Monosilicic Acid Research Articles

In situ observations of silica nanoparticle growth in geothermal brine at the Sumikawa geothermal station, Japan, by dynamic light scattering

Silica nanoparticle growth in geothermal brine was examined during the polymerization of silicic acid by observation with dynamic light scattering (DLS) at the Sumikawa geothermal station, examining raw (pH 6.6), pH adjusted (pH 8), and diluted brines (100 to 60%). The monosilicic acid concentration rapidly decreased over time in the raw brine but was almost constant in the samples with lower silicic acid concentrations. The average polysilicic acid particle diameter in the raw brine rapidly increased, from 1 to 6 nm, within 5 min (stage I) and then was almost constant at 7 nm for the subsequent 30 min (stage II).

What effect does liming have on silicon availability in agricultural soils?

Controversy surrounds the effects of pH on Si availability in agricultural soils with some workers reporting a negative and others a positive relationship. The factors contributing to this contradiction are examined and discussed. Because soil development typically involves both desilication and decreasing pH, when a group of soils from a region with different ages and weathering rates are compared, there is typically a positive relationship between pH and Si extractability. Raising pH by liming can effect Si availability through a number of mechanisms including weathering. Over the normal range of liming (i.e. pH 4.5 to 6.5) increased pH decreases the solubility of crystalline and amorphous aluminosilicates but above about pH 7 their solubility increases. Specific adsorption of monomeric monosilicic acid (the major form found in soil solution) is at a maximum between pH 9 and 10 (pK1 for silicic acid is 9.8). Thus, increasing pH increases the proportion of Si adsorbed and decreases that present in soil solution leading to a negative relationship between pH and soil solution Si. With time, polymerization of monomeric Si can occur at the surface of metal oxide surfaces and this may hinder desorption reactions. Nonetheless, Si is generally highly mobile in soils and easily leached so that in the longer term, it is conceivable that increased adsorption may be a retention mechanism which effectively increases Si availability. Soils contain a biogenic pool of amorphous silica (mainly of plant phytolith origin) and its solubility has been shown to increase greatly with increasing pH from 2 up to pH 12. Thus, liming would increase Si availability in the short-term by increasing dissolution of biogenic Si but in the longer term it would tend to decrease Si availability through diminution of the biogenic pool of Si. The most common Si fertilizers are slag materials which are both sources of Si and liming materials. Thus when soils with different histories of slag application are compared, there is often a positive relationship between pH and Si extractability. The relationship between pH and Si solubility/availability can therefore be positive or negative depending on the situation and which pool(s) of potentially available Si (lithogenic/pedogenic, biogenic, adsorbed or residual fertilizer Si) is the most important source of soluble and available Si.

Soluble silicon in differently textured mollisols of Argentina

Soluble compounds of silicon (Si), such as monosilicic acid and polysilicic acid, affect many of the soil chemical and physicochemical properties of the soil. In Argentina the Chaco Pampean Plain is hugely important as it is one of the main areas of global agricultural production. The main objectives of this study were to examine the distribution of the concentration of soluble Si in soils of different genesis of the Chaco Pampean Plain and to evaluate the relationship between the physical and chemical properties of soils and the Si solubility. A soil sampling in the Pampa region was performed; where 12 soil profiles samples were taken at 1.5 m depth. The Si soil levels were separated into two groups. Group A (fine texture) had a high Si content while Group B (coarse texture) was lower. All soils show poorly provided of soluble Si in the surface horizon, but differences were observed in the subsurface. A finer soil with >100 years of an agricultural system had 30/40% less of Si soluble.Si correlates positively with pH and with clay content. These clays and the phytoliths can be a source or adsorb silicic acid. There is a negative correlation between Si and sand content, so the sandy loam to sandy soils are to suffer the greatest impact of agriculturalization. There is a significant and negative relationship between Si and phosphorus suggesting a competition might exist between these two elements.Evaluation of Si in these soils is very important due to its relevance in agricultural production worldwide. Si values may directly affect the production since its deficiency may cause crops disease.

