Microbial reduction mechanism of ferric iron in paddy soils (Part I)

In the previous paper¹⁾ the authors proved that the ferric iron reduction in submerged paddy soils is entirely or mostly effected by the activities of microorganisms in the soil. Prior to the study on the ferric iron reducing microorganisms isolated from the soil, the present paper reports the research for the microbial mechanism of iron reduction. working with the soil itself.     

THE OXIDATION OF IRON SULPHIDES IN SOILS IN RELATION TO THE FORMATION OF ACID SULPHATE SOILS, AND OF OCHRE DEPOSITS IN FIELD DRAINS

Aerating pyritic soils causes acidification and the forrnation of acid sulphate soils, or cat-clay. The Oxidation of pyrite in soils is associated with the deposition in tile drains of a form of ochre quite distinct from that formed by the action of filamentous iron bacteria. Pyrite-derived ochre results from the action of Thiobacillus ferrooxidans, which, below pH 3.5–4.0, catalyses the Oxidation of Fe²⁺ and pyrite. In soils less acid than c. pH 4, pyrite oxidizes relatively slowly by chemical reactions to Fe²⁺ and SO²₄^?. Under these conditions iron enters the drains as Fe²⁺ and is there oxidized by T. ferrooicidans and deposited as hydrated ferric oxide. Once the soil becomes acid enough for T. ferrooxidans to multiply, the rate at which pyrite oxidizes increases several-fold, and at c. pH 3 iron appears in the drainage water in the ferric form. Liming seems to decrease the rate of Oxidation.     

Effect of Organic Matters on the Formation of Ferrous Iron in Soils

Under the condition of flooded irrigation, it has been confirmed that ferric iron compounds existing mostly in insoluble forms in soils were appropriately reduced to more soluble ferrous forms, and that the application of organic matters brought about favorable circumstances for the development of the reducing state induced by activated microbes^{1 2}) and consequently the formation of active ferrous iron in soils resulted.     

Effect of iron oxide removal on heavy metal sorption by acid subsoils

The adsorption of Cd, Cu, Pb, and Zn from 0.025 M NaClO₄ solutions by two ferruginous subsoils, Christiana silty clay loam and Dothan sandy clay, was investigated. Under acidic conditions, selective dissolution and removal of the Fe oxide soil component by dithionite-citrate-bicarbonate (DCB) generally increased heavy metal adsorption by the soils. This effect was attributed to increased electrostatic attraction of cations to the DCB-washed soils as evidenced by substantial reduction in the zero point of charge (ZPC) for the Dothan soil following DCB extraction. Alternately, the DCB extraction stripped Fe and Al species bound to structural exchange sites or eliminated coatings which reduce cation accessibility to such sites. Addition of low levels (10^?6 M) of ferric iron suppressed heavy metal adsorption capacity of the DCB-extracted Christiana soil to values comparable to the unmodified whole soil system. While hydrous oxide surfaces represent highly reactive sites for cation binding, Fe oxides can modify both the pH-dependent and structural exchange sites in a manner which hinders heavy metal adsorption. Thus, a soil's Fe-oxide content is unlikely to be a reliable guide to heavy metal adsorption capacity.     

EVALUATION OF POTENTIAL SUBSTRATES TO MONITOR RESPIRATORY NITRATE REDUCTASE ACTIVITY IN SOILS

Different inorganic ions were tested for their ability to replace nitrate as the terminal oxidant for bacterial respiration in anaerobic soils. Chlorate, bromate. selenate. tellurite and ferric ions were all unsuitable substitutes, lodate reduction in soils was similar to nitrate reduction because it required anaerobic conditions, was increased by glucose amendment and decreased by phenylmercuric acetate. Amendment of soils with iodate and measurement of iodide production can be used to measure nitrate reductase activity in a soil and so give a qualitative indication, and possibly a quantitative estimate, of the denitrification capacity of soils.     

Chelation effects on the iron reduction and uptake by low‐iron stress tolerant and non‐tolerant citrus rootstocks

The relative rates of ferric‐iron (Fe³⁺) reduction and uptake by two citrus rootstocks were measured for a series of synthetic Fe³⁺ chelates and microbial siderophores. The rates of Fe³⁺ reduction by the citrus seedlings followed the order: FeHEDTA >> FeDPTA > FeCDTA. No reduction occurred for FeDFOB (ferrioxamine B) and FeTAF (ferric triacetylfusagen). Low rates of Fe³⁺ reduction occurred for Fe2RA3 (ferric rhodotorulic acid). The levels of ⁵⁵Fe taken up the citrus seedlings showed good correlations with the reduction rates. These results indicate the importance of Fe³⁺ reduction in the Fe uptake by citrus rootstocks. The immobility of a large percent of the ⁵⁵Fe taken up by the roots is attributed to the accumulation of Fe in the root apoplasts.     

