Picocyanobacteria and deep-ocean fluorescent dissolved organic matter share similar optical properties

Zhao Zhao,Nianzhi Jiao,Feng Chen,Qinglu Zeng,Xiaoting Fang,Michael Gonsior,Hope Ianiri,Stephen Timko,Jenna Luek,Norbert Hertkorn,Philippe Schmitt-Kopplin

doi:10.1038/ncomms15284

Abstract

Marine chromophoric dissolved organic matter (CDOM) and its related fluorescent components (FDOM), which are widely distributed but highly photobleached in the surface ocean, are critical in regulating light attenuation in the ocean. However, the origins of marine FDOM are still under investigation. Here we show that cultured picocyanobacteria, Synechococcus and Prochlorococcus, release FDOM that closely match the typical fluorescent signals found in oceanic environments. Picocyanobacterial FDOM also shows comparable apparent fluorescent quantum yields and undergoes similar photo-degradation behaviour when compared with deep-ocean FDOM, further strengthening the similarity between them. Ultrahigh-resolution mass spectrometry (MS) and nuclear magnetic resonance spectroscopy reveal abundant nitrogen-containing compounds in Synechococcus DOM, which may originate from degradation products of the fluorescent phycobilin pigments. Given the importance of picocyanobacteria in the global carbon cycle, our results indicate that picocyanobacteria are likely to be important sources of marine autochthonous FDOM, which may accumulate in the deep ocean.

Highlights

Marine chromophoric dissolved organic matter (CDOM) and its related fluorescent components (FDOM), which are widely distributed but highly photobleached in the surface ocean, are critical in regulating light attenuation in the ocean
As major primary producers in the World’s Oceans[3], picocyanobacteria contribute to the marine dissolved organic matter (DOM) pool in the surface ocean[4,5] and to particles sinking to the deep ocean
This study uses a combination of spectroscopic (ultraviolet–Vis absorbance, fluorescence and nuclear magnetic resonance (NMR)) and spectrometric techniques, as well as apparent fluorescence quantum yield (QY) and photochemical degradation experiments to investigate the optical properties and molecular composition of picocyanobacteria-derived DOM, which can be considered as a conceivable source of marine autochthonous CDOM (FDOM), that is efficiently transported to the deep sea via picocyanobacteria cells packed in faecal pellets of zooplankton[8,9]

Summary

Introduction

Marine chromophoric dissolved organic matter (CDOM) and its related fluorescent components (FDOM), which are widely distributed but highly photobleached in the surface ocean, are critical in regulating light attenuation in the ocean. This study uses a combination of spectroscopic (ultraviolet–Vis absorbance, fluorescence and nuclear magnetic resonance (NMR)) and spectrometric (ultrahigh-resolution MS) techniques, as well as apparent fluorescence QYs and photochemical degradation experiments to investigate the optical properties and molecular composition of picocyanobacteria-derived DOM, which can be considered as a conceivable source of marine autochthonous CDOM (FDOM), that is efficiently transported to the deep sea via picocyanobacteria cells packed in faecal pellets of zooplankton[8,9].

Results

Conclusion