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1.
The conformational structure of dissolved humic substances is an important property that controls the reactivity of humus in the soil solution. High performance size-exclusion chromatography was used here to study the changes in molecular size of different humic substances brought about by addition of mineral (HCl) and monocarboxylic (formic, acetic, propionic, and butyric) acids. The CPMAS-NMR spectra showed that humic substances had varying chemical composition and that the ratio of hydrophilic to hydrophobic carbon (HI/HB) was greater for a humic acid from soil than for ones from oxidized coal and lignite. All humic substances showed a decrease in UV absorbance of chromatographic peaks when treated with either HCl or monocarboxylic acids. This was due to the hypochromic effect by which the absorptivity of associated molecules is decreased when they are separated. We attributed the molecular separation upon acid treatment to the formation of intermolecular hydrogen bonding that alters the original conformation stabilized mainly by weaker hydrophobic interactions. Addition of organic acids not only further decreased peak absorbances of humic acids but also caused their shift to larger elution volumes, indicating a larger conformational disruption than with HCl. The extent of the molecular size changes showed a relation to the number of carbons of monocarboxylic acids and to the HI/HB ratios of humic materials. The larger the carbon content of organic acids and the smaller the HI/HB ratio of humic materials, the larger was the decrease of the average molecular size of humic acids. These results suggest that dissolved humic substances associate predominantly by hydrophobic forces and that the apolar components of humic substances largely control their aggregation and reactivity in the environment.  相似文献   

2.
Two different humic materials, one from a forest soil and the other from wormcasts, were used to study the influence of mineral and organic acids on the conformational properties of humic substances. The macromolecular changes were followed by low pressure gel permeation chromatography after titrating humic material to low pHs with acids. All organic acids (mono-, di-, tri-carboxylic, and oxy-acids), added to humic solution prior to a gel permeation in an alkaline buffer, were able to shift the totality of absorbance of the humic chromatographic peak from high to low molecular sizes. Mineral acids, phenol, alcohols, dipolar aprotic solvents, could not produce the same shift and gave total absorbance at the column void volume as in the case of humic substances alone. The chromatographic peak shifted back to elution volumes proper of higher size molecules when the humic-organic acid mixture was back-titrated to high pHs before gel permeation. Elution in a much stronger alkaline buffer did not change the overall macromolecular behaviour. These results suggest that humic substances behave as micelles in solution and that hydrophobic bondings play an important role in holding humic molecules together. The organic acids enter the interior of the humic micelle-like aggregates and alter the stereochemical hydrophobic arrangement of the humic material. In alkaline conditions the negative charges developed disrupt the apparent high molecular size configuration and disperse the humic aggregates into small micelles. Such conformational properties of humic substances appear to be a function of pH and of the concentration of organic acid.  相似文献   

3.
The complete polymerization of phenols and proteins (one of the processes involved in the formation of humic substances) was explained. It was shown that fly (Bibio marci) larvae and earthworms (Aporrectodea caliginosa) participate in the complete polymerization of phenols and proteins. In a laboratory experiment, invertebrates participated in the degradation of organic matter and the synthesis of humic substances, which was proved in experiments with 14C-labeled phenols and proteins. The same organic substances (phenols and proteins) without the impact of invertebrates were used as the control substances. The distributions of the 14C isotope in alkaline extracts separated by solubility in acids (humic and fulvic acids) was compared to those of the control substances. The portion of the 14C isotope in the humic acids in the excrements of Bibio marci was higher than that in the control substances. The content of 14C-labeled humic substances in the excrements of the earthworm Aporrectodea caliginosa exceeded the control values only in the experiment with proteins. When clay material was added to the organic substances, the portion of the 14C isotope in the humic acids increased in both experiments with phenols and proteins. When these substrates passed through the digestive tracts of the invertebrates, the polymerization of organic substances and the inclusion of proteins and phenols into humic acids occurred.  相似文献   

4.
Changes in molecular size distributions of four different humic materials were evaluated through high performance size-exclusion chromatography (HPSEC), before and after treating humic solutions with naturally occurring dicarboxylic (oxalic, malonic, succinic and glutaric) acids. Chromatograms of dissolved humic substances showed a decrease in peak absorbance as well as an increase in peak elution volume when the solution pH was lowered from 7 to 3.5 by addition of dicarboxylic acids before HPSEC analysis. The resulting reduction in molecular size is explained by the disruption of unstable humic superstructures into smaller-sized associations stabilized by the formation of strong intra- and inter-molecular hydrogen bonds among humic molecules. The extent of humic size variation was in the order: oxalic相似文献   

