Species In Soil Solution Research Articles

Reduction of Dimethylarsenate to Highly Toxic Dimethylarsenite in Paddy Soil and Rice Plants.

Dimethylarsenate [DMAs(V)] is a common methylated As species in soils and plants and can cause the physiological disorder straighthead disease in rice. Because DMAs(V) is relatively noncytotoxic, we hypothesize that phytotoxicity of DMAs(V) may arise from trivalent dimethylarsenite [DMAs(III)]. DMAs(III) has been detected in human urine samples but not in environmental samples, likely due to its instability under oxic conditions. We first established methods for preservation and detections of DMAs(III) in soil and plant samples. We showed that DMAs(III) was a major As species in soil solution from an anoxic paddy soil. Enrichment cultures for fermentative, sulfate-reducing, and denitrifying bacteria from the paddy soil could reduce DMAs(V) to DMAs(III). Twenty-two strains of anaerobic bacteria isolated from the soil showed some ability to reduce DMAs(V). Rice plants grown in hydroponic culture with DMAs(V) also showed the ability to reduce DMAs(V) to DMAs(III). Rice plants and grains grown in a flooded paddy soil contained both DMAs(V) and DMAs(III); their concentrations were higher in the spikelets with straighthead disease than those without. DMAs(III) was much more toxic to the protoplasts isolated from rice plants than DMAs(V). Taken together, the ability to reduce DMAs(V) to highly toxic DMAs(III) is common to soil anaerobes and rice plants.

Chemical speciation of copper and manganese in solution of a copper-contaminated soil and young grapevine growth with amendment application

Copper (Cu)-based fungicide application to control foliar diseases in grapevine (Vitis vinifera L.) can increase soil Cu availability. Brazilian soils have high natural Cu and manganese (Mn) concentrations, increasing the potential for toxicity to grapevine plants. Application of amendment substances can reduce the concentrations of toxic chemical species of Cu and Mn in soil solution, especially for the soils grown with young plants. We evaluated the chemical speciation of Cu and Mn in soil solution and young grapevine growth using a contaminated soil with amendment application. Grapevine seedlings of Paulsen 1103 rootstock were grown for 12 months on an old vineyard (> 30 years of cultivation) soil without (control) and with vermicompost or limestone application. Grapevine dry matter, root morphological characteristics, and plant tissue Cu and Mn concentrations were evaluated. The cation and anion concentrations, dissolved organic carbon, pH, and chemical speciation of Cu and Mn in soil solution from different soil layers were analyzed. Vermicompost application did not reduce Cu and Mn phytotoxicity, and grapevine plants died after winter pruning. High soluble Mn concentration in soil (5.56 mg L–1 in 0–45 cm soil layer) and Mn concentration in plant tissue at pruning (380.8 mg kg–1) might be the primary cause of plant death. Limestone application reduced Cu2+ and Mn2+ chemical species in soil solution, thereby increasing plant growth. The Cu2+ and Mn2+ species were negatively correlated (P < 0.05) with grapevine shoot production at pruning (r = –0.92 and –0.97, respectively) and at the end of the trial (r = –0.73 and –0.51, respectively). Limestone application increased grapevine shoot and root dry matter production by 36% and 41%, respectively, while also presenting the highest root length and volume in the 5–10 cm soil layer. Limestone application is a viable and profitable alternative for reducing soil Cu and Mn availability and their phytotoxic effects.

Dissolution and Retention Process of CeO2 Nanoparticles in Soil with Dynamic Redox Conditions.

The time-course association of soil physicochemical properties and fate of CeO2 nanoparticles (NPs) is not well understood. This study for the first time investigated the dissolution and retention of CeO2 NPs (<25 nm) during soil short-term (6 h) and long-term (30 d) aging processes with dynamic redox conditions. Under the additional reductant-induced initial reductive condition, theoretically, up to 220‰ of Ce(IV) was temporarily reductively dissolved within 10 min, accompanied by a slow retention process (180 min) of Ce species in soil solutions. Conversely, the dissolution and slow retention of Ce species were not significant in soil solutions without added reductant. X-ray absorption near edge spectroscopy (XANES) shows that most of Ce species were present as Ce(IV) (94.0%-97.8%) in all soils after a long-term aging process. These results indicate that the soil dynamic redox conditions induced by oxidant/reductant intrinsically determined the different time-course dissolution and retention of CeO2 NPs, highlighting the occasional reductive condition in soil solution that may contribute to the migration and diffusion of Ce species. The time-course study should be also adopted to develop a comprehensive understanding of the nano-soil interactions.

