Biodegradation of clay minerals under the influence of cyanobacterial-actinomycetal associations

The capacity of associations of cyanobacteria and actinomycetes to transform the structure of clay minerals (kaolin, vermiculite, mica, and montmorillonite) was experimentally revealed. First, easily weatherable vermiculite and biotite were transformed. The rate of transformation of micas to mixed-layered minerals depended on their structure: trioctahedral mica (biotite, the component of vermiculite) was changed much faster than dioctahedral mica (the component of kaolin). The lattices of all the phyllosilicates were altered (disordered and disaggregated) under the influence of the cyanobacterial-actinomycetal associations.     

Transformation of Trioctahedral Mica in the Upper Mineral Horizon of Podzolic Soil during the Two-Year-Long Field Experiment

An experiment on transformation of biotite (fraction <1 μm) particles placed into containers with different permeability in the AEL horizon of podzolic soil was performed in order to estimate the contribution of different factors to the transformation of biotite in the modern soil. After two-year-long incubation in the AEL horizon, biotite was transformed into vermiculite, mixed-layer biotite–vermiculite, and pedogenic chlorite. The most intense vermiculitization of the biotite took place under the impact of fungal hyphae and, to a lower degree, fine plant roots and components of the soil solution. The formation of labile structures from biotite was accompanied by thinning of the mica crystallites, the disturbance of the homogeneity of layers, the removal of interlayer K, the removal and oxidation of octahedral Fe, the increase in the sum of exchangeable cations, and the appearance of exchangeable Al. The process of chloritization was definitely diagnosed upon the action of plant roots and fungal hyphae on the biotite. Strong complexing anions released by fungal hyphae partly inhibited chloritization. Chloritization led to a decrease in the cation exchange capacity of vermiculitic structures.     

Biotite weathering in peaty-podzolic gleyic soil under conditions of a model field experiment

Changes in biotite (fraction 1–5 μm) after exposure in the T2, H, Eih, and E horizons of peatypodzolic gleyic soil under conditions of a model field experiment were studied by X-ray diffraction. It was found that the main transformations of the biotite in all horizons included the degradation of its crystal lattice into regularly interstratified biotite-vermiculite and randomly interstratified biotite-smectite structures and vermiculite. The transformation intensity decreased down the profile simultaneously with a reduction in the content of organic matter, roots, and microbiota population and activity. Chloritized structures were also present among the biotite weathering products in the E horizon. The main identified products of biotite weathering formed in horizons Eih and E over a five-year period of the model experiment were detected in the clay and fine silt fractions of these horizons and in native peaty-podzolic gleyic soils. This suggests that vermiculite and soil chlorite in the soils studied are products of soil functioning. It follows from the results, with consideration for literature data, that the weathering of biotite results in the formation of a potassium-buffering system.     

Root-induced irreversible transformation of a trioctahedral mica in the rhizosphere of rape

The ability of the roots of rape (Brassica napus) to promote the transformation and dissolution of a phlogopite mica was studied in the rhizosphere. Rape was cropped for 1 to 32 d on 2–105 μm phlogopite as sole source of both K and Mg. The chemical balance of K and Mg revealed that rape was able to induce a significant release of interlayer-K after 4 d, and even a significant release of octahedral-Mg after 8 d of cropping. After 32 d, the root-induced release amounted to 80 and 21 g kg^?1 of total-K and -Mg, respectively. The weathering products sampled in the close proximity of the roots were analysed by X-ray diffractometry (XRD), and by energy dispersive X-ray (EDX) microanalysis of resin-embedded samples prepared for transmission electron microscopy. The XRD analysis of K-saturated, oriented plates showed that part of the vermiculite formed by root activity behaved as a typical hydroxy-aluminous interlayered vermiculite (HIV). The EDX microanalysis revealed that the release of interlayer-K which occurred during the vermiculitization was compensated mostly by A1 and Mg originating from the octahedral sheet of the phlogopite. Such crystallographic and crystallochemical changes necessarily involved an acid dissolution of the mica structure, which may be related to the root-induced pH decrease encountered simultaneously in the rhizosphere. Proton excretion by rape roots was thus the probable mechanism involved in the root-induced irreversible transformation of the phlogopite.     

