Pore Waters and the Transformation of Nutrients in Marine Subtidal Sands

The contents of ammonia, nitrites, nitrates, phosphates, and silicates were measured in pore waters of subtidal sands in Vostok Bay, the Sea of Japan. The exchange of nutrients between sand and pore waters was studied in the laboratory using a running-water system while percolating the ground with seawater. The composition of pore waters depended on the method and length of time spent sampling, and also on the distance from the ground surface. Statistical analysis did not reveal stable profiles of nutrient concentrations in sand. The velocities of the release and consumption of nutrients in the experiments were rather low and depended on temperature, length of time spent sampling, duration of measurements, and distance from the sand surface. Release and consumption were connected with absorption and desorption, and were not due solely to the biological process of mineralization of organic matter. Analysis of the data obtained is complicated by the canalization of the water flow in the sand and by the consolidation of the sediment during the measurements. The comparison of pore and near-bottom waters makes it possible to hypothesize that the mineralization of organic matter and the release of nutrients into the pore waters occur throughout the whole column of sediment. The mixing of the seawater and groundwater occurs as a result of advection processes, the most important of which is wave percolation.     

Chromatographic study of magnesium and calcium binding to immobilized human serum albumin

The use of immobilized human serum albumin (HSA) as a stationary phase in affinity chromatography has been shown to be useful in resolving optical antipodes or to investigate interactions between drugs and protein. However, to our knowledge, no inorganic ion binding has been studied on this immobilized protein type. To do this, the human serum albumin stationary phase was assimilated to a weak cation-exchanger by working with a mobile phase pH equal to 6.5. A study of the eluent ionic strength effect on ion retention was carried out by varying the buffer concentrations and the column temperatures. The thermodynamic parameters for magnesium and calcium transfer from the mobile to the stationary phase were determined from linear van’t Hoff plots. An enthalpy–entropy compensation study revealed that the type of interaction was independent of the mobile phase composition. A simple model based on the Gouy–Chapman theory was considered in order to describe the retention behavior of the test cations with the mobile phase ionic strength. From this theoretical approach, the relative charge densities of the human serum albumin surface implied in the binding process were estimated at different column temperatures.     

Soil phosphorus flux from emergent marsh wetlands and surrounding grazed pasture uplands

Phosphorus (P) release from wetland soils to overlying waters is important to consider when restoring wetland hydrology. Soil physicochemical characteristics influence P dynamics between underlying soil and overlying water. Our study initially characterized wetland and surrounding upland soils prior to flooding. Deep marsh wetland soils had greater moisture content, soil organic matter, nitrogen (N), P, and lower bulk density than surrounding upland pasture soils, which indicates a nutrient concentration gradient between wetland and upland soils. To determine the short-term P dynamics between soils and overlying water, we conducted four laboratory soil water core studies during a 15-month period. Surface soils (0-10 cm) collected October 2005, February 2006, October 2006 and December 2006 from wetlands and their surrounding uplands within cow-calf grazed pastures were flooded for 7 days, and we measured P release from soil to overlying water. Phosphorus release rates from wetland (deep marsh and shallow marsh) and upland soils were similar. Values ranged between ?20 mg m^?2 d^?1 (retention) and 77 mg m^?2 d^?1 (release). There was a significant, although weak, negative linear relationship between P release from deep marsh soils and hydroperiod. Thus, it may be important for land managers to consider increasing hydroperiod of wetland soils to decrease P release and increase retention. In addition, there was a significant negative exponential relationship between P release and days since deep marsh soil inundation. This suggests that to decrease P release from soils, soils should be wet rather than dry for prolonged periods, prior to flooding. We found significant relationships between P release from upland soils and their nutrient content (N, P and carbon). Reducing nutrient content in upland soils may help reduce the magnitude of P release from soil.     

Mobilization of broad host range plasmid from Pseudomonas putida to established biofilm of Bacillus azotoformans. I. Experiments

A strain of Pseudomonas putida harboring plasmids RK2 and pDLB101 was exposed to a pure culture biofilm of Bacillus azotoformans grown in a rotating annular reactor under three different concentrations of the limiting nutrient, succinate. Experimental results demonstrated that the broad host range RSF1010 derivative pDLB101 was transferred to and expressed by B. azotoformans. At the lower concentrations, donor mediated plasmid transfer increased with increasing nutrient levels, but the highest nutrient concentration yielded the lowest rate of donor to recipient plasmid transfer. For transconjugant initiated transfer, the rate of transfer increased with increasing nutrient concentrations for all cases. At the lower nutrient concentrations, the frequency of plasmid transfer was higher between donors and recipients than between transconjugants and recipients. The reverse was true at the highest succinate concentration. The rates and frequencies of plasmid transfer by mobilization were compared to gene exchange by retrotransfer. The initial rate of retrotransfer was slower than mobilization, but then increased dramatically. Retrotransfer produced a plasmid transfer frequency more than an order of magnitude higher than simple mobilization.     