Effect of bio-silica on drought tolerance in plants

Drought is considered the single most devastating environmental stress, which decreases crop productivity more than any other environmental stresses. The main consequences of drought in crops are reduced rate of cell division, leaf size, stem elongation, root proliferation, disturbed stomatal oscillations, plant water and nutrient relations with diminished crop productivity. Many studies demonstrated that the deposition of silica in plant tissues can reduce drought stress. Silicon (Si) has beneficial effects on many crops, mainly under biotic and abiotic stress. Despite its abundance, silicon is never found in plants in an available form and is always combined with other elements, usually forming oxides or silicates. Monosilicic acid (H4SiO4) is the form of silicon used by plants, which is found both in liquid and adsorbed phases of silicon in soils. The concentration of the H4SiO4 in soil solution is influenced by the soil pH, clay, minerals, organic matter and Fe/Al oxides/hydroxides, which are collectively related to the geological age of the soil. Furthermore, to improve plant-available Si in the soil, silicate solubilizing microorganisms (SSM) are potentially useful in solubilizing insoluble forms of silicate. This paper aimed to review an important issue of bio-silica effects on plants under drought stress and water deficiency.

Silicon foliar application on nutrition and growth of Phalaenopsis and Dendrobium orchids

Abstract Foliar application of silicon can be beneficial to orchid growth, but it may also impair growth depending on the source and solution concentration. Due to the lack of information on silicon toxicity in long-term orchid nutrition, experiment with two different orchid species, Phalaenopsis Golden Peoker and Dendrobium Valentine, were performed. The plants were grown in plastic trays with dry Sphagnum in a greenhouse, being fed the nutrient solution without silicon in the first six months. After that, the plants were transplanted to individual plastic vessels (0.9 L). The treatments followed a completely randomized design with a 5 × 3 factorial consisting of five Si concentrations (control, 14.3, 28.6, 42.9 and 57.2 mmol L−1) and three sources (monosilicic acid, potassium silicate, and potassium silicate and sodium silicate mixture), with five replicates. After 18 months of Si foliar application, the Si, C, N, P, K, Ca, Mg and S levels, lignin content and biometric variables were determined for both species. The application of 27 and 16 mmol L−1 Si (potassium silicate and monosilicic acid) resulted in the highest values for the evaluated biometric parameters for Phalaenopsis and Dendrobium, respectively. The results suggest that silicon foliar application affected nutrient absorption and green color index of Phalaenopsis and Dendrobium, and the lignin content of Phalaenopsis. Application of concentrations greater than 39 and 18 mmol L−1 Si over 18 months was toxic to Phalaenopsis and Dendrobium, respectively, since the orchid dry matter decreased by 10% (critical level due to toxicity). Applying increasing concentrations of Si sources decreased the C:N:P stoichiometric ratio of orchids.

Effect of Moisture Deficiency and Increased Salt Content on Silicon State of Some Soils of European Part of Russia and Central China

Soluble forms of silicon affect a number of physical, chemical, and biological soil properties. Optimization of silicon nutrition enhances plant tolerance to biotic and abiotic stresses. Current climate change and anthropogenic impacts can alter the soil silicon state. Model laboratory experiments conducted with upper horizons of sod-podzolic soil, gray forest soil under different plant associations, chernozem, paddy soil, and red subtropical soil showed that insufficient soil moistening led to a reduction in soil monosilicic acid by 15 to 36% and simultaneous increases in polysilicic acid by 9 to 45%. Soil cultivation resulted in a decrease in plant-available soil silicon. An increase in NaCl concentration in the soil caused an increase in both monomers and polymers of silicic acid by 6 to 79%. The mobile equilibrium and lability of the numerical values of the parameters of the silicon state of the soil–plant system are revealed. These factors should be taken into account when implementing the 4R-STRATEGY for optimizing mineral nutrition in agricultural crops.

