Acidification increases microbial polysaccharide degradation in the ocean

Abstract

Abstract.With the accumulation of anthropogenic carbon dioxide (CO 2 ), a proceeding decline in seawater pH has been induced that is referred to as ocean acidification. The ocean's capacity for CO 2 storage is strongly affected by biological processes, whose feedback potential is difficult to evaluate. The main source of CO 2 in the ocean is the decomposition and subsequent respiration of organic molecules by heterotrophic bacteria. However, very little is known about potential effects of ocean acidification on bacterial degradation activity. This study reveals that the degradation of polysaccharides, a major component of marine organic matter, by bacterial extracellular enzymes was significantly accelerated during experimental simulation of ocean acidification. Results were obtained from pH perturbation experiments, where rates of extracellular α-and β-glucosidase were measured and the loss of neutral and acidic sugars from phytoplanktonderived polysaccharides was determined. Our study suggests that a faster bacterial turnover of polysaccharides at lowered ocean pH has the potential to reduce carbon export and to enhance the respiratory CO 2 production in the future ocean.

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

“…The HMW-CCHO was thus to some extent subject to bacterial reworking, and the high proportions of Ara may be a result of the selective removal of other monomers. In accordance with the findings of Aluwihare (1999), concentration of Ara in dCCHO remained unchanged during a degradation experiment with the same E. huxleyi strain investigated here, while dCCHO was reduced by ∼ 60 % (Piontek et al, 2010;J. Piontek, personal communication, 2014).…”

“…Composition of HMW-dCCHO in seawater is usually determined on the basis of monomeric sugars after hydrolysis of the polymer chains, and resembles either phytoplankton biomass itself (Pakulski and Benner, 1994;Børsheim et al, 1999) or extracellular CCHO from phytoplankton cultures (Biersmith and Benner, 1998;Aluwihare and Repeta, 1999;Aluwihare et al, 2002). The latter are usually comprised of neutral hexoses, pentoses and deoxy sugars like glucose, galactose and mannose; by amino sugars like glucosamine and galactosamine; and by uronic acids, e.g., galacturonic acid and glucuronic acid (Aluwihare et al, 1997;Biersmith and Benner, 1998;Aluwihare and Repeta, 1999;Engel et al 2010, Borchard and.…”

CO<sub>2</sub> increases <sup>14</sup>C primary production in an Arctic plankton community

“…However, higher export fluxes and therewith a higher loss of organic matter from the water column in the high pCO 2 bags were not directly observed during this study . (ii) Recent studies suggest that bacterial processes such as organic matter solubilization and hydrolysis by extracellular enzymes are enhanced by ocean acidification (Grossart et al, 2006;Piontek et al, 2010Piontek et al, , 2013Yamada and Suzumura, 2010;Endres et al, 2013). Higher activities of hydrolytic enzymes were observed at reduced pH also during side-experiments of this study (Piontek et al, 2013), and may have resulted in faster degradation of organic matter, including autotrophic biomass.…”

Dissolved organic matter (DOM) release by phytoplankton in the contemporary and future ocean

“…The complexity of these relationships is shown by recent research. For example, extracellular glucosidase activity was enhanced under conditions simulating ocean acidification, leading to a greater degradation of algalderived polysaccharides (Piontek et al, 2010). Other work has found that acidification had negligible effects on some enzymes and reduces the activity of others (Yamada & Suzumura, 2010).…”