On the components of soil humic acids (part 9)

The carbohydrates in soil organic matter seem to be derived from undecomposed or partially decomposed plant and microbial residues, In soil, these carbohydrates exist chiefly in such from as polysaccharide hemicellulose, and their polyuronide has been the chief object of investigation^1)-3). In various soil, the polyuronide is found in a large quantity in fulvic fraction of soil organic matter and has been considered as important in connection with the physical structure of soil^4),5). According to Lynch ⁵⁾, the carbohydrate content of humic acid is markedly smaller than that of fulvic acid. His work also indicates that a' considerable change is noted in the content and composition of the carbohydrate in humic acid because of the addition of some organic substances to the soils, or of the cultivation of virgin soils. Further, some investigators⁷⁾ believe that uronic acid is introduced into the aromatic structure of the humic acid by changing into pentose and furan. Accordingly, it seems that the role of carbohydrate in the formation of soil humic acid should not be overlooked.     

On the components of soil humic acids (Part iv) on the absorption spectra of the components of B-type humic acid

Introduction

Concerning the A-type humic acid found in different kinds of soil the writers fractionated each of its components and measured its lightabsorbing power and compared the characteristics of those components.     

On the components of soil humic acids VII

The writers already made it clear that by active alumina the humic acids of A- and B-types contained in various soils could be separated into 3 or 4 components (1). And moreover, absorption spectra (2), nitrogen constituents (3) and colloidal nature (4) of them were studied for the purpose of examining their qualities.     

Reduction of Cr(VI) by soil humic acids

The rate of hexavalent chromium reduction by a soil humic acid (SHA) was investigated in aqueous solutions where concentrations of Cr(VI), H⁺, and SHA were independently varied. Rate experiments were done with a large excess of SHA over Cr(VI). Rates of reduction depend strongly on [H⁺], increasing with decreasing pH. Typical Cr(VI)-SHA reactions display a nonlinear reduction of Cr(VI) with time that cannot be modelled with simple first- or second-order rate equations. An empirical rate equation is developed for Cr(VI)-soil humic acid reactions over a range of experimental conditions. The model is in part based on a reactive continuum concept developed for soil fulvic acids. The rate equation describing Cr(VI) reduction by SHA is: R= -(k₀+k[H⁺]^1/2)[HCrO₄^?]^1/2X_e^?1, where k₀ is (8·3 ± 1·2) × 10^?12, s^?1k is (2·04 ± 0·05) × 10^?9 l^1/2 mol^?1/2 s^?1, and X_e is the equivalent fraction of SHA oxidized. The rate equation adequately models Cr(VI) reduction in an experiment with [Cr(VI)]₀ four times greater than the maximum concentration used in its derivation. Cr(VI) reduction at pH 3 by two other SHAs can also be modelled using the rate equation. The difference between the rate coefficients for the humic acid and the fulvic acid from the same soil was greater than the difference in the rate coefficients for humic acids from different soils.     

腐殖酸对钾在褐土中迁移和转化的影响

采用室内土柱实验研究了腐殖酸与钾共施时腐殖酸对钾在褐土施肥点附件微域中迁移和形态转化的影响。研究结果表明,与单施KCl处理相比,共施腐殖酸没有明显改变肥料钾在褐土中的迁移距离,在培养7天时增加了肥际微域中的水溶性钾含量,而在培养28天时则降低了其含量;共施腐殖酸明显增加了交换性钾含量以及在土壤中的迁移量,但减少了非交换性钾的含量和迁移量。说明共施腐殖酸减少了土壤晶格对钾离子的固定,提高了外源钾在褐土中的有效性。     

The carbon distribution among the functional groups of humic acids isolated by sequential alkaline extraction from gray forest soil

Preparations of humic acids (HAs) were isolated from a gray forest soil by sequential alkaline extraction. From a sample of 500 g, HA preparations of 2.24, 0.23, and 0.20 g were obtained from the first, second, and third alkaline extracts, respectively. The structure of the preparations was determined by ¹³C NMR spectroscopy. At each next extraction step, the portion of aliphatic fragments in the HA preparations increased and the content of aromatic structures decreased. The conclusion was drawn that a single extraction is sufficient for obtaining a representative HA sample.     