RELEASE OF SILICON FROM SILICATE MATERIALS AND ITS UPTAKE BY RICE PLANT

<p class="abstrakinggris">Plants absorb silicon (Si) from soil solution in the form of monosilicic acid, also called orthosilicic acid (H<sub>4</sub>SiO<sub>4</sub>). Application of organic and inorganic materials containing readily soluble Si can increase Si supply in the soil and its uptake by plant. The study aimed to evaluate the release of Si from organic and inorganic material sources and its uptake by rice plant. The released phosphorus (P) from those materials was also evaluated. The inorganic materials evaluated included fly ash, steel slag, silica gel and Japanese silica gel (JSG), while the organic materials consisted of rice husk ash (RHA), rice husk burnt (RHB), media of mushroom (MM), cacao shell biochar (cacao SB) and rice straw compost (RSC). The dynamics of Si and P were observed by periodical samplings at 7, 17, 24 and 34 days after transplanting (DAT). Tiller number and plant height were measured at 16, 21 and 36 DAT. The results showed that Si concentration in solution derived from inorganic material was highest for JSG followed by silica gel (1.107 and 0.806 mmol L<sup>-1</sup>, respectively). The release of Si from organic material was higher for RHB and RHA (0.618 and 0.539 mmol L<sup>-1</sup>, respectively). Cacao SB, silica gel, JSG and RHB significantly increased plant height at 36 DAT. Meanwhile, Si materials did not significantly affect the tiller number. Of the materials used, steel slag and JSG significantly affected Si uptake by rice plant.</p>

Effect of Amorphous Silicon Dioxide on Cadmium Behavior in the Soil–Rice Plant System

The effect of amorphous silicon dioxide (SiO2) on cadmium behavior in the soil–plant system was studied in a field experiment on a flooded paddy soil slightly contaminated by cadmium. The application of amorphous SiO2 results in a 1.3- to 1.8-fold smaller cadmium accumulation in the aboveground organs of rice and a 1.8- to 2.6-fold decrease in the content of its available compounds, which can be explained by metal sorption on the surface of applied silicon dioxide and by the reaction of monosilicic acid, which forms in the SiO2 solution, with cadmium. The decrease in cadmium availability is most intensive in the first 2 weeks after SiO2 application. Amorphous silicon causes a 26.6% increase in rice productivity in the first season and 72.9% in the second. The data obtained testify to the fact that the application rates of traditional mineral fertilizers can be decreased without risk to rice productivity if silicon compounds are used. They should become an integral and important part of implementing the 4R-STRATEGY for fertilizer application and plant nutrition optimization.

Effect of Si soil amendments on As, Cd, and Pb bioavailability in contaminated paddy soils

Numerous greenhouse and laboratory experiments have shown that the application of Si-rich materials may affect the mobility and transport of hazardous elements in the soil–plant system. The effects of three types of Si-based soil amendments on As, Cd, and Pb in paddy soil and their translocation into the rice roots, leaves, and grain were evaluated in four field tests. The Si-based soil amendments had positive influence on the rice productivity and crop quality: increased yield and reduced the total content of pollutants in leaves and grain by 2.2–54.0% for As, 11.4–51.9% for Cd, and 3.2–51.4% for Pb. The rice yield was mostly related to the water-extractable monosilicic acid from fresh soil sample (r = 0.60–0.96) as compared with the 0.1 M HCl-, 0.01 M CaCl2- or 0.5 M acetic acid-extractable Si from dry soil sample. Several mechanisms were proposed to be responsible for the Si-material-assisted reduction in the soil contaminant mobility: (a) pollutant sorption by the Si material applied; (b) reaction of the newly formed monosilicic acid with pollutants followed the sorption or precipitation of the silicates on soil particles; (c) primary sorption of newly formed monosilicic acid by soil solid components and then interaction between the sorbed monosilicic acid and pollutants. Additional plant Si nutrition activated physiological mechanism of reduction in the root-to-grain transport of the hazardous elements. Physiological mechanisms were more significant than soil mechanisms in decreasing grain accumulation of the tested hazardous elements under application of the Si-rich soil amendments.

