Ocean acidification modifies biomolecule composition in organic matter through complex interactions

Julia Grosse,Anja Engel,Sonja Endres

doi:10.1038/s41598-020-77645-3

Julia Grosse, Anja Engel + Show 1 more

Open Access

https://doi.org/10.1038/s41598-020-77645-3

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Abstract

The main source of marine organic carbon (OC) is autotrophic production, while heterotrophic degradation is its main sink. Increased anthropogenic CO2 release leads to ocean acidification and is expected to alter phytoplankton community composition, primary production rates and bacterial degradation processes in the coming decades with potential consequences for dissolved and particulate OC concentration and composition. Here we investigate effects of increased pCO2 on dissolved and particulate amino acids (AA) and carbohydrates (CHO), in arctic and sub-arctic planktonic communities in two large-scale mesocosm experiments. Dissolved AA concentrations responded to pCO2/pH changes during early bloom phases but did not show many changes after nutrient addition. A clear positive correlation in particulate AA was detected in post-bloom phases. Direct responses in CHO concentrations to changing pCO2/pH were lacking, suggesting that observed changes were rather indirect and dependent on the phytoplankton community composition. The relative composition of AA and CHO did not change as a direct consequence of pCO2 increase. Changes between bloom phases were associated with the prevailing nutrient status. Our results suggest that biomolecule composition will change under future ocean conditions but responses are highly complex, and seem to be dependent on many factors including bloom phase and sampling site.

Highlights

The main source of marine organic carbon (OC) is autotrophic production, while heterotrophic degradation is its main sink
During two mesocosm campaigns we determined the responses of amino acids (AA) and CHO quantity and quality as a response to C O2 addition
The quantity of AA and CHO is controlled by biomass production and their subsequent release into the dissolved organic carbon (DOC) p ool[32,33]

Summary

Introduction

The main source of marine organic carbon (OC) is autotrophic production, while heterotrophic degradation is its main sink. Increased anthropogenic CO2 release leads to ocean acidification and is expected to alter phytoplankton community composition, primary production rates and bacterial degradation processes in the coming decades with potential consequences for dissolved and particulate OC concentration and composition. Ocean acidification promotes the uptake of inorganic carbon by phytoplankton leading to higher primary production rates, and can subsequently result in an increased release of dissolved organic matter (DOM)[3,4,5]. The molecular composition of marine DOM is highly complex, changes with depth, season, and region[6], and only a few compounds can be identified in terms of structure by chemical analysis These compounds include labile and semi-labile components, such as carbohydrates (CHO), amino acids (AA), proteins, peptides, lipids, and nucleic acids, all of which are enriched in freshly produced D OM6–8. These particles provide a surface for bacteria to attach and grow, and can become hotspots of microbial

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