Fixation of radiocaesium traces in a weathering sequence mica → vermiculite → hydroxy interlayered vermiculite

Radiocaesium fixation in soils is reported to occur on frayed edge sites of micaceous minerals. The weathering of mica in acid soils may therefore influence the Cs⁺ fixation process and thereby the mobility of the radiopollutant. We produced a laboratory weathering model biotite → trioctahedral vermiculite → oxidized vermiculite → hydroxy interlayered vermiculite (HIV) and quantified the Cs⁺ fixation of each mineral both in a fixed K⁺–Ca²⁺ background and in acid conditions. The transformation process was achieved through K depletion by Na-tetraphenylboron, oxidation with Br₂ and Al-intercalation using NaOH and AlCl₃. In a constant K⁺–Ca²⁺ background, vermiculite fixed 92–95% of the initial ¹³⁷Cs⁺ contamination while biotite and HIV fixed only 18–33%. In acid conditions, the interlayer occupancy by either potassium (biotite) or hydroxy-Al groups (HIV) strongly limited Cs⁺ fixation to 1–4% of the initial ¹³⁷Cs⁺ contamination. Cs⁺ fixation occurred on vermiculitic sites associated with micaceous wedge zones. Though both oxidized and trioctahedral vermiculites fixed similar Cs⁺ amounts in a constant K⁺–Ca²⁺ background (92–95%), the oxidized vermiculite retained much more radiocaesium in acid conditions (78–84% against 54–59%), because of its dioctahedral character.     

Microbial degradation of phyllosilicates during simulated podzolization

Perfusion experiments were conducted to study mechanisms in the transformation of phyllosilicates by oxalic acid and other complexing agents synthesized by microorganisms that survived partial sterilization. Those resistant to thymol were mostly non-pigmented Pseudomonas sp. and Bacillus but included a few yeasts. The organic acids formed by the microorganisms dissolved large amounts of mineral elements from samples of granites and granitic sand. Organo-metal complexes were formed with Fe and Al. 70–100% of the dissolved Fe were in complexes stable over a wide range in pH. 10–30% of the dissolved Fe and Al were in very stable anionic complexes that were not exchangeable with strong cationic resins. The acidic compounds that were formed solubilized appreciable amounts of ferromagnesian minerals, mainly biotite, and destroyed primary chlorite and some vermiculite. Under some experimental conditions, illite-vermiculite was transformed into vermiculite and biotite into vermiculite or into a white and brittle residue of Si and Al. Because similar mineral transformations have been shown to occur during podzolization in the field, our experiments are thought to provide a satisfactory model of weathering in that soil-forming process.     

Transformation of micas of various crystal chemistry under influence of cyanobacteria and actinomycetes association

The ability of experimental cyanobacteria and actinomycetes associations to change the structure of micas has been revealed. It was noticed that the rates of mineral transformation depend on their crystalchemical composition??the structure of biotite??trioctahedral mica that transformed sustainably under the influence of cyanobacteria and actinomycetes association??s growth, which was detected by the emergence of mixed-layered biotite-vermiculite formation in the fraction sample. In the case of dioctahedral mica??muscovite??the significant transformational changes under the influence of association has not been revealed. The symmetry and high clearness of mineral reflexes after the association??s growth indicates a high tolerance of muscovite to biological weathering.     

Biotite weathering in podzolic soil under conditions of a model field experiment

The biotite changes in the 1–5 μm fraction after its occurrence in the F, H, AE, and E horizons of a pale-podzolic soil for five years under conditions of a model field experiment were assessed by X-ray diffraction analysis. It was found that the main changes of the biotite in all the horizons included the degradational transformation of its crystal lattice to interstratified mica-vermiculite structures and vermiculite. The intensity of this process gradually decreased from the F horizon down the profile in parallel with the decrease in the amount of roots and the abundance and activity of microbiota. Chloritized structures were present among the products of the biotite weathering in the H, AE, and E horizons; the degree of chloritization gradually increased from the H horizon to the E horizon. The main identified products of the biotite weathering in the AE and E horizons formed during the 5 years of the model experiment were identified in the clay and fine-silt fractions from these horizons of the native pale-podzolic soils. Therefore, the vermiculite, soil chlorite, and mixed-layer illite-vermiculite minerals in the soils studied could be considered as products of the recent soil functioning. The obtained results and literature data showed that the weathering of biotite resulted in the formation of K- and Al-buffer systems.     