Cadmium and arsenic adsorption in aqueous systems in the presence of monosilicic acid

The effect of different concentrations of monosilicic acid on the sorption capacity of quartz sand, diatomite, zeolite, and brown coal with respect to cadmium and arsenic has been studied in laboratory conditions. The applicability of different adsorption models, including exponential, semilogarithmic, and linear dependences, as well as the Langmuir and Freundlich equations, has been compared. An increase in monosilicic acid concentration from 0 to 2 mM increased the sorption capacity of all materials. It has been suggested that either the interaction of monosilicic acid with a pollutant takes place directly in the solution followed by sorption of the reaction products on the surface or in the pores of the sorbent, or first adsorption of the monosilicic acid by the sorbent occurs followed by interaction of the sorbed silicic acid with cadmium and arsenic; it is also possible that both process proceed in parallel.

As and Cd Sorption on Selected Si-Rich Substances

The processes of pollutant sorption by soil components control their mobility, migration, and transformation in the soil-plant system and depend on numerous properties, among which the elemental composition and surface area are dominant. In a laboratory experiment, the sorption of As and Cd by Si-rich substances differing in surface area, solubility of Si, and mineralogical composition was studied. The adsorption data were fitted to the linear, logarithmic, exponential, Langmuir, and Freundlich equations. Both size of the particles and mineral solubility of Si affected the As and Cd sorption. In the systems with lower initial concentrations of As and Cd, size of the particles had more pronounced effect on the sorption capacity. In the systems with high initial concentrations of As and Cd, the concentration of monosilicic acid was more significant than the surface area.

Evidence for Active Uptake and Deposition of Si-based Defenses in Tall Fescue.

Silicon (Si) is taken up from the soil as monosilicic acid by plant roots, transported to leaves and deposited as phytoliths, amorphous silica (SiO2) bodies, which are a key component of anti-herbivore defense in grasses. Silicon transporters have been identified in many plant species, but the mechanisms underpinning Si transport remain poorly understood. Specifically, the extent to which Si uptake is a passive process, driven primarily by transpiration, or has both passive and active components remains disputed. Increases in foliar Si concentration following herbivory suggest plants may exercise some control over Si uptake and distribution. In order to investigate passive and active controls on Si accumulation, we examined both genetic and environmental influences on Si accumulation in the forage grass Festuca arundinacea. We studied three F. arundinacea varieties that differ in the levels of Si they accumulate. Varieties not only differed in Si concentration, but also in increases in Si accumulation in response to leaf damage. The varietal differences in Si concentration generally reflected differences in stomatal density and stomatal conductance, suggesting passive, transpiration-mediated mechanisms underpin these differences. Bagging plants after damage was employed to minimize differences in stomatal conductance between varieties and in response to damage. This treatment eliminated constitutive differences in leaf Si levels, but did not impair the damage-induced increases in Si uptake: damaged, bagged plants still had more leaf Si than undamaged, bagged plants in all three varieties. Preliminary differential gene expression analysis revealed that the active Si transporter Lsi2 was highly expressed in damaged unbagged plants compared with undamaged unbagged plants, suggesting damage-induced Si defenses are regulated at gene level. Our findings suggest that although differences in transpiration may be partially responsible for varietal differences in Si uptake, they cannot explain damage-induced increases in Si uptake and deposition, suggesting that wounding causes changes in Si uptake, distribution and deposition that likely involve active processes and changes in gene expression.

Si-based technologies for reduction of the pollutant leaching from landfills and mine tails

ABSTRACTMonosilicic and polysilicic acids were shown to react with different types of the pollutants. The direction of these reactions can be managed by changing the monosilicic and polysilicic acid concentration in soil or water media. The objective of this study was to determine the effect of Si-treated calcium metallurgical slag and battery slag on the As, Se, Cd, Pb, Ni, Cr, and Hg mobility and bioavailability in mine tailings (Xikuangshan mine, Hunan, China). The results of column experiment showed that the Si-activated slags reduced leaching of As, Se, Cd, Pb, Ni, Cr, and Hg by 13–89% and transformed them into plant-unavailable forms. The greenhouse test has demonstrated that the Si-treated slags provided reinforced plant resistance to heavy metal toxicity and reduced pollutants in barley and pea leaves. Si-treated local solid slags could be used for creating the biogeochemical barriers on the pollutant streams from landfills or mine tailings sites.

