Combined Effects of Ocean Acidification and Light or Nitrogen Availabilities on 13 C Fractionation in Marine Dinoflagellates

• Published in: PLOS ONE
• Main Authors: Hoins, M., Eberlein, T., Großmann, C.H., Brandenburg, K., Reichart, G.-J., Rost, B., Sluijs, A., Van de Waal, D.B.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2016
• Subjects: Ocean acidification
• Online Access: https://www.vliz.be/imisdocs/publications/81/291181.pdf

Along with increasing oceanic CO2 concentrations, enhanced stratification constrains phytoplankton to shallower upper mixed layers with altered light regimes and nutrient concentrations. Here, we investigate the effects of elevated pCO2 in combination with light or nitrogen-limitation on 13C fractionation (ep) in four dinoflagellate species. We cultured Gonyaulax spinifera and Protoceratium reticulatum in dilute batches under low-light (‘LL’) and high-light (‘HL’) conditions, and grew Alexandrium fundyense and Scrippsiella trochoidea in nitrogen-limited continuous cultures (‘LN’) and nitrogen-replete batches (‘HN’). The observed CO2-dependency of ep remained unaffected by the availability of light for both G. spinifera and P. reticulatum, though at HL ep was consistently lower by about 2.7‰ over the tested CO2 range for P. reticulatum. This may reflect increased uptake of (13C-enriched) bicarbonate fueled by increased ATP production under HL conditions. The observed CO2-dependency of ep disappeared under LN conditions in both A. fundyense and S. trochoidea. The generally higher ep under LN may be associated with lower organic carbon production rates and/or higher ATP:NADPH ratios. CO2-dependent ep under non-limiting conditions has been observed in several dinoflagellate species, showing potential for a new CO2-proxy. Our results however demonstrate that light- and nitrogen-limitation also affect ep, thereby illustrating the need to carefully consider prevailing environmental conditions.