Iron limits primary productivity in vast regions of the ocean. Given that marine phytoplankton contribute up to 40% of global biological carbon fixation, it is important to understand what parameters control the availability of iron (iron bioavailability) to these organisms. Most studies on iron bioavailability have focused on the role of siderophores; however, eukaryotic phytoplankton do not produce or release siderophores. Here, we report on the pivotal role of saccharides—which may act like an organic ligand—in enhancing iron bioavailability to a Southern Ocean cultured diatom, a prymnesiophyte, as well as to natural populations of eukaryotic phytoplankton. Addition of a monosaccharide (>2 nM of glucuronic acid, GLU) to natural planktonic assemblages from both the polar front and subantarctic zones resulted in an increase in iron bioavailability for eukaryotic phytoplankton, relative to bacterioplankton. The enhanced iron bioavailability observed for several groups of eukaryotic phytoplankton (i.e., cultured and natural populations) using three saccharides, suggests it is a common phenomenon. Increased iron bioavailability resulted from the combination of saccharides forming highly bioavailable organic associations with iron and increasing iron solubility, mainly as colloidal iron. As saccharides are ubiquitous, present at nanomolar to micromolar concentrations, and produced by biota in surface waters, they also satisfy the prerequisites to be important constituents of the poorly defined "ligand soup," known to weakly bind iron. Our findings point to an additional type of organic ligand, controlling iron bioavailability to eukaryotic phytoplankton—a key unknown in iron biogeochemistry.

Item Type:	Refereed Article
Keywords:	trace metals, carbohydrates, organic matter, exopolymeric substances, plankton
Research Division:	Earth Sciences
Research Group:	Oceanography
Research Field:	Chemical Oceanography
Objective Division:	Environment
Objective Group:	Physical and Chemical Conditions of Water
Objective Field:	Physical and Chemical Conditions of Water in Marine Environments
UTAS Author:	Boyd, PW (Professor Philip Boyd)
ID Code:	95613
Year Published:	2011
Web of Science® Times Cited:	139
Deposited By:	IMAS Research and Education Centre
Deposited On:	2014-10-06
Last Modified:	2017-11-01
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