Determining competitive nitrate and chloride adsorption in an andisol by the unsaturated transient flow method

Abstract

Activated sludge from a sewage disposal plant was labeled with ¹⁵N in the laboratory. The labeled sludge (dewatered cake) was then incubated under aerobic conditions for 30 days with four kinds of cultivated soils: volcanic ash soil, red-yellow soil, paddy soil, and sandy dune soil. The nitrogen mineralization of the soil organic matter was remarkable only in the case of the paddy soil. In this soil, a priming effect caused by the addition of the sludge was observed. After 30 days of incubation, the ¹⁵N organic fractions remaining in the red-yellow soil were determined. It was found that the amino acid and the unidentified fractions in the hydrolyzable nitrogen forms of the sludge contributed mainly to the amount of nitrogen mineralized. Finally, using sludges which originated from the same organic matter source, the lnftuence of a generally-used inorganic coagulator Oime and ferric chloride) of sludge on the nitrogen cycle was clarified. This coagulator caused a reduction in the amount of inorpnic nitrogen mineralized in the soil and also accelerated the nitrification process.     

THE REACTION OF FLUORIDE WITH SOILS AND SOIL MINERALS

The reaction of sodium fluoride solution with soils and soil minerals at constant pH has been assessed as a possible single-value characteristic in the classification of soils, particularly those containing significant amounts of poorly ordered inorganic material. A suitable method involves reaction of the soil or clay at 25°C with 0·85 M sodium fluoride at pH 6·8, the amount of OH^? released after 25 min being taken as the single-value characteristic. There was a statistically significant correlation between the amount of OH^? released and the amount of alumina extracted with cold 5 per cent sodium carbonate solution from both freely drained and poorly drained Scottish soils. The multiple correlation coefficients were improved for freely drained soils by including the dithionite-extracted ferric oxide and the silica soluble in 5 per cent sodium carbonate solution. The procedure is not suitable for surface soils, because of interference by organic matter, or for carbonate-containing soils unless carbonate is removed.     

无定形氧化铁作为嫌气下NH4+氧化时电子受体的研究

通过¹⁵N示踪试验,以及根据嫌气条件下含¹⁵NH₄⁺培养液加无定形氧化铁后全氮回收量下降(损失¹⁵N约15%),以及产生¹⁵NO₂、¹⁵N₂O、¹⁵N¹⁴NO、¹⁵NO、¹⁵N₂和¹⁵N¹⁴N等含N气体的研究结果,初步证明无定形氧化铁可作为嫌气下NH₄⁺氧化时的电子受体,这可能是引起水田土壤中铵态氮肥损失的又一机理。目前因无各种合¹⁵N氧化物标准气体,无法对其形成的含¹⁵N气体组分进行定量,这一机理对氮素损失的贡献究竟有多大?尚需进一步研究。     

Reduction in phosphorus availability in poultry and diary manure by mineral amendments

Abstract

Phosphorus (P) loading of soils from the repeated application of manure and the associated loss of P to water systems is a serious and increasing problem in today's agricultural landscape. The hypothesis of this study was that the application of mineral amendments to manure might reduce P availability in manure and soil without affecting crop productivity. An incubation experiment was conducted to evaluate the ability of aluminum sulfate, ferric chloride or calcium hydroxide at 100 and 200 g kg^?1 of manure to reduce phytoavailable (Mehlich-3 extractable) P in liquid dairy, laying hen and broiler chicken manure. Mehlich-3 extractable P was reduced from 59 to 97% in all manure treated with aluminum sulfate and ferric chloride. The calcium hydroxide treatment resulted in a Mehlich-3 extractable P reduction ranging from ?17 to 51%. A container experiment was then carried out to examine the effect of soil with pre-treated manure on timothy (Phelum pretense L.) growth and soil P levels. Timothy yields in all dairy manure treatments were 45–57% lower compared to an N–P–K control, but were not lower compared to the untreated manure control. Dairy manure + aluminum sulfate (200 g kg^?1) reduced water-extractable P by 82% relative to the N–P–K control. All other manure and amendment treatment combinations were not statistically different from the N–P–K or the untreated soil controls in terms of water-extractable P, Mehlich-3 extractable P or grass yield. Significant reductions in Mehlich-3 extractable P were observed with the aluminum sulfate or ferric chloride amendments, while varied results were observed with the calcium hydroxide amendment. Results suggest that the use of manure amended with aluminum sulfate or ferric chloride has little effect on growth or P accumulation by timothy. Overall, this study demonstrated that mineral pre-treatment of manure can reduce the extractable P content of the manure and soil without negative effects on plant growth.     

