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Low microbial respiration of leucine at ambient oceanic concentration in the mixed layer of the central Atlantic Ocean

Low microbial respiration of leucine at ambient oceanic concentration in the mixed layer of the central Atlantic Ocean
Low microbial respiration of leucine at ambient oceanic concentration in the mixed layer of the central Atlantic Ocean
Bacterioplankton are the primary consumers of dissolved organic matter in the ocean, thus the quantification of bacterioplankton production (BP) is essential to our understanding of carbon cycling in the largest ecosystems on Earth. We compared BP, measured as the rate of 14C-leucine or 3H-leucine uptake at close to saturating concentration (20 nmol L?1), with ambient uptake measured from dilution bioassays. We hypothesized that saturation with leucine would lead to its respiration as a carbon source, thereby not truly representing ambient BP. Seawater was collected from the photic zone throughout the Atlantic Ocean. Respiration as a proportion of total consumption (uptake + respiration) of close to ambient (0.4 nmol L?1) and close to saturating (20 nmol L?1) 14C-leucine concentrations were compared. Saturating 3H-leucine additions overestimated ambient leucine uptake at low rates (200% ± 100% ambient) and underestimated uptake at high rates (90% + 20% ambient). The proportion of total leucine uptake that was respired was threefold higher for 20 nmol L?1 14C-leucine additions than 0.4 nmol L?1 14C-leucine additions (15% ± 8% and 5% ± 4%, respectively). Consequently, microbial efficiency of leucine assimilation—an indicator of bacterioplankton growth efficiency—was significantly higher and more stable at close to ambient 14C-leucine additions than at saturating concentrations (95% ± 4% and 85% ± 8%, respectively). Thus, saturation of oligotrophic open Atlantic Ocean bacterioplankton with leucine, or other molecules indicative of microbial metabolism, leads to the measurement of a response to a nutrient addition, rather than an ambient measurement.
0024-3590
1597-1604
Hill, Polly G.
03ff729d-1c24-45f8-8bf7-3bcc9bf882e9
Warwick, Phillip E.
f2675d83-eee2-40c5-b53d-fbe437f401ef
Zubkov, Mikhail V.
b1dfb3a0-bcff-430c-9031-358a22b50743
Hill, Polly G.
03ff729d-1c24-45f8-8bf7-3bcc9bf882e9
Warwick, Phillip E.
f2675d83-eee2-40c5-b53d-fbe437f401ef
Zubkov, Mikhail V.
b1dfb3a0-bcff-430c-9031-358a22b50743

Hill, Polly G., Warwick, Phillip E. and Zubkov, Mikhail V. (2013) Low microbial respiration of leucine at ambient oceanic concentration in the mixed layer of the central Atlantic Ocean. Limnology and Oceanography, 58 (5), 1597-1604. (doi:10.4319/lo.2013.58.5.1597).

Record type: Article

Abstract

Bacterioplankton are the primary consumers of dissolved organic matter in the ocean, thus the quantification of bacterioplankton production (BP) is essential to our understanding of carbon cycling in the largest ecosystems on Earth. We compared BP, measured as the rate of 14C-leucine or 3H-leucine uptake at close to saturating concentration (20 nmol L?1), with ambient uptake measured from dilution bioassays. We hypothesized that saturation with leucine would lead to its respiration as a carbon source, thereby not truly representing ambient BP. Seawater was collected from the photic zone throughout the Atlantic Ocean. Respiration as a proportion of total consumption (uptake + respiration) of close to ambient (0.4 nmol L?1) and close to saturating (20 nmol L?1) 14C-leucine concentrations were compared. Saturating 3H-leucine additions overestimated ambient leucine uptake at low rates (200% ± 100% ambient) and underestimated uptake at high rates (90% + 20% ambient). The proportion of total leucine uptake that was respired was threefold higher for 20 nmol L?1 14C-leucine additions than 0.4 nmol L?1 14C-leucine additions (15% ± 8% and 5% ± 4%, respectively). Consequently, microbial efficiency of leucine assimilation—an indicator of bacterioplankton growth efficiency—was significantly higher and more stable at close to ambient 14C-leucine additions than at saturating concentrations (95% ± 4% and 85% ± 8%, respectively). Thus, saturation of oligotrophic open Atlantic Ocean bacterioplankton with leucine, or other molecules indicative of microbial metabolism, leads to the measurement of a response to a nutrient addition, rather than an ambient measurement.

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More information

Published date: September 2013
Organisations: Geochemistry, Marine Biogeochemistry

Identifiers

Local EPrints ID: 358204
URI: http://eprints.soton.ac.uk/id/eprint/358204
ISSN: 0024-3590
PURE UUID: ad0a36c3-1bf3-4375-a239-d8ab26482baf
ORCID for Phillip E. Warwick: ORCID iD orcid.org/0000-0001-8774-5125

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Date deposited: 01 Oct 2013 09:42
Last modified: 15 Mar 2024 02:49

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Contributors

Author: Polly G. Hill
Author: Mikhail V. Zubkov

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