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

Solange Duhamel, Karin M. Björkman, David M. Karl

Research output: Contribution to journalArticlepeer-review

24 Scopus citations


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 (±SD, n = 42) between 5 and 45 m and 1.25 ± 0.70 (±SD, 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.

Original languageEnglish (US)
Pages (from-to)225-238
Number of pages14
JournalAquatic Microbial Ecology
Issue number3
StatePublished - 2012
Externally publishedYes


  • Flow cytometry cell sorting
  • Light
  • Oligotrophic gyre
  • Phosphorus uptake
  • Picoplankton

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Aquatic Science


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