Foliar application of selenite and selenate to potato (Solanum tuberosum): effect of a ligand agent on selenium content of tubers

The effect of a foliar spray of selenium on potatoes was investigated for 2 years. Amounts of 0, 50, and 150 g of Se ha(-)(1) were applied both as sodium selenate and as sodium selenite in water, either pure or with the addition of 0.15% of soluble leonardite as a source of humic acids (pH 7). Tuber selenium concentration increased with the application levels, both with sodium selenate and with sodium selenite, when only aqueous solutions were used. When humic acids were added, the tuber selenium level rose more markedly after the application of sodium selenate as compared to the case of the aqueous solutions; however, in the case of sodium selenite, the level showed a large increase only after the application of 50 g of Se ha(-)(1). Kinetics showed that humic acids raised the selenate availability, but no differences were found in the distribution of selenium in the tuber fractions. Foliar application of selenium with humic acids was proven to be a good way to increase the selenium content of potatoes, but the assimilation process of selenium was simpler with selenate than with selenite.     

Selenite adsorption by a variety of oxides

Abstract

Selenite adsorption by a variety of oxides consisting of iron (Fe), aluminum (Al), titanium (Ti), manganes (Mn), and silicon (Si), and by two humic acids were investigated in order to grasp selenite behavior and fixation mechanisms in soil. It was found that selenite was apparently adsorbed even by the Mn oxides on which surface negative charge was dominant in normal pH range (pH <4). No selenite adsorption was observed in the silicon dioxide (SiO₂) and the two humic acids. A sequential extraction of adsorbed selenite with competitive anions showed the differences of binding force or stability of adsorbed selenite among the minerals. While the goethite fixed selenite strongly, selenite adsorbed on the Mn oxide was easily released to the liquid phase with other anions, such as phosphate. Each mineral had its inherent characteristic in ligand exchange reactions accompanied with selenite sorption. Selenite sorption by the Mn and the Ti oxides resulted in large increase of surface negative charge, while only a little increase in the Fe and Al oxides. Proton consumption with selenite sorption was extremely smaller for the Mn oxide than for the others.     

陕西地区土壤中的硒

硒是人和动物体必需的微量元素之一,早已证明,土壤和饲草中过量的硒会导致牲畜中毒而罹患“碱质病”和“盲跚症”,而土壤和饲草硒含量过低则会引起牲畜白肌病等多种缺硒病^[9]。近年来国外又有资料报道食物和饮水中的低硒容易使人体产生癌症、心血管病、关节炎、婴幼儿碎死症等多种疾病^[6]。鉴于在土壤一植物一动物和人的生态系统中,土壤是最基本的因素,因此对土壤硒的研究在许多国家早已受到人们的重视。国内对土壤硒的研究,始于七十年代对人体地方性疾病的研究,现已证实,地方性克山病、大骨节病的发生与环境和机体缺乏硒有密切关系^[1,3,11]。     

Direct evidence of basic aluminium sulphate minerals in an S-impacted Andosol

The formation of basic aluminium sulphate (BAS) minerals [(K,Na)_nAl_x(OH)_y(SO₄)_z] has often been invoked to explain sulphate retention in soils. These minerals have not yet, however, been directly observed in the soil. We extracted the clay fractions of Andosols intercepting large inputs of volcanogenic sulphur dioxide and acids (HCl, HF), simply by dispersing clays with Na⁺‐resins in deionized water without any other chemical treatment. Clay fractions concentrate 39–63% of total sulphur content of soil. Transmission electron microscopy coupled with energy‐dispersive analysis revealed the presence of BAS particles, appearing as nodules and spheres. These particles have an equivalent diameter smaller than 0.2 µm. They have an Al:S ratio close to 2.2 and 3.8 and are possibly amorphous aluminite or basaluminite, respectively. They seem to have been formed in microenvironments enriched in sulphate, but also in fluoride anions. Their formation seems to have been enhanced by the combination of large inputs of acids and SO₂ and an effective Al supply from weathering of volcanic glass.     

The sodium-amalgam reduction of soil and fungal humic substances

Two soil humic acids and a “humic acid” synthesized in the laboratory by Stachybotrys chartarum were reduced with Na-amalgam. The reduction products were methylated, separated by preparative gas chromatography and identified by matching their mass and micro-infrared spectra with those of authentic specimsens.Yields of reduction products identified ranged from 2.7 to 4.2% of the initial weights of the humic materials. Major products identified were N-methyl-benzylsulfonamide, methylated phenolic acids, aromatic aldehydes and C₆C₂ - and C₆C₃ - compounds with 0 in the side chains. Since the Na-amalgam reduction of both soil and fungal humic materials produces the same or similar compounds, the method provides little information on the origin of these compounds, that is, whether they are lignin- or flavonoid-derived or synthesized by microorganisms. Compared with oxidative degradation methods, Na-amalgam reduction appears to be inefficient and tells little about the chemical structure of humic acid polymers.     

