Iron Biogeochemistry in Aquatic Systems: From Source to Bioavailability

Abstract

Iron (Fe) is an essential trace element for several key metabolic processes in phytoplankton; however Fe is present in low concentration in many aquatic systems including vast oceanic regions and large lakes. In these systems, Fe can limit the growth of phytoplankton and atmospheric carbon dioxide biological fixation. Indeed Fe limitation exerts a global impact on the carbon cycle and the imprint of aquatic systems on our climate. In order to understand how aquatic systems function and increase our ability to predict their response to changing conditions, it is therefore paramount to understand when and how Fe controls operate. This review presents the complex relationship between Fe chemistry and the biology of surface waters to highlight the parameters defining the forms of Fe that are accessible for phytoplankton growth (or bioavailable). Particular attention is given to the identification of Fe sources and Fe organic complexation as these, in conjunction with biological recycling and remineralisation, mostly control Fe residence time, chemistry and bioavailability.

First Evaluation of the Role of Salp Fecal Pellets on Iron Biogeochemistry

“…Fe-binding ligands are key compounds that control both Fe reactivity (Barbeau, 2006;Rijkenberg et al, 2006) and bioavailability to phytoplankton (Hassler et al, 2011a(Hassler et al, ,b, 2015Norman et al, 2014). In this study, we could not detect, after any treatment ("freezer, " "VIS, " "UV, " and "dark"), a release of ligands by salp FPs.…”

Physiological responses of the freshwater N2‐fixing cyanobacterium Raphidiopsis raciborskii to Fe and N availabilities

“…This metalloenzyme is composed of two component proteins, namely dinitrogenase (an Fe-X protein where X represents Fe, Mo or V) and dinitrogenase reductase (an Fe protein) (Yang et al, 2017). Numerous studies indicate that the Fe requirements for growth of phototrophic diazotrophs are higher than those for nondiazotrophs (Dutkiewicz et al, 2012;Dutkiewicz et al, 2014;Schoffman et al, 2016) with N 2 -fixation commonly limited by the low Fe availability in oceanic and lake waters (Berman-Frank et al, 2007;Whittaker et al, 2011;Norman et al, 2014;Snow et al, 2015). Numerous studies indicate that the Fe requirements for growth of phototrophic diazotrophs are higher than those for nondiazotrophs (Dutkiewicz et al, 2012;Dutkiewicz et al, 2014;Schoffman et al, 2016) with N 2 -fixation commonly limited by the low Fe availability in oceanic and lake waters (Berman-Frank et al, 2007;Whittaker et al, 2011;Norman et al, 2014;Snow et al, 2015).…”

“…Nitrogenase synthesis requires a large amount of Fe [25-39 atoms of Fe per nitrogenase molecule (Postgate, 1998) with 236 μmol of Fe bound to nitrogenase per mol of cellular carbon (Whittaker et al, 2011)]. Numerous studies indicate that the Fe requirements for growth of phototrophic diazotrophs are higher than those for nondiazotrophs (Dutkiewicz et al, 2012;Dutkiewicz et al, 2014;Schoffman et al, 2016) with N 2 -fixation commonly limited by the low Fe availability in oceanic and lake waters (Berman-Frank et al, 2007;Whittaker et al, 2011;Norman et al, 2014;Snow et al, 2015). For example, N 2 -fixation rates of the marine diazotrophic cyanobacterium Trichodesmium increased from 0.07 to 0.5 mmol-NÁmol-C −1 Áh −1 on Fe supplementation from 4 nM to 4 μM (Berman-Frank et al, 2007).…”

Impact of nutrients on photoacclimation of phytoplankton in an oligotrophic lake measured with long-term and high-frequency data: implications for chlorophyll as an estimate of phytoplankton biomass

“…Secondly, a lack of chlorophyll response to higher nutrients might be associated with iron stress and the peculiar way in which algal cells can form unphotosynthetically available chlorophyll under iron-limited conditions, which occurs in high-nitrate low-chlorophyll (HNLC) regions of the world's oceans (Behrenfeld & Milligan, 2013) and similar to that suggested for flagellates as discussed above. Iron is one of the most important micronutrients for photosynthesis and can be limiting in various lake an ocean environments (Norman et al, 2014). When iron and nitrogen are colimiting, chlorophyll is downregulated and the excess chlorophyll is energetically detached from photosystem reaction centers causing a reduction in growth (Halsey & Jones, 2015).…”