Variability in the organic ligands released by <em>Emiliania huxleyi</em> under simulated ocean acidification conditions

Guillermo Samperio-Ramos; J. Magdalena Santana-Casiano; Melchor González-Dávila; Sonia Ferreira; Manuel A. Coimbra; Guillermo Samperio-Ramos; J. Magdalena Santana-Casiano; Melchor González-Dávila; Sonia Ferreira; Manuel A. Coimbra

doi:10.3934/environsci.2017.6.788

AIMS Environmental Science

2017, Volume 4, Issue 6: 788-808. doi: 10.3934/environsci.2017.6.788

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Variability in the organic ligands released by Emiliania huxleyi under simulated ocean acidification conditions

1.
Institute of Oceanography and Global change, University of Las Palmas de Gran Canaria, Tafira Campus, 35017 Las Palmas, Spain
2.
QOPNA, Department of Chemistry, University of Aveiro, Portugal

Received: 01 August 2017 Accepted: 15 December 2017 Published: 25 December 2017

The variability in the extracellular release of organic ligands by Emiliania huxleyi under four different pCO₂ scenarios (225, 350, 600 and 900 μatm), was determined. Growth in the batch cultures was promoted by enriching them only with major nutrients and low iron concentrations. No chelating agents were added to control metal speciation. During the initial (IP), exponential (EP) and steady (SP) phases, extracellular release rates, normalized per cell and day, of dissolved organic carbon (DOC_ER), phenolic compounds (PhC_ER), dissolved combined carbohydrates (DCCHO_ER) and dissolved uronic acids (DUA_ER) in the exudates were determined.
The growth rate decreased in the highest CO₂ treatment during the IP (＜48 h), but later increased when the exposure was longer (more than 6 days). DOC_ER did not increase significantly with high pCO₂. Although no relationship was observed between DCCHO_ER and the CO₂ conditions, DCCHO was a substantial fraction of the freshly released organic material, accounting for 18% to 37%, in EP, and 14% to 23%, in SP, of the DOC produced. Growth of E. huxleyi induced a strong response in the PhC_ER and DUA_ER. While in EP, PhC_ER were no detected, the DUA_ER remained almost constant for all CO₂ treatments. Increases in the extracellular release of these organic ligands during SP were most pronounced under high pCO₂ conditions. Our results imply that, during the final growth stage of E. huxleyi, elevated CO₂ conditions will increase its excretion of acid polysaccharides and phenolic compounds, which may affect the biogeochemical behavior of metals in seawater.
- Emiliania huxleyi; acidification; extracellular release; phenolic compounds dissolved uronic acids
Citation: Guillermo Samperio-Ramos, J. Magdalena Santana-Casiano, Melchor González-Dávila, Sonia Ferreira, Manuel A. Coimbra. Variability in the organic ligands released by Emiliania huxleyi under simulated ocean acidification conditions[J]. AIMS Environmental Science, 2017, 4(6): 788-808. doi: 10.3934/environsci.2017.6.788

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Abstract

The variability in the extracellular release of organic ligands by Emiliania huxleyi under four different pCO₂ scenarios (225, 350, 600 and 900 μatm), was determined. Growth in the batch cultures was promoted by enriching them only with major nutrients and low iron concentrations. No chelating agents were added to control metal speciation. During the initial (IP), exponential (EP) and steady (SP) phases, extracellular release rates, normalized per cell and day, of dissolved organic carbon (DOC_ER), phenolic compounds (PhC_ER), dissolved combined carbohydrates (DCCHO_ER) and dissolved uronic acids (DUA_ER) in the exudates were determined.
The growth rate decreased in the highest CO₂ treatment during the IP (＜48 h), but later increased when the exposure was longer (more than 6 days). DOC_ER did not increase significantly with high pCO₂. Although no relationship was observed between DCCHO_ER and the CO₂ conditions, DCCHO was a substantial fraction of the freshly released organic material, accounting for 18% to 37%, in EP, and 14% to 23%, in SP, of the DOC produced. Growth of E. huxleyi induced a strong response in the PhC_ER and DUA_ER. While in EP, PhC_ER were no detected, the DUA_ER remained almost constant for all CO₂ treatments. Increases in the extracellular release of these organic ligands during SP were most pronounced under high pCO₂ conditions. Our results imply that, during the final growth stage of E. huxleyi, elevated CO₂ conditions will increase its excretion of acid polysaccharides and phenolic compounds, which may affect the biogeochemical behavior of metals in seawater.

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