A new method for determining ferrous iron in paddy soils

Introduction

To make clear the chemical behavior of free iron compounds in paddy soils, it is necessary to find an accurate and rapid method for determining ferrous iron in waterlogged paddy soils. Several methods^1,2,3) have been proposed for this purpose, most of which use dilute acids, such as sulfuric and hydrochloric acid, as extracting reagents. According to the writers' experience, however, these methods seem to be inadequate. The reason is that the acid solutions extract not only ferrous iron, but also ferric iron and reducing substances from soils, and the latter two react immediately in the extract to produce ferrous iron, thus we obtain larger value for ferrous iron than the one actually existing in soils. The writers have found that acetate buffer of pH 2.8 is a very suitable extractant for ferrous iron, and they have been able to establish a new method for the determination of ferrous iron in soils using this buffer. The experimental details will be given in this paper.     

Role of root-induced changes in the rhizosphere for iron acquisition in higher plants

Plants can mobilize iron (Fe) in the rhizosphere by non-specific and specific (adaptive) mechanisms. Non-specific mechanisms are, for example, rhizosphere acidification related to high cation-anion uptake ratios, or citric acid excretion. The specific mechanisms are root responses to Fe deficiency and can be classified into two different strategies. The Strategy I is typical for dicots and monocots except for grasses (graminaceous species) and is characterized by increased plasma membrane-bound reductase activity, enhanced net excretion of protons and enhanced release of reducing compounds, mainly phenolics. The reductase activity is stimulated by low pH, and with supply of Fe^III chelates, ferric reduction at the plasma membrane takes place prior to uptake. In contrast, in graminaceous species (Strategy II) these root responses are absent, but enhancement of release of Fe^III chelating compounds - phytosiderophores - takes place. These phytosiderophores are very efficient in mobilizing Fe^III from artificially prepared sparingly soluble inorganic compounds (e.g. Fe^III hydroxide) and from calcareous soils. The ferrated phytosiderophores are taken up by grasses at rates 10² to 10³ times higher than Fe supplied either as synthetic chelate or microbial siderophores (e.g. ferrioxamine B), indicating a specific membrane transport system for ferrated phytosiderophores in roots of grasses. In calcareous soils phytosiderophores not only mobilize Fe, but also Zn, Mn, and Cu by chelation. However, only the Fe^III phytosiderophores are taken up preferentially by Fe deficient grasses. The ecological advantages and disadvantages of Strategy I and Strategy II for Fe acquisition from calcareous soils are discussed.     

Solubility Relationships of Iron and Evaluation of its Fertility Status in Degraded Soils

This study was conducted to determine the solubility of iron (Fe) and identify the solid phases responsible for controlling its solubility in these soils by using Baker soil test (BST) computer program. The results indicated that the ferric ion (Fe³⁺) activity in all the soils, except the acidic ones, nearly approached the theoretical solubility line of known minerals, namely soil-Fe, amorphous-Fe, maghemite, and lepidocrocite. Solubility of Fe in acid soils of Ranchi (soil 3) and Cooch-Behar (soil 6) did not match the theoretical solubility lines of any of the known minerals. The acidic soils of Ranchi and Cooch-Behar were sufficient for Fe with respect to both quantity and intensity factor based on BST rating, while alkaline (soil 1) and calcareous (soil 5) were sufficient in reserve Fe; deficiency of iron still could be suspected because of high pH. These findings elucidate the role of solid phase controlling iron solubility in soil solution of degraded soils.     