Silicon Cycling in Soils Revisited.

Silicon (Si) speciation and availability in soils is highly important for ecosystem functioning, because Si is a beneficial element for plant growth. Si chemistry is highly complex compared to other elements in soils, because Si reaction rates are relatively slow and dependent on Si species. Consequently, we review the occurrence of different Si species in soil solution and their changes by polymerization, depolymerization, and condensation in relation to important soil processes. We show that an argumentation based on thermodynamic endmembers of Si dependent processes, as currently done, is often difficult, because some reactions such as mineral crystallization require months to years (sometimes even centuries or millennia). Furthermore, we give an overview of Si reactions in soil solution and the predominance of certain solid compounds, which is a neglected but important parameter controlling the availability, reactivity, and function of Si in soils. We further discuss the drivers of soil Si cycling and how humans interfere with these processes. The soil Si cycle is of major importance for ecosystem functioning; therefore, a deeper understanding of drivers of Si cycling (e.g., predominant speciation), human disturbances and the implication for important soil properties (water storage, nutrient availability, and micro aggregate stability) is of fundamental relevance.

Arsenic geochemistry and mineralogy as a function of particle-size in naturally arsenic-enriched soils

Naturally arsenic (As) enriched agricultural soils represent a significant global human health risk. In this study, As fractionation and mineralogy were investigated in naturally As-enriched agricultural soils and their corresponding sand, silt and clay fractions. Median As increased generally in the order (mg/kg)∶ silt (280) < bulk (314) < sand (323)<clay (484). Sequential extraction showed that amorphous and well-crystalline Fe- and Al-oxide bound and residual As forms accounted 27-42% of total As. Well-crystalline Fe- and Al-oxide bound As was highest (40-42%) in silt and clay fractions, while residual As was generally greatest (41-55%) in bulk and sand fractions. The sand, silt and bulk soils released a consistently higher percentage of non-specifically sorbed As than the clay, but clay released more specifically-sorbed As. Arsenate (As(V)) was the dominant species in soil solutions, although arsenite (As(III)) was significant in a few samples. XRD analysis showed the presence of arsenolite (As2IIIO3) in soils and fractions. SEM/EDS observations revealed that scorodite (FeAsVO4·2H2O) and amorphous Fe-oxides were the main As-bearing minerals in soils and fractions, which were consistent with the geochemical analysis. Outcomes from this research highlight the significant environmental risks of naturally As-enriched soils.

Size-resolved analysis of trace elements in the dissolved fraction (&lt;0.45 μm) of soil solutions using a novel lysimeter and asymmetrical flow field-flow fractionation coupled to ultraviolet absorbance and inductively coupled plasma mass spectrometry

The distributions of dissolved (&lt;0.45 μm) trace elements (TEs) amongst major colloidal forms in soils have implications for their availability, accessibility, and toxicity to plants and animals. The size-resolved distributions of TE species in soil solutions were collected using lysimeters and were measured using asymmetrical flow field-flow fractionation (AF4) coupled to ultraviolet absorbance (UV) and inductively coupled plasma mass spectrometry (ICP-MS). Using this AF4-UV-ICPMS system, dissolved TEs were separated by size, and concentrations in major forms were quantified: “truly dissolved” primarily ionic and small molecules &lt;ca. 1 kDa, organic-dominated colloids, and primarily inorganic colloids. The soil solutions were collected under vacuum using a novel surgical (316L) stainless steel (SS) lysimeter with a 5 μm pore size. Analyses were performed in the metal-free, ultraclean SWAMP laboratory. The acid-cleaned lysimeters yielded excellent blank values for TEs of environmental interest (i.e., Li, Al, V, Mn, Co, Cu, As, Mo, Ag, Cd, Ba, Pb, Th, and U). Lysimeter sampling offers the major advantage that it can minimize disturbances to the natural TE concentrations and distributions amongst major dissolved colloidal forms in soil solutions and thus provides information that is relevant to plant uptake.

Effects of crop straw biochars on aluminum species in soil solution as related with the growth and yield of canola (Brassica napus L.) in an acidic Ultisol under field condition.