The effect of substratum type, orientation and depth on the development of bacterial deep-sea biofilm communities grown on artificial substrata deployed in the Eastern Mediterranean

An increasing number of deep-sea studies have highlighted the importance of deep-sea biofouling, especially in relation to the protection of deep-sea instruments. In this study, the microbial communities developed on different substrata (titanium, aluminum, limestone, shale and neutrino telescope glass) exposed for 155 days at different depths (1500?m, 2500?m, 3500?m and 4500 m) and positions (vertical and horizontal) in the Eastern Mediterranean Deep Sea were compared. Replicated biofilm samples were analyzed using a Terminal Restriction Fragment Length Polymorphisms (T-RFLP) method. The restriction enzymes CfoI and RsaI produced similar total numbers (94, 93) of different T-RFLP peaks (T-RFs) along the vertical transect. In contrast, the mean total T-RF number between each sample according to substratum type and depth was higher in more samples when CfoI was used. The total species richness (S) of the bacterial communities differed significantly between the substrata, and depended on the orientation of each substratum within one depth and throughout the water column (ANOVA). T-RFLP analyses using the Jaccard similarity index showed that within one depth layer, the composition of microbial communities on different substrata was different and highly altered among communities developed on the same substratum but exposed to fouling at different depths. Based on Multidimensional Scaling Analyses (MDS), the study suggests that depth plays an important role in the composition of deep-sea biofouling communities, while substratum type and orientation of substrata throughout the water column are less important. To the authors' knowledge, this is the first study of biofilm development in deep waters, in relation to the effects of substratum type, orientation and depth.     

Transport of groundwater-borne nutrients from watersheds and their effects on coastal waters

Anthropogenic activities on coastal watersheds increase nutrient concentrations of groundwater. As groundwater travels downslope it transports these nutrients toward the adjoining coastal water. The resulting nutrient loading rates can be significant because nutrient concentrations in coastal groundwaters may be several orders of magnitude greater than those of receiving coastal waters. Groundwater-borne nutrients are most subject to active biogeochemical transformations as they course through the upper 1 m or so of bottom sediments. There conditions favor anaerobic processes such as denitrification, as well as other mechanisms that either sequester or release nutrients. The relative importance of advective vs. regenerative pathways of nutrient supply may result in widely different rates of release of nutrients from sediments. The relative activity of denitrifiers also may alter the ratio of N to P released to overlying waters, and hence affect which nutrient limits growth of producers. The consequences of nutrient (particularly nitrate) loading include somewhat elevated nutrient concentrations in the watercolumn, increased growth of macroalgae and phytoplankton, reduction of seagrass beds, and reductions of the associated fauna. The decline in animals occurs because of habitat changes and because of the increased frequency of anoxic events prompted by the characteristically high respiration rates found in enriched waters.     

Development of associations between microalgae and denitrifying bacteria in streams of contrasting anthropogenic influence

We compared the development of microalgal and bacterial-denitrifier communities within biofilms over 28 days in a restored-prairie stream (RP) and a stream receiving treated wastewater effluent (DER). Inorganic nutrient concentrations were an order of magnitude greater in DER, and stream waters differed in the quality of dissolved organics (characterized via pyrolysis-GC/MS). Biofilm biomass and the densities of algae and bacteria increased over time in both systems; however, algal and denitrifier community composition and the patterns of development differed between systems. Specifically, algal and denitrifier taxonomic composition stabilized more quickly in DER than RP, whereas the rates of algal and denitrifier succession were more closely coupled in RP than DER. We hypothesize that, under unenriched conditions, successional changes in algal assemblages influence bacterial denitrifiers due to their dependence on algal exudates, while under enriched conditions, this relationship is decoupled. Between-system differences in organic signatures supported this, as RP biofilms contained more labile, aliphatic compounds than DER. In addition, potential denitrification rates (DNP) were negatively correlated with the percentage of aromatic compounds within the biofilm organic signatures, suggesting a significant relationship between algal exudate composition and denitrification. These results are significant because anthropogenic factors that affect biofilm community composition may alter their capacity to perform critical ecosystem services.     