Effects of Several Metals on Both Fe(III)‐ and Cu(II)‐Reduction by Roots of Fe‐Deficient Cucumber Plants

Abstract

The ferric‐chelate reductase induced by Fe deficiency is also able to reduce other ions such as Cu²⁺. This Cu(II)‐reduction has been less studied and it has been suggested that Cu²⁺ ion rather than Cu²⁺‐chelate serves as the substrate. Ferric‐chelate reductase activity is inhibited by some metals, but the mechanisms implicated are not known. In the present work we use Fe‐deficient cucumber seedlings to study the interactions of Cu²⁺, Ni²⁺, Mn⁴⁺, and Fe³⁺ on both Fe(III)‐reduction and Cu(II)‐reduction activities. The response of Cu(II)‐reduction activity to Cu concentration, in the presence or absence of citrate, was also studied. Results showed that inhibition of the ferric‐chelate reductase activity by Cu²⁺ or Ni²⁺ could be partially reversed by increasing the concentration of Fe‐EDTA. The Cu(II)‐reduction activity was even stimulated by Fe‐EDTA or Ni²⁺; it was inhibited by a high concentration of Cu²⁺ itself; and it was not affected by the absence of citrate. Mn⁴⁺ caused a moderate inhibition of both Fe(III)‐reduction and Cu(II)‐reduction activities. Results agree with the hypothesis that free Cu²⁺ ion is the substrate for Cu(II)‐reduction and suggest that the mechanisms involved in Fe(III)‐reduction and Cu(II)‐reduction could have some differences and be affected by metals in different ways. The mode of action of metals on the reductase activity are discussed, but they are still not well known.     

Mineralization of 14C-labelled unripe straw in soil with and without rape (Brassica napus L.)

Soil was amended with ¹⁴C-labelled unripe straw only (C:N ratio ca. 20), with ¹⁴C-labelled unripe straw plus unlabelled ripe straw (C:N ratio ca. 100) or with ¹⁴C-labelled unripe straw plus glucose. Half the samples with ¹⁴C-labelled straw and half the samples with ¹⁴C-labelled plus unlabelled straw were cropped with rape plants. A decreased rate of mineralization of the ¹⁴C-labelled straw was found in the planted soil compared with the unplanted soil. The reduction was most profound in the soil amended with both labelled and unlabelled straw, indicating that at least part of the reduction was due to competition between plants and microorganisms for mineral N. No other explanations for the decrease in mineralization in the presence of plants were found. The soil amended with glucose which simulated the effect of root exudates showed an increased rate of mineralization. Therefore, the reduction in the presence of plants was probably not due to microbial use of the rhizodeposition in favour of the labelled straw. Only a minor part of the reduction was apparently due to uptake of labelled C by the plant, as only small amounts were found in the roots and shoots at harvest. The difference in ¹⁴C mineralization between treatments was not reflected in the number of bacteria in the soil at harvest. The number of bacteria, which was determined by plate counts and direct microscopy, was the same in all the soils, rhizosphere soils as well as bulk soils.     

Potential of Chitosan (Chemically Modified Chitin) for Extraction of Lead-Arsenate Contaminated Soils

Arsenic, lead, and phosphorous contamination in soils represents a health risk. Chitosan (poly-N-acetyl glucosamine) inexpensive by-product derived from chitin has been used as a metals adsorbent. Objectives of this research were to evaluate the effectiveness of chitosan solution for arsenic, lead, and phosphorous extraction from lead-arsenate contaminated soils, and evaluate the effectiveness of protonated chitosan flakes (PCF) and ferric hydroxide chitosan beads (Fe(III)-CB) for water-soluble As removal from these soils. Percentage of arsenic, lead, and phosphorous removed from the soils by chitosan solution ranged from 0.96% to 17%, 1.80% to 31%, and 0.66% to 11%, respectively. Percentage of water-soluble arsenic removed by PCF and by Fe (III)-CB ranged from 12% to 47% and 36% to 77%, respectively. Averaged over soils, Fe (III)-CB removed slightly more arsenic (As) (42 mg kg^?1) compared to Mehlich III (40 mg kg^?1) extractant. Results indicate potential for the use of chitosan as an extraction for lead-arsenate contaminated soils.     

Action des ions ferreux sur la reduction de l'acide nitreux dans les sols hydromorphes

It was postulated that chemical denitrification per se can take place in soils especially in the presence of certain metallic cations. Denitrification was measured by gas evolution from soil and changes in the proportion of different gases (N₂, N₂O and NO). Such measurements showed that in hydromorphous soils reduction of nitrite occurs in the presence of ferrous-iron. The influence of different extractant solutions and stirring of the soil during such experiments was investigated. In field soils N₂O and N₂ appear to be the only products of the reduction of NO₂^?-N by Fe²⁺.     