Silicification in Grasses: Variation between Different Cell Types.

Plants take up silicon as mono-silicic acid, which is released to soil by the weathering of silicate minerals. Silicic acid can be taken up by plant roots passively or actively, and later it is deposited in its polymerized form as amorphous hydrated silica. Major silica depositions in grasses occur in root endodermis, leaf epidermal cells, and outer epidermal cells of inflorescence bracts. Debates are rife about the mechanism of silica deposition, and two contrasting scenarios are often proposed to explain it. According to the passive mode of silicification, silica deposition is a result of silicic acid condensation due to dehydration, such as during transpirational loss of water from the aboveground organs. In general, silicification and transpiration are positively correlated, and continued silicification is sometimes observed after cell and tissue maturity. The other mode of silicification proposes the involvement of some biological factors, and is based on observations that silicification is not necessarily coupled with transpiration. Here, we review evidence for both mechanisms of silicification, and propose that the deposition mechanism is specific to the cell type. Considering all the cell types together, our conclusion is that grass silica deposition can be divided into three modes: spontaneous cell wall silicification, directed cell wall silicification, and directed paramural silicification in silica cells.

Effect of silicon fertilizers on cadmium in rice (Oryza sativa) tissue at tillering stage.

Silicon has been found to enhance the plants' tolerance to heavy metal stress. In a field study, the effect of different types of Si-rich soil amendments (slag, ground slag, and diatomaceous earth) and fertilizers (activated slag, ground activated slag, and commercial Si fertilizer) on the distribution of soluble and insoluble forms of Cd in the rice plant organs grown on long-term cultivated paddy soil contaminated with Cd (central part of Hunan Province, China) was investigated. The soluble Si and Cd were tested in the apoplast and symplast of the roots, stems, and leaves of rice at a tillering stage. The Si-rich materials increased rice biomass by up to 15.5% and reduced the total leaf Cd by 8.5 to 21.9%. Commercial Si fertilizer was the most effective. Three main locations of the most active Si-Cd interactions were distinguished in the soil-plant system: soil, where monosilicic acid affords adsorption and fixation of the bioavailable Cd and root apoplast and apoplast above roots, where monosilicic acid can precipitate Cd. The transport of Cd to stems and leaves and the mobility of Cd in the soil depend on the content of monosilicic acid in the system.

The role of Fe on the formation and diagenesis of interstratified glauconite-smectite and illite-smectite: A case study of Upper Cretaceous shallow-water carbonates