含钾矿物中钾的释放及其与溶液环境中离子种类的关系

通过室内试验研究探讨5种含K矿物中K在不同溶液中的释放规律(释放量和释放速率).结果表明,不同含K矿物中K释放速率和释放量的顺序均表现为:黑云母>蛭石>金云母≥白云母>钾长石,不同K矿物释K速率在酸溶液中差异最大,其次在钙和钠盐溶液中,在水中的速率差异最小,这主要是受其矿物本身结构的影响.不同离子对含K矿物中非交换态K释放的促进作用差异显著:H~+>>Ca~(3+)>Na~+>H_2O>NH_4~+.随矿物K有效性增加,H~+和Ca~(2+)对矿物K释放的促进作用越大,而且H~+较Ca~(2+)对黑云母、金云母和长石中的K有更突出的促释作用.此外,Ca~(2+)较Na~+显著促进了黑云母和蛭石中K的释放,但对其他矿物中K释放的影响两者无显著差异.NH~+_4则显著抑制了各种矿物中K的释放,对黑云母和蛭石的抑制作用更强于对金云母和白云母的作用.     

四苯硼钠溶液中含钾矿物非交换态钾的释放特性研究

含钾矿物的全钾含量、非交换态钾总量以及非交换态钾的释放速率因矿物种类而异,且3种参数之间没有必然的相关性。供试5种含钾矿物非交换态钾总量由高到低的顺序是:金云母 5.19% 黑云母3.08% 蛭石2.01% 白云母1.18% 钾长石0.24%,占各矿物全钾的比例分别为:58.4% 、99.7% 、62.5% 、14.2% 和4.98% ,平均达48%。选择较弱提取力的四苯硼钠溶液进行非交换态钾的释放特性研究,5种矿物非交换态钾3d释放累积量顺序为:黑云母 蛭石 金云母 白云母 钾长石;非交换态钾平均释放速率也表现为同样的顺序。上述5种矿物在弱提取力的四苯硼钠溶液中释放3 d,非交换态钾的平均释放速率分别为5.99、2.34、0.52、0.22和0.17 mg/(kgmin),差异明显。如何根据非交换态钾的释放量和释放速率来综合评价矿物钾的生物有效性是未来研究中需要明确的问题。     

The weathering of biotite in a profile on gneiss in Malaysia

Biotite and its pseudomorphs were studied in a deep profile on gneiss from Malaysia. Alteration of biotite to halloysite takes place within a few centimeters of the fresh rock (at 18.5 m depth) in this humid tropical environment. The halloysite crystals are arranged parallel to the planar surface of the biotite (SEM studies) in the interlamellar spaces. There are zones in the profile where iron has accumulated and some of the iron crystallises as goethite on the edges and surfaces of the flakes. Once this coating has formed, further alteration is retarded as is shown by the fact that pseudomorphs with the coating contain both halloysite and vermiculite though the environment where they are present (position in the profile) is acidic and leaching.     

富钾植物籽粒苋(Amaranthus spp.)对土壤矿物钾的吸收利用研究

运用土培、石英砂培、有机酸释钾实验及矿物X衍射分析研究了不同基因型籽粒苋(Amaranthusspp.)对土壤矿物钾的吸收利用及其机制。结果表明,籽粒苋能有效地利用土壤和云母(黑云母和金云母)中的钾;籽粒苋品种R104、CX4对钾的吸收量高于一般型品种(CX77);籽粒苋根系能引起云母矿物向蛭石转化;籽粒苋根系分泌物中的草酸比一般有机酸具有更高的释放矿物中钾素的能力。     

Rapid effects of plant species diversity and identity on soil microbial communities in experimental grassland ecosystems