5.
Humic substance fractions obtained from a degraded loess soil taken from a long-term lysimeter experiment with the fungicide anilazine were incubated in aerated liquid cultures together with native soil microorganisms. Biomineralization, remobilization of [U-phenyl-(14)C]anilazine, respectively, its metabolites, and changes of the humic matrix were observed under variable nutrient conditions. Stimulated microbial activity favored the degradation of nonextractable (14)C-anilazine residues. However, nitrogen deficiency enhanced structural changes in the humic substances, which seemed to be used then as a nitrogen source. Along with the microbial degradation of the humic substances, parts of the bound anilazine residues became remobilized. Furthermore with the use of AMD-TLC, dihydroxy anilazine was detected within the nonextractable residues. The portion of rather weak bondings between the soil organic acids and the anilazine residues turned out to be considerably lower in the humic acids fractions than in the fulvic acids fraction.  相似文献   

6.
By incorporating molecular weight fractions of humic acids of various origins into selective substrates designed for the enumeration of physiological groups of microorganisms, it was found that the presence of humic acids at concentrations of up to 30mgl?1 normally resulted in increased numbers of soil microbes active within a particular physiological group. Observed increases could be as much as 2000-fold. Microbes in an organic humus-rich soil were more stimulated by humic substances than organisms from a sandy soil.In certain microbes humic substances appeared to induce a change in metabolism, allowing the organisms to proliferate on substrates which previously they could not utilize. Indications were obtained that within the 10–30 mgl?1 concentration range lower molecular weight humic fractions (approx. 5500 dallons) were more effective than higher molecular weight material. At higher concentrations the reverse was sometimes noticed. Similarly, fulvic acids at concentrations of up to approximately 50mgl?1 would appear to have a more pronounced physiological effect than humic acids, whereas the latter might be more effective at higher concentrations.The response of certain physiological groups to humic products of natural origin appeared to be comparable to that of surfactants such as Tween and Brij. This would suggest that the physiological action of humic substances is, at least partly, the result of their surface activity, making the membrane one of the prime targets of the physiological action of humics on living cells.  相似文献   

7.
Chromatographic distinction of humic and non humic substances in chernozem-humus Fulvic acids, brown humic acids and grey humic acids from a chernozem from the Austrian Marchfeld were analyzed chromatographically on controlled pore glass with pore diameters of 177 and 259 Å. Concentration of coloured material and concentration of carbon were recorded in the chromatogramms. Specific extinctions at 400 nm were calculated for unit of C and maximal values were taken as constants specific for “pure” humic substances. These were 445,6 ± 10,5,388,7 ± 19,3 and 128,9 ± 0,8 for “pure” grey humic acids, brown humic acids and fulvic acids, respectively. With the aid of these constants, “pure” humic substances could be distinguished from accompanying non humic substances. “Pure” humic substances amounted to 63%, non humic substances to 37% of extractable organic C. 53%, 22% and 25% of the carbon of “pure” humic substances were from grey humic acids, brown humic acids and fulvic acids, respectively.  相似文献   

8.
Data were analyzed on the elemental composition of humic and fulvic acids isolated from organic and mineral horizons of different-aged podzols developed on sand quarry dumps in Leningrad oblast. It was shown that the humic substances from the young podzols significantly differed from those isolated from the mature soils. The humic acids (HAs) of the young podzols composed a more homogeneous group of natural compounds compared to the fulvic acids (FAs). The HAs isolated from the organic, podzolic, and illuvial horizons of the embryopodzols significantly differed in their structure. The litter HAs were characterized by the minimum aromaticity and the maximum content of aliphatic components. The HAs from the illuvial horizons contained the maximum portion of aromatic components; a significant portion of carboxyls, ethers, polysaccharides, carbohydrates, and amino acids; and the minimum portion of aliphatic components. The HAs from the podzolic horizons occupied an intermediate position between the humic substances of the organic and illuvial horizons. It was shown that Mendeleev’s formula was more suitable than Aliev’s formula for calculating the calorific values of the HAs because of their structural features. Based on the particular features of the humic substances studied, they were classified as prohumic substances.  相似文献   

9.
Sample preparation for the study of humic acids involves a purification treatment to remove both mineral and organic components extracted along with the humic substances. The effects of HCl–HF purification on the chemical composition and structure of humic acids were studied in samples from eight different composts. Only small increases in the concentrations of C, N and H and a decrease in O were found in purified humic acids when compared with the unpurified materials, no more than 10% of average concentration. Total and phenolic acidity increased in the purified materials, whereas carboxylic and carbonyl acidity showed no statistically significant differences as a result of the purification. Gel permeation chromatography showed that only minor changes occurred in molecular size distribution of the humic acids, and the infrared spectra showed no appreciable differences between the purified humic acids and the untreated materials. We conclude that the HCl–HF treatment successfully reduced the ash contents of the humic acids without modifying their chemical composition and structure significantly.  相似文献   

