Acidification increases microbial polysaccharide degradation in the ocean

M Lunau,N Händel,J Piontek,A Engel,C Borchard,M Wurst

doi:10.5194/bg-7-1615-2010

Abstract

Abstract. With the accumulation of anthropogenic carbon dioxide (CO2), a proceeding decline in seawater pH has been induced that is referred to as ocean acidification. The ocean's capacity for CO2 storage is strongly affected by biological processes, whose feedback potential is difficult to evaluate. The main source of CO2 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 phytoplankton-derived 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 CO2 production in the future ocean.

Highlights

Organic matter in the ocean is one of the largest dynamic carbon reservoirs on Earth that interacts with atmospheric CO2 concentrations on time scales of 1000 to 10 000 years (Hedges, 1992)
In CultExp I and CultExp II, experiments conducted with organic matter freshly produced by E. huxleyi, the higher loss of polysaccharides at lowered pH coincided with a higher loss of particulate organic carbon (POC) (Fig. 1)
Because a light/dark cycle was applied and a low but constant nutrient supply was provided during this experiment, concentrations of polysaccharides and POC are the net result of phytoplankton production and of simultaneous bacterial degradation

Summary

Introduction

Organic matter in the ocean is one of the largest dynamic carbon reservoirs on Earth that interacts with atmospheric CO2 concentrations on time scales of 1000 to 10 000 years (Hedges, 1992). Polysaccharides are a major component of marine organic matter and comprise up to 15% of sinking and suspended particulate organic carbon (Tanoue and Handa, 1987; Bhosle et al, 1992; Hernes et al, 1996) and up to 32% of dissolved organic carbon (DOC) (Pakulski and Benner, 1994). They can account for more than 50% of total phytoplankton primary production (Baines and Pace, 1991) and provide a labile energy and carbon source to heterotrophic bacterioplankton in form of structural cell components, storage glucan, and phytoplankton exudates.

Methods

Results

Conclusion