Iron and phosphorus co-limit nitrogen fixation in the eastern tropical North Atlantic

By M. Mills, C. Ridame, M. Davey, J. Roche, R. Geider. Nature, 2004

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The role of iron in enhancing phytoplankton productivity in high nutrient, low chlorophyll oceanic regions was demonstrated first through iron-addition bioassay experiments and subsequently confirmed by large-scale iron fertilization experiments. Iron supply has been hypothesized to limit nitrogen fixation and hence oceanic primary productivity on geological timescales, providing an alternative to phosphorus as the ultimate limiting nutrient. Oceanographic observations have been interpreted both to confirm and refute this hypothesis, but direct experimental evidence is lacking. We conducted experiments to test this hypothesis during the Meteor 55 cruise to the tropical North Atlantic. This region is rich in diazotrophs and strongly impacted by Saharan dust input. Here we show that community primary productivity was nitrogen-limited, and that nitrogen fixation was co-limited by iron and phosphorus. Saharan dust addition stimulated nitrogen fixation, presumably by supplying both iron and phosphorus. Our results support the hypothesis that aeolian mineral dust deposition promotes nitrogen fixation in the eastern tropical North Atlantic.

Subfields: Ecology, Oceanography

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Citations in the corpus

Evidence of active dinitrogen fixation in surface waters of the eastern tropical South Pacific during El Niño and La Niña events and evaluation of its potential nutrient controls (2013, background): “, 2003a, 2003b], it is also suspected to control N2 fixation [Paerl et al., 1994; Mills et al., 2004; Saito et al., 2011], but this process and its controlling factors have been very poorly studied in this area.”
Some thoughts on the concept of colimitation: Three definitions and the importance of bioavailability (2008, neutral): “…1995 a ; c, Benitez-Nelson 2000; d, Hein and Sand-Jensen 1997; Riebesell et al. 1994; e, Saito et al. 2005; f, Franck et al. 2003, Wisniewski 2006; g, Mills et al. 2004; h, Bertrand et al. 2007; i, Morel et al. 1994; Yee and Morel, 1996; j, Price and Morel 1990; k, Tabares et al. 2003;…”
Nutrient limitation of picophytoplankton photosynthesis and growth in the tropical North Atlantic (2008, background): “0-mg L21 dust treatments, respectively (Ridame and Guieu 2002; Bonnet and Guieu 2004; Mills et al. 2004).”
Elevated CO2 enhances nitrogen fixation and growth in the marine cyanobacterium Trichodesmium (2007, background): “Natural Trichodesmium populations mostly inhabit oceanic areas where light is not limiting, although in certain regions P and Fe availability appear to control Trichodesmium populations (Sanudo-Wilhelmy et al., 2001; Mills et al., 2004; Moutin et al., 2005; White et al., 2006).”
Nutrient limitation of primary productivity in the Southeast Pacific (BIOSOPE cruise) (2007, background): “Nitrogen fixation is thus controlled in these oceanic gyres by Fe availability, as well as phosphate, which can (co)limit the process (Sanudo-Wilhelmy et al., 2001; Mills et al., 2004).”
Global assessment of limitation to symbiotic nitrogen fixation by phosphorus availability in terrestrial ecosystems using a meta‐analysis approach (2013, background): “[3] In aquatic ecosystems, SNF is probably limited, among other factors like temperature or sunlight, by the concentrations of P and Fe in the water [Dutkiewicz et al., 2012; Hutchins et al., 2009; Mills et al., 2004; Sanudo-Wilhelmy et al., 2001; Vitousek et al., 2002].”
CO2 control of Trichodesmium N2 fixation, photosynthesis, growth rates, and elemental ratios: Implications for past, present, and future ocean biogeochemistry (2007, background): “Furthermore, diazotrophic growth across most of the ocean is believed to be limited by P or Fe (SañudoWilhelmy et al. 2001; Mills et al. 2004; Fu et al. 2005a), so determining how variables like temperature and P availability interact with changing pCO2 is critical.”
Pelagic functional group modeling: Progress, challenges and prospects (2006, positive): “Recent experimental work in the eastern subtropical Atlantic suggests that Trichodesmium growth and N2 fixation are co-limited by iron and phosphorus (Mills et al., 2004).”
Competition and facilitation between unicellular nitrogen‐fixing cyanobacteria and non—nitrogen‐fixing phytoplankton species (2007, background): “2000) and on the growth and distribution of nitrogen-fixing cyanobacteria (Sañudo-Wilhelmy et al. 2001; Kustka et al. 2003; Mills et al. 2004).”
Nitrogen fixation and release of fixed nitrogen by Trichodesmium spp. in the Gulf of Mexico (2006, background): “Oceanic concentrations of both phosphorus (P) and iron (Fe) have been proposed to limit growth of Trichodesmium and phytoplankton in nature (Karl et al. 1995; SañudoWilhelmy et al. 2001; Mills et al. 2004), but there is little experimental evidence demonstrating relationships between P and Fe turnov”
Salinity controls phytoplankton response to nutrient enrichment in the Great Salt Lake, Utah, USA (2006, background): “Recently, Mills et al. (2004) performed bioassay experiments indicating that low iron and P supplies simultaneously limit N2 fixation in the ocean.”
Iron availability limits the ocean nitrogen inventory stabilizing feedbacks between marine denitrification and nitrogen fixation (2007, background): “In the North Atlantic, where there is high dust deposition, evidence for P limitation or colimitation by Fe and P has been demonstrated [Sañudo-Wilhelmy et al., 2001; Dyhrman et al., 2002; Ammerman et al., 2003; Kustka et al., 2003b; Mills et al., 2004].”
Quantification of ammonia oxidation rates and ammonia‐oxidizing archaea and bacteria at high resolution in the Gulf of California and eastern tropical North Pacific Ocean (2012, background): “Because N is a required nutrient for all organisms and limits primary production across large areas of the ocean (Mills et al. 2004), determining how nitrification may affect N availability is of critical importance.”
Atmospheric iron deposition: global distribution, variability, and human perturbations. (2009, background): “Although controversial, nitrogen-fixing organisms in the ocean may have higher iron requirements than other phytoplankton (e.g., Falkowski et al. 1998, Mills et al. 2004), which would directly link iron and nitrogen biogeochemical cycles (e.g., Moore et al. 2004).”