Changes in plant community structure, including the loss of plant diversity may affect soil microbial communities. To test this hypothesis, plant diversity and composition were experimentally varied in grassland plots cultivated with monocultures or mixtures of 2, 3 or 4 species. We tested the effects of monocultures versus mixtures and of plant species composition on culturable soil bacterial activity, number of substrates used and catabolic diversity, microbial biomass N, microbial respiration, and root biomass. These properties were all measured 10 months after seeding the experiment. Soil bacterial activity, number of substrates used and catabolic diversity were measured in the different plant communities using BIOLOG GN and GP microplates, which are redox-based tests measuring capacity of soil culturable bacteria to use a variety of organic substrates. Microbial biomass N, microbial respiration, and root biomass were insensitive to plant diversity. Culturable soil microbial activity, substrates used and diversity declined with declining plant diversity. Their activity, number of substrates used and diversity were significantly higher in plots with 3 and 4 plant species than in monocultures and in plots with 2 species. There was also an effect of plant species composition. Culturable soil microbial activity and diversity was higher in the four-species plant community than in any of the plant monocultures suggesting that the effect of plant diversity could not be explained by the presence of a particular plant species. Our results showed that changes in plant diversity and composition in grassland ecosystems lead to a rapid response of bacterial activity and diversity.     

Transformations of layered silicates in soils of the boreal and subboreal zones: Literature review

The transformation mechanisms of layered silicates during the formation of vermiculite (vermiculitization), smectite (smectization), illite-like minerals (illitization), and soil chlorites (chloritization) have been considered. The mechanism of olivization has also been discussed. The manifestation features of these processes in different soils and horizons have been analyzed. It has been shown that the rate, direction, and depth of the transformations depend on the climatic conditions; the mineral composition; the acid-base, redox, and hydrological conditions; and the soil solution’s composition. The amount of the accumulated solid-phase products of the transformations depends on the rate of the given transformation stage and (or) the rate ratio between the given and the next transformation stages.     

Smectite formation produced by weathering in a coarse granite saprolite in Galicia (NW Spain)

Weathering of a calcalkaline granite was studied in the south of Galicia (NW Spain) where the average annual precipitation is 1400 mm and the average annual temperature is 12°C. The original rock contains perthitic K-feldspars, plagioclases with inclusions of muscovite and opaque minerals, quartz and chloritized biotite, with apatite, zircon, sphene and opaques as accessories. In the saprolite the structure of the rock is preserved, the plagioclases show up to grade 4 weathering and the biotites, between 2 and 3. Weathering in quartz and potassium feldspar crystals is manifested only by fracturing. Biotite changes following the parallel linear model and its weathering products are interstratified biotite–vermiculite and iron oxyhydroxides. The plagioclases change to a microgranular material by pseudomorphic transformation. This material, which substitutes the plagioclase, includes small clearly delimited units which retain zones with the optic characteristics of muscovite. X-ray diffraction analyses of microsamples show that they are formed by 1:1 diocthaedral phyllosilicate, smectite and a small quantity of mica. From these facts we concluded that smectite is formed inside the plagioclase crystals, and probably originates from the inclusions of muscovite contained in these crystals, as it is suggested by the microscopic study which shows the increase in volume which occurs when the crystals of muscovite are transformed.     

Influence of pH on the formation of the hydroxy Al-montmorillonite complex

The presence of so-valled chlorite-like minerals has been reported in many soils of not only acid but also of alkaline reaction (1). The minerals have been designated by, many terms, for example, dioctahedral vermiculite (2), dioctahedral analogue of vermiculite (3), 14A mineral (4), chlorite-like mineral (5), interstratified chlorite-vermiculite (6), intergradient chlorite-expansible 2:1 layer silicate, intergradient chlorite-vermiculite, intergradient chlorite-vermiculite-montmorillonite, intergrade, or interlayered vermiculite (7), and 2: 1-2: 2 intergrade (1). The minerals designated by these terms are evidently of the same category, and some of them are synonymous. Although they are of intermediate properties, between true chlorite and true vermiculite or montomorillonite, they could be regarded as an independent group of minerals in the course of pedochemical weathering. Jackson (1), for instance, has given the minerals the position of “weathering index 9”, placing them between vermiculite and kaolin as equivalent to montmorillonite, or secondary chlorite and kaolin in his weathering sequence. An explanation of the diagenesis of the minerals has been recently attempted by synthesis of the chlorite-like structures from montmorillonite (8), (9) and vermiculite (10) and mineralogical analyses of soil clay fractions (7).     