Transport of groundwater-borne nutrients from watersheds and their effects on coastal waters

Anthropogenic activities on coastal watersheds increase nutrient concentrations of groundwater. As groundwater travels downslope it transports these nutrients toward the adjoining coastal water. The resulting nutrient loading rates can be significant because nutrient concentrations in coastal groundwaters may be several orders of magnitude greater than those of receiving coastal waters. Groundwater-borne nutrients are most subject to active biogeochemical transformations as they course through the upper 1 m or so of bottom sediments. There conditions favor anaerobic processes such as denitrification, as well as other mechanisms that either sequester or release nutrients. The relative importance of advective vs. regenerative pathways of nutrient supply may result in widely different rates of release of nutrients from sediments. The relative activity of denitrifiers also may alter the ratio of N to P released to overlying waters, and hence affect which nutrient limits growth of producers. The consequences of nutrient (particularly nitrate) loading include somewhat elevated nutrient concentrations in the watercolumn, increased growth of macroalgae and phytoplankton, reduction of seagrass beds, and reductions of the associated fauna. The decline in animals occurs because of habitat changes and because of the increased frequency of anoxic events prompted by the characteristically high respiration rates found in enriched waters.     

The effects of biofilms on chemical processes in surficial sediments

1. The objectives of the present work were: (a) to evaluate the effects of the development and the presence of a photosynthetically active algal biofilm on chemical fluxes and processes at the sediment–water interface; (b) to measure the effects of the biofilm on chemical concentration gradients in the bulk sediment; and (c) to monitor pH and dissolved oxygen concentration in the biofilm, and through the sediment–water interface using microelectrodes. 2. Two experiments were performed over a period of 8 weeks using a recirculating fluvarium channel containing river sediments with an exposed surface of 0.2 m² and 20 dm³ of overlying solution. The first experiment was in darkness with minimal effects of a photosynthetically active biofilm. The second experiment in natural light produced a complex photosynthetic biofilm involving a succession of diatoms, green algae and cyanobacteria. 3. The solution overlying the biofilm was monitored continuously for dissolved calcium, silicon, phosphorus, alkalinity and oxygen, as well as conductivity, temperature and pH. The surface of the sediment was also monitored for biological and physical changes as the biofilm developed. The overlying solution was analysed over a period of 48 h at 2-h intervals to examine the effects of a well-developed algal biofilm. At the end of the 48 h, pH and oxygen microelectrodes were used to measure gradients above and through the biofilm, and porewaters were analysed from sediments which had been longitudinally sectioned at a maximum depth resolution of 0.5 mm. 4. Biofilm development had a large influence on the composition of the overlying solution and the development of vertical concentration gradients of solutes in the porewater. Once a diatom community was established, the concentration of dissolved silicon was low (< 40 μm ), with all the silicon diffusing from the underlying sediment being consumed in the biofilm (≈ 0.026 μmol m^?2 s^?1 at the end of the experiment). 5. The concentrations of calcium, alkalinity and phosphorus in digested sediment increased near the sediment–water interface. X-ray diffraction analysis showed that calcite was formed at the surface. Estimation of the fluxes of alkalinity and calcium in the overlying solution were consistent with calcite formation during daylight and possible dissolution in darkness. The maximum precipitation flux of calcium was 0.87 μmol m^?2 s^?1 and the maximum net release flux was 0.89 μmol m^?2 s^?1. 6. The net loss of soluble reactive phosphorus from the overlying solution measured over the intensive sampling period of 48 h is consistent with a coprecipitation mechanism and a surface density of phosphorus included in the lattice of calcite of 0.097 μmol m^?2. Processes in the biofilm rather than diffusion from the sediment porewater control chemical fluxes of calcium, alkalinity and phosphorus from the sediment to the overlying water.     

