Journal
AQUATIC MICROBIAL ECOLOGY
Volume 66, Issue 3, Pages 211-222Publisher
INTER-RESEARCH
DOI: 10.3354/ame01576
Keywords
Cyanobacteria; North Atlantic; Sargasso Sea; Acidification; Nitrogen fixation; Photosynthesis
Categories
Funding
- NSF
- NSF award [OCE-0752161]
- National Science Foundation Chemical and Biological Oceanography Programs [OCE-0752366]
- Division Of Ocean Sciences
- Directorate For Geosciences [0825192] Funding Source: National Science Foundation
- Emerging Frontiers
- Direct For Biological Sciences [1040965] Funding Source: National Science Foundation
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Cyanobacteria make significant contributions to global carbon and nitrogen cycling, particularly in the oligotrophic subtropical and tropical gyres. The present study examined short-term (days) physiological and acclimation responses of natural cyanobacterial populations to changes in pH/pCO(2) spanning the last glacial minimum, similar to 8.4/similar to 150 ppm, to projected year 2100 values of similar to 7.8/similar to 800 ppm. Fe- and P-replete colonies of Trichodesmium increased N-2-fixation rates (nmol N colony(-1) h(-1)) at pH 7.8 by 54% (range 6 to 156%) over ambient pH/pCO(2) conditions, while N-2-fixation at pH/pCO(2) 8.4 was 21% (range 6 to 65%) lower than at ambient pH/pCO2; a similar pattern was observed when the rates were normalized to colony C. C-fixation rates were on average 13% (range -72 to 112%) greater at low pH than at ambient pH and 37% (-53 to 23%) greater than at high pH. Whole community assemblages dominated by Prochlorococcus and Synechococcus (47 to 95% of autotrophic biomass), whether nutrient-replete or P-limited, did not show a clear response of C-fixation rates to changes in pH/pCO(2). Comparison of initial and final C-fixation responses across pH/pCO(2) treatments suggests rapid acclimation of cellular physiology to new pH/pCO(2) conditions. Changes in cell size and pigment content for Prochlorococcus and Synechococcus were minor and did not vary in a consistent manner with changes in pH/pCO(2). These results for natural populations of all 3 cyanobacteria concur with previous research and suggest that one important response to changes in ocean pH and pCO(2) might be an increase in N-2 and C fixation by Trichodesmium under nutrient-replete conditions. The response of single-cell cyanobacteria to changes in pH/pCO(2) will likely be indirect and controlled by the response to other variables, such as nutrients.
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