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https://doi.org/10.5194/bg-2020-306
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-306
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  25 Aug 2020

25 Aug 2020

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A revised version of this preprint is currently under review for the journal BG.

The effect of salinity, light regime and food source on C and N uptake in a kleptoplast-bearing foraminifera

Michael Lintner1, Bianca Lintner1, Wolfgang Wanek2, Nina Keul3, and Petra Heinz1 Michael Lintner et al.
  • 1University of Vienna, Department of Palaeontology, Vienna, Austria
  • 2University of Vienna, Department of Microbiology and Ecosystem Science, Division of Terrestrial Ecosystem Research, Vienna, Austria
  • 3Christian-Albrechts-Universität zu Kiel, Institute of Geosciences, Germany

Abstract. Foraminifera are unicellular organisms that play an important role in marine organic matter cycles. Some species are able to isolate chloroplasts from their algal food source and incorporate them as kleptoplasts into their own metabolic pathways, a phenomenon known as kleptoplastidy. One species showing this ability is Elphidium excavatum, a common foraminifer in the Kiel fjord, Germany. The Kiel fjord is fed by several rivers and thus forms a habitat with strongly fluctuating salinity. Here, we tested the effects of food source, salinity and light regime on the food uptake (via 15N and 13C algal uptake) in this kleptoplast-bearing foraminifer. In our study E. excavatum was cultured in the lab at three salinity levels (15, 20, 25 PSU) and uptake of C and N (food source: Dunaliella tertiolecta) were measured over time (after 3, 5, 7 days). The species was very well adapted to the current salinity of the sampling region, as both, algal N and C uptake was highest at 20 PSU. It seems that E. excavatum coped better with lower than with higher salinities. The amount of absorbed C from the green algae D. tertiolecta showed a marginal significant effect of salinity, peaking at 20 PSU. Nitrogen uptake was also highest at 20 PSU and steadily increased with time. In contrast, C uptake from the diatom L. arenaria was highest at 15 PSU and decreased at higher salinities. We found no overall significant differences in C and N uptake from green algae versus diatoms. Furthermore, the food uptake at a light/dark rhythm of 16:8 h was compared to continuous darkness. Darkness had a negative influence on algal C and N uptake, and this effect increased with incubation time. Starving experiments showed a stimulation of food uptake after 7 days. In summary, it can be concluded that E. excavatum copes well with changes of salinity to a lower level. For changes in light regime, we showed that light reduction caused a decrease of C and N uptake by E. excavatum.

Michael Lintner et al.

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Michael Lintner et al.

Michael Lintner et al.

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