Fe Limitation Research Articles

Photoprotective Mechanisms of `Concord' Grape Leaves in Relation to Iron Supply

The objective of this study was to quantify how photoprotective mechanisms in the leaves of `Concord' grapevines (Vitis labruscana Bailey) respond to a range of iron (Fe) supply. Own-rooted, 1-year-old container-grown vines were fertigated twice weekly for 11 weeks with a complete nutrient solution containing 1, 10, 20, 50, or 100 μm Fe from ferric ethylenediamine di (o-hydroxyphenylacetic) acid (Fe-EDDHA). Leaf total Fe content did not increase in response to Fe supply; however, “active” Fe (extracted with 2,2′-dipyridyl) and chlorophyll (Chl) increased on a leaf area basis as applied Fe increased. At the lowest active Fe level, leaf absorptance and the efficiency of excitation transfer (Fv′/Fm′) was lower, and nonphotochemical quenching (NPQ) was significantly greater. Photosystem II (PSII) quantum efficiency decreased curvilinearly, and the proportion of PSII reaction centers in the open state (qP) decreased linearly as active Fe content decreased. On a Chl basis, the xanthophyll cycle pool size [violaxanthin (V) + antheraxanthin (A) + zeaxanthin (Z)], lutein, and β-carotene increased curvilinearly as active Fe decreased, and neoxanthin (Neo) increased at the lowest Fe level. On a leaf area basis, as active Fe decreased, V+A+Z and β-carotene decreased curvilinearly, and lutein and Neo decreased linearly. At noon, conversion of V to A and Z increased as active Fe decreased. On a Chl basis, activities of antioxidant enzymes superoxide dismutase (SOD), monodehydroascorbate reductase (MDAR), and dehydroascorbate reductase (DHAR) increased curvilinearly, and glutathione reductase (GR) activity increased linearly as active Fe levels declined. Ascorbate peroxidase (APX) and catalase (CAT), on a Chl basis, were relatively constant. On a leaf area basis, a decrease in active Fe increased SOD and MDAR activity, whereas APX, CAT, DHAR and GR activity decreased. Antioxidant metabolites ascorbate (AsA), dehydroascorbate (DAsA), reduced glutathione (GSH) and oxidized glutathione (GSSG) also increased in response to Fe limitation when expressed on a Chl basis, whereas on a leaf area basis AsA and DAsA decreased and GSH increased curvilinearly. The GSH:GSSG ratio increased as active Fe declined, whereas the AsA:DAsA ratio did not change. In conclusion, both photoprotective mechanisms, xanthophyll cycle-dependent thermal dissipation and the ascorbate-glutathione antioxidant system, are enhanced in response to Fe deficiency to cope with excess absorbed light. In a low soil pH tolerant species such as V. labruscana, the foliar antioxidant system was upregulated in response to excess absorbed light from Fe deficiency-induced chlorosis, and there was no evidence of an increase in oxidative stress from high rates of applied Fe-EDDHA.

Cr(III) Oxidation and Cr Toxicity in Cultures of the Manganese(II)-Oxidizing Pseudomonas putida Strain GB-1

Mn oxides have long been considered the primary environmental oxidant of Cr(III), however, since most of the reactive Mn oxides in the environment are believed to be of biological origin, microorganisms may indirectly mediate Cr(III) oxidation and accelerate the rate over that seen in purely abiotic systems. In this study, we examined the ability of the Mn(II)-oxidizing bacterium, Pseudomonas putida strain GB-1, to oxidize Cr(III). Our results show that GB-1 cannot oxidize Cr(III) directly, but that in the presence of Mn(II), Cr(III) can be rapidly and completely oxidized. Growth studies suggest that in growth medium with few organics the resulting Cr(VI) may be less toxic to P. putida GB-1 than Cr(III), which is generally considered less hazardous. In addition, Cr(III) present during the growth of P. putida GB-1 appeared to cause iron stress as determined by the production of the fluorescent siderophore pyoverdine. When stressed by Fe limitation or Cr(III) toxicity, Mn(II) oxidation by GB-1 is inhibited.

