Biogeochemical response of Emiliania huxleyi (PML B92/11) to elevated CO2 and temperature under phosphorous limitation: A chemostat study

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Abstract

The present study investigates the combined effect of phosphorous limitation, elevated partial pressure of CO2 (pCO2) and temperature on a calcifying strain of Emiliania huxleyi (PML B92/11) by means of a fully controlled continuous culture facility. Two levels of phosphorous limitation were consecutively applied by renewal of culture media (N:P = 26) at dilution rates (D) of 0.3 d 1 and 0.1 d 1. CO2 and temperature conditions were 300, 550 and 900 μatm pCO2 at 14 °C and 900 μatm pCO2 at 18 °C. In general, the steady state cell density and particulate organic carbon (POC) production increased with pCO2, yielding significantly higher concentrations in cultures grown at 900 μatm pCO2 compared to 300 and 550 μatm pCO2. At 900 μatm pCO2, elevation of temperature as expected for a greenhouse ocean, further increased cell densities and POC concentrations. In contrast to POC concentration, C-quotas (pmol C cell 1) were similar at D = 0.3 d 1 in all cultures. At D = 0.1 d 1, a reduction of C-quotas by up to 15% was observed in the 900 μatm pCO2 at 18 °C culture. As a result of growth rate reduction, POC:PON:POP ratios deviated strongly from the Redfield ratio, primarily due to an increase in POC. Ratios of particulate inorganic and organic carbon (PIC:POC) ranged from 0.14 to 0.18 at D = 0.3 d 1, and from 0.11 to 0.17 at D = 0.1 d 1, with variations primarily induced by the changes in POC. At D = 0.1 d 1, cell volume was reduced by up to 22% in cultures grown at 900 μatm pCO2. Our results indicate that changes in pCO2, temperature and phosphorus supply affect cell density, POC concentration and size of E. huxleyi (PML B92/11) to varying degrees, and will likely impact bloom development as well as biogeochemical cycling in a greenhouse ocean.

Highlights

E. huxleyi cell density and POC concentration were higher at elevated CO2 and T. ► Carbon-cell-quotas were similar under P-limitation for all CO2 and T conditions. ► E. huxleyi shows a large plasticity of the P-cell-quota while grown at high CO2. ► Cell sizes were significantly decreased at high CO2 under severe P-stress. ► High C:N:P ratios suggest an enhanced carbon export in the greenhouse ocean.

Introduction

During the anthropocene, atmospheric CO2 increased from a concentration of ~ 280 μatm at the beginning, to 380 μatm in the year 2008, and is predicted to rise further up to 750 μatm (Houghton et al., 2001) or even > 1000 μatm by the end of this century (Meehl et al., 2007, Raupach et al., 2007, Raven et al., 2005). Dissolution of CO2 in the ocean will lead to a lowering of pH in surface waters on the order of 0.5 units over the next 100 years (Caldeira and Wickett, 2003). This acidification of the ocean is projected to be accompanied by an increase in sea surface temperature (SST) ranging between 1.1 and 6.4 °C as a consequence of climate change (Meehl et al., 2007). The increase in temperature will induce complex environmental changes such as surface seawater freshening due to sea-ice-melt, stronger water-column stratification and rising irradiance levels in surface waters (Boyd and Doney, 2002, Sarmiento et al., 2004). Responses of individual plankton species or natural communities to rising pCO2 and temperature have been investigated in several perturbation experiments accomplished with a variety of experimental approaches concerning CO2 manipulation, e.g. addition of HCl/NaOH (Riebesell et al., 2000), or aeration with gas of a defined CO2 concentration (Sciandra et al., 2003), and the type of cultivation, e.g. batch cultures (Iglesias-Rodriguez et al., 2008), mesocosms (Delille et al., 2005, Engel et al., 2005, Riebesell et al., 2007), semi-continuous/dilute batch cultures (Feng et al., 2008, Riebesell et al., 2000) or chemostats (Leonardos and Geider, 2005, Sciandra et al., 2003). These studies indicate that physiological processes such as growth (Feng et al., 2008), primary production (Egge et al., 2009), calcification (Delille et al., 2005), the efficiency and regulation of carbon concentration mechanisms (CCM) (Rost et al., 2003) and the production of extracellular organic matter (Engel, 2002) are affected by changes in pCO2.

