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Consequences of consumer-resource stoichiometric imbalance in planktonic food webs
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (EcoChange)
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: urn:nbn:se:umu:diva-167427ISBN: 978-91-7855-182-8 (print)ISBN: 978-91-7855-183-5 (electronic)OAI: oai:DiVA.org:umu-167427DiVA, id: diva2:1391090
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: 2020-03-02Bibliographically approved
List of papers
1. An operational framework for the advancement of a molecule-to-biosphere stoichiometry theory
Open this publication in new window or tab >>An operational framework for the advancement of a molecule-to-biosphere stoichiometry theory
Show others...
2017 (English)In: Frontiers in Marine Science, E-ISSN 2296-7745, Vol. 4, article id 286Article in journal (Refereed) Published
Abstract [en]

Biological stoichiometry is an approach that focuses on the balance of elements in biological interactions. It is a theory that has the potential to causally link material processes at all biological levels—from molecules to the biosphere. But the lack of a coherent operational framework has so far restricted progress in this direction. Here, we provide a framework to help infer how a stoichiometric imbalance observed at one level impacts all other biological levels. Our framework enables us to highlight the areas of the theory in need of completion, development and integration at all biological levels. Our hope is that this framework will contribute to the building of a more predictive theory of elemental transfers within the biosphere, and thus, to a better understanding of human-induced perturbations to the global biogeochemical cycles.

Place, publisher, year, edition, pages
Lausanne: Frontiers Media S.A., 2017
Keywords
biological organization, biological stoichiometry, consumer-driven nutrient recycling, ecological theory, theory integration, growth-rate hypothesis, light:nutrient hypothesis
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-139395 (URN)10.3389/fmars.2017.00286 (DOI)
Available from: 2017-09-15 Created: 2017-09-15 Last updated: 2020-02-03Bibliographically approved
2. More than stoichiometry: the molecular composition of inorganic and organic substrates controls ammonium regeneration by bacteria
Open this publication in new window or tab >>More than stoichiometry: the molecular composition of inorganic and organic substrates controls ammonium regeneration by bacteria
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The mineralization of nitrogen (N) and especially the regeneration of ammonium are critical processes performed by bacteria in aquatic ecosystems. Quantifying these processes is complicated because bacteria simultaneously consume and produce ammonium. Here we use experimental data on the effects of the molecular composition of the supplied substrates, combined with a classical stoichiometric model of ammonium regeneration, to demonstrate how the quantification of these processes can be improved. We manipulated a batch culture experiment with an isolated bacterial community by adding three different types of N substrates: dissolved inorganic nitrogen (DIN, nitrate), dissolved organic nitrogen (DON, amino acid) and a mixture of DIN and DON. With such experiment set-up, the ammonium regeneration per se could be easily tracked without using complicated methods (e.g. isotope dilution). We compared the experimental data with the predictions of Goldman et al’ model (1987) as well as with a revised version, using the measured consumption carbon:nitrogen ratio (C:N ratio), rather than an estimated consumption ratio. We found that, for all substrates, and in particular, mixed substrates where C and N are partially dissociated between different molecules, estimates of ammonium regeneration rates can be improved by measuring the actual consumption C: N ratio.

Keywords
organic nitrogen, inorganic nitrogen, bacterial stoichiometry, bacterial ammonium regeneration, bacterial net mineralization
National Category
Earth and Related Environmental Sciences
Research subject
environmental science
Identifiers
urn:nbn:se:umu:diva-167424 (URN)
Available from: 2020-01-20 Created: 2020-01-20 Last updated: 2020-02-03Bibliographically approved
3. Organic vs. inorganic nitrogen as promoting nutrient in aquatic microplankton food webs
Open this publication in new window or tab >>Organic vs. inorganic nitrogen as promoting nutrient in aquatic microplankton food webs
(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
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:nbn:se:umu:diva-167425 (URN)
Available from: 2020-01-20 Created: 2020-01-20 Last updated: 2020-03-23
4. Stoichiometric changes in planktonic food web upon environmental fluctuations in northern oligotrophic coastal ecosystem
Open this publication in new window or tab >>Stoichiometric changes in planktonic food web upon environmental fluctuations in northern oligotrophic coastal ecosystem
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Climate-driven changes, e.g. increasing precipitation, will increase terrestrial runoff and freshwater inputs to coastal ecosystems in the future. Consequently, we expect that altered availability of inorganic and organic forms of carbon (C), nitrogen (N) and phosphorus (P) will lead to spatial and temporal variation in the elemental composition of coastal organisms. To identify the major spatiotemporal patterns in seston and zooplankton elemental (C, N and P) composition, we sampled four bays of northern Baltic Sea from May to September 2018. This sampling design covers spatial and temporal variation in freshwater input, as it includes the spring flood driven by snowmelt in May, and bays receiving varying catchment areas. We analyzed CNP composition for different size fractions of seston, and dominant zooplankton taxa. Our results showed that the stoichiometric composition of individual seston size fractions varied more through time than in space. The concentrations of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in water were the major explanatory variables for seston stoichiometry. We also found that zooplankton stoichiometry was relatively similar between taxa within specific months, although the dominant zooplankton taxa differed over time and among sites. This could partly be explained by the similar stoichiometric requirements and homeostasis among zooplankton taxa. Our findings imply that the spatiotemporal variation in physicochemical characteristics of coastal ecosystems will alter the quality of seston and zooplankton. Yet, further investigations on the role of zooplankton in stoichiometry related nutrient cycling in the Baltic Sea coastal ecosystems are needed.

National Category
Earth and Related Environmental Sciences
Research subject
environmental science
Identifiers
urn:nbn:se:umu:diva-167426 (URN)
Available from: 2020-01-20 Created: 2020-01-20 Last updated: 2020-03-23

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