Iron in the Ross Sea: 1. Impact on CO2 fluxes via variation in phytoplankton functional group and non‐Redfield stoichiometry

We present new model results examining nutrient and carbon biogeochemistry within the Ross Sea, focusing on the sensitivity of ecosystem dynamics to taxon‐specific nutrient utilization parameters and the impact of alleviating Fe limitation of phytoplankton growth. The coupled ice‐atmosphere‐ocean ecosystem (CIAO) model of the Ross Sea was modified to include air‐sea CO2 exchange and non‐Redfield C/N/P uptake ratios of the dominant phytoplankton taxa. Model results show that the Ross Sea was a substantial sink for atmospheric CO2, driven by the high primary productivity prior to the onset of Fe limitation. Taxon‐specific C/N/P uptake ratios controlled the relative rate of removal of each macronutrient, while Fe availability constrained the absolute magnitude of utilization. When Redfield C/N/P stoichiometry was applied to both phytoplankton taxa, net primary production (NPP) was overestimated in areas normally dominated by diatoms and underestimated in regions of Phaeocystis antarctica dominance, and macronutrient dynamics were misrepresented. Simulated shifts in phytoplankton taxonomic composition significantly altered uptake of atmospheric CO2 when the phytoplankton were dominated by diatoms (−70%) or P. antarctica (+35%). The ability to bloom later in the season afforded P. antarctica a relatively greater role than diatoms in controlling the air‐sea flux of CO2 in the Ross Sea. In response to alleviation of Fe limitation, both total Ross Sea NPP and CO2 uptake increased by 30%. The response of the carbon cycle to Fe fertilization was predicted to be complex, and its magnitude and nature were dictated by patterns of macronutrient utilization.

Iron resources and oceanic nutrients: advancement of global environment simulations

1. IntroductionIn recent years it has been discovered that tracenutrients and in particular iron (Fe) limit phytoplank-ton productivity in 40% of the global oceans. In thoseHigh Nutrient Low Chlorophyll (HNLC) surfacewaters there always remains an excess pool of majornutrients nitrate, phosphate and silicate. These beingin excess, it was hypothesised (Gran, 1931) and muchlater proved (Martin and Fitzwater, 1988; Buma et al.,1991) that iron was the key limiting factor, in additionto light and temperature. It is therefore more realisticto speak of co-limitation; iron, light and majornutrients in concert would limit phytoplankton growthin vast regions of the remaining 60% of surface waters(Blain et al., 2004). In the early 1990s, the Iron Age ofOceanography started (Coale et al., 1999). Allexperimental evidence on Fe (co)-limitation publisheduntil about 2001–2002 has recently been synthesisedin several reviews (De Baar and Boyd, 2000; De Baarand La Roche, 2003).The century-old paradigm of a single limitingfactor for some or all marine ecosystems has thusgiven way to the awareness of co-limitation byseveral nutrients simultaneously (De Baar, 1994),where grazing and auto-mortality losses furthermoreplay a very important role. Iron is a crucial tracenutrient regulating photosynthetic efficiency andelectron transport, hence the fixation rate of CO

Physiological responses of three species of marine pico-phytoplankton to ammonium, phosphate, iron and light limitation

Experiments were conducted with three species of marine pico-phytoplankton: Synechococcus sp. (CCMP 839), Pelagomonas calceolata (CCMP 1756) and Prasinomonas capsulatus (CCMP 1617) in order to collect physiological parameters for pico-phytoplankton to be utilised in Ocean Biogeochemical Climate Models. The main parameters to follow the effects of ammonium, phosphate, iron and light limitation were cell growth rates (μ), half saturation constants for growth (K m), N, P and Fe quota (per cell or per mol C), and photochemical quantum efficiency (F v/F m). The nitrate and phosphate limitation experiments demonstrated that the small phytoplankton species could grow at low N and P concentrations. K m values were in the micro-molar (NH 4 +) and sub-micro-molar (PO 4 3−) range. N and P quota were in the femto-molar range per cell and varied from nutrient-deplete to nutrient-replete conditions. F v/F m values were only adversely affected at the lowest N and P concentrations in these experiments. In the Fe limitation experiments, it was shown that all three species were adversely affected only at extremely low Fe concentrations. Iron chelating agents had to be added to force the species in Fe limitation till ultimately growth stopped. K m values with respect to dissolved Fe were in the femto-molar range. Fe quota were in the low zepto-molar (10 −21 M) range per cell, and varied considerably from Fe limiting to Fe replete growth conditions. F v/F m values diminished only at the lowest iron concentrations. In the light limitation experiments, growth rates and photochemical quantum efficiencies were adversely affected only at irradiance levels below 10 μmol photons m −2 s −1. These results indicate that the pico-phytoplankton species will hardly ever be completely stopped in their growth by NH 4 +, PO 4 3−, Fe or light (separately) under natural conditions.

