Iron oxide‐humic acid coprecipitates as iron source for cucumber plants

In soil, iron (Fe) solubility depends on complex interactions between Fe minerals and organic matter, but very little is known about plant availability of Fe present in Fe oxides associated with humic substances. For this purpose, this study investigates the effect of Fe mineral crystallinity in the presence of humic acids (HA) on Fe availability to plants. Four Fe–HA mineral coprecipitates were prepared, either in the presence or absence of oxygen, i.e., two goethite (G)‐HA samples containing large amounts of Fe as nanocrystalline goethite and ferrihydrite mixed phases, and two magnetite (M)‐HA samples containing crystalline magnetite. Bioavailability studies were conducted in hydroponic systems on cucumber plants (Cucumis sativus L.) grown under Fe deficient conditions and supplied with the Fe–HA coprecipitates containing goethite or magnetite. Results showed that plants grown in the presence of Fe–HA coprecipitates exhibited a complete recovery from Fe deficiency, albeit less efficiently than plants resupplied with Fe‐chelate fertilizer used as control (Fe‐diethylene triamine penta acetic acid, Fe‐DTPA). However, the supply with either G‐ or M–HA coprecipitates produced different effects on plants: G–HA‐treated plants showed a higher Fe content in leaves, while M–HA‐treated plants displayed a higher leaf biomass and SPAD (Soil–Plant Analysis Development) index recovery, as compared to Fe‐DTPA. The distribution of macronutrients in the leaves, as imaged by micro X‐ray fluorescence (µXRF) spectroscopy, was different in G–HA and M–HA‐treated plants. In particular, plants supplied with the poorly crystalline G–HA coprecipitate with a lower Fe/HA ratio showed features more similar to those of fully recovered plants (supplied with Fe‐DTPA). These results highlight the importance of mineral crystallinity of Fe–HA coprecipitates on Fe bioavailability and Fe uptake in hydroponic experiments. In addition, the present data demonstrate that cucumber plants can efficiently mobilize Fe, even from goethite and ferrihydrite mixed phases and magnetite, which are usually considered unavailable for plant nutrition.     

Reduction of structural Fe(III) in oxyhydroxides by Shewanella decolorationis S12 and characterization of the surface properties of iron minerals

Purpose  

Dissimilatory iron reduction is an important iron biogeochemical process in subsurface soils. Many researchers have studied the effects of various factors on this process. However, this process in the natural environment is complicated; thus, all the factors should be investigated systematically and simultaneously. The aims of this study were to investigate the effects of Fe(III) availability, surface areas, and crystallinity on Fe(III) reduction in different buffers and to characterize the surface properties of iron minerals.     

Long-term reactions of Ni, Zn and Cd with iron oxyhydroxides depend on crystallinity and structure and on metal concentrations

Iron oxyhydroxides are long-term sinks for toxic trace metals and are suggested as factors to explain long-term metal immobilization in soil. It is unknown how crystallinity and crystal structure of iron (Fe) oxyhydroxides affect the long-term kinetics of trace metal adsorption. Adsorption kinetics of nickel (Ni), zinc (Zn) and cadmium (Cd) on to four synthetic Fe oxyhydroxides (hydrous ferric oxide (HFO), ferrihydrite (FH), goethite (GT), haematite (HT)) were characterized in suspensions during 70 days at different initial metal concentrations and various pH values (3.8–7.0) maintained within 0.2 units. The slow reactions, defined as those occurring beyond day 1 were most pronounced in GT and least in HT. The extent of the slow reaction was surprisingly unrelated to crystallinity or microporosity as determined by N₂ adsorption. Freundlich adsorption isotherms fitted to the data show that ageing between 1 and 70 days decreases metal concentrations in solution by factors of 2–30 (Ni), 1–20 (Zn) and 1–4 (Cd) depending on the type of oxyhydroxide. These factors become significantly larger at smaller concentrations for Ni and Zn in some oxyhydroxides and this concentration dependency suggests that slow reactions are not only related to diffusion. The short-term adsorption strength of carrier-free metal radio-isotopes was similar at 1 or 70 days after reaction with these iron oxyhydroxides and excludes the possibility that long-term reactions are related to solid-phase transformations or changes in solution properties. The extent of slow reactions in GT decreased with decreasing pH and was less than a factor 2 within 70 days at pH 3.7. The results confirm that slow reactions in Fe oxyhydroxides can explain lessened metal availability by ageing in pH neutral soils. The uncertainty of their actual structure and crystallinity in soils does not allow quantitative predictions based on the behaviour of synthetic oxyhydroxides.     