Transformation and Bioavailability of Selenate and Selenite Added to a Nicotiana tabacum L. Planting Soil

Selenium (Se) is an essential nutrient for humans and is beneficial for plant growth. To investigate the transformation and bioavailability of Se in tobacco planting soil, selenite and selenate were applied. A pot experiment and sequential extraction scheme were used to investigate the Se contents in different forms in soils treated with Se. A series of equations were applied to model the transformation behavior of Se in this study. The results showed that the forms of selenium were increased significantly by applying the different valence state of water-soluble selenium. The carbonate-bound and iron-manganese (Fe-Mn) oxide–bound species were improved in selenite-added soil, whereas the soluble and exchangeable forms were increased in selenate-added soil. Michaelis-Menten equation fitting results indicated that estimated maximal selenium contents of leaves, stems, and roots in selenate-added soils were 1.83, 15.81, and 20.98 times larger than in selenite-added soils. The utilization levels of selenate were 4.3 to 7.9 times larger than selenite for Nicotiana tabacum L. In conclusion, the bioavailability and mobility of selenate were greater than selenite in Nicotiana tabacum L. planting soil.     

Abbau von Huminstoffen durch Bodenmikroorganismen — eine Übersicht

Degradation of humic substances by soil microorganisms — a review Humic substances which represent differently extractable fractions of the soil organic matter exert multifarious effects on soil as a site for plant growth and a part of terrestrial environments. Among them especially humic acids and fulvic acids are subject to degradation and/or transformation by soil microorganisms. Several authors demonstrated the participation of different species of fungi, actinomycetes and also of non-mycelial aerobic or anaerobic bacteria in those processes under laboratory conditions. Indications exist that humic substances irrespective of their structure undergo degradation on cell surfaces due to the activity of exoenzymes. In this respect microbial phenoloxidases play an extraordinarily important role. The degradation rate of humic substances can be followed by optical, gravimetric and chemoanalytical methods as well as using biochemical and microbiological procedures (CO₂ release, microbial growth, biomass formation). An objective evaluation, however, can be hindered by the adsorption of humic substances on microbial biomass and sometimes also by formation of novel humic-like microbial metabolites. Therefore it is necessary to apply a multifactorial approach in the study of the degradation of humic substances which includes both quantitative and qualitative parameters. To better elucidate how these processes may occur under natural conditions, mixed populations of soil microorganisms should be predominantly involved in future studies.     

Soil and compost humic fractions regulate the response of Sclerotinia sclerotiorum to exogenously added allelochemical compounds

Allelochemical compounds released by plants to signal their presence and needs interact in soils with very important macromolecules, such as humic acids (HAs), which are able to modulate the ultimate effects on target organisms. Most of the available studies on plants and microorganisms report the effects of allelochemicals or those of humic fractions, separately. In this study, we investigated the combined activity of these two types of compounds on the soil-resident fungus Sclerotinia sclerotiorum. Thus, ferulic acid (FA), caffeic acid (CA), benzoic acid (BA), salicylic acid (SA), gallic acid (GA) and phthalic acid (PA), exogenously applied to the fungal growth medium, were tested both alone and in combination with a soil HA (SHA) and a compost HA (CHA). The two HAs were also tested alone on the fungus. When the allelochemicals were applied alone, only FA, BA and SA evidenced a significant inhibition of mycelial growth, whereas FA, BA and CA increased the number of sclerotia formed. The two HAs alone reduced the early growth of the fungus and markedly stimulated sclerotia formation. A significant attenuation or, in some cases, suppression of the allelochemical effect on mycelial growth was caused by the coexistence in the medium of the allelochemical and each HA, especially CHA. Moreover, in general, the combinations of HA-allelochemical significantly stimulated sclerotia formation, with respect to the sole allelochemical, but decreased it with respect to HA alone. Thus, investigations on the response of fungi to plant-released allelochemicals should not exclude interactive aspects of these compounds with ubiquitous coexisting humic macromolecules.     