10.
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.  相似文献   

11.
Lead, copper, and zinc interacted with the soil organic matter when applied to an ordinary chernozem in a pot experiment. Two years after the treatment, an appreciable part of the metals applied was found in the organic substances, predominantly in a loosely bound state. These organic substances were supposed to be organomineral complexes, the formation of which resulted in the partial destruction of humic acid molecules. These processes increased the content of aliphatic structures and the share of fulvic acids and decreased the content of humic acids in the organic matter of the chernozem.  相似文献   

12.
The carbon-isotopic composition of fulvic and humic acid from the A horizons of eight soil types, developed under a wide variety of climatological conditions, was measured. The fulvic acid is always enriched in 13C as compared with the humic acid from the same soil by a rather constant factor of 0.9?. The fulvic acids are isotopically closer to the plant source of the organic matter and thus represent an intermediate stage in the formation of humic substances. Depth sections of peat soil showed that carbon isotopes can be used to evaluate the dynamic nature of the fulvic-acid fraction. With depth, a transfer of carbon groups from polysaccharides to fulvic acid is seen. Based on isotopic evidence it is shown that in addition to formation of β-humus, part of the fulvic acid is condensed with depth to a stable humic fraction — humin.  相似文献   

13.
《Soil biology & biochemistry》2001,33(4-5):563-571
We studied the effect of organic acids of plant, microbial, or anthropic origin on the molecular size distribution of dissolved humic acids (HAs). High Performance Size Exclusion Chromatography (HPSEC) was used to evaluate size changes in four different HAs upon addition of hydroxy- (glycolic and malic), keto- (glyoxylic), and sulfonic (benzenesulfonic and methanesulfonic) acids. All humic substances showed a decrease of peaks absorbance when the pH of HAs dissolved in HPSEC mobile phase was lowered from 7 to 3.5 by acid addition before analysis. This effect, combined with an increase of peaks elution volumes in most cases, was interpreted as a disruption of supramolecular humic associations into smaller-size but energy-richer conformations brought about by the formation of mixed intermolecular hydrogen bonding upon acid treatment. The extent of size variation was related to the pKa of acids and also to the chemical and stereochemical affinity of humic components with the chemical structure of the acids. Dicarboxylic malic acid was the most effective in modifying humic conformations in all HAs whereas the aromatic-rich superstructure of HA from an oxidized coal was effectively disrupted by the relatively small methanesulfonic acid and the chemically akin benzenesulfonic acid. These results suggest that the conformational association of humus dissolved in the soil solution may be systematically altered by organic acids present in the rhizosphere and might have effects on plant and microbial activities.  相似文献   

14.
In view of the considerable interest in laboratory-prepared fungal “humic acids” as possible precursors or incorporated structural components of soil humic substances, we degraded four fungal “humic acids” by the relatively mild alkaline cupric oxide oxidation. The oxidation products were extracted into organic solvents, methylated, separated by thin-layer chromatography and identified on a gas chromatographic-mass spectrometric-computer system.Average yields of major degradation products were: (a) aliphatic compounds, 38 per cent; (b) benzene-carboxylic compounds, 25 per cent; and (c) phenolic compounds, 21 per cent. The remaining 16 per cent consisted of a number of dialkyl phthalates. Our data agree with those that we reported earlier when we degraded a number of fungal “humic acids” by the more drastic alkaline permanganate oxidation and show that fungal “humic acids” are enormously complex organic materials containing aliphatic and aromatic structures, (some of which contain N), but only a relatively small proportion of which is phenolic. Most of the aliphatics isolated consisted of alkanes and fatty acids, which are known to persist in soils over long periods of time and are frequently firmly retained by soil humic substances.  相似文献   

15.
Recently suggested structural models of humic acids (Schulten, Schnitzer, etc.) do not agree with the existing notions on the biochemical origin of some fragmentary groups composing a significant part of the molecules of humic acids. It is hypothesized that free-radical reactions of the polycondensation of low-molecular organic compounds derived directly from soil biota, from primary products of its posthumous decomposition, and from fulvic acids represent an obligatory stage of natural humus formation. Calculations demonstrate that different natural sources of free hydroxyl radicals (forming in the troposphere and deposited with atmospheric precipitation, produced by soil prokaryotes, etc.) ensure the possibility of free-radical condensation of organic substances and the formation of humic acids in the pedosphere of the Earth; moreover, the actual supply of free hydroxyl radicals exceeds the necessary amount by several orders of magnitude. The development of this concept allows us to assume the existence of a general evolutionary scheme of transformation of organic residues of biological origin on the Earth with the formation of stable products (humic substances, peat, and coal).  相似文献   