Availability of iron and major nutrients for phytoplankton in the northeast Atlantic Ocean

Because of recent findings that Fe is a limiting factor for phytoplankton activity even at relatively high dissolved iron (DFe) concentrations, the potential importance of Fe limitation was revisited in the northeast Atlantic Ocean (39−45°N, 17−21°W). We report data gathered during deck incubation experiments performed at three stations in February‐March 2001 with surface seawater containing DFe concentrations of ~0.40 nmol L−1. At all stations, Fe addition enhanced phytoplankton growth. Fe limitation was moderate and occurred simultaneously with limitation by major nutrients. This was clearly demonstrated for diatoms that were colimited by orthosilicic acid. Micro‐, nano‐, and picoplankton benefited from Fe enrichment. Experiments performed with the trihydroxamate siderophore desferrioxamine mesylate B (DFOB) indicated that Fe reserves exist within the cells, especially within the larger cells. This reserve could result from luxurious storage of Fe by colimited cells during episodic atmospheric deposition of Saharan dust. Simulating concentrations of dust resulting from aerosol deposition in well‐stratified surface waters, we determined that the solubility of Saharan dust was very low (<0.1% w/w) but the amount of DFe released in seawater was sufficient to relieve the Fe limitation of the ambient phytoplankton community.

CO2 Assimilation, Photosynthetic Enzymes, and Carbohydrates of `Concord' Grape Leaves in Response to Iron Supply

Own-rooted 1-year-old `Concord' grapevines (Vitis labruscana Bailey) were fertigated twice weekly for 11 weeks with 1, 10, 20, 50, or 100 μm iron (Fe) from ferric ethylenediamine di (o-hydroxyphenylacetic) acid (Fe-EDDHA) in a complete nutrient solution. As Fe supply increased, leaf total Fe content did not show a significant change, whereas active Fe (extracted by 2,2′-dipyridyl) content increased curvilinearly. Chlorophyll (Chl) content increased as Fe supply increased, with a greater response at the lower Fe rates. Chl a: b ratio remained relatively constant over the range of Fe supply, except for a slight increase at the lowest Fe treatment. Both CO2 assimilation and stomatal conductance increased curvilinearly with increasing leaf active Fe, whereas intercellular CO2 concentrations decreased linearly. Activities of key enzymes in the Calvin cycle, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), NADP-glyceraldehyde-3-phosphate dehydrogenase (GAPDH), phosphoribulokinase (PRK), stromal fructose-1,6-bisphosphatase (FBPase), and a key enzyme in sucrose synthesis, cytosolic FBPase, all increased linearly with increasing leaf active Fe. No significant difference was found in the activities of ADP-glucose pyrophosphorylase (AGPase) and sucrose phosphate synthase (SPS) of leaves between the lowest and the highest Fe treatments, whereas slightly lower activities of AGPase and SPS were observed in the other three Fe treatments. Content of 3-phosphoglycerate (PGA) increased curvilinearly with increasing leaf active Fe, whereas glucose-6-phosphate (G6P), fructose-6-phosphate (F6P), and the ratio of G6P: F6P remained unchanged over the range of Fe supply. Concentrations of glucose, fructose, sucrose, starch, and total nonstructural carbohydrates (TNC) at both dusk and predawn increased with increasing leaf active Fe. Concentrations of starch and TNC at any given leaf active Fe content were higher at dusk than at predawn, but both glucose and fructose showed the opposite trend. No difference in sucrose concentration was found at dusk or predawn. The export of carbon from starch breakdown during the night, calculated as the difference between dusk and predawn measurements, increased as leaf active Fe content increased. The ratio of starch to sucrose at both dusk and predawn also increased with increasing leaf active Fe. In conclusion, Fe limitation reduces the activities of Rubisco and other photosynthetic enzymes, and hence CO2 assimilation capacity. Fe-deficient grapevines have lower concentrations of nonstructural carbohydrates in source leaves and, therefore, are source limited.

