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

Abstract

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 (εp) 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 εp remained unaffected by the availability of light for both G. spinifera and P. reticulatum, though at HL εp 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 εp disappeared under LN conditions in both A. fundyense and S. trochoidea. The generally higher εp under LN may be associated with lower organic carbon production rates and/or higher ATP:NADPH ratios. CO2-dependent εp 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 εp, thereby illustrating the need to carefully consider prevailing environmental conditions.

Effects of increasing temperature and acidification on the growth and competitive success of Alexandrium catenella from the Gulf of Maine

“…The growth rate of Scrippsiella sp. used in this study at 15°C was lower than that reported for Scrippsiella trochoidea from the North Sea at this temperature (Hoins et al (2016) (Table 3). This result is not surprising as it has been shown that thermal reaction norms for growth vary not only among species but also between strains within the same species (Boyd et al 2013).…”

Inorganic carbon concentrating mechanisms in free‐living and symbiotic dinoflagellates and chromerids

“…For Alexandrium fundyense and Scrippsiella trochoidea discrimination between 13 C and 12 C increases with CO 2 concentration for growth, as predicted for an increased fraction of CO 2 as the inorganic C species entering the cell, and close to the predictions of a model of Hoins et al (2016a). For Gonyaulax spinifera and Protoceratium reticulatum, the effects of CO 2 increase on C isotope fractionation are more variable, so the fit to the model is less good (Hoins et al 2016b). The isotope fractionation also depends on the fractional CO 2 leakage from the cells (Raven and Beardall 2016); leakage increases with the CO 2 concentration and with increasing isotope fractionation in Alexandrium fundyense; for the other three species tested the fractional CO 2 leakage is more or less independent of the CO 2 concentration for growth (Hoins et al 2016a).…”

“…Burkhardt et al (1999a) and Burkhardt et al (1999b) show that the stable C isotope fractionation e p increased as a function of CO 2 concentrations from 1 to 39 lmol Á kg À1 for growth in marine phytoplankton, including the dinoflagellate Scrippsiella trochoidea. Hoins et al (2016b) examined carbon stable isotope fractionation in four species of marine dinoflagellates (i.e., Alexandrium fundyense, Scrippsiella trochoidea, Gonyaulax spinifera and Protoceratium reticulatum) grown at 180-1200 lmol CO 2 Á mol total gas À1 . For Alexandrium fundyense and Scrippsiella trochoidea discrimination between 13 C and 12 C increases with CO 2 concentration for growth, as predicted for an increased fraction of CO 2 as the inorganic C species entering the cell, and close to the predictions of a model of Hoins et al (2016a).…”

The DeepMIP contribution to PMIP4: methodologies for selection, compilation and analysis of latest Paleocene and early Eocene climate proxy data, incorporating version 0.1 of the DeepMIP database

“…A strong correlation between εpDINO and CO2 was found in four cultured dinoflagellate species (Hoins et al, 2015). Importantly, there appears to be species-specific effects on εpDINO based on uptake and leakage of different carbon species (HCO3and CO2(aq)) and light intensity, making single-species records preferable (Hoins et al 2016a, b). Dinocysts are found in the geological Geosci.…”