Mean TOC concentration and mean bacterioplankton abundance for Sargasso Sea and Santa Barbara Channel CNP- and natural-DOC experiments.

<p>Mean TOC concentration (± SD) and mean bacterioplankton abundance (BA; ± SD) averaged across duplicate incubations through time and as a function of <i>p</i>CO₂ for natural bacterioplankton assemblages incubated with: A: Natural DOC, Sargasso Sea Exp. #1A; B: Natural DOC, South Pacific Subtropical Gyre Exp. #7; C: Natural DOC, Santa Barbara Channel Exp. #2A; D. CNP, Sargasso Sea Exp. #1B; E. CNP, Santa Barbara Channel Exp. #2B. For treatments at all sites, red denotes elevated <i>p</i>CO_2, while blue denotes ambient <i>p</i>CO₂ in the Sargasso Sea experiment and pre-industrial <i>p</i>CO₂ in the Santa Barbara Channel and South Pacific Subtropical Gyre experiments. Squares represent TOC (μmol C L^-1) while triangles denote BA (10⁶ cells mL^-1) over the course of the incubation.</p

Mean TOC concentration and mean bacterioplankton abundance for Santa Barbara Channel phytoplankton-DOC experiments.

<p>Mean TOC concentration (± SD) and mean bacterioplankton abundance (BA; ± SD) averaged across duplicate incubations through time and as a function of <i>p</i>CO₂ for natural bacterioplankton assemblages in the Santa Barbara Channel experiments incubated with: A: <i>D</i>. <i>fragilissimus</i>-derived DOC, Exp. #3; B: <i>T</i>. <i>weissflogii</i>-derived DOC, Exp. #4; C: <i>T</i>. <i>weissflogii</i>-derived DOC, Exp. #5A; D: <i>C</i>. <i>socialis-</i>derived DOC, Exp. #5B; E: <i>A</i>. <i>glacialis</i>-derived DOC, Exp. #5C; F: <i>E</i>. <i>huxleyi</i>-derived DOC, Exp. #6. Red denotes elevated <i>p</i>CO_2, while blue denotes low (250 ppm) <i>p</i>CO₂. Squares represent TOC (μmol C L^-1) while triangles denote bacterioplankton abundance (10⁶ cells mL^-1) over the course of the incubation.</p

Cell-specific TOC removal.

<p>Mean (± SD) cell-specific TOC removal averaged across duplicate incubations and calculated as the change in TOC divided by the concurrent change in bacterioplankton abundance (BA) from the start of the incubations to stationary phase. Numbers on X-axis label refer to the experiment number (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0173145#pone.0173145.t001" target="_blank">Table 1</a>). Colors denote cell-specific TOC removal at elevated <i>p</i>CO₂ (red) and low (ambient or pre-industrial) <i>p</i>CO₂ (blue). Only experiments where a change in TOC was resolvable are shown.</p

Summary of experimental conditions and results.

<p>Summary of experimental conditions and results.</p

Bacterioplankton Carbon Demand.

<p>Mean (± SD) bacterioplankton carbon demand (BCD) averaged across duplicate incubations and calculated as the change in DOC from T₀ to stationary phase. Change in DOC was calculated as TOC less the carbon content of bacterioplankton biomass (using a carbon conversion factor of 30 fg C cell^-1 for bacterioplankton in the Santa Barbara Channel and 10 fg C cell^-1 for bacterioplankton in the Sargasso Sea and South Pacific Subtropical Gyre). Colors denote BCD at elevated <i>p</i>CO₂ (red) and low (ambient or pre-industrial) <i>p</i>CO₂ (blue). Numbers refer to the experiment number (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0173145#pone.0173145.t001" target="_blank">Table 1</a>). Only experiments where a change in TOC was resolvable are shown.</p

Mean TOC concentration and mean bacterioplankton abundance for phytoplankton-DOC South Pacific Subtropical Gyre experiments.

<p>Mean TOC concentration (± SD) and mean bacterial abundance (BA; ± SD) averaged across duplicate incubations through time and as a function of <i>p</i>CO₂ for natural bacterioplankton assemblages in the South Pacific Subtropical Gyre experiments incubated with <i>E</i>. <i>huxleyi</i>-derived DOC: A: Exp. #7B; B: Exp. #8B; C: Exp. #9B. The same experimental design was used for these experiments (note that only the amended treatments are shown). Red denotes elevated <i>p</i>CO_2, while blue denotes low (250 ppm) <i>p</i>CO₂. Squares represent TOC (μmol C L^-1) while triangles denote BA (10⁶ cells mL^-1) over the course of the incubation.</p

Effects of <i>p</i>CO₂ on bacterioplankton removal of organic carbon.

<p>A depiction of the short-term effects of <i>p</i>CO₂ on the use of DOC by bacterioplankton communities in ocean surface waters. Elevated <i>p</i>CO₂ may increase the use of DOC at lowered bacterioplankton growth efficiencies by natural bacterioplankton communities, increasing the respiration of DOC and decreasing the magnitude of accumulated DOC in these regions, ultimately decreasing the amount of DOC available for vertical export (i.e. export potential). Arrows represent the flux of carbon between identified pools. Red represents processes occurring under elevated (> ambient) <i>p</i>CO₂ conditions while blue represents processes occurring under low (ambient or pre-industrial) <i>p</i>CO₂ conditions. Dotted black arrows denote the flux of carbon between identified pools at low <i>p</i>CO₂ to enable an easy comparison between elevated and low <i>p</i>CO₂ fluxes.</p

Bacterioplankton growth efficiency.

<p>Mean (± SD) Bacterioplankton growth efficiency averaged across duplicate incubations and calculated as the change in bacterioplankton biomass carbon (using a carbon conversion factor of 30 fg C cell^-1 for bacterioplankton in the Santa Barbara Channel and 10 fg C cell^-1 for bacterioplankton in the Sargasso Sea and South Pacific Subtropical Gyre) divided by the concurrent change in DOC from T₀ to stationary phase. Colors denote bacterioplankton growth efficiency at elevated <i>p</i>CO₂ (red) and low (ambient or pre-industrial) <i>p</i>CO₂ (blue). Numbers refer to the experiment number (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0173145#pone.0173145.t001" target="_blank">Table 1</a>). Only experiments where a change in TOC was resolvable are shown.</p

P values for bacterioplankton carbon removal and growth dynamics.

<p>P values for bacterioplankton carbon removal and growth dynamics.</p