AME 67:225-238 (2012)  -  doi:10.3354/ame01593

Light dependence of phosphorus uptake by microorganisms in the subtropical North and South Pacific Ocean

Solange Duhamel1,2,*, Karin M. Björkman1, David M. Karl

1Department of Oceanography, Center for Microbial Oceanography: Research and Education (C-MORE) and School of Ocean & Earth Science & Technology (SOEST), University of Hawaii, 1000 Pope Road, Honolulu, Hawaii 96822, USA
2Present address: Lamont-Doherty Earth Observatory (LDEO), Division of Biology and Paleo Environment, Columbia University, PO Box 1000, 61 Route 9W, Palisades, New York 10964, USA

ABSTRACT: Light and dark phosphate (PO43−) uptake rates were investigated in the North Pacific Subtropical Gyre (NPSG) and along a coastal to open ocean transect in the South Pacific Ocean. PO43− uptake rates were consistently higher when incubated in the light, but the ratio of uptake in the light and dark (L:D) decreased with depth. In the NPSG, the L:D ratio of euphotic-layer integrated PO43− uptake was 1.58 ± 0.08 (±SE, n = 15 profiles), and the average L:D ratio was 1.60 ± 0.45 (±SE, n = 42) between 5 and 45 m and 1.25 ± 0.70 (±SE, n = 28) between 150 and 175 m. The L:D ratio was higher for the pigmented plankton-enriched size fractions (0.6 to 2 µm and >2 µm), but results were difficult to interpret at the oligotrophic stations where non-pigmented and pigmented plankton cell sizes overlapped. Group-specific measurements obtained using flow cytometric cell sorting demonstrated that Prochlorococcus PO43− uptake rates were higher when the samples were incubated under ambient light. Adenosine-5′-triphosphate (ATP) uptake by Prochlorococcus was also higher in the light for the uptake of both the terminal PO43− group ([γ‑33P]ATP) and adenine moiety ([2,8-3H]ATP). This could be the result of secondary uptake of PO43− and/or adenine after ATP cleavage by non-pigmented picoplankton. There was no significant difference in P-assimilation by non-pigmented picoplankton between light and dark incubated samples. Light dependence of phytoplankton PO43− uptake could thus influence the functioning of the microbial loop and the flows of matter and energy in marine environments by creating temporal patterns of resource utilization.

KEY WORDS: Light · Phosphorus uptake · Flow cytometry cell sorting · Picoplankton · Oligotrophic gyre

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Cite this article as: Duhamel S, Björkman KM, Karl DM (2012) Light dependence of phosphorus uptake by microorganisms in the subtropical North and South Pacific Ocean. Aquat Microb Ecol 67:225-238

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