The toxicity of aluminum (Al) to plants in acidic soils depends on the Al species in soil solution. The effects of crop straw biochars on Al species in the soil solution, and canola growth and yield were investigated in this study. In a long-term field experiment, there were four treatments, which were a control, rice straw biochar (RSB), canola straw biochar (CSB), and peanut straw biochar (PSB). The soil solution was collected in situ, the Al species were identified, and the relationships between the concentration of phytotoxic Al and canola growth and yield were evaluated. The results showed that applying the three biochars resulted in significant decreases in the concentrations of total Al, monomeric Al, and monomeric inorganic Al (P < 0.05). The Al3+, Al-OH, and Al-SO4 proportions of the total Al also decreased. The abilities of the different biochars to reduce dissolved Al followed the order PSB > CSB > RSB, which was consistent with the alkalinity of these biochars. Application of the biochars significantly decreased the concentration of phytotoxic Al (Al3+ + Al-OH), which improved canola growth and increased the canola seed and straw yields. Plant height, leaf number per plant, area per leaf, chlorophyll content, and canola yield were negatively correlated with the Al3+ + Al-OH concentrations. Therefore, the results showed that crop straw biochars can be used to ameliorate soil acidity and alleviate Al toxicity in acidic soils, and that peanut straw biochar is the best amendment for acidic soils.

Cu isotopic compositions in Elsholtzia splendens: Influence of soil condition and growth period on Cu isotopic fractionation in plant tissue

This study investigates the magnitude and direction of Cu isotopic fractionation in the Cu-tolerant, strategy I plant, Elsholtzia splendens, considering the effect of soil condition and plant growth cycle. Uptake of Cu by E. splendens from soil was found to favor light Cu isotopic enrichment (δ65Cu<0‰) due to reduction at the soil–root interface. The magnitude of fractionation between soil and plant was found to be dependent on free Cu ion species in soil solution correlated with pH value of soil other than the phytoavailable component of soil or total soil for the same parent soil.Cu isotopic fractionation occurs in plant, the fractionation direction and magnitude would vary between different plant organs (i.e., root and stem) as well as different plant tissues (i.e., xylem and phloem). Remobilization of Cu associated with plant senescence was found to have a considerable effect on Cu isotopic fractionation within the plant, and the fractionation factor was found to change with the degree of remobilization. Overall, the results show that the Cu isotopic composition is useful as a tracer for probing the mechanisms of Cu translocation and retranslocation between soil and plants, and within plants.

Evaluation of the effects of application of iron materials on the accumulation and speciation of arsenic in rice grain grown on uncontaminated soil with relatively high levels of arsenic

The Codex Committee adopted a maximum level of 0.2mgkg−1 for inorganic arsenic in polished rice at the 37th Session of the Commission (Codex Alimentarius Commission, 2014). It is thus necessary to establish agronomic management practices for reducing the accumulation of As in rice grain even in As-uncontaminated soil. We examined the effect of the application of different kinds of iron (Fe) materials on As uptake in rice plants grown in bottomless concrete frames filled with soil collected from an area surrounding a formerly As-polluted region. We assessed the concentration and speciation of As in soil solution throughout the rice cultivation period. Application of Fe materials had a significant effect on the concentration of arsenite, arsenate, inorganic As (sum of arsenite and arsenate) and total As, in the soil solution. The concentration of these forms of As in soil solution treated with Fe materials was significantly lower than the control. The lowest concentrations of As were observed in the plot to which a metal Fe powder composed mainly of a zero-valence Fe was applied throughout the rice cultivation period. The application of metal Fe powder and Fe oxide material composed mainly of ferrihydrite significantly reduced the amount of available As in the soil. The amount of acid ammonium oxalate extractable Fe was significantly increased by the application of metal Fe powder and Fe oxide material compared to that of the control and converter furnace slag. Concentrations of all forms of As in soil solution showed a significant positive correlation with the amount of available As and a significant negative correlation with the amount of acid ammonium oxalate extractable Fe in soil; this indicated that the increase of acid ammonium oxalate extractable Fe by application of Fe materials retarded the release of As from the soil solid phase to soil solution by fixing As and Fe. The concentrations of arsenite, dimethylarsinic acid (DMA), the sum of As species, and total As in grain with applied metal Fe powder and Fe oxide material were significantly lower than the control, reflecting the concentration of soluble As species in soil solution. These results strongly suggest that the application of metal Fe powder and Fe oxide material effectively reduced As accumulation in rice grain, making it a promising agronomic management practice for reducing the risk of As accumulation.