CO2 Assimilation, Photosynthetic Enzymes, and Carbohydrates of Grape Leaves (Vitis labrusca L. cv. Concord) in Response to Iron Supply

Own-rooted one-year-old `Concord' grapevines were fertigated twice weekly for 11 weeks with 1, 10, 20, 50, OR 100 μmol iron (Fe) from ferric ethylenediamine di (o-hydroxyphenylacetic) acid in a complete nutrient solution. As Fe supply increased, leaf total Fe content did not change, whereas active Fe (extracted by 2, 2'-dipyridyl) and total chlorophyll content increased curvilinearly. CO2 assimilation and stomatal conductance increased curvilinearly with increasing active Fe, whereas intercellular CO2 concentrations decreased linearly. Activities of key Calvin cycle enzymes, Rubisco, NADP-glyceraldehyde-3-phosphate dehydrogenase, phosphoribulokinase, stromal fructose-1,6-bisphosphatase (FBPase), and a key enzyme in sucrose synthesis, cytosolic FBPase, all increased linearly with increasing active Fe. No difference was found in the activities of ADP-glucose pyrophosphorylase and sucrose phosphate synthase of leaves between the lowest and the highest treatments, whereas slightly lower activities were observed in the middle Fe treatments. Content of 3-phosphoglycerate increased curvilinearly with increased active Fe, whereas glucose-6-phosphate and fructose-6-phosphate did not change. Glucose, fructose, sucrose, starch, and total non-structural carbohydrates at both dusk and pre-dawn increased with increasing active Fe. Carbon export from starch breakdown during the night, calculated as the difference between dusk and predawn levels, increased as active Fe increased. In conclusion, Fe limitation reduces the activities of Rubisco and other photosynthetic enzymes, and hence CO2 assimilation capacity. Fe-deficient grapevines have lower concentrations of non-structural carbohydrates in source leaves, and therefore, are source limited.

Photoprotective Mechanisms of Grape Leaves (Vitis labrusca L. cv. Concord) in Relation to Iron Supply

One-year-old `Concord' grapevines (Vitis labrusca L.) were fertigated twice weekly for 11 weeks with a complete nutrient solution containing 1, 10, 20, 50 or 100 μmol iron (Fe) from ferric ethylenediamine di (o-hydroxyphenylacetic) acid (Fe-EDDHA). Leaf total Fe content did not increase in response to Fe supply, however both “active” Fe (extracted with 2, 2'-dipyridyl) and chlorophyll (Chl) content increased as applied Fe increased. At the lowest active Fe level, leaf absorptance and maximum PSII efficiency (Fv/Fm) were slightly decreased, and non-photochemical quenching was significantly greater. PSII quantum efficiency decreased curvilinearly as active Fe content decreased. On a Chl basis, the xanthophyll cycle pool size, lutein, and beta-carotene increased curvilinearly as active Fe decreased, and neoxanthin increased at the lowest Fe level. Activities of antioxidant enzymes superoxide dismutase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase followed a similar trend and increased under Fe deficiency, when expressed on a Chl basis. Antioxidant metabolites also increased in response to Fe limitation. On a Chl basis, ascorbate (AsA), dehydroascorbate (DAsA), reduced glutathione (GSH) and oxidized glutathione (GSSG) content was greater at the lowest active Fe levels. We did not find a difference in the ratio of AsA to DAsA or GSH to GSSG. In conclusion, both photoprotective mechanisms, xanthophyll cyle-dependent thermal dissipation and the ascorbate-glutatione antioxidant system, are enhanced in response to iron deficiency to cope with excess absorbed light.

참조응력법에 입각한 표면균열배관의 파괴역학 해석 -참조하중의 영향 분석-

To investigate relevance of the definition of the reference stress to estimate J and C* for surface crack problems, this paper compares FE J and C* results for surface cracked pipes with those estimated according to the reference stress approach using various definitions of the reference stress. Pipes with part circumferential inner surface crack and finite internal axial crack are considered, subject to internal pressure and global bending. The crack depth and aspect ratio are systematically varied. The reference stress is defined in four different ways using (i) the local limit load, (ii) the global limit load, (iii) the global limit load determined from the FE limit analysis, and (iv) the optimised reference load. It is found that the reference stress based on the local limit load gives overall excessively conservative estimates of J and C*. Use of the global limit load clearly reduces the conservatism, compared to that of the local limit load, although it can provide sometimes non-conservative estimates of J and C*. The use of the FE global limit load gives overall non-conservative estimates of J and C*. The reference stress based on the optimised reference load gives overall accurate estimates of J and C*, compared to other definitions of the reference stress. Based on the present finding, general guidance on the choice of the reference stress for surface crack problems is given.