The effect of substratum type,orientation and depth on the development of bacterial deep-sea biofilm communities grown on artificial substrata deployed in the Eastern Mediterranean

An increasing number of deep-sea studies have highlighted the importance of deep-sea biofouling, especially in relation to the protection of deep-sea instruments. In this study, the microbial communities developed on different substrata (titanium, aluminum, limestone, shale and neutrino telescope glass) exposed for 155 days at different depths (1500 m, 2500 m, 3500 m and 4500 m) and positions (vertical and horizontal) in the Eastern Mediterranean Deep Sea were compared. Replicated biofilm samples were analyzed using a Terminal Restriction Fragment Length Polymorphisms (T-RFLP) method. The restriction enzymes CfoI and RsaI produced similar total numbers (94, 93) of different T-RFLP peaks (T-RFs) along the vertical transect. In contrast, the mean total T-RF number between each sample according to substratum type and depth was higher in more samples when CfoI was used. The total species richness (S) of the bacterial communities differed significantly between the substrata, and depended on the orientation of each substratum within one depth and throughout the water column (ANOVA). T-RFLP analyses using the Jaccard similarity index showed that within one depth layer, the composition of microbial communities on different substrata was different and highly altered among communities developed on the same substratum but exposed to fouling at different depths. Based on Multidimensional Scaling Analyses (MDS), the study suggests that depth plays an important role in the composition of deep-sea biofouling communities, while substratum type and orientation of substrata throughout the water column are less important. To the authors’ knowledge, this is the first study of biofilm development in deep waters, in relation to the effects of substratum type, orientation and depth.     

Competitive interaction of monovalent cations with DNA from 3D-RISM

The composition of the ion atmosphere surrounding nucleic acids affects their folding, condensation and binding to other molecules. It is thus of fundamental importance to gain predictive insight into the formation of the ion atmosphere and thermodynamic consequences when varying ionic conditions. An early step toward this goal is to benchmark computational models against quantitative experimental measurements. Herein, we test the ability of the three dimensional reference interaction site model (3D-RISM) to reproduce preferential interaction parameters determined from ion counting (IC) experiments for mixed alkali chlorides and dsDNA. Calculations agree well with experiment with slight deviations for salt concentrations >200 mM and capture the observed trend where the extent of cation accumulation around the DNA varies inversely with its ionic size. Ion distributions indicate that the smaller, more competitive cations accumulate to a greater extent near the phosphoryl groups, penetrating deeper into the grooves. In accord with experiment, calculated IC profiles do not vary with sequence, although the predicted ion distributions in the grooves are sequence and ion size dependent. Calculations on other nucleic acid conformations predict that the variation in linear charge density has a minor effect on the extent of cation competition.     

The contribution of <Emphasis Type="Italic">Potamogeton crispus</Emphasis> to the phosphorus budget of an urban shallow lake: Lake Monger,Western Australia

Lake Monger (Perth, Western Australia) is a highly eutrophic lake, characterised by very low species richness of macrophytes with the dominance of Potamogeton crispus. Mesocosm experiments were performed using water and plants collected from the lake to determine the effects of vegetation decay on the phosphorus (P) concentrations in the overlying waters. After 2 weeks of experimental incubation of mesocosms with and without re-oxygenation, P concentrations in the water column were significantly higher, showing a quite similar effect of P. crispus on the phosphorus release in different mesocosms. The results of our study provide clear evidence that the P concentrations in overlying waters mainly depend upon the plant P content and developmental stage. Although many sources contribute to the nutrient load of Lake Monger, macrophyte harvesting, prior to its senescence, might constitute a significant in-lake measure for reducing the internal P load.     

Nutrient cycling and productivity in a desert saline lake: observations from a dry,low-productivity year

Seasonal variability of nutrients and productivity were examined in Pyramid Lake, a hyposaline, N-deficient, terminal desert lake, during a dry period. River inflow and N-fixation during 1990 were minimal allowing internal nutrient cycling to be more closely studied. Nutrient cycling was strongly affected by seasonal thermal stratification that was typical for a warm monomictic lake. Concentrations of nitrate, phosphate, and silicate in surface waters were highest during winter mixing and decreased rapidly in the spring due to a diatom bloom. Maximum average chlorophyll concentration in surface waters was 2.7 ± 1.2 µg 1^–1 and occurred in April while surface nutrients were being depleted. In contrast to chlorophyll, maximum particulate carbon in surface waters occurred in July–August when areal productivity was highest (367–398 mg C m^–2 day^–1). Concurrent with spring nutrient depletion in surface waters was increasing N-deficiency in the plankton. After the spring bloom dissipated in May, particulate matter (POM) became increasingly N-deficient reaching maximum elemental C : N of > 18 during summer-fall. Profiles of the C : N ratio of POM were nearly constant with depth for individual sampling dates suggesting that the residence time of POM in the water column was short (< 1 month). While surface waters were nutrient depleted during summer stratification, nutrient concentrations of bottom waters progressively increased, presumably through the oxidation of POM sinking to the bottom (103 m). Converting the rate of oxygen depletion in bottom waters to carbon equivalents of POM suggests that 42 % of mean annual phytoplankton production in overlying waters during 1990 was mineralized in bottom waters.     