Coccolithophores play a major role in the global carbon cycle and are known to be sensitive to rising pCO2 (Paasche, 2002, Thierstein and Young, 2004). The expected changes in the ocean carbonate chemistry will thus likely affect the performance of coccolithophores, and may change global biogeochemical cycling in the future (Gattuso and Buddemeier, 2000). Emiliania huxleyi, a prominent cosmopolitan species of coccolithophores, was investigated in field, batch and chemostat studies under a variety of growth rates and nutrient concentrations. E. huxleyi has a low affinity for CO2 and a low efficient CCM and is therefore suggested to be carbon limited in the present day ocean (Paasche, 2002, Rost et al., 2003). Under nutrient replete conditions, E. huxleyi generally increases photosynthetic rates and concentrations of produced particulate organic carbon (POC) while grown at high pCO2 (Riebesell et al., 2000, Rost et al., 2003, Zondervan et al., 2001). At nitrogen limitation however, elevated pCO2 (700 μatm) led to decreased photosynthetic rates and C cell quotas (Sciandra et al., 2003), while a non-calcifying strain of E. huxleyi grown at phosphorous limitation was found to exhibit higher cellular POC at high pCO2 concentrations of 2000 μatm (Leonardos and Geider, 2005). Continuous culture experiments with E. huxleyi revealed that sole nutrient limitation generally increases cell quotas for POC, especially under phosphorous control (Paasche, 1998, Riegman et al., 2000). With respect to calcification in coccolithophores, increasing pCO2 was found to either decrease (Berry et al., 2002, Riebesell et al., 2000, Rost et al., 2003, Sciandra et al., 2003, Zondervan et al., 2002) or increase the concentration of biogenic calcite produced (Iglesias-Rodriguez et al., 2008) or induce complex responses (Langer et al., 2006, Langer et al., 2009).

In order to better estimate effects of global change on E. huxleyi, and potential consequences for biogeochemical cycling in the ocean, a better understanding of individual and combined effects of pCO2, temperature and growth conditions, and other environmental factors, such as nutrients and light, is required (Engel, 2010, Riebesell et al., 2010, Rost et al., 2008). Therefore, we used a chemostat set-up to address combined pCO2 and temperature effects on E. huxleyi under two controlled levels of phosphorous depletion. We further give a detailed description of the CO2–aeration system used in this study and advocate that pCO2- and temperature-controlled continuous culture facilities are likely to be an important tool for future ocean research. Earlier studies with E. huxleyi (PML B92/11) revealed increased POC production at elevated CO2 (Riebesell et al., 2000) and temperature (Langer et al., 2007) while grown at nutrient replete conditions. In the future, the rise in CO2 and temperature will occur simultaneously and is likely to be accompanied by changed nutrient conditions. Therefore, we tested for the combined effect of elevated CO2 and temperature on inter alia POC production under phosphorous limiting conditions in order to investigate a more realistic greenhouse ocean scenario.

Section snippets

The chemostat

Chemostats allow for the full control of growing conditions during the cultivation of plankton organisms and were originally developed for the investigation of bacterial physiology by Monod, 1950, Novick and Szilard, 1950. In chemostats, the cell yield is controlled by the concentration of nutrients, while the growth rate μ (d 1) is balanced to the dilution rate D (d 1), which is defined asD=FVwith F (mL d 1) for the rate of inflow of nutrient media, and V (mL) for total volume of the incubator.

Evaluation of temperature control and CO2 regulation

The pre-tests showed good stability of CO2 concentrations in gas streams obtained by the CO2 regulation system. Concentrations of 200, 370 and 760 μatm CO2 in airstreams were stable over a period of 7 d within standard deviations of ± 0.7, ± 1.7 and ± 1.6%, respectively. Equilibration of gas with preset CO2 concentrations in artificial seawater was reached after a maximum of 60 h, observed by the development of pH (Fig. 4, Table 1). As temperature control was set before slowly filling the incubator

CO2- and temperature-control in chemostats

A simultaneous pCO2 and temperature control to chemostats allows for the investigation of co-effects, i.e. with nutrient availability over a prolonged period of time. In comparison to other cultivation methods, the continuous culture is the only approach that enables the full control of growth at any given rate within minimum and maximum growth rate of investigated organisms. Therefore, chemostats have the great advantage to investigate distinct responses induced by environmental factors, such

Acknowledgements

We thank the AWI-workshop-team of Erich Dunker for technical support, Klaus-Uwe Richter for helpful discussions on the CO2 aeration system and Christiane Lorenzen for assistance during the C/N-analysis. Judith Piontek and Gerald Langer are gratefully acknowledged for supportive discussions improving this manuscript. This research was supported by the Helmholtz Association contract no HZ-NG-102 and contributes to the Belgian Federal Science Policy Office PEACE project (contract no. SD/CS/03A/B).

