Controls on tropical Pacific Ocean productivity revealed through nutrient stress diagnostics

Behrenfeld, Michael J.; Worthington, Kirby; Sherrell, Robert M.; Chávez, Francisco P.; Strutton, Peter G.; McPhaden, Michael J.; Shea, Donald M.

doi:10.1038/nature05083

Cited by 239 publications

(258 citation statements)

References 29 publications

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“…This value is close to the maximum value observed in the ocean (Falkowski et al, 2004) and did not increase after Fe or dust addition. Behrenfeld et al (2006) found the same pattern (high F v /F m , absence of nocturnal decrease) in the North Tropical Pacific, but the ambient dissolved Fe concentrations there are two to seven times higher (Boyle et al, 2005) than in the South Pacific Gyre, where our experiments were carried out. Our data also indicate that the addition of Fe did not change Chl-a concentrations or primary productivity (p>0.05), indicating that, in contrary to the HNL sta-tion, the photoautotrophic community was not Fe-limited in the gyre.…”

Section: The Role Of Fesupporting

confidence: 73%

Nutrient limitation of primary productivity in the Southeast Pacific (BIOSOPE cruise)

et al. 2008

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Abstract.Iron is an essential nutrient involved in a variety of biological processes in the ocean, including photosynthesis, respiration and dinitrogen fixation. Atmospheric deposition of aerosols is recognized as the main source of iron for the surface ocean. In high nutrient, low chlorophyll areas, it is now clearly established that iron limits phytoplankton productivity but its biogeochemical role in low nutrient, low chlorophyll environments has been poorly studied. We investigated this question in the unexplored southeast Pacific, arguably the most oligotrophic area of the global ocean. Situated far from any continental aerosol source, the atmospheric iron flux to this province is amongst the lowest of the world ocean. Here we report that, despite low dissolved iron concentrations (∼0.1 nmol l −1 ) across the whole gyre (3 stations located in the center and at the western and the eastern edges), primary productivity are only limited by iron availability at the border of the gyre, but not in the center. The seasonal stability of the gyre has apparently allowed for the development of populations acclimated to these extreme oligotrophic conditions. Moreover, despite clear evidence of nitrogen limitation in the central gyre, we were unable to measure dinitrogen fixation in our experiments, even after iron and/or phosphate additions, and cyanobacterial nif H gene abundances were extremely low compared to the North Pacific Gyre. The South Pacific gyre is therefore unique with respect to the physiological status of its phytoplankton populations.

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Section: The Role Of Fesupporting

confidence: 73%

Nutrient limitation of primary productivity in the Southeast Pacific (BIOSOPE cruise)

et al. 2008

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“…Fe stress responsive LHC gene products, such as CP43Ј and Tidi, which are found in cyanobacteria and green algae (22), respectively, function as peripheral light-harvesting antennas coupled to PSI reaction centers. Large-scale patterns in open ocean variable fluorescence suggest that such specialized pigment-protein complexes are typical in phytoplankton populations found in iron-limited HNLC waters (17). Thus, although levels of Chl a per cell decreased, we propose that de novo pigment synthesis and changes in the antenna polypeptide composition may be required to compensate for the relative decrease of PSI units under periods of Fe limitation (10) and to enhance the NPQ response (Table 1).…”

Section: Resultsmentioning

confidence: 84%

“…S1]. Reductions in cell volume, chlorophyll (Chl) per cell, photosynthetic efficiency of PSII (Fv/Fm), and content of Fe-rich complexes and/or electron carriers of the electron transfer chain are all common responses to Fe limitation (Table 1) (15,16), reflecting compromised photosystem reaction centers, reduced photosynthetic electron transport rates, decreased reductant production, and an inability to process absorbed photons (4,17,18).…”

Section: Resultsmentioning

confidence: 99%

Whole-cell response of the pennate diatom Phaeodactylum tricornutum to iron starvation