Effects of root iron plaque on selenite and selenate dynamics in rhizosphere and uptake by rice (Oryza sativa)

Iron plaque commonly forms on rice root surfaces under flooded conditions. However, little is known about the role of iron plaque in Se movement from rhizosphere to plant. A compartmented soil-quartz sand culture system was applied to investigate the effects of iron plaque on Se uptake by rice and document Se speciation dynamics in soil solution under flooded conditions. Rice seedlings were planted in a nylon bag containing sand and surrounded by soil amended with Se combined at rates of 0 or 0.5 mg of Se kg−1 of soil in the form of selenate or selenite. Plants were harvested at seedling stage and at maturity. Fe and Se concentrations in soil solution, in DCB extracts and Se concentrations in rice roots and shoots were determined. A visible reddish coating on root surfaces could be observed when sampled at the seedling stage and at maturity. Iron plaque on root surfaces greatly influenced Se uptake and had a higher affinity for selenite. The distribution of Se in different components of rice seedlings followed iron plaque > shoot > root, while it followed shoot > root > iron plaque at maturity. The addition of Se initially increased the soluble Se concentrations, and selenate was the main species in soil solution. Iron plaque greatly influenced Se uptake and might act as a pool to Se uptake during rice growth. Selenate or selenite addition to paddy soil showed the same effect in increasing Se concentrations in rice grain.

Elevated CO2 concentration increase the mobility of Cd and Zn in the rhizosphere of hyperaccumulator Sedum alfredii

The effects of elevated CO2 on metal species and mobility in the rhizosphere of hyperaccumulator are not well understood. We report an experiment designed to compare the effects of elevated CO2 on Cd/Zn speciation and mobility in the rhizosphere of hyperaccumulating ecotype (HE) and a non-hyperaccumulating ecotype (NHE) of Sedum alfredii grown under ambient (350μll(-1)) or elevated (800μll(-1)) CO2 conditions. No difference in solution pH of NHE was observed between ambient and elevated CO2 treatments. For HE, however, elevated CO2 reduced soil solution pH by 0.22 unit, as compared to ambient CO2 conditions. Elevated CO2 increased dissolved organic carbon (DOC) and organic acid levels in soil solution of both ecotypes, but the increase in HE solution was much greater than in NHE solution. After the growth of HE, the concentrations of Cd and Zn in soil solution decreased significantly regardless of CO2 level. The visual MINTEQ speciation model predicted that Cd/Zn-DOM complexes were the dominant species in soil solutions, followed by free Cd(2+) and Zn(2+) species for both ecotypes. However, Cd/Zn-DOM complexes fraction in soil solution of HE was increased by the elevated CO2 treatment (by 8.01% for Cd and 8.47% for Zn, respectively). Resin equilibration experiment results indicated that DOM derived from the rhizosphere of HE under elevated CO2 (HE-DOM-E) (90% for Cd and 73% for Zn, respectively) showed greater ability to form complexes with Cd and Zn than those under ambient CO2 (HE-DOM-A) (82% for Cd and 61% for Zn, respectively) in the undiluted sample. HE-DOM-E showed greater ability to extract Cd and Zn from soil than HE-DOM-A. It was concluded that elevated CO2 could increase the mobility of Cd and Zn due to the enhanced formation of DOM-metal complexes in the rhizosphere of HE S. alfredii.

Chemodynamics of chromium reduction in soils: Implications to bioavailability

Chromium toxicity in soils can be mitigated by reduction of Cr(VI) to Cr(III) which is influenced by the presence of free Cr(VI) species in soil solution, and the supply of protons and electrons. In this study, the effects of Cr(VI) adsorption (i.e. availability of free Cr(VI) species in soil solution), soil pH (i.e. supply of protons) and three electron donor carbon sources [black carbon (BC), chicken manure biochar (CMB) and cow manure (CM)] on the reduction of Cr(VI) to Cr(III) in soils were investigated. The results indicated that the rate of Cr(VI) reduction decreased with an increase in Cr(VI) adsorption and soil pH, which is attributed to decreased supply of free Cr(VI) ions and protons, respectively. Among the three different amendments tested, BC showed the highest rate of Cr(VI) reduction followed by CM and CMB. Furthermore, addition of BC, CM and CMB decreased the bioavailability of Cr(VI) in contaminated soils. The high efficiency of BC on Cr(VI) reduction was due to the electron donor's functional groups such as phenolic, hydroxyl, carbonyl and amides. The study demonstrated that free form of Cr(VI) ions in soil solution and carbon amendments enriched with acidic functional groups favored the reduction of Cr(VI), thereby mitigating its bioavailability and toxicity in contaminated soils.

