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1.
The chemical composition of leaf fibers of curaua (Ananas erectifolius), an herbaceous plant native of Amazonia, was studied. Special attention was paid to the content and composition of lignin and lipophilic compounds. The analysis of lignin in the curaua fibers was performed in situ by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and showed a lignin composition with a p-hydroxyphenyl:guaiacyl:syringyl units (H:G:S) molar proportion of 30:29:41 (S/G molar ratio of 1.4). The presence of p-hydroxycinnamic acids (p-coumaric and ferulic acids) in curaua fibers was revealed upon pyrolysis in the presence of tetramethylammonium hydroxide. On the other hand, the main lipophilic compounds, analyzed by GC/MS, were series of long-chain n-fatty acids, n-fatty alcohols, alpha- and omega-hydroxyacids, monoglycerides, sterols, and waxes. Other compounds, such as omega-hydroxy monoesters and omega-hydroxy acylesters of glycerol, were also found in this fiber in high amounts.  相似文献   

2.
The chemical composition of lignin and lipids of bast fibers from kenaf (Hibiscus cannabinus) used for high-quality paper pulp production was studied. Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) of fibers showed a lignin with a high syringyl/guaiacyl ratio (5.4) and minor amounts of p-hydroxyphenyl units. Simultaneously, sinapyl and coniferyl acetates were also identified, indicating that this lignin is partially acetylated. p-Hydroxycinnamic acids were found in only trace amounts. The main lipids identified by GC/MS of extracts from kenaf fibers were series of long-chain n-fatty acids, waxes, n-alkanes, and n-fatty alcohols. Free and esterified sterols and triterpenols, steroid hydrocarbons, and steroid and triterpenoid ketones, as well as steryl glycosides, were also found. Finally, the fate of the main constituents of kenaf fibers in alkaline pulping was also investigated.  相似文献   

3.
The chemical composition of leaf fibers of abaca (Musa textilis), which are commonly used for high-quality paper pulp production, was thoroughly studied. The results revealed that the lignin content was 13.2% of the total fiber. The analysis of abaca fibers by pyrolysis coupled to gas chromatography-mass spectrometry (Py-GC/MS) released predominantly compounds arising from lignin and p-hydroxycinnamic acids, with high amounts of 4-vinylphenol. The latter compound was demonstrated to arise from p-coumaric acid by pyrolysis of abaca fibers in the presence of tetramethylammonium hydroxide, which released high amounts of p-coumaric acid (as the methyl derivative). Products from p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) propanoid units, with a predominance of the latter (H:G:S molar ratio of 1.5:1:4.9), were also released after Py-GC/MS of abaca fibers. Sinapyl and coniferyl acetates, which are thought to be lignin monomer precursors, were also found in abaca. The extractives content of the abaca fiber (0.4%) was low, and the most predominant compounds were free sterols (24% of total extract) and fatty acids (24% of total extract). Additionally, significant amounts of steroid ketones (10%), triglycerides (6%), omega-hydroxyfatty acids (6%), monoglycerides (4%), fatty alcohols (4%), and a series of p-hydroxycinnamyl (p-coumaric and ferulic acids) esterified with long chain alcohols and omega-hydroxyfatty acids were also found, together with minor amounts of steroid hydrocarbons, diglycerides, alpha-hydroxyfatty acids, sterol esters, and sterol glycosides.  相似文献   

4.
The chemical composition of lipids from bast fibers of flax (Linum usitatissimum), which are commonly used for high-quality paper pulp production, was thoroughly studied by gas chromatography-mass spectrometry. The main compounds identified were waxes, series of long chain n-fatty alcohols, n-aldehydes, n-fatty acids, and n-alkanes. Free and esterified sterols and triterpenols, steroid hydrocarbons, steroid and triterpenoid ketones, as well as sterol glycosides were also found in the flax bast fibers. On the other hand, the fate of these lipophilic compounds in alkaline pulping of flax fibers was investigated by analyzing two pulps obtained under distinct industrial cooking conditions. The results revealed that while waxes could be efficiently hydrolyzed during pulping depending on the alkali charge, most of the other lipophilic compounds present in flax fibers survived cooking and were present in the unbleached pulps.  相似文献   

5.
The composition of lipophilic extractives in the cortex and pith of elephant grass ( Pennisetum purpureum Schumach.) stems was thoroughly studied by gas chromatography-mass spectrometry. The predominant compounds were fatty acids followed by sterols (in free and conjugated forms as esters and glycosides). Other steroid compounds, as steroid hydrocarbons and ketones, were also present. Additionally, important amounts of mono-, di-, and triglycerides were identified. Other aliphatic series such as n-alkanes, n-fatty alcohols, and n-alkyl ferulates, together with tocopherols and a series of high molecular weight esters, were also found, although in minor amounts. The analyses also revealed the presence of a β-diketone (12,14-tritriacontanedione), which was particularly abundant in the cortex. Finally, two lignans, matairesinol and syringaresinol, were also detected. In general terms, the abundances of the different classes of compounds were higher in the pith, except for the series of n-fatty alcohols, n-alkyl ferulates, β-diketones, and lignans, which were more prominent in the cortex.  相似文献   