Semiconductor applications of nanoliter droplet methodology with total reflection x-ray fluorescence analysis

In this study, the nanoliter dried spot method was applied to semiconductor contamination analysis to enhance vapor phase decomposition processes with total reflection X-ray fluorescence detection. Nanoliter-sized droplets (10 and 50 nl) were deposited onto native silicon oxide wafer surfaces in a clean room environment from both single and multielemental standards containing various concentrations of iron in different matrices. Direct comparisons were made to droplets formed by conventional VPD with similar iron standards. Nanoliter dried spots could be reproducibly deposited and dried in air with typical drying times ranging from 20 s to 2 min depending on the nanoliter volume deposited, compared to VPD spots which have drying times ranging from tens of minutes to several hours. Both types of residues showed a linear relationship between Fe intensity and mass deposited. Variable angle experiments showed that both nanoliter and VPD deposits of single element standards were film-like in character, while residues formed from much more complex matrices and higher mass loadings were particulate in character. For the experimental conditions used in this study (30 kV, 100 mA), typical TXRF spectral Fe limits of detection were calculated to be on the order of picograms or ∼1×10 10 atoms/cm 2 for a 0.8 cm 2 X-ray excitation beam area for both nanoliter dried spots and VPD spots prepared from single elemental standards. Calculated Fe detection limits for 200 mm diameter silicon wafers used in this study were in the ∼1×10 8 atoms/cm 2 range. By using nanoliter sized droplets, the required sample volume is greatly reduced resulting in higher sample throughput than with conventional VPD methods.

Phytoplankton community response to a manipulation of bioavailable iron in HNLC waters of the subtropical Pacific Ocean

Studies in high nutrient, low chlorophyll (HNLC) regions have demonstrated that increased Fe availability results in an increase in phytoplankton biomass and changes in community composition. Here we present experiments in which the availability of iron (Fe) was increased or reduced to monitor the response of individual groups of phytoplankton (large eukaryotes, pico- eukaryotes and cyanobacteria) by flow cytometry. Additions (0.5 to 5.0 nM Fe) and reductions in available Fe (through addition of 1 to 10 nM of the fungal siderophore desferrioxamine B) were made to enclosed communities from the South American eastern boundary current off Peru, where ambi- ent dissolved Fe concentrations were <100 pM. As predicted, chlorophyll concentrations increased in the added Fe treatments relative to the control, indicative of Fe limitation. Flow cytometry demon- strated that this was due to increases in the abundance of large eukaryotes that are Fe-starved under ambient conditions. Cyanobacterial abundance increased and decreased linearly with Fe availabil- ity, suggesting that cyanobacteria were Fe-limited but not Fe-starved. In contrast, picoeukaryote cell abundance increased with decreasing Fe availability, although chlorophyll cell -1 in this group responded in an inverse manner. The results demonstrate that members of the marine phytoplankton community respond differently to Fe availability, which may influence the outcome of biological competition among organisms in Fe-limited environments.

Iron limitation of phytoplankton in an urbanized vs. forested southeastern U.S. salt marsh estuary