The widespread formation of interstratified glauconite-smectite (Gl-S) and illite-smectite (I-S) in modern and ancient diagenetic settings records the physicochemical conditions prevailing during clay mineral authigenesis. To date, however, significant gaps in our knowledge persist in respect to the influence of interstitial solution chemistry, temperature and reaction kinetics on the evolution of composition, mineralogy and microstructure of Gl-S and I-S. Herein, we present a study on the reaction mechanisms and the physicochemical conditions that led to the precipitation of early diagenetic Gl-S and late diagenetic I-S on a stable carbonate platform during the Cenomanian at Langenstein in the Northern German Basin.The texture and the K-Ar age (95.0±1.8Ma) of the green glauconitized grains revealed that green-clay authigenesis progressed in initially organic-rich, semi-confined micromilieus, i.e., in fecal pellets and in foraminifera, close to the sediment-seawater interface. The composition of Gl-S varied in the range (K+0.20–0.74Na+0–0.10Ca2+0–0.05)0.28–0.75 (Fe3+0.63–1.20Fe2+0.08–0.24Al3+0.19–0.97Mg2+0.29–0.52)2.01–2.12 [Al3+0.09–0.35Si4+3.65–3.91O10](OH2), and depended on the rate of aqueous Fe2+ and K+ ion diffusion, the micromilieu of glauconitization and on the bulk sedimentation rate. The mineralogical, microstructural and chemical changes of the ongoing Gl-S products revealed the following reaction for green-clay authigenesis at Langenstein: Fe(III)-smectite reacted with monosilicic acid, goethite and aqueous K+, Mg2+ and Fe2+ to form glauconite and aqueous Na+, Ca2+ and H+ ions. This process considers complex mineral transformations commonly associated with glauconitization, such as early diagenetic oxidation of organic matter and microbial-catalyzed dissolution of Fe-(oxy)hydroxides, carbonates and detrital silicates. In contrast, the K-Ar age of I-S (68.0±1.6Ma) and its compositional variability, (K+0.29–0.45Na+0–0.10Ca2+0–0.06)0.30–0.55 (Fe3+0.16–0.29Fe2+0–0.10Al3+1.37–1.68Mg2+0.18–0.43)2.00–2.12 [Al3+0.17–0.39Si4+3.61–3.83O10](OH2), indicate a burial diagenetic origin for this mineral phase, rather than transformation of illitic clays into I-S during weathering under warm and humid climatic conditions. The results from kinetic modelling support a diagenetic origin of I-S (50–60%I layers and 50–40%S layers) and imply its formation by the replacement of pre-existing K-feldspar at high pore-fluid activity K/Na ratios and at low Fe2+ concentrations.We propose that the substitution of Al3+ for Fe3+, Fe2+ and Mg2+ in the octahedral sheet shifts the stability field of the kaolinite–Fe-Al-Mg-smectite–Fe-Al-Mg-illite (or glauconite) triple point to much lower monosilicic acid activities, and stabilizes the I-S (or Gl-S) structure. This reaction supports the idea that the (bio)availability of Fe is the rate-limiting factor for glauconitization, which is not the case for the diagenetic growth of I-S, whereby the pore water Fe2+ concentration may be limited by the competing formation of Fe-(oxy)hydroxides and/or Fe-sulfides.

CONTENT OF SILICON IN FRACTIONS OF PLANT PROTEIN

Silicon is biologically important element that is necessary not only for plant, but for all living organisms. Silicon was discovered in all plant organs, where its much quantity accumulates in plan cell walls of leaf and root, giving them a mechanical durability and resistance against abiotic and biotic stresses. Earlier, it was supposed that the silicon was absorbed by plants in form of monosilicic acid and then being deposited as phytoliths or accumulated in epidermal plant cells. Moreover the silicon is not only a basic structural element, but it controls many biological and chemical processes. Water soluble monosilicic acid enters into reaction with metals, organic compounds, showing properties of weak acid. Gels of silicic acid can be a catalyst and a matrix, on which the inner cellular synthesis of organic compounds occurs. In the present study the method to determinate three forms of silicon in plants, such as free, easily hydrolyzed and tightly combined is given. Thus, the part of silicon, 0.5-0.7% was observed in protein preparation of leaves of amaranth. Protein was divided into two fractions, albumins and globulins by precipitation with ammonium sulfate. After that each protein fraction was divided into two by Sephadex, where one of which come out in inner volume of gel, and second one come out in outer volume of gel (G-75). The gel distribution into fractions was of the same type characteristics. The tightly combined silicon was absent in high molecular fraction of albumins and globulins. Most of the silicon was discovered in high molecular fraction of globulins, where 80% of the element was represented by an easily hydrolyzed form. The silicon combined with proteins apparently is in a form of orthosilicic ester of hydroxy-amino acids; however it cannot be excluded that there is the formation of SiN bonds with free amino groups. Biophile silicon is a part of plant silicon (organogenic), which is basically in the form of orthosilicic esters bonded with proteins, phospholipids and pectins that are the plant components being assimilated primarily by human’s organism. In our opinion, this fraction of silicon as a microelement should be taken into account in evaluation of nutritional, forage and pharmaceutical values of plant raw material.