References (74)

  • P.W. Boyd et al.

    Modelling regional responses by marine pelagic ecosystems to global change

    Geophys. Res. Lett.

    (2002)
  • K. Caldeira et al.

    Anthropogenic carbon and ocean pH

    Nature

    (2003)
  • J. Caperon

    Population growth response of Isochrysis galbana to nitrate variation at limiting concentrations

    Ecology

    (1968)
  • Delille, B., Harlay, J., Zondervan, I., Jacquet, S., Chou, L., Wollast, R., Bellerby, R.G.J., Frankignoulle, M.,...
  • A. Dickson

    The carbon dioxide system in sea water: equilibrium chemistry and measurements

  • A.G. Dickson et al.

    Dissociation constant of bisulfate ion in aqueous sodium chloride solutions to 250 °C

    J. Phys. Chem.

    (1990)
  • M.R. Droop

    Vitamin B12 and Marine Ecology. IV. The kinetics of uptake, growth and inhibition in Monochrysis lutheri

    Journal of the Marine Biological Association of the UK

    (1968)
  • J.K. Egge et al.

    Primary production during nutrient-induced blooms at elevated CO2 concentrations

    Biogeosciences

    (2009)
  • A. Engel

    Direct relationship between CO2 uptake and transparent exopolymer particles production in natural phytoplankton

    Journal of Plankton Research

    (2002)
  • A. Engel et al.

    Temporal decoupling of carbon and nitrogen dynamics in a mesocosm diatom bloom

    Limnol. Oceanogr.

    (2002)
  • A. Engel et al.

    Polysaccharide aggregation as a potential sink of marine dissolved organic carbon

    Nature

    (2004)
  • Engel, A., Ramos, J.B.e., Geider, R., Hutchins, D., Lee, C., Rost, B., Röttgers, R., Thingstad, F., 2010. Organic and...
  • A. Engel et al.

    Testing the direct effect of CO2 concentration on a bloom of the coccolithophorid Emiliania huxleyi in mesocosm experiments

    Limnol. Oceanogr.

    (2005)
  • R.W. Eppley et al.

    Particulate organic matter flux and planktonic new production in the deep ocean

    Nature

    (1979)
  • V.J. Fabry

    Ocean science — marine calcifiers in a high-CO2 ocean

    Science

    (2008)
  • Y. Feng et al.

    Interactive effects of increased pCO2, temperature and irradiance on the marine coccolithophore Emiliania huxleyi (Prymnesiophyceae)

    European Journal of Phycology

    (2008)
  • J.J. Fritz

    Carbon fixation and coccolith detachment in the coccolithophore Emiliania huxleyi in nitrate-limited cyclostats

    Mar. Biol.

    (1999)
  • J.-P. Gattuso et al.

    Approaches and tools to manipulate the carbonate chemistry

  • J.P. Gattuso et al.

    Ocean biogeochemistry — calcification and CO2

    Nature

    (2000)
  • R.J. Geider et al.

    Redfield revisited: variability of C:N:P in marine microalgae and its biochemical basis

    European Journal of Phycology

    (2002)
  • M. Giordano et al.

    CO2 concentrating mechanisms in algae: mechanisms, environmental modulation, and evolution

    Annual Plant Biology

    (2005)
  • G. Gran

    Determination of the equivalence point in potentiometric titrations of seawater with hydrochloric acid

    Oceanology Acta

    (1952)
  • K. Grasshoff et al.

    Methods of Seawater Analysis; Third, Completely Revised and Extended Edition

    (1999)
  • R.R.L. Guillard et al.

    Studies of marine planktonic diatoms

    I. Cyclotella nana Hustedt and Detonula confervacea Cleve. Canadian Journal of Microbiology

    (1962)
  • C. Hoppe et al.

    On CO2 pertubation experiments: over-determination of carbonate chemistry reveals inconsistencies

    Biogeosciences Discussions

    (2010)
  • Houghton, J.T., Ding, Y., Griggs, D.J., Noguer, M., Van der Linden, P.J., Dai, X., Maskell, K., Johnson, C.A., 2001....
  • D.A. Hutchins et al.

    A shipboard natural community continuous culture system for ecologically relevant low-level nutrient enrichment experiments

    Limnology and Oceanography-Methods

    (2003)
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