Over the last two decades, escalating rates of coastal development have altered macro- and micronutrient loading patterns to many southeastern U.S. estuaries. This study addresses a potential consequence of urbanization-associated coastal deforestation that may have important implications for estuarine ecosystem productivity: a reduction in bioavailable Fe. We compared the potential for Fe limitation at representative sites in two neighboring South Carolina salt marsh estuaries, one (“Parsonage Creek” site in Murrells Inlet estuary) impacted by urbanization-associated clear-cutting, and the other (“Oyster Landing” site in North Inlet estuary) undeveloped and surrounded by forests. The urbanized estuarine site was marked by lower dissolved Fe concentrations compared to the forested estuarine site. In bioassay experiments conducted from 1996 to 1999, the addition of chelated Fe to natural phytoplankton populations stimulated chlorophyll a concentrations in water from Parsonage Creek on 6 of 11 sampling dates. Chlorophyll responses in Oyster Landing water also were observed on two of those sampling times, dates that followed periods of relatively low rainfall. In one experiment, the addition of Fe+NO 3 − to Parsonage Creek water led to significantly higher chlorophyll concentrations than when NO 3 − was added alone, but Fe+NH 4 + addition did not result in higher chlorophyll than NH 4 + addition alone. It was hypothesized that the difference in NO 3 − and NH 4 + responses was related to a greater tendency towards Si depletion in Fe-stressed NO 3 −-grown samples, or alternatively, to the higher Fe requirement for NO 3 − assimilation relative to that needed for NH 4 + assimilation. In bioassay experiments using Fe-deplete semi-continuous cultures of Synechococcus WH8101, Fe addition did not affect the net growth rate of cultures transferred to water from either estuary, but increased the chlorophyll a content of cells transferred to Parsonage Creek water. Finally, photosynthesis vs. irradiance parameters ( α, P max) obtained from Oyster Landing samples (<2 μm size fraction) were similar to those measured in Fe-replete Synechococcus continuous cultures, while the same parameters derived from Parsonage Creek samples were much lower and comparable to those from Fe-deplete cultures. The results indicate that phytoplankton population growth from high salinity salt marsh estuaries can be Fe-limited. Also, the potential for Fe limitation was more prevalent in a urbanized deforested estuary than in an undeveloped forested estuary, consistent with the hypothesis that organically bound Fe from coastal forests plays an important role in supplying Fe for the growth of estuarine phytoplankton.

Iron, nutrient and phytoplankton biomass relationships in upwelled waters of the California coastal system

We report measurements of dissolvable and particulate iron, particulate Al, nutrients and phytoplankton biomass in surface waters during the termination of one upwelling event and the initiation of a second event in August 2000. These events occurred in the area of the Año Nuevo upwelling center off the coast of central California. The first event was observed after ∼8 days of continuous upwelling favorable winds, while the second event was observed through the onset of upwelling favorable winds to wind reversals ∼3 days later. Coincident with the upwelling signatures of low temperature and high salinity were significantly elevated concentrations of nitrate and silicate with average concentrations greater than 15 and 20 μM, respectively, during both upwelling events. Dissolvable Fe concentrations (TD-Fe) were significantly higher in the second event, 6.5 versus 1.2 nM Fe found in the first event. Nitrate was reduced by ∼5 μM day −1 within this second upwelled plume as compared to a drawdown of ∼2 μM day −1 within the first plume. Silicate was reduced in a ratio of 1.2 mol Si:mol NO 3 in the high Fe waters of the second plume as compared to a ratio of 2.2 in the lower Fe waters of the first plume. The observed differences in nutrient utilization are consistent with some degree of iron limitation. The area of increased dissolvable Fe in the second upwelling event was coincident with elevated particulate Fe concentrations, indicating the particulate pool as a possible source of the observed increase in TD-Fe. The elevated particulate Fe in surface waters was a result of resuspended sediments in the bottom boundary layer (BBL) of the shallow shelf being transported to the surface during upwelling. Particulate (and dissolvable) iron concentrations were significantly reduced as upwelling continued. This was most probably due to a decoupling of the BBL from upwelled source waters as the upwelling front moved offshore and/or reduced turbulence in the BBL as upwelling continued. The observed reduction in both particulate and dissolvable Fe, as upwelling continued to deliver macronutrients to surface waters, may result in varying levels of Fe limitation.

Organic Acid Metabolism in Roots of Various Grapevine (Vitis) Rootstocks Submitted to Iron Deficiency and Bicarbonate Nutrition

The effects of Fe limitation and bicarbonate addition to the nutrient medium on the organic acid metabolism were investigated in the root tips of various grapevine genotypes. Cuttings of two limestone‐tolerant and two limestone‐susceptible Vitis genotypes were grown for four weeks in nutrient solutions containing 10 or 0.5 µM Fe. The effect of bicarbonate addition (5 mM) was studied for two of these genotypes. Compared to 10 µM, Fe limitation (0.5 µM) significantly increased citrate concentration in root tips after 2 weeks, and malate concentration after 4 weeks. When Fe limitation and bicarbonate addition were combined, citrate and malate concentrations were significantly increased after 2 weeks. Fe limitation or addition of 5 mM bicarbonate had a larger effect on citrate than on malate concentrations. Addition of 5 mM bicarbonate discriminated more clearly tolerant and susceptible genotypes than Fe limitation. High malate and citrate concentrations in the roots were associated to high PEPC activities. These results confirm that root organic acid metabolism is involved in grapevine response to Fe deficiency stress. If verified on a larger range of genotypes, a procedure using bicarbonate effect on root tip citrate concentration could be proposed to screen limestone‐tolerant Vitis rootstocks.

