Colorado mountains
From Long-Term Data to Understanding: Toward a Predictive Ecology
2015 LTER ASM Estes Park, CO - August 30 - September 2, 2015

Elevated pCO2 Increases Respiration of DOC by Natural Bacterioplankton

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Anna James
Craig Carlson
Uta Passow
Mark Brzezinski
Rachel Parsons
Jennifer N Trapani

The size of the oceanic dissolved organic carbon (DOC) and atmospheric carbon dioxide (CO2) reservoirs are comparable at ~700 PgC (Hansell and Carlson 2015) such that small changes in DOC removal or production have significant implications with regards to CO2 exchange between the ocean and atmosphere. Heterotrophic bacterioplankton are the dominant consumers of DOC in the ocean. DOC that escapes or resists consumption by bacterioplankton can accumulate in the surface ocean and be transported to depth by physical processes (vertical export), where it is removed from exchange with the atmosphere on a variety of timescales. Therefore, factors that affect the ability of heterotrophic bacterioplankton to consume DOC (i.e. DOC bioavailability) can impact the rate of DOC accumulation and the role of DOC in vertical export. Once DOC is consumed, the growth efficiency of heterotrophic bacterioplankton communities dictates how much organic carbon is retained within marine food webs versus how much is respired to CO2. The present study investigated the direct effects of elevated pCO2 on the consumption of DOC and the efficiency of its use by marine bacterioplankton. Elevated pCO2 enhanced both the rate and magnitude of DOC consumption by bacterioplankton and decreased bacterial growth efficiencies relative to responses under low and ambient pCO2 conditions. These results suggest that short-term perturbations of elevated pCO2 may increase both DOC bioavailability and bacterial respiration, ultimately decreasing the effectiveness of DOC as a sink of carbon in the ocean and enhancing the respiratory loss of DOC to CO2.

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