COMPARISON OF AQUEOUS ACETYLACETONE AND POTASSIUM PYROPHOSPHATE SOLUTIONS FOR SELECTIVE EXTRACTION OF ORGANIC-BOUND Fe FROM SOILS

Seven samples of iron oxyhydroxides, characterised by crystallinity and surface area (monolayer water content), were examined for solubility in aqueous acetylacetone (0.68 M), potassium pyrophosphate pH 10 (0.1 M) and acid ammonium oxalate pH 3 (0.2 M). Solubilities in acetylacetone and oxalate were dependent on surface area, being 30 per cent Fe or more for non-crystalline oxides in 40 h. Solubility in pyrophosphate was 2 per cent Fe or less in 40 h even when surface area was 300 m²/g. Pyrophosphate solution was more suitable than aqueous acetylacetone for selective extraction of iron-organic complexes from soils which contain amorphous or poorly crystalline iron oxides.     

Aluminiumsubstitution in pedogenen Eisenoxiden – eine Übersicht

Al-substitution in Fe-oxides This article resumes the present knowledge on Al-substitution in Fe (III)oxides. Al-substitution is known for goethite, hematite, lepidocrocite, magnetite and maghemite. The extent of substitution is mineral specific and varies for different soil environments for which it may have some indicator value. Al-substituted Fe-oxides are easily to synthesize. A number of characteristics of the synthetic samples have been measured. The result was that most of the changes in characteristics except the unit cell size is more an indirect effect of Al-substitution because Al in the system also affects crystallinity. Crystallinity will, however, also be strongly influenced by other conditions during crystallization. Therefore, thermal behaviour, X-ray line intensity and width, magnetization, dissolution, OH-content, IR absorption characteristic etc. depend more directly on crystallinity than on Al-substitution. The variation of these characteristics for soil iron oxides is essentially unknown so far.     

海南岛北部玄武岩上土壤发生研究Ⅱ.铁氧化物特征

研究了海南岛北部玄武岩上发育的不同风化成土年代土壤系列的铁氧化物特征。研究表明,随风化成土时间增加,土壤发生过程中形成的游离铁（Fed）以及铁游离度（Fed/Fet）增大,铁活化度（Feo/Fed）降低。穆斯堡尔谱分析显示风化成土时间从9×104a、64×104a至 181× 104a,土壤黏粒中形成的赤铁矿含量占铁氧化物的比例从16％、25％增至 48％。风化成土时间越短,土壤中针铁矿结晶程度越差。X-射线衍射结果表明土壤细土和黏粒中赤铁矿含量与风化成土时间呈正比增加。同时,土壤有磁铁矿含量减少、磁赤铁矿增加的趋势。     

Crystallization of single and binary iron‐ and aluminum hydroxides affect phosphorus desorption

In acidic soils, phosphorus availability is affected by its strong affinity for mineral surfaces, especially Fe‐ and Al‐hydroxides. Plant roots have developed adaptive strategies to enhance the availability of phosphorus, including producing and exuding low molecular weight organic acids with a high affinity for phosphorus that competes with high molecular weight organic ligands formed during humification and mineralization. The aim of this study was to characterize the kinetics and mechanism of phosphorus desorption from Fe‐ and Al‐hydroxides of variable crystallinity, as well as binary Fe:Al‐hydroxide mixtures. Long‐term desorption experiments (56 days) were conducted with CaCl₂, CaSO₄, citric acid, and humic acid as competitive sorptives. CaCl₂ and CaSO₄ were selected as general inorganic sorptives and citric and humic acids were selected as organic ligands produced by organisms in the rhizosphere or following humification. The cumulative phosphorus desorption increased following the order CaCl₂ < CaSO₄ < humic acid < citric acid. Amorphous ferrihydrite and Fe‐rich Fe:Al‐hydroxides exhibited much less desorption when exposed to inorganic solutions than the crystalline and Al‐rich Fe:Al‐hydroxide mixtures. Models of the desorption data suggest phosphorus desorption with citric acid is diffusion‐controlled for ferrihydrite and Fe‐rich amorphous Fe:Al‐hydroxides. When humic acid was the sorptive, metal‐organic complexes accumulated in the solution. The results suggest organic compounds, especially citric acid, are more important for liberating phosphorus from Fe‐ and Al‐minerals than inorganic ions present in the soil solution.     

