AME 32:229-237 (2003)  -  doi:10.3354/ame032229

P-limitation of respiration in the Sargasso Sea and uncoupling of bacteria from P-regeneration in size-fractionation experiments

Ingrid Obernosterer1,2, Nobu Kawasaki1, Ronald Benner1,*

1University of South Carolina, Department of Biological Sciences and Marine Science Program, Columbia, 29208 South Carolina, USA
2Present address: Observatoire Océanologique, CNRS UMR 7621, BP 44, 66651 Banyuls sur Mer, France
*Corresponding author. Email:

ABSTRACT: Community respiration rates were measured in unfiltered seawater collected in the upper 75 m of the water column along a transect in the Sargasso Sea and at the Bermuda Atlantic Time-series Study (BATS) station (31°50¹00 N; 64°10¹00 W) during a cruise in June and July 2001. Community respiration rates in the upper 75 m of the water column averaged 1.1 ± 0.4 μM O2 d-1 and exhibited significant spatial and temporal variability. Concurrent determination of the heterotrophic and autotrophic community revealed no relationship between community respiration and the abundance of any of the major metabolic groups. Addition of inorganic nutrients (NO3 and PO4) and organic carbon (glucose) indicated that community respiration was P-limited in the surface mixed layer. Size-fractionation experiments indicated that the abundance of heterotrophic bacteria in the <0.6 μm fraction was ~80% of the abundance in unfiltered seawater, but respiration rates in the <0.6 μm size fraction accounted for only 23% of community respiration. Addition of P to the <0.6 μm size fraction increased respiration rates ~2-fold, indicating bacterial respiration was P-limited. It appears that the uncoupling of bacteria from nutrient regeneration in size fractionation experiments resulted in a reduction of bacterial metabolism in the P-limited surface waters of the Sargasso Sea.

KEY WORDS: Community respiration · Size-fractionation · P-limitation · Sargasso Sea · BATS

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