Inducing phytoplankton iron limitation in iron-replete coastal waters with a strong chelating ligand

摘要

Dissolved iron (Fe) concentrations in the California coastal upwelling regime vary over two orders of magnitude (from <0.05 to >5 nM), which leads to a wide range in Fe effects on phytoplankton growth. Fe-addition experi ments are appropriate to use to assess the biological role of Fe in low-Fe areas, but other methods are needed in Fe-replete regions. We present experiments that use additions of the exogenous siderophore desferrioxamine B (DFOB, obtained from a terrestrial actinomycete fungus) to sequester ambient Fe and to markedly decrease its availability to the biota. DFOB additions resulted in artificial Fe limitation of the phytoplankton community in high- Fe areas of the upwelling region. Results of these "Fe-removal" experiments mirror those of Fe-addition experi- ments in low-Fe, high-nutrient, low-chlorophyll (HNLC) waters. When DFOB is added to Fereplete waters, changes in nuttient concentrations, biomass, and other biological parameters closely resemble those seen in Felimited controls in HNLC areas. while the controls without DFOB behave much like HNLC Fe-addition bottles. DFOB additions in high-Fe waters greatly reduced biological Fe uptake and, consequently, nitrate, silicic acid, and carbon- uptake rates as well as paniculate production. Diatoms and other phytoplankton bloomed profusely in unamended controls but not in Fe-limited +DFOB bottles. Bacterial numbers and zooplankton grazing activity were also severely reduced in DFOB-addition bottles. These experiments demonstrate that artificially lowering Fe availability can induce limitation of autotrophic an