Iron requirements for dinitrogen‐ and ammonium‐supported growth in cultures of Trichodesmium (IMS 101): Comparison with nitrogen fixation rates and iron: carbon ratios of field populations

We quantified the relationships among the specific growth rate, intracellular iron content, and steady state iron uptake rate for cultures of the marine diazotrophic cyanobacterium Trichodesmium (IMS 101) grown under differing conditions of Fe and N availability. The Fe quotas necessary to support a moderately Fe‐limited growth rate (70% mmax) of 0.1 d−1 under diazotrophy and ammonium were 38 and 8 µmol mol−1, indicating a fivefold increased Fe cost for diazotrophy. This increased demand reflects the influences of both the ninefold lower marginal use efficiency and the greater maintenance Fe :C requirement at zero growth rate under diazotrophy (13.5 versus 5.2 µmol mol−1). For diazotrophic growth at µ = 0.1 d−1, we estimate that 19%–53% of the cellular Fe is bound in nitrogenase. Trichodesmium is capable of luxury uptake of at least 13‐fold greater amounts of Fe than needed for moderately Fe‐limited growth. At least half of the populations sampled from the continental shelf of northern Australia had Fe :C ratios within the range of iron limitation of laboratory cultures. Bottle incubations showed that, after 3–4 d with added iron, a low Fe :C population (21 µmol mol−1) had higher N2 fixation rates than controls, whereas a high Fe :C population (78 µmol mol−1) showed no response. The cellular N: P quotas and N2 fixation rates were compared to those previously reported for the Atlantic Ocean. Empirically, these data suggest a critical N: P ratio ~40–50 for the onset of P limitation of growth. Only 10% of the Trichodesmium populations from coastal Australia had N: P ratios within the putative P‐limitation range (&gt;40), whereas 40% the Atlantic populations fell within this range. These comparisons, along with those for N fixation versus colony Fe :C ratio, suggest that Fe limitation is more prevalent in the Australia Trichodesmium populations, while P limitation predominates in the Atlantic populations.

Characterization and field trials of a bioluminescent bacterial reporter of iron bioavailability

To better understand Fe cycling in marine and freshwater systems, we have developed a biomolecular tool to track the perceived bioavailability of Fe to heterotrophic bacteria. Bioluminescent reporters, constructed by fusing the fepA–fes promoter of Escherichia coli (an Enterobactin biosynthesis gene regulated by the ferric uptake regulatory [Fur] system) to a luxCDABE cassette, were integrated into the chromosome of a halotolerant Pseudomonas putida, which uses the Fur system to regulate high-affinity Fe uptake. The resultant P. putida bioreporter has been successfully tested both in lab and field studies. Laboratory cultures were maintained at a range of concentrations of total Fe (0–25 nM) or limited by the addition of concentrations of well-characterized siderophores (desferrioxamine B [DFB], ferrichrome, 2,2′-dipyridyl [DP] and Rhodotorulic acid [RA], 0–200 nM) and used to establish the dynamic range of this reporter system. Analysis of sample incubations after only 4 h suggest that both of the trihydroxamate-type siderophores DFB and ferrichrome efficiently reduced Fe availability, resulting respectively in a 1.77- and 1.88-fold increase in luminescence relative to Fe-replete conditions. In contrast, additions of the dihydroxamate-type siderophore RA and the synthetic chelator DP resulted in no response from the system, suggesting that cells could access Fe complexed to these compounds without activating high-affinity Fe transport systems. Field studies were performed in the central basin of Lake Erie, which has previously been shown to undergo sporadic Fe limitation during summer stratification. DFB concentrations were titrated across a range of 0–50 nM into unfiltered water to manipulate Fe availabilities. Bioreporters expressed Fe stress (ca. a 2-fold increase in luminescence) at concentrations of DFB equivalent to the total (dissolved+particulate) Fe in the system (≈30 nM), indicative of the concentration of bioavailable Fe. In a similar experiment with 0.2-μm pre-filtered water (2.25–5.24 nM Fe), a 6-fold increase in luminescence (relative to controls) was observed at the lowest (15 nM) concentration of chelators. The results of this study demonstrate the validity of bioreporters as a complimentary tool to measurements of total Fe. Moreover, these results suggest that a significant source of bioavailable Fe flux may be particulate in nature, and support the hypothesis that Fe recycling from microorganisms may play a key role in the regeneration of bioavailable forms of Fe.

