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1.
Summary Leaf explants of Nicotiana plumbaginifolia were compared in cultures supplemented with hormones or humic substances (extracted from faeces of Allolobophora caliginosa) of various molecular complexity and concentration. The results showed that the humic substances (F1, F2, and T) at the concentration of 1 mg C l-1 produced greater leaf explants than those grown in the control. Furthermore, humic fractions like gibberellic alone induced a rhizogenic activity in leaf explants. Quantitative differences were also observed in the peroxidase activity induced in Nicotiana plumbaginifolia by humic matter (F2, F2, and T). In addition, the Nicotiana sp. tissue treated with humic fractions revealed, in the esterase enzyme pattern, the appearance of the 2a band, which was attributable to indoleacetic acid, since its profile was consistent with those obtained from tissues treated with indoleacetic acid. These differences demonstrate that humic substances exhibited a hormone-like behaviour, but no evidence of a relationship between biological activities and chemical characteristics of humus substances was found.  相似文献   

2.
Abstract

Laboratory bioassays were used to investigate plant growth‐regulating effects of three different experimental soil additives, designated EXP95, W91, and Z96. A yeast growth test was used as a general assay of bioactivity, responses to soil additives were compared to those of known plant growth regulators [indoleacetic acid (IAA), gibberellic acid (GA3), and kinetin]. A corn coleoptile elongation test was used to assay for auxin‐like activity and a dwarf pea bioassay was used for gibberellin‐like activity. The three soil additives were tested at five solution concentrations ranging from 1 to 10,000 ppm (by volume). All three soil additives stimulated yeast growth, depending on the concentration of the test solutions. However, all three soil additives inhibited plant growth in the two plant bioassays. Although this study clearly demonstrated that the three soil additives had significant biological activity at very low concentrations, there was little evidence for auxin‐like or gibberellin‐like activity.  相似文献   

3.
To investigate the chemical heterogeneity of humic substances in relation to molecular size, fulvic and humic acids were extracted and purified from the surface horizon of a Humic Gleysol in northern Switzerland. A fractionation scheme using hollow‐fibre ultrafiltration cartridges was developed and used to obtain four size fractions of the humic acid with nominal molecular weight ranges > 300 kDa, 100–300 kDa, 30–100 kDa, and 10–30 kDa. The fulvic acid and all humic acid fractions were characterized by size exclusion chromatography, elemental analysis (C, H, N, S), as well as spectroscopic techniques including UV‐VIS, CP‐MAS 13C‐NMR, FT‐IR, and fluorescence spectroscopy. Clear chemical differences between the humic acid size fractions were observed. Smaller size fractions of the soil humic acid contained more chargeable functional groups and a larger percentage of aromatic carbon than the larger size fractions. Conversely, the percentage of aliphatic carbon increased with increasing apparent molecular weight. The chemical composition of the smallest humic acid fraction differed clearly from the fulvic acid fraction, despite similar apparent molecular size and carboxyl carbon content. Small humic acids contained much more aromatic carbon and less aliphatic carbon than the fulvic acid fraction. Apparently, humic size fractions differ in their chemical composition, which can have important implications for their environmental behaviour.  相似文献   

4.
We studied the acid‐base properties of 16 fulvic acids and 16 humic acids isolated from the surface (3–15 cm) and subsurface (> 45 cm) horizons of two types of acid forest soils, derived respectively from amphibolite and granite rocks, under five different types of vegetation. The observed differences between the contents of humic substances in the two types of soils were related to the degree of Al‐saturation of the soil organic matter, as indicated by the molar ratio between pyrophosphate extractable Al and C. Humic fractions were characterized in terms of elemental composition, and CPMAS 13C NMR spectrometry. The contents of carboxylic and phenolic groups were estimated by potentiometric titrations conducted in 0.1 m KNO3 in a nitrogen atmosphere. The fulvic acids contained more carboxylic groups but less phenolic groups than the humic acids: the ratio of phenolic to carboxylic groups in the humic acids was 0.48 ± 0.10 and in the fulvic acids 0.23 ± 0.05. The mean values of the protonation constants of each of the humic substance fractions can be used as generic parameters for describing the proton binding properties. The fulvic acids isolated from the subsurface horizon of the soil contained between 2.6 and 23% more carboxylic groups, and the humic acids between 8 and 43% more carboxylic groups than those isolated from the surface horizon of the same soil.  相似文献   