Mobilization of cadmium by dissolved organic matter in the rhizosphere of hyperaccumulator Sedum alfredii

Pot experiments were conducted to investigate the role of dissolved organic matter (DOM) in the Cd speciation in the rhizosphere of hyperaccumulating ecotype (HE) and non-hyperaccumulating ecotype (NHE) of Sedum alfredii and its effects on Cd mobility. After growing HE S. alfredii, the rhizosphere soil solution pH of heavily polluted soil (HPS) and slightly polluted soil (SPS) was reduced by 0.49 and 0.40 units, respectively, due to enhanced DOC derived from root exudation. The total Cd concentration in soil solution decreased significantly but the decrease accounted for less than 1% of the total Cd uptake in the shoots of HE S. alfredii. Visual MINTEQ speciation predicted that Cd–DOM complexes were the dominant Cd species in soil solutions after the growth of S. alfredii for both soils, followed by the free metal Cd2+ species. However, Cd–DOM complexes fraction in the rhizosphere soil solution of HE S. alfredii (89.1% and 74.6% for HPS and SPS, respectively) were much greater than NHE S. alfredii (82.8% and 64.7% for HPS and SPS, respectively). Resin equilibration experiment results indicated that DOM from the rhizosphere (R-DOM) of both ecotypes of S. alfredii had the ability to form complexes with Cd, whereas the degree of complexation was significantly higher for HE-R-DOM (79–89%) than NHE-R-DOM (63–74%) in the undiluted sample. The addition of HE-R-DOM significantly (P<0.05) increased the solubility of four Cd minerals while NHE-R-DOM was not as effective at the same concentration. It was concluded that DOM in the rhizosphere of hyperaccumulating ecotype of S. alfredii could significantly increase Cd mobility through the formation of soluble DOM–metal complexes.

Release kinetics and distribution of boron in different fractions in some calcareous soils

The aim of this study was to evaluate the release kinetics, speciation, and fractionation of boron (B) in some calcareous soils of western Iran. Ten surface soil samples were incubated with 100 mg B kg−1 for a week at field capacity moisture. After air drying of samples, the trend of B release was experimented using sequential extraction with 10 mM CaCl2. B speciation in soil solution was calculated for the first and the last steps of extraction by the visual MINTEQ program. The distribution of B among five fractions including exchangeable (F1), specially adsorbed (F2), bound by Fe–Mn oxides (F3), organically bound (F4) and residual (F5), was determined in control and spiked soils. The results indicated that the release rates were initially rapid followed by a slower reaction and the main proportion of the added B was extracted by CaCl2. The release kinetics of B was described well with Elovich, parabolic diffusion, power function, and first-order equations. The speciation results revealed that the uncharged boric acid (H3BO30) was the dominant species in soil solutions. In control soils, B concentration in different fractions decreased in the following order: F5 > F1 > F2 > F3 > F4. In spiked soils, however, the largest and the smallest fractions were exchangeable and residual, respectively. This implies that B transformation from soluble to less mobile and non-labile forms is not a rapid process and requires more than a week. The significant relationship observed between kinetic parameters of power and parabolic equations and organically bound B fraction and OM content indicated that organic matter played an important role in B adsorption and release in calcareous soils.