Composition and transformation of 1.4 nm minerals in cutan and matrix of alfisols in central China

Background, Aims, and Scope  Hydroxy interlayered vermiculite (HIV) and vermiculite are commonly referred to as 1.4 nm minerals. In the subtropical soils of central China, the concentration of vermiculites decreased while that of HIVs increased gradually from north to south as the intensity of soil formation or eluviation increases in the same direction. The cutans in these soils closely interact with air, roots, microbes, water and dissolved ions in soils. Cutans may therefore be expected to exert an important influence on the formation of 1.4 nm minerals relative to the matrix soils. However, little is known about the transformation of 1.4 nm minerals in Alfisols in central China. Here, we investigate the compositional differences of 1.4 nm minerals in cutans and matrix soils, and the probable transformation of vermiculite to HIV or vice versa when sodium citrate and sodium acetate are added to matrix Alfisols. Methods  Cutans and matrix soils were separated from three soils in the northern subtropical zone in China. The samples were analyzed for Fe, Mn, exchangeable cations, organic matter(O.M.), pH, and clay minerals. To 10 mL of matrix soil, suspensions containing about 250 mg (oven-dry weight) of clay was added with 5 mL of 0.4 mol/dm³ or 2 mol/dm³ of sodium citrate or sodium acetate solution and 5 mL of 0.2 mol/dm³ mixed solutions of CaCl₂, Mg(NO₃)₂ and KCl. After its pH was adjusted to 6.0, the mixture was ‘incubated’ for 120 or 210 days (more than one season or half a year) during which period it was shaken for 1 hour every day. The clay mineral composition of the samples was determined after incubation. Results  Both vermiculites and HIVs were present in matrix soils, but only vermiculties were detected in cutans. The addition of organic ligands (citrate and acetate) promoted the transformation of HIV to vermiculite. This transformation was obvious for the matrix soils that had been incubated with 0.5 mol/dm³ sodium citrate for 210 days while sodium acetate was less effective in this regard. The promoting effect of organic ligands is dependent on type and concentration as well as incubation time. This would suggest the reverse transformation occurred in the formation of cutans compared with a vermiculite-to-HIV transformation in the subtropical soils of central China from north to south. Discussion  The position and environment of cutans in the B horizon together with the pH, organic matter and exchangeable base status in cutans seem conducive to the co-existence of vermiculite and HIV in the soils, but only vermiculite is found in cutans. The transformation of HIV to vermiculite in incubation experiments could be divided into two steps: 1) Cheluviation of organic matter to the interlayer hydroxy-aluminums from HIVs. 2) Rebasification of hydrated cations into the interlayers of vermiculites. Conclusions  The clay minerals in cutans can interact with organic ligands and nutrient elements excreted by roots. Under conditions of frequent wetting and drying and high pH, and when the concentrations of exchangeable bases, iron-manganese oxides, clays, and organic matter are high, the exchangeable cations can be incorporated into the interlayers of HIV, thereby promoting the partial transformation of HIV to vermiculite in rhizosphere soils. Recommendations and Perspectives  Cutan is at the interface of material and energy exchange involved in physical, chemical and biochemical reactions in the rhizosphere. These factors strongly affect the compositions of cutans. HIVs in (upper or adjacent) matrix soils may transform to vermiculites during cutan formation in these special soil environments. ESS-Submission Editor: Jizheng (Jim) He (jzhe@rcees.ac.cn)     

Comparison of silicate minerals as sources of potassium for plant nutrition in sandy soil