5.
Abstract

The knowledge of soil organic matter (SOM) composition is important for research in soil science. This is why two classical wet chemical extraction procedures were tested and combined to characterize SOM. Twenty‐five samples from typical forest and arable soils in Schleswig‐Holstein, Northwest Germany, were investigated in the laboratory. Lipids were extracted using a pre‐step method. Several polysaccharide fractions were extracted sucessively with inorganic acids in a litter compound analysis (LCA). Proteins and lignins were determined in the bulk soil sample. In a humic compound analysis (HCA), fulvic and humic acids were extracted in the classical way with NaOH, and the non‐humic substances were removed with the aid of the “Sulfacetolysis” from the residues (= usually “humins")‐ The combination of these two wet chemical extraction proce dures (LCA and HCA) permitted quantitative estimations of the SOM composition in several soil horizons. The LCA method produced a better recovery rate (104%±4%) than the HCA methode (95%±15%). The litter compound/humic compound ratio of both analyses, and the combination of both correlated with visible humification grades in a significant way (r = ‐0.733 to ‐0.742***). LCA may be sufficient for solving special pedogenetic problems, because of its high recovery rate and the strong correlation between LCA and HCA.  相似文献   

6.
The basic principles of the electrophoretic behaviour of humic substances (HS) still need to be systematically investigated. HS extracted from a Cryorthod (HS–1) and from an Haplumbrept (HS–2) were first fractionated by ultrafiltration to obtain two series of fractions of reduced polydispersity with a nominal mean relative molecular mass (M) of 7500, 20000, 40000, 75000 and 200 000 Da. Fractions extracted from the same soil behaved like an homologous series when tested by size exclusion chromatography, showing a linear relation of M with molecular size. When plotted against their mean M, the elution volumes of HS fractions extracted from the two different soils originated lines of different slope. Absolute electrophoretic mobilities of the fractions were determined in polyacrylamide gel slabs of increasing polyacrylamide concentration using a single buffer system; in all gels there was a close linear relation between the electrophoretic mobility and the logarithm of the mean M of HS fractions. Extrapolation of mobilities of HS–1 at zero gel concentration gave intercepts that did not differ significantly, showing that there was a constant mobility for all fractions in free solution. These results mean that charge differences have little effect on the electrophoretic mobilities of HS extracted from the same soil and imply the theoretical possibility of determining M distributions of HS by polyacrylamide gel electrophoresis in a single buffer system. Mobilities of HS–2 fractions were compared with those of HS–1: the latter fitted the regression equations of mobility against logarithm of the molecular weight obtained from HS–1 humic substances only in gels of small acrylamide concentration. Deviations were larger at small M, probably because of the increasing fulvic character of the fractions, and increased in gels of greater acrylamide concentration, indicating that charge differences may not be negligible when comparing humic substances extracted from different soils.  相似文献   