Effects of Competing Anions and Iron Bioreduction on Arsenic Desorption

Dissimilatory iron-reducing bacteria play a fundamental role in catalysing the redox transformations that ultimately control the mobility of As in anoxic environments, a process also controlled by the presence of competing anions. In this study, we investigated the decoupling of As from loaded Al and Fe (hydr)oxides by competing anions in the presence of iron-reducing bacteria. Hematite, goethite, ferrihydrite, gibbsite and three aluminium-substituted goethites (AlGts) were synthesised and loaded with arsenate, followed by anaerobic incubation with different phosphate or carbonate-containing media in the presence of catalytic iron-reducing bacteria. Soluble Al, As, Fe and P contents were measured in aliquots by inductively coupled plasma optical emission spectrometry following periodical sampling. Shewanella putrefaciens cells were able to utilise both non-crystalline and crystalline Fe (hydr)oxides as electron acceptors, releasing Fe and As into solution. Phosphate and carbonate affected the Fe bioreduction, probably due to the precipitation of metastable mineral phases and also to phosphate-induced stabilisation on the hydroxide surfaces. Phosphate precipitation acted as a sink for As, thus limiting its mobilisation. The highest fraction of desorbed As by phosphate was observed for gibbsite, followed by AlGts. Similarly, gibbsite showed significant amounts of arsenate displaced by carbonate. In spite of its low crystallinity, ferrihydrite was the most efficient compound in retaining arsenate, possibly due to As co-precipitation. This study provides new insight into the management of As-contaminated soils and sediments containing Al-goethites and gibbsite, where the Fe activity may be too low to co-precipitate As-bearing vivianite. Thus, the dynamics of As(V) in flooded soils are significant in agriculture and environmental management.     

Properties of soil kaolinites from south-western Australia

The clay fraction of soils from south-western Australia is dominated by kaolinite. These soil kaolinites give broad basal reflections (median value for WHH 001 =0.41° 2θ) and have poorly ordered structures. The median value of the Hughes & Brown crystallinity index for 35 soil kaolinites is 5.4 compared to 42.0 for mineral standard kaolinites. The median values for surface area and cation exchange capacity of soil kaolinites are 35 m² g⁻¹ and 56.7 mmol_c kg⁻¹, respectively, compared to 10 m² g⁻¹ and 4.8 mmol_c kg- ^l for standard kaolinites. The dehydroxylation temperature of soil kaolinites is about 50 K lower than for standard kaolinites and decreases with increasing Fe content. Soil kaolinite crystals are much smaller (c. 0.10 pm) and are irregular subrounded to rounded plates in comparison to the larger (c. 0.28 pm), perfectly hexagonal euhedral plates of Georgia kaolinite. Analytical electron microscopy of single soil kaolinite crystals indicates that the Fe content varies with an average value of c. 2.5% Fe,₂O₃. X-ray diffraction line broadening data indicate that crystal size decreases as the Fe content increases. Crystal order also decreases with increasing Fe content. The P sorption maximum of soil kaolinite ranges from 486–654 μg P g^−l and is thus about six times larger than for the clay fraction of Georgia kaolinite.     

Iron distribution in the clay fraction of Cambisols as determined by Mössbauer spectroscopy,X-ray diffractometry and selective dissolution

Iron forms which characterize the clay fraction of four Cambisols from granite and the distribution of iron oxides in the soil profiles are studied by Mössbauer spectroscopy, X-ray diffractometry and selected chemical methods. The results obtained show that about 50 % of the Fe_t(6–10 % Fe) is not extracted by dithionite. The Fe_o/Fe_d ranges between 0.15 and 0.35. Oxalate dissolves goethite in different amounts, probably depending on the particle size and the Al-substitution level. The highest amount of hematite is found in the samples characterized by the lowest internal magnetic fields, suggesting that the soil distribution of hematite and goethite is related to environmental factors favouring or disfavouring Al-for-Fe substitution and crystallinity of the oxides.     