Effects of starvation and different culture conditions on the phospholipid content of isolated pancreatic islets

Three forms of the normal human plasma fibrinogen gamma-chain which differ in molecular weight have been purified. Plasma fibrinogen was separated by ion exchange chromatography on DEAE-Sephacel into three populations of molecules, each with a unique gamma-chain composition. Following reduction and S-carboxymethylation, the fibrinogen polypeptide chains in each chromatographic peak were separated by ion exchange chromatography on DEAE-Sephacel and identified following sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The A alpha, B beta and smallest gamma-chain (gamma 50) eluted at progressively higher ionic strengths, but the elution positions of A alpha, B beta and gamma 50 chains were identical for fibrinogen from each of the three different chromatographic fractions. The unique gamma chain of fibrinogen in the second chromatographic peak (gamma 55) eluted at an ionic strength higher than that of the gamma 50 chain, while the largest gamma-chain (gamma 57.5), which was contained only in the third chromatographic peak of fibrinogen, eluted at the highest ionic strength. The higher ionic strengths needed to elute fibrinogen in the second and third peaks was paralleled by the higher ionic strengths needed to elute the gamma-chains unique to them, suggesting that the gamma-chain composition of the three fibrinogen fractions accounted for their differential binding to the ion exchange resin. Following desialation with neuraminidase, the differences in electrophoretic mobilities between the three gamma-chain forms was maintained, indicating that differential migration on SDS-polyacrylamide gel electrophoresis was not due to variation in sialic acid content.     

Nutrient uptake in streams draining agricultural catchments of the midwestern United States

1. Agriculture is a major contributor of non‐point source pollution to surface waters in the midwestern United States, resulting in eutrophication of freshwater aquatic ecosystems and development of hypoxia in the Gulf of Mexico. Agriculturally influenced streams are diverse in morphology and have variable nutrient concentrations. Understanding how nutrients are transformed and retained within agricultural streams may aid in mitigating increased nutrient export to downstream ecosystems. 2. We studied six agriculturally influenced streams in Indiana and Michigan to develop a more comprehensive understanding of the factors controlling nutrient retention and export in agricultural streams using nutrient addition and isotopic tracer studies. 3. Metrics of nutrient uptake indicated that nitrate uptake was saturated in these streams whereas ammonium and phosphorus uptake increased with higher concentrations. Phosphorus uptake was likely approaching saturation as evidenced by decreasing uptake velocities with concentration; ammonium uptake velocity also declined with concentration, though not significantly. 4. Higher whole‐stream uptake rates of phosphorus and ammonium were associated with the observed presence of stream autotrophs (e.g. algae and macrophytes). However, there was no significant relationship between measures of nutrient uptake and stream metabolism. Water‐column nutrient concentrations were positively correlated with gross primary production but not community respiration. 5. Overall, nutrient uptake and metabolism were affected by nutrient concentrations in these agriculturally influenced streams. Biological uptake of ammonium and phosphorus was not saturated, although nitrate uptake did appear to be saturated in these ecosystems. Biological activity in agriculturally influenced streams is higher relative to more pristine streams and this increased biological activity likely influences nutrient retention and transport to downstream ecosystems.     

Role of sulfate‐reducing bacteria in corrosion of mild steel: A review

The influence of sulfate‐reducing bacteria on corrosion of mild steel is reviewed, with special emphasis on the effects of biofilm structure and function, medium composition (dissolved oxygen and ferrous ion concentrations) and the physical and chemical properties of iron sulfides. A summary of different corrosion mechanisms is critically discussed, based on electrochemical and rate process analyses. A mechanism is proposed which explains the high corrosion rates observed in the field.     

