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The Role of Picophytoplankton in Lake Food Webs
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Faculty of Science and Technology, Biology, Department of Evolutionary Biology, Limnology.
2002 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Picophytoplankton were inferior competitors for inorganic phosphorus compared to heterotrophic bacteria. This may be due to the source of energy available for the heterotrophs, while cell-size was of minor importance. However, picophytoplankton were superior to large phytoplankton in the competition for nutrients at low concentrations.

Biomass of picophytoplankton was low in brownwater lakes and high in clearwater lakes, compared to the biomass of heterotrophic bacteria. The results suggest that picophytoplankton are inferior to heterotrophic bacteria in the competition for inorganic nutrients in brownwater lakes, where the production of heterotrophic bacteria is subsidized by humic dissolved organic carbon (DOC)

Relative to large phytoplankton, picophytoplankton were most important in lakes with intermediate water colour, despite the fact that the lowest nutrient concentrations were found in the clearwater lakes. Large phytoplankton in the clearwater lakes may be able to overcome nutrient competition with picophytoplankton by vertical migration.

In conclusion, changes in nutrient content, light availability and concentrations of DOC affect the interactions of heterotrophic bacteria, picophytoplankton and large phytoplankton and are therefore important factors for the structure of the food web in the pelagic zones of lakes.

Picophytoplankton (planktonic algae and cyanobacteria, < 2 µm) constitute an important component of pelagic food webs. They are linked to larger phytoplankton and heterotrophic bacteria through complex interactions including competition, commensalism and predation. In this thesis, field and laboratory studies on the competitive ability of picophytoplankton are reported.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2002. , p. 35
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 763
Keywords [en]
Biology, picophytoplankton, competition, heterotrophic bacteria, nutrients, humic DOC
Keywords [sv]
Biologi
National Category
Biological Sciences
Research subject
Limnology
Identifiers
URN: urn:nbn:se:uu:diva-2710ISBN: 91-554-5440-2 (print)OAI: oai:DiVA.org:uu-2710DiVA, id: diva2:162087
Public defence
2002-11-21, Lecture hall at the Department of Limnology, Norbyv. 20, Uppsala, 13:00
Opponent
Available from: 2002-10-23 Created: 2002-10-23Bibliographically approved
List of papers
1. Competition between picoplanktonic cyanobacteria and heterotrophic bacteria along crossed gradients of glucose and phosphate
Open this publication in new window or tab >>Competition between picoplanktonic cyanobacteria and heterotrophic bacteria along crossed gradients of glucose and phosphate
2002 (English)In: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 44, no 4, p. 327-335Article in journal (Refereed) Published
Abstract [en]

A laboratory experiment was performed to test whether differences in nutrient and energy demands between picophytoplankton and heterotrophic bacteria can explain the apparent inverse biomass relationship between these organisms in lakes along gradients of organic carbon and nutrients. Growth rates and final yield of cells were analyzed in crossed gradients of glucose and phosphate. Concentrations of phosphate (10, 25, and 60 microg P L(-1)) and glucose (0, 0.3, and 3 mg C L(-1)) were used in all possible combinations giving 9 different treatments. Heterotrophic bacteria had higher maximum growth rates in all treatments and became larger than picophytoplankton in many treatments. The variance in abundance of heterotrophic bacteria between treatments could almost completely be explained by the combined effects of glucose and P. In treatments where carbon limitation slowed down the growth of heterotrophic bacteria, picophytoplankton became abundant and these organisms showed a positive response to P in combination with a negative response to glucose. The negative effect of glucose on picophytoplankton is suggested to be indirect and caused by competition with bacteria that are favored by organic C. The results suggest that competition for phosphate between phytoplankton and bacteria is not size-dependent, that heterotrophic bacteria are superior competitors for P, and that organic C produced by picophytoplankton was of minor importance for heterotrophic bacteria.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-90042 (URN)10.1007/s00248-002-1013-4 (DOI)12399896 (PubMedID)
Available from: 2002-10-23 Created: 2002-10-23 Last updated: 2017-12-14Bibliographically approved
2. Effects of additions of DOC on pelagic biota in a clearwater system: Results from a whole lake experiment in northern Sweden
Open this publication in new window or tab >>Effects of additions of DOC on pelagic biota in a clearwater system: Results from a whole lake experiment in northern Sweden
Show others...
2001 In: Microbial Ecology, Vol. 42, p. 383-394Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-90043 (URN)
Available from: 2002-10-23 Created: 2002-10-23Bibliographically approved
3. Primary production and phytoplankton composition in relation to DOC input and bacterioplankton production in Lake Örträsket
Open this publication in new window or tab >>Primary production and phytoplankton composition in relation to DOC input and bacterioplankton production in Lake Örträsket
2002 In: Freshwater Biology, Vol. 47, no 1, p. 41-52Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-90044 (URN)
Available from: 2002-10-23 Created: 2002-10-23Bibliographically approved
4. Relationships between picophytoplankton and their environment along a gradient of lakes of different water colour and nutrient content
Open this publication in new window or tab >>Relationships between picophytoplankton and their environment along a gradient of lakes of different water colour and nutrient content
In: Freshwater BiologyArticle in journal (Refereed) Submitted
Identifiers
urn:nbn:se:uu:diva-90045 (URN)
Available from: 2002-10-23 Created: 2002-10-23Bibliographically approved

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