CO2-dependent carbon isotope fractionation in dinoflagellates relates to their inorganic carbon fluxes

Abstract

Carbon isotope fractionation (εp) between the inorganic carbon source and organic matter has been proposed to be a function of pCO2. To understand the CO2-dependency of εp and species-specific differences therein, inorganic carbon fluxes in the four dinoflagellate species Alexandrium fundyense, Scrippsiella trochoidea, Gonyaulax spinifera and Protoceratium reticulatum have been measured by means of membrane-inlet mass spectrometry. In-vivo assays were carried out at different CO2 concentrations, representing a range of pCO2 from 180 to 1200 μatm. The relative bicarbonate contribution (i.e. the ratio of bicarbonate uptake to total inorganic carbon uptake) and leakage (i.e. the ratio of CO2 efflux to total inorganic carbon uptake) varied from 0.2 to 0.5 and 0.4 to 0.7, respectively, and differed significantly between species. These ratios were fed into a single-compartment model, and εp values were calculated and compared to carbon isotope fractionation measured under the same conditions. For all investigated species, modeled and measured εp values were comparable (A. fundyense, S. trochoidea, P. reticulatum) and/or showed similar trends with pCO2 (A. fundyense, G. spinifera, P. reticulatum). Offsets are attributed to biases in inorganic flux measurements, an overestimated fractionation factor for the CO2-fixing enzyme RubisCO, or the fact that intracellular inorganic carbon fluxes were not taken into account in the model. This study demonstrates that CO2-dependency in εp can largely be explained by the inorganic carbon fluxes of the individual dinoflagellates.

Seasonal variability in phytoplankton stable carbon isotope ratios and bacterial carbon sources in a shallow Dutch lake

“…Additionally, ε values decrease during spring and summer when p CO 2 decreases and production rates are typically enhanced. This trend is suggestive of uptake of bicarbonate as an alternative carbon source during periods when the concentration of CO 2(aq) is low (Hoins et al ).…”

Upwelling as the major source of nitrogen for shallow and deep reef‐building corals across an oceanic atoll system

“…As corals can depend more on heterotrophy in regions of high primary productivity (Fox et al, ), the twofold difference in the isotopic niche size of shallow versus deep G. fascicularis from a well‐mixed water column is likely due to changes in symbiont autotrophy over depth. Because symbiont physiology and irradiance can affect carbon acquisition (Ezzat, Fine, Maguer, Grover, & Ferrier‐Pagès, ), future work could examine carbon isotope fractionation in relation to DIC fluxes in symbionts especially since G. fascicularis can associate with two symbiont clades (Dong, Huang, Huang, & Li, ; Hoins et al, ; Maier et al, ).…”

“…Pagès, 2017), future work could examine carbon isotope fractionation in relation to DIC fluxes in symbionts especially since G. fascicularis can associate with two symbiont clades(Dong, Huang, Huang, & Li, 2009;Hoins et al, 2016;Maier et al, 2010).Coral host P. speciosa showed consistent δ 13 C values over depth, resulting in an overlap of both its isotopic niches with that of host G. fascicularis from shallow reefs. Although the isotopic niche size and position of shallow and deep P. speciosa did not differ with depth, P. speciosa colony abundance was greater in deep reefs.…”

The relative availability of inorganic carbon and inorganic nitrogen influences the response of the dinoflagellate Protoceratium reticulatum to elevated CO2

“…, Hoins et al. ), their photosynthesis is not always saturated by the extant pCO 2 (Ratti et al. , Montechiaro and Giordano , Brading et al.…”