Extractable Al and Soil Solution Ionic Concentrations in Strongly Leached Soils from Northwest Iberia: Effects of Liming

Strongly leached soils occurring in Northwest Iberia contain high concentration of Al which may affect crop growth. Information regarding the extractability of Al and lime required to eliminate toxic Al species in the soil solution is scarce. In this context, the extractability of Al on these soils was determined using 1 M KCl, 0.33 M LaCl3 and 0.5 M CuCl2. The effects of lime on the concentration and activity of Al species in soil solution, using the GEOCHEM program was also evaluated. Extractability of Al was in the order: 1 M KCl &lt; 0.33 M LaCl3 &lt; 0.5 M CuCl2, with ranges from 0.7–3.3, 1.3–4.4, and 1.8–13.5 cmolc kg-1, respectively. These values were positively correlated with cation exchange capacity and organic C, clay, Alo and Feo contents. Application of 6 t CaCO3 ha-1 increased the total concentrations of Ca+2, Mg+2, K+, and Na+ ions in soil solution, whereas, application of 2 t CaCO3 ha-1 reduced the concentration and activity of Fe+3, Al+3, Mn+2, Zn+2, Cu+2, SO4-2, and PO4-3 ions,and eliminated toxicity threshold of free Al+3 and Al soluble complexes in the soil solution. Application of low amounts of lime may prevent the negative effects of soluble Al on crops.

Diversity and community structure of culturable arsenic-resistant bacteria across a soil arsenic gradient at an abandoned tungsten–tin mining area

We studied the bacterial diversity at a single location (the Terrubias mine; Salamanca province, Spain) with a gradient of soil As contamination to test if increasing levels of As would (1) change the preponderant groups of arsenic-resistant bacteria and (2) increase the tolerance thresholds to arsenite [As(III)] and arsenate [As(V)] of such bacteria. We studied the genetic and taxonomic diversity of culturable arsenic-resistant bacteria by PCR fingerprinting techniques and 16S rRNA gene sequencing. Then, the tolerance thresholds to As(III) and As(V) were determined for representative strains and mathematically analyzed to determine relationships between tolerances to As(III) and As(V), as well as these tolerances with the soil contamination level. The diversity of the bacterial community was, as expected, inversely related to the soil As content. The overall preponderant arsenic-resistant bacteria were Firmicutes (mainly Bacillus spp.) followed by γ-Proteobacteria (mainly Pseudomonas spp.), with increasing relative frequencies of the former as the soil arsenic concentration increased. Moreover, a strain of the species Rahnella aquatilis (γ-Proteobacteria class) exhibited strong endurance to arsenic, being described for the first time in literature such a phenotype within this bacterial species. Tolerances of the isolates to As(III) and As(V) were correlated but not with their origin (soil contamination level). Most of the strains (64%) showed relatively low tolerances to As(III) and As(V), but the second most numerous group of isolates (19%) showed increased tolerance to As(III) rather than to As(V), even though the As(V) anion is the prevalent arsenic species in soil solution at this location. To our knowledge, this is the first study to report a shift towards preponderance of Gram-positive bacteria (Firmicutes) related to high concentrations of soil arsenic. It was also shown that, under aerobic conditions, strains with relatively enhanced tolerance to As(III) predominated over the most As(V)-tolerant ones.

Identification of Fe‐polycarboxylic complexes by electrospray ionization mass spectrometry and reduction of interferences by ion chromatography/inductively coupled plasma mass spectrometry with an octopole reaction system

Stable complexes are required during the ion chromatographic (IC) separation of Fe-polycarboxylic acid complexes. Electrospray ionization mass spectrometry (ESI-MS) was used to identify 1:1 stoichiometric complexes of Fe[HEDTA], Fe[EDTA](1-) and Fe[DTPA](2-), and the spectra showed that these Fe complexes were stable in solution. Furthermore, inductively coupled plasma mass spectrometry (ICP-MS) using an octopole reaction system (ORS) reduced polyatomic ion (40)Ar(16)O(+) interference in the detection of (56)Fe via the addition of either H(2) or He to the ORS, with He at a flow rate 3.5 mL min(-1) being the optimum collision gas. Finally, IC/ICP-MS was used for the separation and detection of Fe complexes with an eluent containing 30 mM (NH(4))(2)HPO(4) at pH 8.0, but only Fe[HEDTA], Fe[EDTA](1-) and Fe[DTPA](2-) were observed within 10 min with reasonable resolution. Detection limits in the range of 10-13 µg L(-1) were achieved using He as the collision gas. The proposed method was used for the determination of Fe species in soil solutions.