Given the cost of conventional fertilizers and increasing demand as a result of increasing population growth, new sources of potassium (K) for plant nutrition need to be considered. Readily soluble nutrients are rapidly lost from well‐drained soils, and so it is appropriate to consider silicate minerals that release K slowly during weathering. In this paper, we compare the availability to plants grown in sandy soils of K from microcline (feldspar), biotite (mica) and nepheline syenite (nepheline + microcline) using leek (Allium ampeloprasum var. porrum L.) as a model plant. Pot experiments were carried out under controlled environmental conditions using natural and artificial soil. The performance of the minerals was compared with treatment with KCl and a negative control (no K added). Plant shoot diameter was measured weekly to assess growth rates. After 10 weeks, plant dry mass and soil and plant contents of soluble K were measured to determine offtake; mineralogical changes in biotite‐treated soils were assessed. Results for artificial and natural soil differed, reflecting differences in their mineralogy. With no added K, plant growth ceased after 2 weeks. Growth rates were greatest for KCl, followed by biotite; linear growth continued for 5 weeks in the natural soil and for the entire 10 weeks in the artificial soil. Growth rates with nepheline syenite (natural soil) and microcline (both soils) did not differ significantly from the negative control, but for nepheline syenite, leek shoot K content was significantly greater, demonstrating availability of K from this source. X‐ray diffraction analysis showed that biotite reacted to form vermiculite.     

A stepwise change of frayed edge site content in biotite in response to the gradual release of potassium from the interlayers

ABSTRACT

Radiocesium (RCs) is selectively adsorbed on weathered micaceous minerals (mica) in soils. Although it is clear that weathered mica has selective adsorption sites for RCs, which have been called ‘frayed edge sites (FES),’ the relationship between the degree of mica weathering and the FES content has not been fully investigated. To evaluate the effect of mica weathering on its FES content, we investigated the changes in the FES content with the release of K⁺ from biotite samples by using sodium tetraphenylborate solution. The FES content was estimated from radiocesium interception potential. The vermiculitic layer charge (Vt charge) was also determined as an indicator of the degree of mica weathering. The amount of K extracted from biotite increased from 154 to 803 mmol kg^?1 as the condition of the K extraction was more intensive (i.e., longer time, lower solid/liquid ratio, and higher temperature). As K⁺ was removed to a greater extent, the FES content increased from 3.96 to 11.5 mmol kg^?1, whereas the Vt charge value increased from 17.1 to 329 mmol kg^?1. At the earlier stage of mica weathering, the formation of FES was proportional to the increasing amount of K⁺ released and to the Vt charges. However, at the later stage of mica weathering, when vermiculite was detected by an X-ray diffraction analysis, FES was not necessarily increased in proportion to the increase in K⁺ released and the amount of Vt charge. These findings indicated that although mica weathering largely increased the FES, the increase was not continuous throughout the weathering stage but evident at the earlier stage of weathering.     

Bilanzierung der Tonbildung und -verlagerung sowie der Tonmineralumwandlung in Löß-Parabraunerden

Balances of alteration and migration of clay fractions and clay minerals in Gray Brown Podzolic Soils from Loess Balances of alteration and migration of clay fractions, clay minerals, K, Mg and Fe bound in clay silicates were calculated for Gray Brown Podzolic Soils (Parabraunerden) derived from Young Pleistocene Loess below arable and forest land in the district south of Würzburg. The extent of clay formation lies between 63 and 98 kg/m², of which 60–80 % belong to the fraction <0.1 μm. The clay migration varies between 35 and 51 kg/m², the fractions < 0.2 μm (especially the fraction <0.1 μm) predominating, the coarse clay being involved only to a smaller extent. During Holocene soil formation 121 kg illite, 16 kg vermiculite and 11 kg kaolinite per m² are formed in the clay fraction (< 2 pm). The loss of smectite amounts to 68 kg/m². The biggest alterations of the clay mineral quantities occur in the fraction <0.1 pm; they indicate a smectite-illite transformation. Illite, at 23 kg/m², accounts for half of the clay migration, followed by smectite and vermiculite each at 9 kg/m² and kaolinite at 5 kg/m². When comparing the migrated with the present amounts no preference of certain clay minerals during clay migration can be determined. In the clay fractions the gained Fe (3.07?4.32 kg/m²) and K (2.75?3.84 kg/m²) predominate over Mg (0.57?1.15 kg/m²). The three elements accumulate to the greatest extent in the fine clay fraction. The element migration parallels the gain. The balances of the elements are discussed in connection with pedogenic illite formation as well as biotite and vermiculite disintegration.