Plant uptake of selenium and LSe -values in different soils

Rye-grass was grown in six different soils with four additions of ⁷⁵Se-labelled selenite through six cutting in a pot experiment. Following the last cutting, the soils were extracted with a series of solvents to fractionate the residual soil selenium. The plant content of added and total selenium was determined. The results showed that equilibrium between added and native selenium was obtained before the third cutting, giving a nearly constant L_Se-value for the last four cuttings. The L_Se-values differed between the soils, and there was a positive correlation between the L_Se-values and the plant uptake of native selenium. In accordance with this, the best correlation with the total selenium concentration in the plants was obtained with the isotopically exchangeable selenium in the soil after the last cutting. It is concluded that isotopically exchangeable selenium approximates the fraction of soil selenium from which plant uptake of selenium occurs.     

ACIDIC PROPERTIES OF PLANT LIGNINS AND HUMIC MATERIALS OF SOILS

The acidic properties of lignins from the native vegetation of a virgin Ella loamy sand and the humic acids, the 1, 4-dioxane extractable humic fraction and residual humic acids from the virgin and cultivated soils were investigated by determining solid-state cation exchange capacities for Cu and Ca and by non-aqueous potentiometric titration, using potassium methoxide in a benzene-methanol mixture as titrant. The lignins and soil dioxane extracts were titrated in pyridine; the humic acids in dimethylformamide. Platinized Pt and CH₃OH modified calomel electrodes formed the electrode combination. The CEC of the humic acids were much higher than the CEC of lignins with both cations but the Cu: Ca absorption ratios were less for humic acids than for lignins. Titration curves of lignins showed two potential breaks with total acidities of 960 to 1,190 me/100 g. Titration curves of the humic acids showed three to six potential breaks while curves of the soil dioxane extracts showed three and four. The total acidities of the two types of humic isolates were 1,100-1,200 me/100 g. The equivalent weights of most lignins and humic materials were very similar although the acid groups might be different with respect to types and acid strength. Lignins from other plant materials and humic isolates from other soils were also investigated by non-aqueous titration to determine the general applicability of the results obtained with isolates from the Ella soils.     

Effects of Organic Matter-Rich Amendments on Selenium Mobility in Soils

Soil organic matter (SOM) plays an important role in the Se dynamics in soil. The potential effects of vermicompost and digestate as important sources of SOM on selenium (Se) mobility were assessed in this study. Three soils differing in their physicochemical parameters, fluvisol, chernozem, and luvisol, were chosen, and three types of vermicomposts based on various bio-waste materials as digestate (vermicompost 1), kitchen waste with woodchips (vermicompost 2), and garden bio-waste (vermicompost 3) were used due to their high organic matter content. Additionally, digestate samples alone were applied. To evaluate the potential effect of vermicompost application on sorption characteristics of soils, batch sorption experiments were performed. The results showed a predominant effect on Se species in the soils, where selenite sorbed more intensively compared to selenate, regardless of the soil and ameliorative material applied. In the control, the soil sorption ability of selenite tended to decrease in the order:fluvisol > luvisol > chernozem. However, these differences were not significant. Moreover, the effects of the ameliorative materials depended on both soil and amendment used. In fluvisol, all the amendment applications resulted in a decrease in distribution coefficient (K_d values) of Se, whereas in chernozem, this effect was observed only for the digestate-based vermicompost 1. Increasing K_d levels were reported in luvisol treated with digestate; the application of garden bio-waste-based vermicompost 3 tended to decrease the K_d values. Further studies are required on long-term effects of these amendments on Se mobility in soils and the role of individual organic matter fractions in this context.     

Biosynthesis of schwertmannite by <Emphasis Type="Italic">Acidithiobacillus ferrooxidans</Emphasis> and its application in arsenic immobilization in the contaminated soil

Purpose

Soil contamination with arsenic (As) is an increasingly worldwide concern. Immobilization is a potentially reliable, cost-effective technique for the reclamation of As-contaminated soils. The aim of this study is to develop new soil amendments with high As immobilization efficiency, cost-effective, environmental-friendly, and without soil acidification for As-contaminated soil remediation.

Materials and methods

Biosynthesis of schwertmannite by Acidithiobacillus ferrooxidans has been conducted, and two types of biogenetic schwertmannites SCH and A-SCH were prepared and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), etc. The A-SCH was formed through pretreating SCH by acidic and alkaline activation. The potential of SCH and A-SCH in As immobilization in contaminated soil was evaluated. The effect of ferrous sulfate and A-SCH on soil pH and immobilization of NaHCO₃-extractable As were also investigated for comparison.