Toxicity thresholds for oat (Avena sativa L.) grown in Ni-impacted agricultural soils near Port Colborne, Ontario, Canada

This study established Ni phytotoxicity thresholds for oat (Avena sativa L.) in four soil types, each created by blending a low and a high Ni soil, to generate a range of concentrations. The first quartile effective concentration (EC25) for soil and shoot tissue Ni concentration and reduction in shoot dry weight (DW) was determined using a Weibull function. The EC25 (for soil Ni concentration) was 1350, 1950, 1880 and &gt; 2400 mg Ni kg-1 soil, for sand, till clay, heavy clay and organic muck, respectively. The EC25 (for shoot Ni concentration) was 71, 21, 52 and &gt; 35 mg Ni kg-1 shoot DW, for sand, till clay, heavy clay and organic muck, respectively. Total soil Ni concentration, soil pH and soil cation exchange capacity (CEC) accounted for 70% of the variation of Ni accumulation in tissue when the data for all four of the soils were combined; this was similar to the amount of variation accounted for by fitting Ni concentration in tissue to ammonium oxalate extractable soil Ni. Manganese deficiency may have impaired plant growth at higher soil Ni concentrations in the clay soils. Speciation of Ni was similar in all soils studied, and the relationship between Ni concentrations in soil and in tissue was less closely related to chemically extracted soil Ni than it was to a combination of total soil Ni, soil pH and CEC. These are the soil characteristics known to influence both equilibrium among metal species in soil solution, and uptake of cations by plants. Key words: Avena sativa L., EC25, Ni, oat

GYPSUM AMENDMENT AND EXCHANGEABLE CALCIUM AND MAGNESIUM EFFECTS ON PLANT NUTRITION UNDER CONDITIONS OF INTENSIVE NUTRIENT EXTRACTION

In general, increasing the concentration of one cation species in soil solution can decrease levels of other cations in plants. It is not clear whether adjusting soil cation ratios or adding gypsum will improve plant growth. We studied the effect of adding gypsum to unleached soil, and the effect of changing soil-exchangeable Ca/Mg ratios on corn root and shoot growth and nutrient concentrations. Soil-exchangeable Ca/Mg ratios (8.0, 4.9, 1.8, 0.7, and 0.5) were obtained by leaching soil with Ca and Mg chloride, followed by leaching with Ca and Mg sulfate to remove chloride. An unleached soil treated with gypsum and an untreated control soil were also included. Corn plants were grown for 23 days in a replicated greenhouse experiment. Exchangeable Ca/Mg ratios did not substantially affect root and shoot growth in the leached soils, nor did gypsum addition to the unleached soil. However, growth in the leached soils was less than that in the unleached soils, probably because of removal of K in the leaching process. Shoots from plants from treatments with lower leached Ca/Mg ratios had less Ca and more Mg but showed no consistent changes in K. Addition of gypsum to unleached soil decreased P, increased K and Ca, and did not affect N and Mg concentrations in shoots.

Complexation efficiency of differently fixed 8-hydroxyquinoline and salicylic acid ligand groups for labile aluminium species determination in soils—comparison of two methods

Two methods utilizing the complexation of labile Al species by 8-hydroxyquinoline (HQN) and salicylic acid (SA) ligand groups were developed for aluminium operationally defined fractionation in acid soils. First, the solid phase extraction (SPE) procedure by a short-term ion-exchange batch reaction with chelating resins Iontosorb Oxin and Iontosorb Salicyl containing both ligand groups was used previously. Second, the 8-hydroxyquinoline, salicylic acid and ammonium salicylate agents with different concentrations by a single extraction protocol were applied in this paper. The flame atomic absorption spectrometry (FAAS) and optical emission spectrometry with inductively coupled plasma were used for aluminium quantification. The comparison of results from both methods show the possibility to supersede the first laborious method for the second simpler one in Al environmental risk assessment. The use of 1% 8-hydroxyquinoline in 2% acetic acid and 0.2% salicylic acid by a single extraction protocol without a need of sample filtration can supersede the SPE procedure in the Al pollution soil monitoring. Finally, the new scheme usable in a laboratory and moreover, directly in a field was proposed for Al fractionation in solid and liquid environmental samples. The labile Al species in soils and sediments are separated after their single leaching by 8-hydroxyquinoline or salicylic acid without a need of sample filtration. The labile Al species in soil solutions and natural waters are separated after their ultrafiltration followed by the SPE procedure with Iontosorb Oxin or Iontosorb Salicyl.