Soil development on Late Quaternary river terraces in a high montane valley in Bhutan,Eastern Himalayas

We examined the geochemistry and micromorphology of the soils on a suite of morphologically well-defined and visually distinct fluvial terraces, up to 40 m elevation above the current riverbed, at Thangbi in the upper Bumthang Valley, Bhutan. The alluvia forming each of the terraces are lithologically and structurally similar, with shallow or moderately deep, clast-free sandy loam overbank deposits capping deep clast-supported beds of rounded boulders and interstitial sand. The topsoils on the 40 m terrace have more silt than those on the lower terraces. The soils are interpreted mainly as a monoclinal post-incisive chronosequence. Features that indicate progressive pedogenesis with increasing elevation include subsoil rubefaction, crystallinity of free Fe sesquioxides, and weathering of susceptible primary minerals, such as biotite and hornblende. However other soil attributes show no systematic trends and the overall impression is of limited pedogenesis, even in the soils on the higher terraces. We examine possibilities that the immaturity of the soils is due to pedogenic rejuvenation by post-incision additions to the soil parent materials.     

人工合成绿锈GR1(CO32−)的氧化晶质过程、特点及主要影响因素

通过空气氧化法,采用电化学实时监测,结合X-射线衍射（XRD）、透射电镜（TEM）和溶液化学分析,探讨了 GR1(CO32-)的合成、氧化和晶质化特点。在合成阶段,当悬液pH降至最低或矿物中Fe2 含量升至最高时,GR1(CO32-)完全形成。在随后转化阶段,控制pH在6.5 ~ 10时,随pH增加,GR1(CO32-)的转化速率和氧化速率均减小,氧化产物由纤铁矿向针铁矿向磁铁矿变化,且针铁矿结晶尺寸随pH升高逐渐增加。控制温度在15 ~ 45 ℃时,随反应温度的增加,GR1(CO32-)的转化速率增加而氧化速率减小,氧化产物同样由纤铁矿向针铁矿向磁铁矿变化,且针铁矿粒径随温度升高而增大。控制空气流速在0 ~ 0.1 m3 h-1时,随着空气流速的增加,氧化速率增加,氧化产物中针铁矿含量逐渐减少而纤铁矿含量逐渐增加,且产物结晶度逐渐减弱。因此,在pH、温度和空气流速等影响GR1(CO32-)转化过程中,氧化速率是共同的决定因素,随着氧化速率的增加,产物由磁铁矿向针铁矿向纤铁矿变化,且产物结晶尺寸变小和结晶度减弱。     

高压处理对橡实淀粉晶体特性的影响规律

利用RINT2000 vertical goniometer型X-衍射仪测定经高压处理的橡实淀粉的晶体特性,研究高压处理对橡实淀粉晶体特性的影响规律。结果表明：高压处理不会改变淀粉的晶体类型,对淀粉晶相有一定的影响。高压处理对淀粉晶相结晶度有极显著影响,对微晶相结晶度有显著影响,对亚微晶相结晶度有一般显著影响。高压处理时淀粉含水率对其结晶度有极显著影响,含水率越高,其结晶度越低。高压处理时的压力大小对淀粉晶相、微晶相结晶度显著影响,高压处理的压力增加,其结晶度降低,在一定条件下延长保压时间可以补偿压力不足的现象。     

Crystallinity of kaolin minerals and their weathering sequence in some soils from Nigeria,Brazil and Colombia

A study of the clay mineralogy of a number of soils from West Africa and South America has enabled the construction of a generalized weathering/crystallinity sequence for the 1:1 layer silicates. The kaolin minerals appear to weather via halloysite and disordered kaolin to a well-ordered kaolinite characterized by large flakes and a high crystallinity index. Further weathering results in a reversal of the sequence via small flakes of highly disordered kaolin to gibbsite and ultimately perhaps to amorphous materials. The changes in the value of the crystallinity index as weathering proceeds are shown, together with changes downprofile and downslope.     