How light and nutrients affect the relationship between autotrophic and heterotrophic biomass in a tropical black water periphyton community

This study examines how nutrients and light affect the relationship between autotrophic biomass and non-autotrophic periphyton organic matter in a tropical black water lake biofilm community. We hypothesized that there is no positive correlation between autotrophic and non-autotrophic organic matter in the periphytic community of a black water humic lake, where non-algal components of periphyton can rely on carbon sources external to the periphyton matrix and where nutrient availability is low. Second, we sought to test our hypothesis that non-autotrophic periphyton organic matter will benefit from nutrient enhancement in a lake where the availability of DOC is high. We performed a field experiment using in situ lake mesocosms to manipulate nutrient concentrations and light availability in a 2 × 2 factorial design. Control treatments (no nutrient added) and nutrient treatments (N + P) were compared in different light conditions: high light (near surface water) and low light (near bottom). No positive correlation was found between autotrophic biomass and non-autotrophic periphyton organic matter, but a negative correlation was observed in high nutrient and light conditions. The low C:P and N:P ratios revealed that the non-autotrophic organic matter mostly comprised a heterotrophic microbial biofilm. High levels of light and nutrients together caused significant changes in periphyton community properties. The non-autotrophic periphyton organic matter was negatively affected by nutrient addition, whereas autotrophic biomass was positively affected, especially in high light conditions. Our results strongly suggest that non-autotrophic periphyton organic matter in a humic lake is primarily comprised of a bacterial biofilm that directly competes for nutrients with autotrophs in the periphytic community. We also observed no effect of nutrient addition on periphyton growing in light-limited conditions. These results suggest that heterotrophic periphytic organisms might experience carbon limitation despite the high availability, but usually low quality, of dissolved carbon in the water column of humic lakes.     

Kinetics of ion exchange process for separation of glutamic acid

Kinetics of the separation of L-glutamic acid (GLU) by ion exchange has been studied with strongly acidic H⁺-type cation exchange resin Amberlite IR-122. Since glutamic acid is a trivalent ampholyte and dissociates according to three equilibrium reactions, separation of G⁺ ions by a cation exchange process is accompanied by the dominant reversible reaction, i.e. G⁺+H⁺ ? G⁰. Accompanying reversible reaction has an effect on the ion exchange rate, and decreases the performance of the process comparing with the ideal case that the exchanging ions retain their identity. The analysis was performed first with the ion exchange column, DIC (L/D=0.52); and then with the ion exchange column, IC (L/D=10.9). The data were collected with model glutamic acid solutions for both DIC and IC columns/reactors. IC experimental results were then compared with that of DIC and the effect of scale up on ion exchange process was investigated. The experimental results have provided an adequate basis for the design calculations, and the design parameters were determined. Rate coefficients for the liquid phase mass transfer controlled cation exchange process were calculated and interrelated with a plot of j _Mfactor versus Reynolds number.     

Possible allosteric significance of water structures in proteins

In recent theoretical molecular dynamics studies of ion solvation and transport through the model peptide ionophore, gramicidin A, it has been observed that the waters forming a linear single file within the channel have solvation and dynamic properties quite different from those found in bulk water. Strongly correlated motions among the interior single file column of waters persist over 20 A. A speculation is entertained that related water structures could provide a mechanism for long range enzymatic allosteric effects as an alternative to chemical action at a distance propagated through the protein itself. Two possible specific mechanisms are discussed, hydraulic and "proton wire". As a further control mechanism, the possibility is considered of modulating the allosteric effect though protein motion to open or close the channel thus producing a "valve" in the hydraulic line or a "switch" in the proton wire.     

Salt sensitivity in wheat : a case for specific ion toxicity

Two selected lines of bread wheat, Triticum aestivum L., differing in their relative salt resistance, were grown in isosmotic solutions of different ionic compositions to investigate sensitivity to specific ions. Growth rates and ion accumulation were determined. The salt composition of the various solutions had little effect on the growth of the salt-resistant line, but significantly affected that of the salt-sensitive line. Specifically, solutions containing high Na⁺ concentrations were more toxic than those containing high Cl⁻ concentrations or high concentrations of nutrient ions. There were few differences in ion accumulation between lines in a given treatment, although the sensitive line tended to accumulate more Na⁺ than the tolerant line in the salt treatments with high Na⁺ concentrations. The overall results provide evidence that there is a definite specific ion effect which is related to salt sensitivity in wheat. It is suggested that superior compartmentation of toxic ions, principally Na⁺, may be a mechanism of salt resistance in this case.