Size-fractionated dissolved primary production and carbohydrate composition of the coccolithophore <i>Emiliania huxleyi</i>

Abstract

Abstract. Extracellular release (ER) by phytoplankton is the major source of fresh dissolved organic carbon (DOC) in marine ecosystems and accompanies primary production during all growth phases. Little is known, so far, on size and composition of released molecules, and to which extent ER occurs passively, by leakage, or actively, by exudation. Here, we report on ER by the widespread and bloomforming coccolithophore Emiliania huxleyi grown under steady-state conditions in phosphorus-controlled chemostats (N : P = 29, growth rate of µ = 0.2 d −1 ) at present-day and high-CO 2 concentrations. 14 C incubations were performed to determine primary production (PP), comprised of particulate (PO 14 C) and dissolved organic carbon (DO 14 C). Concentration and composition of particulate combined carbohydrates (pCCHO) and high-molecular-weight (> 1 kDa, HMW) dissolved combined carbohydrates (dCCHO) were determined by ion chromatography. Information on size distribution of ER products was obtained by investigating distinct size classes (< 0.4 µm (DO 14 C), < 0.45 µm (HMWdCCHO), < 1000, < 100 and < 10 kDa) of DO 14 C and HMW-dCCHO. Our results revealed relatively low ER during steady-state growth, corresponding to ∼ 4.5% of primary production, and similar ER rates for all size classes. Acidic sugars had a significant share on freshly produced pCCHO as well as on HMW-dCCHO. While pCCHO and the smallest size fraction (< 10 kDa) of HMW-dCCHO exhibited a similar sugar composition, dominated by high percentage of glucose (74-80 mol %), the composition of HMWdCCHO size classes > 10 kDa was significantly different, with a higher mol % of arabinose. The mol % of acidic sugars increased and that of glucose decreased with increasing size of HMW-dCCHO. We conclude that larger polysaccharides follow different production and release pathways than smaller molecules, potentially serving distinct ecological and biogeochemical functions.

Main drivers of transparent exopolymer particle distribution across the surface Atlantic Ocean

“…These groups are known to be strong TEP producers (Engel, 1998; (b) α = 2.25 and β = 0.65, (Hong et al, 1997); (c) α = 2.27 and β = 0.24, (Yamada et al, 2015); (d) α = 2.06 and β = 0.50, (Ramaiah and Furuya, 2002); (e) α = 1.63 and β = 0.39, (Passow and ; (f) α = 1.63 and β = 0.32, (Corzo et al, 2005); (g) α = 1.08 and β = 0.38, (Ortega-Retuerta et al, 2009b). (Passow and Alldredge, 1994), and besides, previous studies have shown that TEP production rates reach maxima at late stages of the growth cycle, once nutrients have been exhausted (Corzo et al, 2000;Pedrotti et al, 2010;Borchard and Engel, 2015). In the CU, the relatively low Chl a level along with low silicate concentrations suggests that the upwelling-triggered bloom maximum had already passed, which resulted in a high TEP : Chl a ratio.…”

Dissolved organic matter release by phytoplankton in the context of the Dynamic Energy Budget theory

“…6, dashed line) and death (j DOC,D , Fig. 6, dash-dot line), which reflect the passive diffusion of small (<10 kDa) mono and polysacharides, rich in glucose and/or the DOC fraction of the 5 dissolved aminoacids or other phosphorus-containing organic molecules, (Bjørnsen, 1988;Urbani et al, 2005;Flynn et al, 2008;Borchard and Engel, 2015). Moreover, DOC H , is associated with j DOC,R flux (Fig.…”

“…Moreover, DOC H , is associated with j DOC,R flux (Fig. 6, solid line) and reflects the active exudation of DOC due to nutrient limitation, mainly composed of high molecular weight carbohydrates (>10kDa) such as heteropolysacharides or organic carbon associated with the organic forms of nitrogen and phosphate exuded by the cell due to unbalanced growth (Fogg, 1983;Urbani et al, 2005;Flynn et al, 2008;Borchard and Engel, 2015). According to model results, 10 during the nutrient-replete phase, in both scenarios, the main fraction of total DOC (TDOC) is almost entirely comprised by low molecular weight DOC L (mean throughout the nutrient-replete phase: 95 %, Fig.…”

Effect of Organic Fe-Ligands, Released by Emiliania huxleyi, on Fe(II) Oxidation Rate in Seawater Under Simulated Ocean Acidification Conditions: A Modeling Approach

“…In order to explain what ligands condition the oxidation process, it is advised to perform detailed studies of Fe(II) oxidation with individual model ligands. DUA E account for an important fraction of the DOC E , ranging between 1 and 5% of the DOC released by E. huxleyi under different simulated pH conditions (Borchard and Engel, 2015;Samperio-Ramos et al, 2017). Thus, to elucidate the role played by DUA E in the SWEX, the next series of experiments were carried out using a simplified ligand model (i.e., glucuronic acid as DUA) in artificial seawater (ASW).…”

“…In order to explain the key role played by the FeCHO + complex on speciation and overall oxidation rate of Fe(II) in SWEX, we assumed the equilibrium constants and the individual oxidation rate estimated with the DUA model ligand in section Oxidation rate in presence of uronic acids. Uronic acids derived from hexoses (i.e., glucuronic and galacturonic acids) are the main class of sugar acids present in the E. huxleyi exudates (Borchard and Engel, 2015) and, therefore the DUA E , measured in the SWEX ( Figure S2) were considered as hexuronic acids in the model (Table 1). Additionally, to describe the role played by the organic pool ligands in the Fe(II) redox behavior, a non-specific type ligand (denoted as L) was also included in the modeling approach.…”