7.
The dynamics of incorporation of fresh organic residues into the various fractions of soil organic matter have yet to be clarified in terms of chemical structures and mechanisms involved. We studied by 13C‐dilution analysis and CPMAS‐13C‐NMR spectroscopy the distribution of organic carbon from mixed or mulched maize residues into specific defined fractions such as carbohydrates and humic fractions isolated by selective extractants in a year‐long incubation of three European soils. The contents of carbohydrates in soil particle size fractions and relative δ13C values showed no retention of carbohydrates from maize but rather decomposition of those from native organic matter in the soil. By contrast, CPMAS‐13C‐NMR spectra of humic (HA) and fulvic acids (FA) extracted by alkaline solution generally indicated the transfer of maize C (mostly carbohydrates and peptides) into humic materials, whereas spectra of organic matter extracted with an acetone solution (HE) indicated solubilization of an aliphatic‐rich, hydrophobic fraction that seemed not to contain any C from maize. The abundance of 13C showed that all humic fractions behaved as a sink for C from maize residues but the FA fraction was related to the turnover of fresh organic matter more than the HA. Removal of hydrophobic components from incubated soils by acetone solution allowed a subsequent extraction of HA and, especially, FA still containing much C from maize. The combination of isotopic measurements and NMR spectra indicated that while hydrophilic compounds from maize were retained in HA and FA, hydrophobic components in the HE fraction had chemical features similar to those of humin. Our results show that the organic compounds released in soils by mineralization of fresh plant residues are stored mainly in the hydrophilic fraction of humic substances which are, in turn, stabilized against microbial degradation by the most hydrophobic humic matter. Our findings suggest that native soil humic substances contribute to the accumulation of new organic matter in soils.  相似文献   

8.
The objective of this study was to investigate differences in organic matter fractions, such as dissolved organic carbon and humic substances, in soils under different land uses. Soil samples were collected from the upper layer of arable lands and grasslands. Humic substances (HS) were chemically fractionated into fulvic acids (FA), humic acids (HA) and humins (HUM), and based on the separated fractions, the humification index (HI) and the degree of HS transformation (DT) were calculated. Dissolved organic carbon (DOC) was determined by cold (CWE) and hot water (HWE) extractions. Regardless of land use, the results indicated significant differences in soil organic carbon (SOC) and HS composition, with HA and HUM as the dominant fractions. Total SOC was higher in grassland (median = 17.51 g kg?1) than arable soils (median = 9.98 g kg?1); the HI and DT indices did not differ significantly between land uses (HI = 0.3–10.3 and DT = 0.2–6.2 for grasslands, p > 0.05; HI = 0.3–3.9 and DT = 0.2–20.1 for arable lands, p > 0.05). This indicates the relatively high stability of organic carbon and efficient humification processes in both land uses. Additionally, in arable soils lower CWE‐C (0.75 g kg?1) and higher HWE‐C (2.59 g kg?1) than in grasslands (CWE‐C = 1.13 g kg?1, HWE‐C = 1.60 g kg?1) can be related to farming practice and application of soil amendments. The results showed that both labile and humified organic matter are better protected in grassland soils and are consequently less vulnerable to mineralization.  相似文献   

9.
To understand the effect of land use changes on the composition of humus in tropical soils, samples from land under primary forest, secondary forest, coffee plantation, and arable crops were investigated at three sites in south Sumatra, Indonesia. Total carbon and total nitrogen contents were 1.7 to 4.3 times and 1.1 to 2.8 times greater in the topsoil under primary forest than under the other types of land use. Following change from primary forest to other uses, the proportion of humic acids in the organic matter of the topsoils decreased while that of the fulvic acid fraction increased. Within the range of land uses, differences in the yields of humic acids and fulvic acid fractions were, respectively, larger and smaller than those in total carbon content. The humic acids were classified into the low and middle classes in the degree of humification. Absorption due to the green fraction of humic acids, Pg, was detected in the UV‐visible spectra of almost all the humic acids. No relation was observed between the degree of humification of humic acids or the strength of Pg absorption in their spectra and land use change. The fulvic acid fractions were fractionated on insoluble polyvinylpyrrolidone (PVP) into the adsorbed fractions consisting of humic substances and the non‐adsorbed fractions consisting of non‐humic substances. A positive correlation between the amount of the fulvic acid fraction and the percentage of the PVP‐adsorbed fraction within it indicated that the variation in the amount of the fulvic acid fraction was attributable to acid‐soluble humic substances. The ionization difference spectra of solutions between pH 12 and pH 7 suggested that the chemical structures of the PVP‐adsorbed fulvic acids have been altered by land use change.  相似文献   