Results and discussion

The chemical formula of SCH and A-SCH can be expressed as Fe₈O₈(OH)_4.89(SO₄)_1.55 and Fe₈O₈(OH)_5.19(SO₄)_1.41, respectively. Compared to SCH, A-SCH exhibits much higher specific surface area of 74.99 m² g^?1 and contains more hydroxyl groups and inner-sphere sulfate complexes. Immobilization efficiency of water-soluble As above 99.5 % can be achieved with A-SCH dosage of 5 % and SCH dosage of 10 %, respectively. The immobilization percentages of NaHCO₃-extractable As increased from 31.5 to 90.4 % and from 40.2 to 93.8 % with increasing dosage from 0.5 to 10 wt % for SCH and A-SCH, respectively. In general, both SCH and A-SCH immobilize As in contaminated soil effectively, and the immobilization performance of A-SCH was better than that of SCH, especially at lower dosage.

Conclusions

Biogenetic schwertmannite could be used as a potential effective soil amendment for As immobilization in contaminated soil. Our findings in this study also have important implications for in situ immobilization of As in contaminated soils, especially the soils related to acidic iron and sulfate-rich environments.

     

螺旋藻富集同化无机硒研究

以亚硒酸钠做为螺旋藻富硒的来源，研究了亚硒酸钠梯度浓度对钝顶螺旋藻（Spirulinaplatensis）生长及其富硒量的影响，并采用75Se标记的Na2SeO3示踪方法，对富硒螺旋藻含硒成分进行了研究。结果表明，当硒浓度超过360g／mL时，螺旋藻的生长即受抑制，硒浓度为46g／mL时，表现出促进螺旋藻生长的趋势，而硒浓度为184g／mL时，螺旋藻可达到最高富硒量，平均为659.9ng／mg。富硒螺旋藻中结合在大分子上的有机硒达到70％以上，其中主要是含硒蛋白质，含量可达50％以上，主要以硒代蛋氨酸和硒代半胱氨酸形式存在，分别占含硒蛋白的40％和20％。     

Characterization of expandable layer silicates in humic‐ferralic cambisols (umbrept) derived from biotite and hornblende

Samples from a paired soil type (humic ferralic cambisol) derived from biotite schist (soil group 1) and amphibolite bedrock (soil group 2) were investigated mineralogically and chemically. Soil smectites and vermiculites were analyzed by using the improved n‐alkylammonium method (Lp correction and curve fitting). The soils of group 1 contain small smectite concentrations. The source mineral is a low charged biotite of the silt fraction (2—6 μm) with a mean layer charge of ξ = 0.58 mol per O₁₀(OH)₂. The soil smectite of the clay fraction (< 2 μm) has a mean layer charge of ξ = 0.48 mol per O₁₀(OH)₂ with nearly 100% tetrahedral substitution. The soils of group 2 contain high smectite concentrations. The total charge of these smectites varies between 0.38 and 0.43 mol per O₁₀(OH)₂. The mean value lies between 0.39 and 0.40 mol per O₁₀(OH)2; 20% of the total charge originates from octahedral substitution. Thus, the tetrahedral charge amounts to 0.32 mol per O₁₀(OH)₂. These amphibolite derived smectites have low K selectivity (K_G values of about 5 (mol/l)^—1/2) and do not show an illitization tendency. The soils of group 1 have an extremely high K selectivity (K_G values ≫ 180 (mol/l)^—1/2) when the K‐saturation is < 1.5% of CEC. The increase of K saturation up to 8—15% in the system ”︁natural soil solution versus solid soil” results in a K_G decrease to around 10 (mol/l)^—1/2. This trend can be interpreted as illitization of highly charged smectites with 100% tetrahedral substitution developing to K bearing 1.0 nm minerals.     

Elemental,functional group and infrared spectroscopic analysis of actinomycete melanins from brazilian soils

Eleven actinomycete melanins were characterized by elemental and functional group and infrared analysis. A soil humic acid from a Brazilian topsoil, a darkred latosol under savanna grassland, analysed previously, was used for comparative purposes. C, N, total acidity, COOH, and phenolic OH contents were within the ranges reported for soil humic acids and fungal melanins. Compared to the soil humic acid, the actinomycete melanins showed greater detail, indicative of higher aliphaticity. Most of these were, in varying degrees, similar to the type III IR spectra of humic acids, which are characteristically high in proteinaceous material, and with variable amounts of polysaccharides. The exceptions were two melanin spectra that showed more resemblance to the humic acid from the dark-red latosol, which belongs to the type I spectra of soil humic acids, a category that includes most soil humic acids. The probable participation of melanic actinomycetes in the formation of humic polymers in discussed.     