Effects of polyacrylamide,biopolymer and biochar on the decomposition of 14C‐labelled maize residues and on their stabilization in soil aggregates

The efficacy of applying plant residues to agricultural soils as a carbon (C) source for microorganisms and C sequestration is dependent on soil physiochemical properties, which can be improved by aggregation using soil conditioners. However, no attempt has been made to assess the effects of soil conditioners such as biochar (BC), biopolymer (BP) or polyacrylamide (PAM) on plant residue decomposition. We assessed the effects of BC, synthesized BP and anionic PAM on the decomposition of ¹⁴C‐labelled maize residues and on their stabilization in aggregate fractions in sandy and sandy loam soils. Polyacrylamide and BP were applied at 400 kg ha^?1 and BC was applied at 5000 kg ha^?1, and the soils were incubated for 80 days at 22°C. The conditioners improved the physical and biological properties of both soils, as shown by a 24% increase in the 1–2 mm aggregates. Biochar and BP accelerated the decomposition of plant residues as indicated by ¹⁴CO₂ efflux, and resulted in reduced stabilization of residues in both soils relative to that observed in the control and PAM treatments. The reduction in ¹⁴C incorporation and C stabilization in the BC‐ and BP‐treated soils was observed mainly in the < 0.25‐mm aggregates. This was confirmed by reduction of activity of hydrolytic enzymes (β‐cellobiosidase and β‐glucosidase). Decomposition of plant residues in sandy soil was more sensitive to BP and PAM application than that in sandy loam soil. Improved soil structure after applying BC and BP increased aeration and decreased the contact between plant residues and mineral soil particles and consequently accelerated plant residue decomposition and reduced C sequestration.     

Successive Ferric and Sulphate Reduction using Dissimilatory Bacterial Cultures

In the present work the kinetics of ferric reduction was investigated using dissimilatory ferric- and sulphate-reducing bacterial cultures. The effect of sulphate reduction on Fe(III) reduction was also studied. The study is an attempt to improve the biological reduction rate of Fe(III) as an alternative biotechnological way to the reduction step in steelmaking processing operations. The results obtained show that the reduction of ferric iron and sulphate took place in a successive way and none synergetic effect was detected. The simultaneous action of both metabolic activities did not enhance the process but slowed down the kinetics of ferric reduction. The reduction process of 3 g/L of soluble ferric and 3 g/L of sulphate lasted 25 days. Ferric iron was the first electron acceptor to be reduced in the first 15 days followed by the sulphate reduction in the following 10 days. That result suggests that ferric reduction is a preferential metabolic process over sulphate reduction when both electron acceptors coexist. None improvement in the kinetics was observed using an electron donor concentration in excess. In contrast, the total reduction of ferric ion (3 g/L) with adapted bacterial cultures was achieved in only 36 h. The presence of sulphate had no effect on the ferric reduction. Finally, an improved culture medium for ferric-reducing bacteria is also proposed.     

FORMATION OF IRON OXIDES BY DECOMPOSITION OF IRON-PHENOLIC CHELATES

Iron chelates of some simple di-and trihydric phenols can be decomposed by peroxide treatment or by hydrolysis to yield crystalline ferric oxides. The species of ferric oxide obtained depends upon the precipitating conditions and the nature of the chelating ligand. In oxidative virtually anion-free conditions, decomposition of all aged chelates yields a precipitate of disordered ferric oxide, which is referred to as‘protohaematite’, since it ages to haematite in water even at room temperature. Protohaematite is considered to be a discrete form of ferric oxide similar in structure to δ-FeOOH but devoid of hydroxyl groups and may be present in freely drained soils as a precursor of haematite. Hydrolysis of all unaged chelates, except that of iron protocatechuic acid, yields lepidocrocite. The redox cycle undergone by iron in this reaction may be analogous to one prevailing in gley soils. In the presence of montmorillonite, the iron-catechol system forms a clay-metal-organic complex, which also decomposes to yield lepidocrocite provided chloride ions are present on the clay surface. The fact that various inorganic gels amorphous to X-rays can also deplete the ligand content of the chelates indicates a possible inorganic decomposition mechanism for metal-organic chelates in soils.