16.
The alteration of organic matter from three sod-podzolic soils in the course of the extraction of water-soluble humic substances was studied by means of size-exclusion chromatography using a combined UV-DOC detector. A comparison of water-soluble humic substances with humic and fulvic acids extracted from the same soils was carried out.  相似文献   

17.
Thirty eight low molecular weight aromatic compounds, two humic acids, and five lignins were tested for their effects on the growth and survival of the earthworm Eisenia foetida with activated sludge as food source. Benzenoid molecules with two methoxyl or methyl groups were generally more toxic than analogous molecules substituted with one or two hydroxyl groups instead. Placing a carboxyl group or groups on a molecule of relatively high toxicity tended to reduce its toxicity or to result in a totally innocuous substance. Tannins and molecules which could be easily polymerized to form tannin-like substances were generally non-inhibitory to growth, as were humic acids and lignins.  相似文献   

18.
Humic substances improve the efficiency of different iron (Fe) sources overcoming Fe deficiency chlorosis of plants. However, applied at high rates, they can promote negative effects on plants. The main objective of this work was to study the potential adverse effect of three humic acids from different origin when they were applied with two effective Fe sources for plants: Fe- ethylenediaminedihydroxyphenylacetic acid (EDDHA) and Vivianite. To this end, an experiment with lupin (Lupinus albus L.) was performed involving two factors: (i) Fe source, and (ii) humic substances from three different origin (composted cork, leonardite, and compost obtained from a mixture of olive husk with cotton gin trash) applied at 0, 0.1, and 0.5 g organic carbon (C) kg?1 of growing media. At the rates used, humic substances promoted adverse effects on plant development, chlorophyll meter readings, and Fe content in lupin grown in calcareous media. Overall, the effect on dry matter and Fe content in plants was more relevant when Fe was supplied with Vivianite, the effect on chlorophyll meter readings being more significant when Fe was applied as Fe-EDDHA. Differences were also observed depending on the source of humic substances, those from leonardite promoting the greatest decrease in dry matter in roots and shoots. These humic substances possessed the highest values of spectroscopy index for aromaticity (A254 ). On the other hand, the application of humic substances from olive husk compost, which exhibited the lower aromaticity index, resulted in the smallest decrease in dry matter production and chlorophyll meter readings. Dry matter in roots decreased logarithmically with increased values of the estimates of the amounts of aromatic compounds accumulated in the growing media (R2 = 0.92; P < 0.01) with Vivianite as Fe source. Thus, the effects decreasing dry matter production, particularly in roots, and chlorophyll meter readings can be ascribed at least partially to the presence of phytotoxic aromatic compounds in humic substances.  相似文献   

19.
We have tested to see if the generic set of NICA‐Donnan model parameters, used to describe isolated humic substances, can also describe soil humic substances in situ. A potentiometric back‐titration technique was used to determine the variable surface charge of two organic peat soils at three different ionic strengths. The non‐ideal, competitive‐adsorption NICA‐Donnan model was used to simulate the surface charge, by assuming a bimodal distribution of H+ affinity on the soil solid phase. The model provided an excellent fit to the experimental data. The Donnan volume, VD, varied slightly with ionic strength, although the variation was less than for humic substances in solution. The values obtained for the parameters that define the affinity distributions, the intrinsic proton binding constant (log Kiint) and the heterogeneity of the site (mi), were similar to those observed for isolated soil humic acids. The abundance of carboxylic groups in the whole soil represented 30% of the typical value for isolated soil humic acids. The composition of the organic matter of the whole soils, obtained by 13C CPMAS NMR, was comparable to the characteristic composition of soil humic acids.  相似文献   

20.
Liu  Wen Xin  Tao  Shu 《Water, air, and soil pollution》1998,105(3-4):667-675
Naturally occurring organic compounds in water from Jingmi Canal were sequentially fractionated into five fractions using filtration and adsorption columns of XAD-8 and XAD-4 resins in tandem: the fractions being particulates, hydrophobic compounds, humic substances, XAD-4 acids and other hydrophilic neutral solutes. Then each fractions was chlorinated simultaneously with sodium hypochlorite, and the dominant halogenated product determined in this experiment was chloroform. Brominated THMs were detected as well. Both TOC abundance and ratio of CHCl3 product to corresponding fraction of TOC showed that dissolved humic substances and particulate-adsorbed organics were the major precursors of chloroform. Low-molecular-weight hydrophilic XAD-4 acids also possessed noticeable halogenation activity. Other aquatic organic solutes, however, were relatively inert with respect to the three fractions mentioned above. These results suggested that in addition to humic substances, other potential precursors which have not been studied thoroughly before, such as XAD-4 acids, should be considered during water chloronation.  相似文献   

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