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Marine Ecology Progress Series

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MEPS 656:19-33 (2020)  -  DOI:

Stoichiometry of Fe, Mn and Co in the marine diazotroph Crocosphaera subtropica ATCC51142 in Fe- and P-limited continuous cultures

Alexandra Marki1, Robert Fischer2, Thomas J. Browning1, Evangelia Louropoulou1, Robert Ptacnik2, Martha Gledhill1,*

1GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstr. 1-3, 24148 Kiel, Germany
2WasserCluster Lunz-Biologische Station GmbH, Dr. Carl Kupelwieser Promenade 5, 3293 Lunz am See, Austria
*Corresponding author:

ABSTRACT: We investigated trace element stoichiometries of the nitrogen-fixing marine cyanobacterium Crocosphaera subtropica ATCC51142 under steady-state growth conditions. We utilized exponentially fed batch cultures and varied iron (Fe) concentrations to establish nutrient limitation in C. subtropica growing at a constant growth rate (0.11 d-1). No statistical difference in cell density, chlorophyll a, particulate organic carbon (C), nitrogen (N) and phosphorus (P) were observed between consecutive days after Day 14, and cultures were assumed to be at steady state with respect to growth for the remaining 11 d of the experiment. Cultures were limited by P in the highest Fe treatment (41 nmol l-1) and by Fe in the 2 lower-concentration Fe treatments (1 and 5 nmol l-1). Cell size and in vivo fluorescence changed throughout the experiment in the 1 nmol l-1 Fe treatment, suggesting ongoing acclimation of C. subtropica to our lowest Fe supply. Nevertheless, Fe:C ratios were not significantly different between the Fe treatments, and we calculated an average (±SD) Fe:C ratio of 32 ± 14 µmol mol-1 for growth at 0.11 d-1. Steady-state P-limited cells had lower P quotas, whilst Fe-limited cells had higher manganese (Mn) and cobalt (Co) quotas. We attribute the increase in Mn and Co quotas at low Fe to a competitive effect resulting from changes in the supply ratio of trace elements. Such an effect has implications for variability in elemental stoichiometry in marine phytoplankton, and potential consequences for trace metal uptake and cycling in marine systems.

KEY WORDS: Nutrient limitation · Cyanobacteria · Trace elements · Elemental stoichiometry · Manganese · Cobalt

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Cite this article as: Marki A, Fischer R, Browning TJ, Louropoulou E, Ptacnik R, Gledhill M (2020) Stoichiometry of Fe, Mn and Co in the marine diazotroph Crocosphaera subtropica ATCC51142 in Fe- and P-limited continuous cultures. Mar Ecol Prog Ser 656:19-33.

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