10.
A comprehensive sequential extraction procedure was applied to isolate soil organic components using aqueous solvents at different pH values, base plus urea (base‐urea), and finally dimethylsulfoxide (DMSO) plus concentrated H2SO4 (DMSO‐acid) for the humin‐enriched clay separates. The extracts from base‐urea and DMSO‐acid would be regarded as ‘humin’ in the classical definitions. The fractions isolated from aqueous base, base‐urea and DMSO‐acid were characterized by solid and solution state NMR spectroscopy. The base‐urea solvent system isolated ca. 10% (by mass) additional humic substances. The combined base‐urea and DMSO‐acid solvents isolated ca. 93% of total organic carbon from the humin‐enriched fine clay fraction (<2 μm). Characterization of the humic fractions by solid‐state NMR spectroscopy showed that oxidized char materials were concentrated in humic acids isolated at pH 7, and in the base‐urea extract. Lignin‐derived materials were in considerable abundance in the humic acids isolated at pH 12.6. Only very small amounts of char‐derived structures were contained in the fulvic acids and fulvic acids‐like material isolated from the base‐urea solvent. After extraction with base‐urea, the 0.5 m NaOH extract from the humin‐enriched clay was predominantly composed of aliphatic hydrocarbon groups, and with lesser amounts of aromatic carbon (probably including some char material), and carbohydrates and peptides. From the combination of solid and solution‐state NMR spectroscopy, it is clear that the major components of humin materials, from the DMSO‐acid solvent, after the exhaustive extraction sequence, were composed of microbial and plant derived components, mainly long‐chain aliphatic species (including fatty acids/ester, waxes, lipids and cuticular material), carbohydrate, peptides/proteins, lignin derivatives, lipoprotein and peptidoglycan (major structural components in bacteria cell walls). Black carbon or char materials were enriched in humic acids isolated at pH 7 and humic acids‐like material isolated in the base‐urea medium, indicating that urea can liberate char‐derived material hydrogen bonded or trapped within the humin matrix.  相似文献   

11.
The kinetic parameters of nitrate uptake (Imax, Km and Cmin) were evaluated in young seedlings of Triticum durum L., cv. Appulo, exposed to nitrate and/or to soil‐extracted humic acids (HAs) of different molecular weight. The uptake was enhanced after induction at low levels of nitrate (50 μM KNO3), while it was inhibited after induction at higher concentrations (2000 μM). The kinetic parameters of uptake were selectively influenced by pre‐treatment with HAs: total (TE) and, at a greater extent, low (LMS, < 3500 Da) molecular size humic fraction increased either the nitrate uptake rate (Imax) and the efficiency of the whole transport system (low Km and Cmin), while an opposite result was evidenced in high molecular size (HMS, > 3500 Da)‐treated plants. An additive effect was shown when nitrate and humic substances were provided simultaneously: the uptake rate was enhanced in TE‐ and LMS‐treated plants, but was strongly delayed in HMS‐treated plants. Removal of nitrate and/or humic fractions de‐induced the system and NO3— uptake rate decreased. Exposure to HAs was not able to induce nitrate reductase activity in root and leaf tissues. Inhibitors of protein synthesis p‐fluorophenylalanine and cycloheximide reversed the positive effect of LMS fraction on nitrate uptake. This would support the hypothesis of a promoting effect of HAs on the molecular expression of proteins of the nitrate transport system.  相似文献   

