Oxidation state of bioavailable dissolved organic matter influences bacterioplankton respiration and growth efficiency

Oxygen consumption by oceanic microbes can predict respiration (CO₂ production) but requires an assumed respiratory quotient (RQ; ΔO₂ /ΔCO₂). Measured apparent RQs (ARQs) can be impacted by various processes, including nitrification and changes in dissolved organic matter (DOM) composition, leading to discrepancies between ARQ and actual RQ. In DOM remineralization experiments conducted in the eastern North Atlantic Ocean, ARQs averaged 1.39 ± 0.14, similar to predictions for complete consumption of plankton biomass. DOM removed with an elevated nominal oxidation state (i.e., more oxidized DOM), detected by liquid chromatography-tandem mass spectrometry, coincided with increased hydrolyzable amino acid removal, increased ARQs and bacterioplankton respiration (BR), and a decreased bacterioplankton growth efficiency (BGE). Across experiments, evidence emerged that DOM partial oxidation and nitrification elevate BR relative to bacterial consumption of plankton-derived carbon. These rare synoptic measurements of interrelated variables reveal complex biochemical and cellular processes underlying variability in large-scale CO₂ production estimates.

Presentation Preference: Oral

Primary Presenter: Brandon Stephens, National Taiwan University (bstephens@ntu.edu.tw)

Authors:

Paolo Stincone, University of Tuebingen  (paolo.stincone88@gmail.com)

Daniel Petras, University of California, Riverside  (dpetras@ucr.edu)

Chance English, University of California, Santa Barbara  (cje@ucsb.edu)

Keri Opalk, University of California, Santa Barbara  (keri.opalk@ucsb.edu)

Stephen Giovannoni, Oregon State University  (steve.giovannoni@oregonstate.edu)

Craig Carlson, University of California, Santa Barbara  (craig_carlson@ucsb.edu)