Silica scaling in forward osmosis: From solution to membrane interface

Membrane silica scaling hinders sustainable water production. Understanding silica scaling mechanisms provides options for better membrane process management. In this study, we elucidated silica scaling mechanisms on an asymmetric cellulose triacetate (CTA) membrane and polyamide thin-film composite (TFC) membrane. Scaling filtration showed that TFC membrane was subjected to more severe water flux decline in comparison with the CTA membrane, together with different scaling layer morphology. To elucidate the silica scaling mechanisms, silica species in the aqueous solution were characterised by mass spectrometry as well as light scattering. Key thermodynamic parameters of silica surface nucleation on the CTA and TFC membranes were estimated to compare the surface nucleation energy barrier. In addition, high resolution X-ray photoelectron spectroscopy resolved the chemical origin of the silica-membrane interaction via identifying the specific silicon bonds. These results strongly support that silica scaling in the CTA membrane was driven by the aggregation of mono-silicic acid into large silica aggregates, followed by the deposition from bulk solution onto the membrane surface; by contrast, silica polymerised on the TFC membrane surface where mono-silicic acid interacted with TFC membrane surface, which was followed by silica surface polymerisation.

Root-applied silicon in the early bud stage increases the rapeseed yield and optimizes the mechanical harvesting characteristics

A liquid silicon fertilizer [Si(OH)4] was root sprayed at various concentrations during the seedling stage (T1) and early bud stage (T2) using the rapeseed varieties (Brassica napus L.) Huayouza 62 and Fengyou 520. The lodging- and yield-related index, silique shatter were evaluated. Our results indicated that the lodging resistance, silique shatter resistance, and yield all increased significantly in the two rapeseed varieties after the application of silicon fertilizer in both stages. The seed number per silique was reduced after silicon application, but the silique number per plant and 1000-grain weight were increased, especially the silique number on the branches, thereby improving the overall yield, where the most obvious effect on the yield increase occurred at the T2 stage with 0.96mM silicon. At the T1 and T2 stages, the higher concentration of silicon fertilizer increased the root diameter, as well as the stem SiO2 content and breaking strength, but reduced the plant height and lodging index. There were also increases in the expression levels of the key genes related to stem lignin biosynthesis (phenylalanine ammonia lyase (PAL) and 4-coumarate: CoA ligases), the lignin content, thereby increasing the resistance to lodging. At stages T1 and T2, the higher concentration of silicon fertilizer increased the expression of the PAL, which induced the accumulation of lignin. There was a significant correlation between the silique dry weight and silique shatter index. The silique SiO2 content and dry weight also increased, thereby improving the shatter resistance. Considering the yield and mechanical harvesting properties, the results of the present study show that the optimum effect of the liquid silicon fertilizer on both rapeseed varieties occurred during the early bud stage (bolting height of 8–12cm) with a monosilicic acid content was 0.96mM.

Binding of transition metals to monosilicic acid in aqueous and xylem (Cucumis sativus L.) solutions: a low-T electron paramagnetic resonance study.

The supplementation of monosilicic acid [Si(OH)4] to the root growing medium is known to protect plants from toxic levels of iron (Fe), copper (Cu) and manganese (Mn), but also to mitigate deficiency of Fe and Mn. However, the physicochemical bases of these alleviating mechanisms are not fully understood. Here we applied low-T electron paramagnetic resonance (EPR) spectroscopy to examine the formation of complexes of Si(OH)4 with Mn(2+), Fe(3+), and Cu(2+) in water and in xylem sap of cucumber (Cucumis sativus L.) grown without or with supply of Si(OH)4. EPR, which is also useful in establishing the redox state of these metals, was combined with measurements of total concentrations of metals in xylem sap by inductive coupled plasma. Our results show that Si(OH)4 forms coordination bonds with all three metals. The strongest interactions of Si(OH)4 appear to be with Cu(2+) (1/1 stoichiometry) which might lead to Cu precipitation. In line with this in vitro findings, Si(OH)4 supply to cucumber resulted in dramatically lower concentration of this metal in the xylem sap. Further, it was demonstrated that Si(OH)4 supplementation causes pro-reductive changes that contribute to the maintenance of Fe and, in particular, Mn in the xylem sap in bioavailable 2+ form. Our results shed more light on the intertwined reactions between Si(OH)4 and transition metals in plant fluids (e.g. xylem sap).