12.
Rock fragments in soil can contain significant amounts of organic carbon. We investigated the nature and dynamics of organic matter in rock fragments in the upper horizons of a forest soil derived from sandstone and compared them with the fine earth fraction (<2 mm). The organic C content and its distribution among humic, humin and non‐humic fractions, as well as the isotopic signatures (Δ14C and δ13C) of organic carbon and of CO2 produced during incubation of samples, all show that altered rock fragments contain a dynamic component of the carbon cycle. Rock fragments, especially the highly altered ones, contributed 4.5% to the total organic C content in the soil. The bulk organic matter in both fine earth and highly altered rock fragments in the A1 horizon contained significant amounts of recent C (bomb 14C), indicating that most of this C is cycled quickly in both fractions. In the A horizons, the mean residence times of humic substances from highly altered rock fragments were shorter than those of the humic substances isolated in the fine earth. Values of Δ14C of the CO2 produced during basal respiration confirmed the heterogeneity, complexity and dynamic nature of the organic matter of these rock fragments. The weak 14C signatures of humic substances from the slightly altered rock fragments confirmed the importance of weathering in establishing and improving the interactions between rock fragments and surrounding soil. The progressive enrichment in 13C from components with high‐14C (more recent) to low‐14C (older) indicated that biological activity occurred in both the fine and the coarse fractions. Hence the microflora utilizes energy sources contained in all the soil compartments, and rock fragments are chemically and biologically active in soil, where they form a continuum with the fine earth.  相似文献   

13.
The behavior of phenolic substances in the decaying process of rice straw, ladino clover, and fanen leaves of red oak under moist conditions, and also of rice straw under various conditions were compared in the laboratory. The amounts of phenolic substances, divided into either humic acid and fulvic acid fractions, or ether-extractable, butanol-extractable and organic solvent-unextractable fractions, and the amounts of individual phenolic acids were periodically determined during incubation for 150 days. The following results were obtained.

1) The amounts and behavior of phenolic substances in various fractions differed considerably among the plant materials. The total amount of phenolic substances was remarkably larger in red oak leaves than in the others during the whole period of incubation. The amounts of phenolics in the fulvic acid fraction changed to a larger extent than those in the humic acid fraction during the decaying process of plant materials. The changes in total amount of phenolics in decaying red oak leaves and ladino clover were mainly due to changes in the level of relatively hydrophilic phenolics in the fulvic acid fraction, but the changes in decaying rice straw were mainly due to changes in the level of relatively lipophilic phenolics.

2) Rice straw and ladino clover, especially the former, contained large amounts of p-coumaric and ferulic acids, but these decreased rapidly in the early stage of the decaying process. The amounts in red oak leaves were small, but did not decrease markedly during incubation.

3) The changes in amounts of phenolics in both humic acid and fulvic acid fractions in the decaying process of rice straw were largely influenced by temperature, moisture, and pH, but not to a large extent by C/N ratio and the presence of soil. At higher temperatures under moist conditions, phenolic substances disappeared rapidly. Also, acidification of the system inhibited the degradation process.  相似文献   

14.
A greenhouse experiment was conducted to evaluate the effects of humic substances extracted from composted sewage sludge on growth, phenological development, and photosynthetic activity of pepper (Capsicum annuum L. cv. Piquillo) plants. Humic substances derived from composted sludge (HSS) were compared with those derived from leonardite (HSL). Two doses of both humic substances were assayed (200 and 500 mg C [L substrate]–1) and compared with a control (C). HSS showed higher nitrogen content and a higher percentage of aliphatic carbon, as well as a lower content of aromatic and phenolic carbon than HSL. HSS significantly increased plant dry‐matter production (up to 560%), plant height (86%–151%), and leaf area (436%–1397%) during the early stages of pepper development. Net photosynthesis and stomatal conductance increased in the treatments with HSS (up to 48% and 63%, respectively) at the vegetative stage. In addition, HSS accelerated the phenological development of pepper plants, reducing significantly the number of days to flowering and ripening, which occurred 12 and 14 d earlier than in control plants, respectively. In general, the treatments with HSS and HSL did not markedly affect chlorophyll and nutrient concentrations in the leaves. At maturity, only small differences in total fruit yield, number of fruits per plant, and fruit size were observed between amended and control plants. The results suggest that the mechanisms through which HSS affected plant growth and development were not associated with an improved nutrient uptake. Although the identity of the growth‐promoting factors remains to be found, the results suggest that they may be linked to the chemical structure of the humic substances.  相似文献   