Analysis of polynuclear aromatic and aliphatic components in soil humic acids using ruthenium tetroxide oxidation

Although condensed aromatic components are considered to be one of the major structural units of soil humic acids (HAs) and to be responsible for the dark colour of HAs, their amount and composition remain largely unknown. In ruthenium tetroxide oxidation (RTO), condensed aromatic components are detectable as their degradation products, mainly benzenepolycarboxylic acids (BPCAs). We applied this technique to soil HAs with various degrees of humification (darkening). The yields of water‐ and dichloromethane‐soluble products from HAs upon RTO after methylation ranged from 210 to 430 mg g⁻¹ and 10–40 mg g⁻¹, respectively. Eight kinds of BPCAs with two to six carboxyl groups, and seven kinds of BPCAs with additional side chains (tentative assignment) were obtained as methylated counterparts. The yield of each BPCA and the sum of the yields of BPCAs (12–85 mg g⁻¹ HAs) increased with increasing degree of humification and aromatic C content. The compositions of BPCAs indicated that the degree of condensation was greater in the HAs with greater degrees of humification. The sum of the yields of aliphatic compounds ranged from 0.1 to 6.5 mg g⁻¹, and decreased with increasing degree of humification. The C₁₂ to C₃₀ monocarboxylic acid methyl esters accounted for > 56% of the aliphatic compounds assigned, which may be present mainly as end alkyl groups in the HA molecules. We also obtained the methylated counterparts of C₁₄ to C₂₄ dicarboxylic acids; these were possibly derived from polymethylene bridges between adjacent aromatic rings.     

Inhibition by soil humic acids of native and acetylated proteolytic enzymes

The activities of acetyltrypsin and acetylcarboxypeptidase were unaffected by neutralized solutions of soil humic acids in concentrations which markedly inhibited the non-acetylated enzymes. Further, acetyltrypsin, unlike trypsin, did not coprecipitate with humic acids. The results support the conclusion that humic acids bind the proteases by a cationexchange mechanism whereby protease amino groups are linked to humic acid carboxyl groups.     

Separation and characterization of the constituents of compost and soil humic acids by two-dimensional electrophoresis

To investigate the chemical heterogeneity of humic acids (HAs), we applied two-dimensional (2-D) electrophoresis to HAs from a compost and two types of soils. In this method, HAs are first separated by isoelectric focusing (IEF) and then separated by polyacrylamide gel electrophoresis (PAGE). IEF and PAGE were carried out in the presence of 7?M urea. Upon 2-D electrophoresis of HAs, dark-colored substances were spread out across the gel mainly in the isoelectric point (pI) range of 3.0–4.5. Green fluorescence was observed in the smaller molecular size region of the gel, especially in the pI range of 3.0–4.5, and the most intense fluorescence was found at the moving front. The gels were divided into 36 sections, and then HA constituents were extracted from the individual sections and recovered by precipitation with acid. The distribution of organic carbon (C) among the gel sections coincided with that of the dark-colored substances on the gel. The total C recoveries were only 43–50%, suggesting that a considerable amount of HA constituents was lost during the extraction from the gels and purification. High-performance size-exclusion chromatography confirmed that the constituents of HAs were separated based on their molecular sizes by PAGE. The measurement of diffuse reflectance infrared Fourier transform (DRIFT) spectra indicated that the chemical properties of the HA constituents differed depending on the position on the gels and were affected by the molecular size rather than the pI. The fractions of the compost HA were characterized by higher proportions of aliphatic, proteinous and polysaccharide moieties and by the presence of lignin-derived structures. For the soil HAs, the fractions were characterized by a high proportion of the carboxyl group and a low proportion of aliphatic moieties. The proportion of proteinous and polysaccharide moieties in the fractions of soil HAs decreased with decreasing molecular size. The chemical properties of the green fluorescent substances remained unclear, since there was not enough of the substances to measure the DRIFT spectra. The present study showed that 2-D electrophoresis in the presence of concentrated urea offers an effective method for fractionating and isolating the constituents of HAs.     

On the fractionation of humic acids by a fractional precipitation technique

When humic acid is investigated from the standpoint of high polymer chemistry, its fractionation is one of the most important and interesting problems. In this paper, some experimental results will be reported on the fractionation of humic acid by the fractional precipitation technique proposed by SCHULZ (I), which had been successfully applied on a soil humic acid by KYUMA (2).     

冷硝酸浸提法对表征富钾石灰性土壤有效钾的适用性研究

通过研究西北黄土区富钾石灰性土壤中钾素形态及各形态之间的关系,为"冷硝酸浸提土壤有效钾法"在富钾石灰性土壤上的适用性提供理论依据。以关中平原麦玉轮作不同秸秆还田模式多年定位试验农田土壤为供试材料,用2 mol·L-1冷硝酸浸提测定土壤有效钾,并以常规方法测得土壤钾素的其他7种组分,通过相关分析、主成分分析和通径分析,揭示上述8种组分间的关系。在麦玉轮作体系不同秸秆还田模式下,耕层土壤中各组分钾素含量均存在较大变异性,变异系数1.9%~33.8%,不同秸秆还田模式下差异不显著;冷硝酸浸提钾的含量分别约为速效钾和缓效钾含量的1.43和0.30倍,且与土壤速效钾存在极显著正相关关系(r=0.82);主成分分析表明,冷硝酸浸提钾与土壤速效钾同在第一主成分中,且均具有较高载荷;通径分析表明,冷硝酸浸提钾主要由土壤非特殊吸附钾、特殊吸附钾以及非交换性钾3种化学形态组成,其含量来自土壤交换性钾的贡献最大,与速效钾类似。冷硝酸浸提法可以作为表征石灰性富钾土壤有效钾水平的可靠方法,土壤交换性钾是土壤有效钾主要供方。     

