Experimental assessment of diazotroph responses to elevated seawater pCO2 in the North Pacific Subtropical Gyre. Issue 6 (10th June 2014)

• Record Type: Journal Article
• Authors: Böttjer, Daniela; Karl, David M.; Letelier, Ricardo M.; Viviani, Donn A.; Church, Matthew J.
• Is Part Of: Global biogeochemical cycles. Volume 28:Issue 6(2014:Jun.)
• Page Start: 601
• Page End: 616
• Publication Date: 2014-06-10
• Subjects: Biogeochemical cycles -- Periodicals; Electronic journals; 577.1405
• DOI: 10.1002/2013GB004690
• Languages: English
• ISSNs: 0886-6236

Abstract

<abstract abstract-type="main"> <title>Abstract</title> <p>We examined short‐term (24–72 h) responses of naturally occurring marine N<sub>2</sub> fixing microorganisms (termed diazotrophs) to abrupt increases in the partial pressure of carbon dioxide (<italic>p</italic>CO<sub>2</sub>) in seawater during nine incubation experiments conducted between May 2010 and September 2012 at Station ALOHA (A Long‐term Oligotrophic Habitat Assessment) (22°45′N, 158°W) in the North Pacific Subtropical Gyre (NPSG). Rates of N<sub>2</sub> fixation, nitrogenase (<italic>nifH</italic>) gene abundances and transcripts of six major groups of cyanobacterial diazotrophs (including both unicellular and filamentous phylotypes), and rates of primary productivity (as measured by <sup>14</sup>C‐bicarbonate assimilation into plankton biomass) were determined under contemporary (~390 ppm) and elevated <italic>p</italic>CO<sub>2</sub> conditions (~1100 ppm). Quantitative polymerase chain reaction (QPCR) amplification of planktonic <italic>nifH</italic> genes revealed that unicellular cyanobacteria phylotypes dominated gene abundances during these experiments. In the majority of experiments (seven out of nine), elevated <italic>p</italic>CO<sub>2</sub> did not significantly influence rates of dinitrogen (N<sub>2</sub>) fixation or primary productivity (two‐way analysis of variance (ANOVA), <italic>P</italic> > 0.05). During two experiments, rates of N<sub>2</sub> fixation and primary productivity were significantly lower (by 79 to 82% and 52 to 72%, respectively) in the elevated <italic>p</italic>CO<sub>2</sub> treatments relative to the ambient controls (two‐way ANOVA, <italic>P</italic> < 0.05). QPCR amplification of <italic>nifH</italic> genes and gene transcripts revealed that diazotroph abundances and <italic>nifH</italic> gene expression were largely unchanged by the perturbation of the seawater <italic>p</italic>CO<sub>2</sub>. Our results suggest that naturally occurring N<sub>2</sub> fixing plankton assemblages in the NPSG are relatively resilient to large, short‐term increases in <italic>p</italic>CO<sub>2</sub>.</p> </abstract>