title: Comparison of phosphate uptake rates by the smallest plastidic and aplastidic protists in the North Atlantic subtropical gyre.
abstract: The smallest phototrophic protists (<3 μm) are important primary producers in oligotrophic subtropical gyres - the Earth's largest ecosystems. In order to elucidate how these protists meet their inorganic nutrient requirements, we compared the phosphate uptake rates of plastidic and aplastidic protists in the phosphate-depleted subtropical and tropical North Atlantic (4-29°N) using a combination of radiotracers and flow cytometric sorting on two Atlantic Meridional Transect cruises. Plastidic protists were divided into two groups according to their size (<2 and 2-3 μm). Both groups of plastidic protists showed higher phosphate uptake rates per cell than the aplastidic protists. Although the phosphate uptake rates of protist cells were on average seven times (P<0.001) higher than those of bacterioplankton, the biomass-specific phosphate uptake rates of protists were one fourth to one twentieth of an average bacterioplankton cell. The unsustainably low biomass-specific phosphate uptake by both plastidic and aplastidic protists suggests the existence of a common alternative means of phosphorus acquisition - predation on phosphorus-rich bacterioplankton cells.
authors.affiliation: Ocean Biogeochemistry and Ecosystems Research Group, National Oceanography Centre, European Way, Southampton, UK.
authors.forename: Manuela
authors.initials: M
authors.lastname: Hartmann
authors.forename: Carolina
authors.initials: C
authors.lastname: Grob
authors.forename: David J
authors.initials: DJ
authors.lastname: Scanlan
authors.forename: Adrian P
authors.initials: AP
authors.lastname: Martin
authors.forename: Peter H
authors.initials: PH
authors.lastname: Burkill
authors.forename: Mikhail V
authors.initials: MV
authors.lastname: Zubkov
mesh_terms: D001267:Atlantic Ocean; D018533:Biomass; D055669:Ecological and Environmental Phenomena; D017753:Ecosystem; D056890:Eukaryota / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D005434:Flow Cytometry; D010710:Phosphates / Q000032:analysis / Q000378:metabolism*; D012623:Seawater / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000378:metabolism*
chemical_list: D010710:Phosphates; D014874:Water Pollutants, Chemical