The chemical nature of components of PG (Green fraction of P type humic acid)

P type humic acids showing characteristic absorption maxima at 615, 575, and 450 nm have been found in various types of soils around the world (3, 5, 7,8). P type humic acid was fractionated into a brown fraction (Pb) and a green fraction (Pg) by column chromatography using cellulose powder (4) or Sephadex gel (3). The Pg fraction which has a strong absorption maxima at 615, 575, and 450 nm causes the characteristic absorption pattern of P type humic acid.     

Characterization of fungal melanins and soil humic acids by chemical analysis and infrared spectroscopy

Summary Humic acids from two Brazilian topsoils under savanna grassland and five soil fungal melanins were characterized by elemental, functional group and infrared analysis. C, N, total acidity, COOH, and phenolic OH contents were within the ranges reported for several other fungal melanins and soil humic acids. Compared with the soil humic acids, the infrared spectra of the fungal melanins showed greater detail, indicative of higher aliphaticity. They were similar to the type III infrared spectra of humic acids, which are characteristically high in proteinaceous material and polysaccharides. The infrared spectra of the humic acids from the two Brazilian soils studied were classified as type I, which includes most soil humic acids. Notwithstanding the greater detail, in some areas the fungal melanin spectra were similar to those reported for other fungal melanins and humic acids of different origins. The probable contribution of the melanic fungi to the formation of soil humic polymers is discussed.     

Effects of in-situ straw decomposition on composition of humus and structure of humic acid at different soil depths

Purpose

Returning straw to soil improved soil carbon sequestration capacity and increase soil organic matter. However, in different soil depth, especially in subsoil, there were few studies on the effects of straw decomposition on soil carbon sequestration and the properties of humic substances. Therefore, an in-situ incubation study, with six different straw rates and three different soil depths, was carried out to explore the effects of straw decomposition on soil organic carbon and humic substance composition at different soil depths.

Materials and methods

The experiment was composed of six straw rates: 0, 0.44, 0.88, 1.32, 2.64, and 5.28% of soil dry mass. The maize straw was proportionately mixed with soil and put into nylon bags. Then, the nylon bags were buried in soil at three depths (15, 30, and 45 cm) and the straw decomposition trial lasted for 17 consecutive months in-situ. Soil samples were collected after completion of the field trial. Humic substances were quantitatively and qualitatively analyzed using the modification method of humus composition and the methods specified by the International Humus Association. Fourier transform infrared spectroscopy and fluorescence spectroscopy were used in this study.

Results and discussion

Results indicated that CO₂ concentration increased with increase in soil depth. Compared with the “zero” straw control, soil organic carbon contents in the treatments amended with 1.32, 2.64, and 5.28% maize straw increased significantly, and most accumulations were at 30–45 cm depths. FTIR and fluorescence emission spectra analyses indicated that the addition of straw enhanced the aliphatic structure and decreased the aromaticity of humic acid (HA), that was to say that HA molecular structure approaches to the development of simplification and younger. The maximum change in HA molecular structure was under the 5.28% treatment in the 30–45 cm depth.

Conclusions

Returning maize straw to the subsoil layers is more conducive to the accumulation of soil organic carbon and improvement of the quality and activity of HA and the organic carbon in the subsoil can be renewed.

     

Selective digestion of the peptide and polysaccharide components of synthetic humic acids by the humivorous larva of Pachnoda ephippiata (Coleoptera: Scarabaeidae)

In order to identify the potential nutrient and energy sources of humivorous beetle larvae, we carried out feeding trials with soil supplemented with specifically ¹⁴C-labeled model humic acids synthesized by peroxidase-initiated radical polymerization, using the cetoniid beetle Pachnoda ephippiata (Coleoptera: Scarabaeidae) as a model organism. Ingestion of soil by the larvae significantly increased the mineralization of humic acids labeled in their peptide (HA-*peptide) or polysaccharide components (HA-*peptidoglycan and HA-*chitin), whereas the mineralization of humic acids labeled in the aromatic components (HA-*catechol) did not increase significantly. Mineralization was accompanied by a reduction of residual radiolabel in the acid-soluble fraction and an increase in the humic acid and humin fractions of the fecal pellets. During the gut passage, the residual label in peptide or polysaccharide components was transformed into acid-soluble products, especially in the alkaline midgut. High-performance gel-permeation chromatography demonstrated that the changes in solubility were accompanied by large changes in the molecular weight of the residual material. The amount of radiolabel derived from the peptide and polysaccharide components recovered from the larval body and hemolymph was significantly higher than that derived from the aromatic component, which supports the hypothesis that humivorous beetle larvae selectively digest the peptide and polysaccharide components of humic substances, whereas the aromatic components of humic substances are not an important source of nutrients and energy. This is also the first experimental evidence that also chitin and peptidoglycan, the major structural polymers in fungal and bacterial biomass, can be protected from microbial degradation in soil by a copolymerization with phenols and might contribute substantially to the refractory nitrogen pool in soil organic matter.     