Allen

LaRoche²,

Maheswari

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

396

505

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Marine primary productivity is iron (Fe)-limited in vast regions of the contemporary oceans, most notably the high nutrient low chlorophyll (HNLC) regions. Diatoms often form large blooms upon the relief of Fe limitation in HNLC regions despite their prebloom low cell density. Although Fe plays an important role in controlling diatom distribution, the mechanisms of Fe uptake and adaptation to low iron availability are largely unknown. Through a combination of nontargeted transcriptomic and metabolomic approaches, we have explored the biochemical strategies preferred by Phaeodactylum tricornutum at growth-limiting levels of dissolved Fe. Processes carried out by components rich in Fe, such as photosynthesis, mitochondrial electron transport, and nitrate assimilation, were down-regulated. Our results show that this retrenchment is compensated by nitrogen (N) and carbon (C) reallocation from protein and carbohydrate degradation, adaptations to chlorophyll biosynthesis and pigment metabolism, removal of excess electrons by mitochondrial alternative oxidase (AOX) and non-photochemical quenching (NPQ), and augmented Fe-independent oxidative stress responses. Iron limitation leads to the elevated expression of at least three gene clusters absent from the Thalassiosira pseudonana genome that encode for components of iron capture and uptake mechanisms.genome ͉ metabalomics ͉ photosynthesis ͉ transcriptomics ͉ nutrients

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“…However, the biogeochemistry is less defined here compared with the Pacific and Atlantic Oceans. Satellite measurements of fluorescence quantum yield of phytoplankton has been proposed as a measure of iron stress (44), and using this, Behrenfeld et al (25) observed extended iron stress in part of the Indian Ocean gyre. Thus, it is conceivable that the iron concentration is low in the Indian Ocean sites, where we detect the HNLC clades of Prochlorococcus.…”

Section: Discussionmentioning

confidence: 99%

Characterization ofProchlorococcusclades from iron-depleted oceanic regions

Rusch

Martiny

Dupont

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

161

190

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Prochlorococcus describes a diverse and abundant genus of marine photosynthetic microbes. It is primarily found in oligotrophic waters across the globe and plays a crucial role in energy and nutrient cycling in the ocean ecosystem. The abundance, global distribution, and availability of isolates make Prochlorococcus a model system for understanding marine microbial diversity and biogeochemical cycling. Analysis of 73 metagenomic samples from the Global Ocean Sampling expedition acquired in the Atlantic, Pacific, and Indian Oceans revealed the presence of two uncharacterized Prochlorococcus clades. A phylogenetic analysis using six different genetic markers places the clades close to known lineages adapted to high-light environments. The two uncharacterized clades consistently cooccur and dominate the surface waters of high-temperature, macronutrient-replete, and low-iron regions of the Eastern Equatorial Pacific upwelling and the tropical Indian Ocean. They are genetically distinct from each other and other high-light Prochlorococcus isolates and likely define a previously unrecognized ecotype. Our detailed genomic analysis indicates that these clades comprise organisms that are adapted to iron-depleted environments by reducing their iron quota through the loss of several iron-containing proteins that likely function as electron sinks in the photosynthetic pathway in other Prochlorococcus clades from high-light environments. The presence and inferred physiology of these clades may explain why Prochlorococcus populations from iron-depleted regions do not respond to iron fertilization experiments and further expand our understanding of how phytoplankton adapt to variations in nutrient availability in the ocean.

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Controls on tropical Pacific Ocean productivity revealed through nutrient stress diagnostics

Cited by 239 publications

References 29 publications

Nutrient limitation of primary productivity in the Southeast Pacific (BIOSOPE cruise)

Nutrient limitation of primary productivity in the Southeast Pacific (BIOSOPE cruise)

Whole-cell response of the pennate diatom Phaeodactylum tricornutum to iron starvation

Characterization ofProchlorococcusclades from iron-depleted oceanic regions

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