Phosphate desorption from flooded and reoxidized soils as compared with adsorption characteristics

Abstract

The purpose of this study was to show how phosphorus (P) desorption can bring further information to what is inferred from adsorption experiments. A simple calculation procedure is proposed to predict the P amount that would be desorbed by washing with salt solution if adsorption was completely reversible. Consequently, the interpretation of P desorption can focus on the irreversible part of adsorption. This approach is applied to samples of acid sulfate soil from Vietnam that have been submerged for different periods of time, at 20°C and 30°C, and also to samples that were reoxidized after flooding. Phosphate desorption linearly increases with P concentration in solution and exponentially decreases with increasing adsorption capacity as expressed by the Freundlich coefficient of adsorption isotherms. These two types of relationships are correctly predicted by our calculation procedure. As far as reversibility is concerned, we find that with respect to calculated desorption, the proportion of irreversible adsorption greatly differ according to treatments. In relative terms, adsorption reversibility is lowest in the reoxidized soils and highest in the wet soils incubated at 30°C. This is related to the type and crystallinity of Fe‐oxihydroxides and consequent differences in P‐bonding energies.     

Physical Properties of Extruded Wheat Starch-Additive Mixtures

The effects of the addition of fatty acids, monoglycerides (MG), and wheat germ oil (WGO) on the level of crystallinity and the crystalline structure of extrusion-cooked wheat starch have been studied using twin-screw extruders. Measurements of water solubility and water absorption indices were made on the extrudates, together with specific mechanical energy (SME) consumption and die pressure for the extruder. MG and the fatty acids added to a level of 4% caused an increase in V_hydrate type crystallinity. WGO addition to a level of 8% caused no change in crystallinity, although the E_hydrate type was favored at lower moisture contents. All additives caused a decrease in SME and an increase or maximum in die pressure. WGO behaved differently than MG and fatty acids in that its addition caused the water solubility index and expansion to increase, as previously observed for other oils added to flours.     

Gallium(III) does not actively substitute for iron(III) in iron/gallium competition studies

Strategy II plants respond to Fe stress by releasing a phytosiderophore and are believed to absorb Fe as Fe(III). Gallium(III) has chemical characteristics which have made it useful as a substitute for Fe(III) in biological systems. The objectives of our study were to: 1) determine if Ga(III) acts competitively to reduce Fe(III) uptake or otherwise substitutes for Fe(III) in barley (Hordeum vulgare L.), and 2) determine if the competition for Fe(III) between EDDHA or BPDS and barley further elucidates the form of Fe absorbed by barley. Chlorosis ratings, phytosiderophore production, and tissue Fe contents were indexes of Fe stress.

Gallium was absorbed and translocated by the plant both in the presence and absence of Fe, and slightly alleviated Fe stress in the absence of Fe. However, Fe uptake was not affected by the presence of Ga. Thus, Ga(III) did not seem to compete with Fe(III) for uptake. Increasing EDDHA in solution intensified chlorosis and phytosiderophore production and reduced root Fe, but did not reduce leaf Fe concentration. Increased BPDS had no influence on either chlorosis or leaf Fe, but did cause phytosiderophore production to increase and root Fe to decline. The presence of Fe(II) in solutions containing BPDS suggests a potential for reducing Fe(III) in the roots of barley.     

Iron‐Enriched Azolla as a slow‐release biofertilizer for cucumber plants grown in a hydroponic system

The unique ability of dried plant residues Azolla to adsorb iron (Fe) was employed to formulate and test an organic Fe biofertilizer. A simplified experimental system was established to examine the effectiveness of Fe‐enriched Azolla as a source of Fe for the remedy of Fe‐deficient plants. The optimal Fe‐enrichment level needed to achieve a complete recovery of starved plant by the Fe‐Azolla complex was tested using a bioassay system of hydroponically grown cucumbers. Dried Azolla plants were mixed a with a solution of ferrous sulfate (FeSO₄) at pH 2.0, rinsed, and dried to form organic, compact material containing 4% (w/w) Fe bound to Azolla. The Fe‐Azolla complex was applied to the nutrient solutions of Fe‐deficient cucumber seedlings. Growth rates and development measurements as well as chlorophyll and the Fe‐containing catalase activity tests have been performed. The effect of the slowly released Fe in correcting Fe deficiency were followed for three weeks and compared with the efficiency of additions of several synthetic Fe chelates. Iron‐starved plants exhibited fast regreening of the chlorotic interveinal tissues after the addition of Fe‐Azolla complex to the nutrient solutions. Iron starvation decreased the activity of catalase. Iron‐treated‐starved plants exhibited recovery of catalase activity compared to the low level activity measured untreated Fe‐starved plants. Iron‐enriched Azolla treatment was found equivalent to Fe‐EDTA and Fe‐EDDHA. This study is the first step in our research program aimed to establish the application of Fe‐enriched Azolla as a bioagent for the benefit of Fe‐deficient crops.     

