Abstract
Dissolved oceanic CO2 concentrations are rising as result of increasing atmospheric partial pressure of CO2 (pCO2), which has large consequences for phytoplankton. To test how higher CO2 availability affects different traits of the toxic dinoflagellate Alexandrium ostenfeldii, we exposed three strains of the same population to 400 and 1,000 µatm CO2, and measured traits including growth rate, cell volume, elemental composition, 13C fractionation, toxin content, and volatile organic compounds (VOCs). Strains largely increased their growth rates and particulate organic carbon and nitrogen production with higher pCO2 and showed significant changes in their VOC profile. One strain showed a significant decrease in both PSP and cyclic imine content and thereby in cellular toxicity. Fractionation against 13C increased in response to elevated pCO2, which may point towards enhanced CO2 acquisition and/or a downscaling of the carbon concentrating mechanisms. Besides consistent responses in some traits, other traits showed large variation in both direction and strength of responses towards elevated pCO2. The observed intraspecific variation in phenotypic plasticity of important functional traits within the same population may help A. ostenfeldii to negate the effects of immediate environmental fluctuations and allow populations to adapt more quickly to changing environments.
Highlights
The atmospheric partial pressure of CO2 is increasing at an exceptional rate due to anthropogenic activities (Honisch et al, 2012; Stocker et al, 2013)
AON13 grew at 0.17±0.008 d− 1, which was significantly slower than the two other strains, AON15 and AON5.26, that had average growth rates of 0.22±0.01 and 0.22±0.006 d− 1, respectively (Fig. 1a; P
Toxin contents varied between the strains, with significantly different cyclic imine toxin contents of 4.25, 5.74 and 3.02 pg cell− 1, for AON13, AON15 and AON5.26, respectively (Fig. 1b; P
Summary
The atmospheric partial pressure of CO2 (pCO2) is increasing at an exceptional rate due to anthropogenic activities (Honisch et al, 2012; Stocker et al, 2013). The oceans act as the world’s largest exogenic carbon reservoir and will take up more CO2 as atmospheric concentra tions rise (Post et al, 1990; Riebesell et al, 2009) This will result in a change in the speciation of dissolved inorganic carbon (DIC) in the upper ocean layer, and a subsequent drop in pH values. For organisms living in the surface layer of the oceans, such as phytoplankton, that utilize CO2 for photosynthesis (Beardall et al, 2009) Phytoplankton vary in their inorganic carbon (C) acquisition due to differences in the operation of carbon concentrating mechanisms (CCMs; Giordano et al, 2005). They could benefit from higher CO2 concentrations by downscaling their CCMs and reallocate energy and resources towards other cellular processes (Rost et al, 2008; Van de Waal and Litchman, 2020)
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