15.
Thermostable soil protein, known as glomalin, is an important component of soil carbon stocks. Thought to originate from endomycorrhizal fungi, Glomales, this operationally‐defined fraction of soil organic matter contains proteins of diverse origin as well as non‐protein material, including humic substances. Accumulation results from the balance between production/release and subsequent degradation. Quantification of the protein is subject to uncertainty because of the co‐extraction of other components that interfere with the Bradford assay. We studied 10 topsoils from French temperate forests, taken from the national forest monitoring network (Renecofor). Two fractions were extracted, easily extractable (EE) at neutral pH and total extractable (T) at pH 8. Protein was quantified with the colorimetric Bradford method, either by direct calibration using bovine serum albumin (BSA) or by extrapolation of the standard addition plot of BSA. Solubilized organic matter was characterized by using absorbance at 465 and 665 nm and by three‐dimensional fluorescence excitation‐emission spectroscopy. Neither soil properties nor forest cover influenced glomalin‐related soil protein (GRSP) content. Direct assay gave the GRSPEE to be about 1 g kg?1 soil, and GRSPT in the range 3–10 g kg?1, accounting for about 2% of soil organic carbon and about 15% of soil nitrogen. Standard addition plots indicated a two to sixfold under‐estimation of protein in total extracts, caused by negative interference with the Bradford assay. The GRSPEE was correlated significantly with both estimates of GRSPT. Under‐estimation of GRSPT by direct assay was not related to the E4:E6 ratio but was correlated significantly with the intensity of absorbance at either 460 or 660 nm and with one of the fluorescence peaks. We conclude that GRSPEE is not necessarily more recent than GRSPT and that both fractions may be probes of protein content, but that absolute contents may be under‐estimated because of co‐extracted humic substances.  相似文献   

16.
This study investigates if Araucaria forest (C3 metabolism) expansion on frequently burnt grassland (C4 metabolism) in the southern Brazilian highland is linked to the chemical composition of soil organic matter (SOM) in non‐allophanic Andosols. We used the 13C/12C isotopic signature to group heavy organo‐mineral fractions according to source vegetation and 13C NMR spectroscopy, lignin analyses (CuO oxidation) and measurement of soil colour lightness to characterize their chemical compositions. Large proportions of aromatic carbon (C) combined with small contents of lignin‐derived phenols in the heavy fractions of grassland soils and grass‐derived lower horizons of Araucaria forest soils indicate the presence of charred grass residues in SOM. The contribution of this material may have led to the unusual increase in C/N ratios with depth in burnt grassland soils and to the differentiation of C3‐ and C4‐derived SOM, because heavy fractions from unburnt Araucaria forest and shrubland soils have smaller proportions of aromatic C, smaller C/N ratios and are paler compared with those with C4 signatures. We found that lignins are not applicable as biomarkers for plant origin in these soils with small contents of strongly degraded and modified lignins as the plant‐specific lignin patterns are absent in heavy fractions. In contrast, the characteristic contents of alkyl C and O/N‐alkyl C of C3 trees or shrubs and C4 grasses are reflected in the heavy fractions. They show consistent changes of the (alkyl C)/(O/N‐alkyl C) ratio and the 13C/12C isotopic signature with soil depth, indicating their association with C4 and C3 vegetation origin. This study demonstrates that soils may preserve organic matter components from earlier vegetation and land‐use, indicating that the knowledge of past vegetation covers is necessary to interpret SOM composition.  相似文献   

