework that summarizes how the stoichiometric imbalance is transferred from one biological level to another. The framework highlights the importance of the distribution of elements among different chemical forms and the distribution of elements among connected ecosystems. The framework then served as a guideline for the empirical work of my thesis.  Second, I studied the response of bacterial community mineralization to the relative availability of different forms of nitrogen (inorganic vs. organic form) in a batch culture experiment. The study shows that different forms of nitrogen can significantly influence the growth of bacteria. More importantly, my results show that it is crucial to measure the actual bacterial carbon to nitrogen consumption ratio, rather than use classical theoretical models, to be able to make an accurate prediction of bacterial ammonium regeneration. Third, I tested the effect of different forms of nitrogen on microplankton food web dynamics in a microcosm experiment. I found that differences between nitrogen forms have a strong impact on food web dynamics that is channeled by the bacteria-phytoplankton interaction at the base of the food web. The whole microplankton food web benefits from organic forms of nitrogen as a result of increased mutualistic interactions between bacteria and phytoplankton. Hence, the form of nitrogen is an important factor to be considered in microplanktonic food web dynamics, at least on the short-term. In the final part of this thesis, I explored resource quality and quantity effects on the stoichiometric response of a natural coastal ecosystem in a field study. I expected that the relative availability of inorganic or organic forms of carbon, nitrogen and phosphorus in our sampling bays may affect organismal elemental composition both temporally and spatially. The results indicate that the stoichiometry among seston size fractions and zooplankton varied more through time than in space. However, zooplankton stoichiometry was relatively stable among species within specific months. Overall, the concentration of dissolved organic carbon and dissolved organic nitrogen in the water column were the major explanatory variables for the seston stoichiometry. In summary, this thesis uses multiple systems to elucidate how the form and input of nutrients shape the plankton food web dynamics and its stoichiometric responses.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2020. p. 36
National Category
Earth and Related Environmental Sciences
Research subject
environmental science
Identifiers
urn:nbn:se:umu:diva-167427 (URN)978-91-7855-182-8 (ISBN)978-91-7855-183-5 (ISBN)
Public defence
2020-02-28, Lilla Hörsalen, KBC, Umeå, 14:12 (English)
Opponent
Supervisors
Available from: 2020-02-07 Created: 2020-02-03 Last updated: 2020-02-05Bibliographically approved

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Guo, JunwenBrugel, SoniaAndersson, AgnetaCherif, Mehdi

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