Soybean response to iron‐deficiency stress as related to iron supply in the growth medium

The Fe‐inefficient T203 and the Fe‐efficient A7 and Pioneer 1082 (P1082) soybeans (Glycine max (L.) Merr.) were grown hydroponically with no (0 mg Fe L^‐1 ; ‐Fe) and a minute level (0.025 mg Fe L^‐1 ; +Fe) of Fe to (a) compare their responses to Fe‐deficiency stress and (b) relate Fe‐efficiency in soybeans to their ability to initiate the Fe‐stress‐response mechanism at low levels of Fe. With no Fe in solution, P1082 released similar levels of H⁺ ions, but released less reductant from their roots and there was less reduction of Fe³⁺ to Fe²⁺ by their roots than by A7 roots. These responses were also one day later and occurred after a more severe chlorosis and a lower leaf Fe had developed in P1082 than in A7. With 0.025 mg L^‐1 of solution Fe, it was not necessary for the Fe‐stress response mechanism to be fully activated to make Fe available in A7 soybean, whereas a strongly enhanced Fe stress response was observed in P1082. Increased Fe uptake and regreening of leaves immediately succeeded initiation of the Fe stress response in both cultivars and at both levels of Fe. Thus, P1082 was slightly less efficient than A7 soybean, but would be classed more efficient than the previously studied soybean cultivars A2, Hawkeye, Bragg, Pride, Anoka, and T203. These results support the hypothesis that the most efficient soybeans are those which can initiate the Fe‐stress response mechanism with little or no Fe in the growth medium. The near simultaneous occurrence of the factors in the Fe‐stress response mechanism (H ion and reductant release, reduction of Fe to Fe by roots), and the immediate increase in leaf Fe and chorophyll contents following that response suggest that all these factors act in concert, not independently, to aid in the absorption and transport of Fe to plant tops.     

Activities of Iron‐Containing Enzymes in Leaves of Two Tomato Genotypes Differing in Their Resistance to Fe Chlorosis

Abstract

Two tomato (Lycopersicon esculentum Mill., cvs. Pakmor and Target) genotypes differing in resistance to iron (Fe) deficiency were grown in nutrient solution under controlled environmental conditions over 50 days to study the relationships between severity of leaf chlorosis, total concentration of Fe, and activities of Fe‐containing enzymes in leaves. The activities of Fe‐containing enzymes ascorbate peroxidase, catalase, and guaiacol peroxidase, and additionaly the activity of glutathione reductase, an enzyme that does not contain Fe, were measured. Plants were supplied with 2 × 10^?7 M (Fe deficient) and 10^?4 M (Fe sufficient) FeEDTA, respectively. Leaf chlorosis appeared more rapidly and severely in Target (Fe deficiency senstive genotype) than Pakmor (Fe deficiency resistant genotype). On day 50, Pakmor had 2‐fold more chlorophyll than Target under Fe deficiency, while at adequate supply of Fe the two genotypes were very similar in chlorophyll concentration. Despite distinct differences in development of leaf chlorosis and chlorophyll concentrations, Pakmor and Target were very similar in concentrations of total Fe under Fe deficiency. In contrast to Fe concentration, activities of Fe‐containing enzymes were closely related to the severity of leaf chlorosis. The Fe‐containing enzymes studied, especially catalase, showed a close relationship with the concentration of chlorophyll and thus differential sensitivity of tomato genotypes to Fe deficiency. Glutathione reductase did not show relationship between Fe deficiency chlorosis and enzyme activity. The results confirm that measurement of Fe‐containing enzymes in leaves is more reliable than the total concentration of Fe for characterization of Fe nutritional status of plants and for assessing genotypical differences in resistance to Fe deficiency. It appears that Fe deficiency‐resistant genotype contains more physiologically available Fe in tissues than the genotype with high sensitivity to Fe deficiency.