Influence of humic acids on laurel growth,associated rhizospheric microorganisms,and mycorrhizal fungi

Summary Increasing concentrations of humic acids were tested in order to determine their effects on the microbial rhizosphere and the growth of laurel (Laurus nobilis L.). Plants that were treated with 300 mg kg^-1 of humic acids had the heaviest weights of both fresh and dry shoots; however, doses of 3000 mg kg^-1 were highly phytotoxic and inhibited the growth of laurel. Total aerobic bacteria and actinomycetes were stimulated by doses of 1500 and 3000 mg kg^-1 of humic acids at the first harvest. Nevertheless, at the end of the experiment no significant differences were found among the different doses. The number of fungi living in the laurel rhizosphere was not affected by any concentration of humic acids. Vesicular-arbuscular mycorrhizal (VAM) colonization was only slightly affected by the addition of increasing concentrations of humic substances to the soil, while the hyphal growth of Glomus mosseae was reduced.     

Humus quantity and quality of an entic Haplustoll under different soil‐crop management systems

Abstract

The effects of different management systems on the level and composition of humified organic matter in an entic Haplustoll from the semiarid Pampean region were studied. The systems were: TPc, wheat‐mixed pasture; TV, wheat (Triticum aestivum), oat (Avena sativa), corn (Zea mays) and triticale grasses; TP, wheat‐cattle grazing; and V, virgin, non cultivated. Humic acids were extracted, fractionated, and analyzed for their organic carbon (OC) content, elemental composition, and E4:E6 spectral ratios. The infrared (IR), electron spin resonance (ESR). and ¹³C‐NMR spectra were registered on these humic acids. The TP rotation showed the lowest humic acid‐carbon to fulvic acid‐carbon (HA‐C:FA‐C) ratio. The lower O:C ratio of humic acids from the cropped soils indicates a higher level of oxidation than that of the virgin one. The comparison of the different methodologies allowed us to conclude that crop rotations and conservation tillage were adequate to mantain the level and composition of the soil organic matter and humus which affected the soil fertility and level of productivity     

Selective determination and formation of elemental selenium in soils

A selective method for the determination of elemental selenium in soil was developed and was applied to the study of elemental selenium in soil. (1) Elemental selenium extracted with carbon disulfide from soil was selectively transformed into selenocyanate ion by reacting with potassium cyanide in carbon disulfide. The selenocyanate ion formed was recovered into an aqueous solution and the amount of selenium in the aqueous solution was determined. This method was specific to elemental selenium and did not interfere with the other selenium compounds and soil components. The method was also highly sensitive and enable to determine more than 0.1 μg kg^-1 of elemental selenium in soil. (2) The formation of elemental selenium was confirmed, when a soil was submerged and the redox potential of the soil decreased. The amount of elemental selenium formed was proportional to the selenite content of the soil, indicating that elemental selenium is transformed from selenite upon its reduction.     

Retention and Uptake by Plants of Added Selenium in Peat Soils

In soil, adsorption of selenium (Se) onto mineral surfaces is accompanied by poorly known retention via organic matter. The effects of these components on the availability of Se were examined in two pot experiments. Spring wheat was grown with increasing amounts of selenate (SeO₄ ^2–) in one sand and three peat soils, and ryegrass with selenate and selenite (SeO₃ ^2–) in sphagnum peat manipulated by iron (Fe) hydroxide. Selenate persisted in soluble form, whereas selenite was fixed in the soil. In wheat, 5–50% of the selenate addition was recovered in the plant, the proportion increasing with increasing Se. In ryegrass, 30–40% of the added selenate but less than 2% of the selenite was found within the leaves. The Fe hydroxide enrichment enhanced the selenite uptake. Phosphate buffer desorbed a minor proportion of the added selenite, except in peat amply enriched with Fe hydroxide. The results suggest that the retention mechanism of selenite was changed due to the hydroxide amendment.     

Aluminum speciation in soil solutions: Equilibrium calculations

A computer simulation was done to illustrate how the equilibrium solubility and speciation of Al in well-aerated soil solutions may be affected by pH (from 2.0 to 10.0), organic acids (citric, oxalic, phthalic, and salicylic acid), metal ions (K, Mg, Ca, Al, Fe), inorganic ligands (F, OH, SO₄, PO₄, CO₃, and SiO₃), and type of Al-containing solid [kaolinite, gibbsite, or amorphous Al(OH)₃] thought to be present. The simulation indicated that the type of Al-oxide/hydroxide considered has a substantial influence on the inorganic and organic equilibrium composition of the soil solution, and on the occurrence (or non-occurrence) of other Al-minerals such as KA1₃(SO₄)₂(OH)₆ (alunite) and Al(SO₄)(OH)-5H₂O (jurbanite).