Potential bioavailability of organic matter from atmospheric particles to marine heterotrophic bacteria

Kahina Djaoudi,Christos Panagiotopoulos,Sandra Nunige,Dominique Lefèvre,Servanne Chevaillier,Marc Tedetti,France Van Wambeke,Aude Barani,Amel Nouara,Elvira Pulido-Villena,Nagib Bhairy,Mohamed Labiadh,Thierry Henry Des Tureaux,Karine Desboeufs

doi:10.5194/bg-17-6271-2020

Abstract

Abstract. The surface ocean receives important amounts of organic carbon from atmospheric deposition. The degree of bioavailability of this source of organic carbon will determine its impact on the marine carbon cycle. In this study, the potential availability of dissolved organic carbon (DOC) leached from both desert dust and anthropogenic aerosols to marine heterotrophic bacteria was investigated. The experimental design was based on 16 d incubations, in the dark, of a marine bacterial inoculum into artificial seawater amended with water-soluble Saharan dust (D treatment) and anthropogenic (A treatment) aerosols, so that the initial DOC concentration was similar between treatments. Glucose-amended (G) and non-amended (control) treatments were run in parallel. Over the incubation period, an increase in bacterial abundance (BA) and bacterial production (BP) was observed first in the G treatment, followed then by the D and finally A treatments, with bacterial growth rates significantly higher in the G and D treatments than the A treatment. Following this growth, maxima of BP reached were similar in the D (879 ± 64 ng C L−1 h−1; n=3) and G (648 ± 156 ng C L−1 h−1; n=3) treatments and were significantly higher than in the A treatment (124 ng C L−1 h−1; n=2). The DOC consumed over the incubation period was similar in the A (9 µM; n=2) and D (9 ± 2 µM; n=3) treatments and was significantly lower than in the G treatment (22 ± 3 µM; n=3). Nevertheless, the bacterial growth efficiency (BGE) in the D treatment (14.2 ± 5.5 %; n=3) compared well with the G treatment (7.6 ± 2 %; n=3), suggesting that the metabolic use of the labile DOC fraction in both conditions was energetically equivalent. In contrast, the BGE in the A treatment was lower (1.7 %; n=2), suggesting that most of the used labile DOC was catabolized. The results obtained in this study highlight the potential of aerosol organic matter to sustain the metabolism of marine heterotrophs and stress the need to include this external source of organic carbon in biogeochemical models for a better constraining of the carbon budget.

Highlights

Marine dissolved organic matter (DOM) is the largest reservoir of reduced carbon in the ocean
A lag time period was recorded in the G treatment, it was shorter than that in the A and D treatments, which could suggest a non-immediate bioavailability of aerosol organic matter compared to glucose
Organic carbon derived from anthropogenic aerosols exhibited a higher solubility (32 %) with respect to Saharan dust (13 %)

Summary

Introduction

Marine dissolved organic matter (DOM) is the largest reservoir of reduced carbon in the ocean. At the global scale, dissolved organic carbon (DOC) export from the surface to the deep ocean contributes to 20 % of the total organic carbon flux (Hansell et al, 2009). This percentage reaches more than 50 % of the total carbon export in the oligotrophic oceans Djaoudi et al.: Marine bioavailability of atmospheric organic matter al., 1994; Guyennon et al, 2015; Letscher and Moore, 2015; Roschan and DeVries, 2017; Bif et al, 2018)

Methods

Results

Discussion

Conclusion