腐殖酸共聚物改良后土壤中磷肥有效性的研究

本文研究了腐植酸共聚物改良土壤后土壤中磷肥的有效性。改良后的土壤减少对PO43 的固定,土壤中吸附态PO43 和有效态PO43 含量增加,改良后的土壤磷肥的利用率提高。     

Catalytic synthesis of humic acids from phenolic compounds by Mn(IV) oxide (Birnessite)

Abstract

Extract

Humic acids are natural organic polymers and are important constituents of soils (Kononova 1966). Although the mechanisms of the formation of humic acids are very complicated, the oxidative polymerization of polyphenols is considered to be one of the most important mechanisms (Kononova 1966; Stevenson 1982). The oxidative polymerization can be accelerated by enzymes (e.g., Haider et al. 1975; Flaig et al. 1975) as well as by inorganic components (e.g., Kyuma and Kawaguchi 1964; Shindo and Huang 1982; Kumada 1987). Shindo and Huang (1985) and Shindo and Higashi (1986) compared the relative effectiveness of several oxides, primary minerals, and clay minerals in promoting the synthesis of humic polymers from hydroquinone, and found that the promoting effect of Mn(IV) oxide was most striking among the inorganic components studied. The catalytic power of inorganic components in the synthesis of humic polymers from phenolic compounds may be influenced by the chemical structure of the compounds. However, little information is available on this aspect.     

Biotransformation of soil humic acids by blue laccase of Panus tigrinus 8/18: an in vitro study

We describe here the role of the polyphenoloxidases in the oxidation of recalcitrant soil organic compounds and consider what changes occur in their structure during experiments on the biotransformation of soil and peat-derived humic acids (HA). These transformations were carried out by laccase (EC 1.10.3.2.) of the white-rot basidiomycete Panus tigrinus 8/18. It was shown that purified laccase alone is capable both of polymerizing and depolymerizing HA in vitro. The direction of transformations depends on the nature and properties of HA. Those fractions of HA are affected by laccase, which cause the lowest inhibitory effect on the enzyme. Contrary to previous studies depolymerization of HA was not necessarily accompanied by decolorization: chernozem-derived HA showed increase in absorbance of its aqueous solution in the region of 240-500 nm during depolymerization, while peat-derived HA showed decrease in absorbance throughout the entire spectrum during polymerization. All studied HA were competitive inhibitors of laccase towards oxidation of synthetic substrate 2,2′-azino-bis-(3-ethylthiazoline-6-sulfonate) (ABTS). When studying the nature of the inhibitory effect, it was shown that more ‘hydrophobic’ HA as well as more ‘hydrophobic’ HA fragments were stronger inhibitors of blue laccase.     

Effects of liming on organic matter decomposition and phosphorus extractability in an acid humic Ranker soil from northwest Spain

Summary A laboratory incubation experiment was carried out over 17 weeks to determine the effect of liming on soil organic matter. The amount of lime as calcium hydroxide [Ca(OH)₂] required to completely neutralise exchangeable Al was found to be five times the standard lime requirement. This large amount of lime had a limited overall effect on the short-term stability of soil organic matter, causing the release of 1300 g g^-1 of C (1.7% total soil C) above the control during the incubation. Liming may have altered the potential availability of soil organic matter and organic P, as shown by a marked reduction in the extractability of soil organic P with sodium bicarbonate and sodium hydroxide. The latter was unlikely to be due to the formation of calclium-P artefacts, and may be attributed to the combined chemical effects of added calcium hydroxide and precipitation of exchangeable Al on the nature and solubility of soil organic constituents and organomineral complexes. The addition of lime increased the degradation of added oak leaf litter by 50%, from 3.2 to 4.7 mg g^-1, as determined by CO₂ evolution. The enhanced litter degradation indicated increased microbial activity in limed soil, but this improvement had only minor effects on the stability of native organic matter. This study highlights the need for further research into the relationships between the chemical nature of organic P in soil and the physical, chemical, temporal, and agronomic factors that control its turnover and availability.