17.
We investigated carbon (C) incorporation and sources of C in the surface CO2 flux at two sites in northern England on peaty (stagnohumic) gley soil, one afforested by Picea sitchensis, the other under continuous Molinia grassland cover. Radiocarbon (14C) derived from atmospheric nuclear weapons testing was used to trace the incorporation of C into the soil and sources of C in the soil CO2 flux from the soil surface and deeper layers. Larger values of 14CO2 in surface flux were found at the afforested site (109–110 per cent modern (pM) compared with 107–108 pM at the grassland site). Surface litter fractions (Oi horizon) from the afforested site showed larger 14C signatures than the equivalent fractions in the grassland (113–115 pM in the forest compared with 106–109 pM in the grassland). Fine root fractions (<2 mm, Oe horizon) had similar signatures at both sites (109 pM in the forest compared with 109–111 pM in the grassland). Humified fractions at 10‐cm depth (Oa horizon) showed smaller signatures (100–103 pM) in the forest than the equivalent fraction in the grassland soil (106–114 pM). According to a mixing model that takes into account pool size and 14C signature, the contributions to surface CO2 fluxes from slow turnover fractions that had resided in the soil for more than one year were greater at the forested site than the grassland site, but contributions from fast‐turnover C fixed within the year prior to study showed the opposite trend. The results, taken together with previous work indicating that both site preparation and clear‐felling lead to a net loss of C, indicate that long‐term fixation in deep soil organic fractions is limited on this soil type under plantation forest over 40–50‐year commercial rotations.  相似文献   

18.
ABSTRACT

In vitro grown kiwifruit (Actinidia deliciosa, Liang and Ferguson) plantlets were treated with two humic fractions distinguished by two different relative molecular mass and characterized through their elemental composition and 13Carbon (C) nuclear magnetic resonance. The effects exerted on plant growth, root morphology, and nutrition were evidenced by means of leaves and roots mineral content, root respiration, and nitrate reductase activity. The two humic substances differentially influenced the studied parameters. The lower molecular fraction humic substance, endowed with a higher content of phenolic and carboxylic groups, caused an enhanced content of micro- and macro-elements, together with a higher root respiration at lower concentrations (0.5–1 mg C L? 1). The high molecular fraction humic substance, needed higher concentrations (> 5 mg C L? 1) in order to achieve similar effects. This fraction also caused major changes on root morphology. The ability to improve micronutrient assimilation, in particular iron, confirmed the agronomic importance of humic substances on soil fertility.  相似文献   

19.
Abstract

The cation exchange capacity (CEC) and content of COOH groups in bulky water hyacinth compost were estimated over the rotting period. The progressive increase observed in the estimates was ascribed to continuing oxidation processes in the composted materials.

Fractionation of organic carbon extracted with Na4P2O7-NaOH from the composted materials over the rotting period on the basis of acid-soluble and -insoluble fractions, was carried out. The carbon of humic-like substances (precipitated at pH 2) in the dry matter was almost stable from 0- to 124-day composted materials. There were successive increases in total acidity, and content of carboxyl and phenolic hydroxyl groups in the humic substance extracts indicating progressive oxidation processes in these substances over the rotting period. Elementary analysis and IR spectra provided fürther support for the above inference and led us to conclude that humification of the water hyacinth consists mainly of structural modification of humic-like substances initially occurring rather than a condensation of simple organic carbon to form high molecular weight material. Such structural modification is dominated by biochemical oxidation and increases in oxygen-containing functional groups. This conclusion is consistent with the view that “humic acids are formed by processes involving oxidation of plant lignin and lignoprotein entering the soil.”  相似文献   

20.
Differentiated interactions between humic substances and isoelectric focusing-carrier ampholytes were demonstrated by comparing specific absorption ratios from the supernatant after precipitation with 2 M HCl and with acid ampholytes (pH 2–4) containing both carboxylic and sulphate groups. An increasingly stronger interaction was observed when comparing soil humic substances to those of synthetic origin or those extracted from young reclaimed soil material. Electrofocusing of the humic substances under study revealed a fingerprint-like quality; the band patterns observed were consistent with the concept of three main fractions.  相似文献   

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