Inorganic carbon and pH dependency of photosynthetic rates in Trichodesmium

Tobias G. Boatman*, Niall M Mangan, Tracy Lawson, Richard J. Geider

*Corresponding author for this work

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

Increasing atmospheric CO2concentrations are leading to increases in dissolved CO2and HCO 3 - concentrations and decreases in pH and CO 3 2- in the world's oceans. There remain many uncertainties as to the magnitude of biological responses of key organisms to these chemical changes. In this study, we established the relationship between photosynthetic carbon fixation rates and pH, CO 2, and HCO 3 - concentrations in the diazotroph, Trichodesmium erythraeum IMS101. Inorganic 14 C-assimilation was measured in TRIS-buffered artificial seawater medium where the absolute and relative concentrations of CO 2, pH, and HCO 3 - were manipulated. First, we varied the total dissolved inorganic carbon concentration (TIC) (<0 to ∼5 mM) at constant pH, so that ratios of CO2and HCO 3 - remained relatively constant. Second, we varied pH (∼8.54 to 7.52) at constant TIC, so that CO2increased whilst HCO 3 - declined. We found that 14 C-assimilation could be described by the same function of CO2for both approaches, but it showed different dependencies on HCO 3 - when pH was varied at constant TIC than when TIC was varied at constant pH. A numerical model of the carbon-concentrating mechanism (CCM) of Trichodesmium showed that carboxylation rates are modulated by HCO 3 - and pH. The decrease in assimilation of inorganic carbon (Ci) at low CO 2, when TIC was varied, was due to HCO 3 - uptake limitation of the carboxylation rate. Conversely, when pH was varied, Ci assimilation declined due to a high-pH mediated increase in HCO 3 - and CO2leakage rates, potentially coupled to other processes (uncharacterised within the CCM model) that restrict Ci assimilation rates under high-pH conditions.

Original languageEnglish (US)
Pages (from-to)3651-3660
Number of pages10
JournalJournal of Experimental Botany
Volume69
Issue number15
DOIs
StatePublished - Jun 27 2018

Fingerprint

Trichodesmium
Carbon
carbon
assimilation (physiology)
Carbon Monoxide
carboxylation
concentrating
Trichodesmium erythraeum
Photosynthesis
Seawater
Oceans and Seas
Uncertainty
uncertainty
seawater
oceans

Keywords

  • CO
  • Carbon acquisition
  • Cyanobacteria
  • Trichodesmium
  • carbon concentrating mechanism (CCM)
  • gross photosynthesis
  • net photosynthesis
  • ocean acidification

ASJC Scopus subject areas

  • Physiology
  • Plant Science

Cite this

Boatman, Tobias G. ; Mangan, Niall M ; Lawson, Tracy ; Geider, Richard J. / Inorganic carbon and pH dependency of photosynthetic rates in Trichodesmium. In: Journal of Experimental Botany. 2018 ; Vol. 69, No. 15. pp. 3651-3660.
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abstract = "Increasing atmospheric CO2concentrations are leading to increases in dissolved CO2and HCO 3 - concentrations and decreases in pH and CO 3 2- in the world's oceans. There remain many uncertainties as to the magnitude of biological responses of key organisms to these chemical changes. In this study, we established the relationship between photosynthetic carbon fixation rates and pH, CO 2, and HCO 3 - concentrations in the diazotroph, Trichodesmium erythraeum IMS101. Inorganic 14 C-assimilation was measured in TRIS-buffered artificial seawater medium where the absolute and relative concentrations of CO 2, pH, and HCO 3 - were manipulated. First, we varied the total dissolved inorganic carbon concentration (TIC) (<0 to ∼5 mM) at constant pH, so that ratios of CO2and HCO 3 - remained relatively constant. Second, we varied pH (∼8.54 to 7.52) at constant TIC, so that CO2increased whilst HCO 3 - declined. We found that 14 C-assimilation could be described by the same function of CO2for both approaches, but it showed different dependencies on HCO 3 - when pH was varied at constant TIC than when TIC was varied at constant pH. A numerical model of the carbon-concentrating mechanism (CCM) of Trichodesmium showed that carboxylation rates are modulated by HCO 3 - and pH. The decrease in assimilation of inorganic carbon (Ci) at low CO 2, when TIC was varied, was due to HCO 3 - uptake limitation of the carboxylation rate. Conversely, when pH was varied, Ci assimilation declined due to a high-pH mediated increase in HCO 3 - and CO2leakage rates, potentially coupled to other processes (uncharacterised within the CCM model) that restrict Ci assimilation rates under high-pH conditions.",
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Inorganic carbon and pH dependency of photosynthetic rates in Trichodesmium. / Boatman, Tobias G.; Mangan, Niall M; Lawson, Tracy; Geider, Richard J.

In: Journal of Experimental Botany, Vol. 69, No. 15, 27.06.2018, p. 3651-3660.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Inorganic carbon and pH dependency of photosynthetic rates in Trichodesmium

AU - Boatman, Tobias G.

AU - Mangan, Niall M

AU - Lawson, Tracy

AU - Geider, Richard J.

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AB - Increasing atmospheric CO2concentrations are leading to increases in dissolved CO2and HCO 3 - concentrations and decreases in pH and CO 3 2- in the world's oceans. There remain many uncertainties as to the magnitude of biological responses of key organisms to these chemical changes. In this study, we established the relationship between photosynthetic carbon fixation rates and pH, CO 2, and HCO 3 - concentrations in the diazotroph, Trichodesmium erythraeum IMS101. Inorganic 14 C-assimilation was measured in TRIS-buffered artificial seawater medium where the absolute and relative concentrations of CO 2, pH, and HCO 3 - were manipulated. First, we varied the total dissolved inorganic carbon concentration (TIC) (<0 to ∼5 mM) at constant pH, so that ratios of CO2and HCO 3 - remained relatively constant. Second, we varied pH (∼8.54 to 7.52) at constant TIC, so that CO2increased whilst HCO 3 - declined. We found that 14 C-assimilation could be described by the same function of CO2for both approaches, but it showed different dependencies on HCO 3 - when pH was varied at constant TIC than when TIC was varied at constant pH. A numerical model of the carbon-concentrating mechanism (CCM) of Trichodesmium showed that carboxylation rates are modulated by HCO 3 - and pH. The decrease in assimilation of inorganic carbon (Ci) at low CO 2, when TIC was varied, was due to HCO 3 - uptake limitation of the carboxylation rate. Conversely, when pH was varied, Ci assimilation declined due to a high-pH mediated increase in HCO 3 - and CO2leakage rates, potentially coupled to other processes (uncharacterised within the CCM model) that restrict Ci assimilation rates under high-pH conditions.

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KW - gross photosynthesis

KW - net photosynthesis

KW - ocean acidification

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