Article

Elevated atmospheric carbon dioxide increases organic carbon fixation by Emiliania huxleyi (Haptophyta), under nutrient-limited high-light conditions

Department of Biological Sciences, University of Essex, Colchester CO4 3SQ, Essex, UK
Journal of Phycology (Impact Factor: 2.84). 12/2005; 41(6):1196 - 1203. DOI: 10.1111/j.1529-8817.2005.00152.x

ABSTRACT Phytoplankton play a key role in determining the partitioning of CO2 between the atmosphere and the ocean on seasonal, interannual, and millennial time scales. The magnitude of biological draw-down of atmospheric CO2 and C storage in the oceans is affected by concurrent changes in other environmental factors, like nutrient supply. Furthermore, variations in carbon-to-nitrogen (C:N) and carbon-to-phosphorus (C:P) assimilation ratios modify the oceanic CO2 storage capacity. Here we show that increased atmospheric CO2 concentration enhances CO2 fixation into organic matter by a noncalcifying strain of Emiliania huxleyi (Lohmann) Hay & Mohler only under certain conditions, namely high light and nutrient limitation. Enhanced organic matter production was accompanied by marked deviations of the C:N:P ratio from the canonical stoichiometry of marine particulate matter of 106:16:1 (C:N:P) known as the Redfield ratio. Increased cell organic carbon content, C:N, and C:P were observed at high light when growth was either nitrogen or phosphorus limited. Elevated CO2 led to further increases in the particulate C:N and C:P ratios. Enhanced CO2 uptake by phytoplankton such as E. huxleyi, in response to elevated atmospheric CO2, could increase carbon storage in the nitrogen-limited regions of the oceans and thus act as a negative feedback on rising atmospheric CO2 levels.

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    • "Combined effects of nutrient levels and CO 2 have been reported in many studies. For example, photosynthetic carbon fixation of the coccolithophorid Emiliania huxleyi was enhanced under high light and low nitrogen conditions when the seawater CO 2 concentration was raised to 2000 µatm (Leonardos and Geider, 2005). However, increased seawater CO 2 concentration also showed antagonistic effects with iron in modulating (down-or up-regulating) primary production of marine phytoplankton in the Gulf of Alaska (a nutrient-replete but low-chlorophyll area) (Hopkinson et al., 2010). "
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    • "Thus, chem ostats enable studies of cell physiology and element composition under constant nutrient-limited growth. Few chemostat experiments with phytoplankton at different pCO 2 have been conducted previously (Sciandra et al. 2003a, Leonardos & Geider 2005, Borchard et al. 2011, Borchard & Engel 2012). Interestingly, these studies often showed the largest response to CO 2 during transient phases, i.e. either when transitioning from low to high pCO 2 (Sciandra et al. 2003a, Leonardos & Geider 2005) or during the initial transition from the batch to the dilution phase (Borchard et al. 2011). "
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    ABSTRACT: Effects of CO2 concentration on elemental composition of the coccolithophore Emiliania huxleyi were studied in phosphorus-limited, continuous cultures that were acclimated to experimental conditions for 30 days prior to the first sampling. We determined phytoplankton and bacterial cell numbers, nutrients, particulate components like organic carbon (POC), inorganic carbon (PIC), total nitrogen (PN), organic phosphorus (POP), transparent exopolymer particles (TEP), as well as dissolved organic carbon (DOC) and nitrogen (DON), in addition to carbonate system parameters at CO2 levels of 180, 380 and 750 μatm. No significant difference between treatments was observed for any of the measured variables during repeated sampling over a 14-day period. We considered several factors, i.e. light, nutrients, carbon overconsumption and transient vs. steady-state growth that might lead to these results. We suggest that the absence of a clear CO2 effect during this study does not necessarily imply the absence of an effect in nature. Instead, the sensitivity of the cell towards environmental stressors such as CO2 may vary depending on whether growth conditions are transient or sufficiently stable to allow for optimal allocation of energy and resources. We tested this idea on previously published data sets where PIC and POC divided by the corresponding cell abundance of E. huxleyi at various pCO2 levels and growth rates were available.
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    • "However, some experimental studies do not support this expectation, as they did not find an increase in carbon : nutrient stoichiometry in response to rising CO 2 concentrations (Montechiaro & Giordano 2010; Gutow et al. 2014). Elevated CO 2 concentrations only seem to change phytoplankton stoichiometry under specific conditions, for instance, at low nutrient availability (Gervais & Riebesell 2001; Leonardos & Geider 2005; Li et al. 2012). These contrasting predictions and results from previous studies indicate that the response of primary producers and their elemental stoichiometry to rising CO 2 may depend on the nutrient status of ecosystems. "
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