Effect of Fe on the constitution of Cu–W alloys at 1200 °C

The phase equilibria of the Cu–W–Fe system were studied experimentally, except for the Cu–Fe limit region. The isothermal section at 1200 °C was determined from analysis of the phases formed after thermal treatment. Forced sedimentation and immersion techniques were used for a reliable sampling of the liquid involved in the liquid/solid phase equilibria. Equilibrium results were complemented by diffusion couple-type experiments. From the Cu–W side, the phase fields formed with increasing Fe content were: {Cu-based liquid+b.c.c. W}, {Cu-based liquid+b.c.c. W+Fe 7W 6}, {Cu-based liquid+Fe 7W 6}, {Cu-based liquid+Fe 7W 6+b.c.c. Fe} and {Cu-based liquid+b.c.c. Fe}. In the ternary system the homogeneity ranges of the Cu-based liquid, b.c.c. W and Fe 7W 6 are very similar to those of the binary phases.

A trace metal clean reagent to remove surface-bound iron from marine phytoplankton

Many recent studies have investigated Fe biogeochemical cycling, chemical speciation, and limitation of phytoplankton growth in the ocean. In current models of marine iron biogeochemistry, however, two critical parameters remain uncertain. These are the partitioning of particulate iron into scavenged and interior pools, and the iron quotas (Fe/C ratios) of natural plankton communities. These values have not been measured in natural samples, because the only reagent that is available to remove surface adsorbed Fe from cells and other particles (Ti(III) citrate/EDTA [Limnol Oceanogr 34 (1989) 1113]) contains substantial levels of contaminating Fe, and is therefore useful only for Fe radiotracer experiments. We developed a new reagent that differentiates between intra- and surface adsorbed Fe pools in marine phytoplankton as effectively as the Ti wash, but that is also trace metal clean, chemically stable, and harmless to cells. This reagent uses oxalate as a reductant to remove surface adsorbed Fe from phytoplankton cells and other particles. A simple cleaning protocol reduces Fe concentrations in the oxalate solution to levels suitable for trace metal clean field measurements. The oxalate reagent was used to measure scavenged and interior Fe pools in suspended particles collected at four stations in the Southern Ocean. Sixteen percent to eighty-six percent of the total Fe associated with these samples was found to be surface-adsorbed. The oxalate reagent provides a new tool to accurately measure the physical partitioning of Fe in marine particles and could be used along with appropriate corrections for lithogenic Fe to estimate the intracellular Fe quotas of natural plankton communities.

Effect of iron limitation on the cadmium to phosphorus ratio of natural phytoplankton assemblages from the Southern Ocean

There is considerable interest in the biogeochemical cycling of cadmium (Cd) and phosphate (PO4) in surface waters, driven in part by the ongoing development of a paleonutrient proxy that utilizes Cd preserved in fossil planktonic foraminifera to determine past PO4 utilization efficiencies in ocean surface waters. The present article reports the results of a field study into the effects of Fe limitation on the Cd : P composition of natural assemblages of marine phytoplankton in the Antarctic Zone of the Pacific sector of the Southern Ocean. Iron enrichment to shipboard incubation bottles led to increases in community growth rate and final biomass. After 10.7 d of incubation, the climax community was dominated by large diatoms of the genus Fragillariopsis, Pseudonitzschia , and Nitzschia. Direct measurements of phytoplankton metal : P ratios from controlled shipboard experiments indicate that Cd : P, Co: P, and Zn : P ratios decreased from control values with increasing initial dissolved Fe concentrations in the incubation bottles, by factors of ~2–10 at highest Fe additions. We suggest that the effect of Fe limitation on resident diatoms is to decrease growth rate, leading to elevated cellular Cd content. The dissolved Cd : P ratio in iron‐limited surface waters of the Southern Ocean may, therefore, respond to the supply of Fe to the resident phytoplankton community, which has implications for the developing paleonutrient proxy. We suggest that the biological uptake of Cd and P is independent of the dissolved Cd: PO4 ratio. As a consequence, the results argue against the use of empirical Rayleigh fractionation models or models with fixed phytoplankton uptake ratios to account for regional variability in surface water dissolved Cd : PO4.