6.
The structural characteristics of the lignins from flax (Linum usitatissimum) fibers and shives were studied. Significant differences in the content and composition of the lignin from both parts were observed. The lignin contents were 3.8% in the fibers and 29.0% in the shives. Analysis by Py-GC/MS indicated a H:G:S molar ratio of 13:72:15 in the milled wood lignin (MWL) isolated from flax fibers and a molar ratio of 5:87:8 in the MWL isolated from flax shives. In addition, 2D-NMR showed a predominance of β-O-4' aryl ether linkages, followed by β-5' phenylcoumaran and β-β' resinol-type linkages in both MWLs, with a higher content of condensed linkages in flax shives. Thioacidolysis (followed by Raney nickel desulfurization) gave further information on the lignin units involved in the different linkages and confirmed the enrichment of G units. The thioacidolysis dimers released were similar from both lignins, with a predominance of the β-5' followed by β-1' and 5-5' structures.  相似文献   

7.
Insoluble fiber fractions from 11 fruits and vegetables were investigated for their lignin composition using the derivatization followed by reductive cleavage (DFRC) methodology. To enrich lignin contents and to minimize polysaccharide excess that led to nonanalyzable DFRC chromatograms, the insoluble fibers were degraded by a carbohydrolases mixture. The residues that were found to be representative for the insoluble fiber lignins were analyzed. The investigated fibers differ considerably in their lignin contents and also in their lignin compositions. With the exception of radish fiber, only trace amounts (or none) of the products resulting from p-hydroxyphenyl units were detected. Lignins noticeably differed in the ratio of the DFRC products resulting from syringyl units (S) and guaiacyl (G) units (G/S ratios ranged from approximately 39 to 0.2). The insoluble fiber lignins were classified as G-rich lignins (G/S ratio > 3; carrot, spinach, kiwi, curly kale, radish, and asparagus), S-rich lignins (S/G ratio > 3; rhubarb), or balanced lignins (0.3 < G/S ratio < 3; pear, apple, small radish, and kohlrabi). Information about further structural characteristics, for example, cinnamyl endgroups, was obtained from the analysis of DFRC minor products.  相似文献   

8.
Miscanthus giganteus lignin was extracted by an organosolv process under reflux conditions (4 h) with varying concentrations of ethanol (65%, 75%, 85%, 95%) and 0.2 M hydrochloric acid as catalyst. The resulting lignin was extensively characterized by size exclusion chromatography (SEC), Fourier-transform infrared spectroscopy (FTIR), gas chromatography-mass spectrometry (GC/MS), two-dimensional nuclear magnetic resonance spectroscopy (2D-NMR), and chemical analysis (residual sugars, Klason lignin, ash). The predominant linkage units present were β-O-4' (82-84%), resinol (6-7%), and phenylcoumaran (10-11%). The 65% ethanol solvent system gave the lowest lignin yield (14% of starting biomass) compared to 29-32% of the other systems. Increasing ethanol concentration resulted in decreasing carbohydrate content of the lignins (3.6-1.1%), a higher solubility in tetrahydrofuran (THF), a slight reduction of the molecular weight (M(w) 2.72-2.25 KDa), an increasing α-ethoxylation, and an increase in ethoxylated phenylpropenoic compounds (p-coumaric and ferulic acid), but the S/G ratio of the monolignols (0.63, GC/MS) and Klason lignin content (86-88%) were unaffected. An extraction method for these ethyl-esterified phenylpropenoids and smaller molecular weight lignin compounds was developed. The effect of reaction time (2, 4, and 8 h) was investigated for the 95% ethanol solvent system. Besides increased lignin yield (13-43%), a slight increase in M(w) (2.21-2.38 kDa) and S/G ratio (0.53-0.68, GC-MS) was observed. Consecutive extractions suggested that these changes were not from lignin modifications (e.g., condensations) but rather from extraction of lignin of different composition. The results were compared to similar solvent systems with 95% acetone and 95% dioxane.  相似文献   

9.
Changes in the molecular composition of soil organic matter (SOM) resulting from compost application are not sufficiently known at the molecular scale even though this is a major issue for soil fertility and soil carbon sequestration. Therefore, the present study investigated effects of long-term compost application in comparison to mineral fertilizer on the molecular composition of SOM in a 34-year-old experiment. Soil samples were taken after 19 and 34 years of constant management and analyzed by Curie point Pyrolysis-Gas Chromatography/Mass Spectrometry (Cp Py-GC/MS) and Pyrolysis-Field Ionization Mass Spectrometry (Py-FIMS). In general, compost application increased the organic carbon (C) content. The Cp PyGC/MS revealed larger relative intensities of alkylphenols/lignin monomers at the expense of carbohydrates in the compost treatments. Py-FIMS indicated higher proportions of labile n-fatty acids, lipids and sterols in the compost than in the mineral fertilizer treatment. Permanent cropping of grass between years 19 and 34 revealed similar signal patterns, which is also maintained after conversion of soil from permanent grass to arable use. Thermograms of volatilization indicated enrichments of stable (compounds volatilized in between 370°C and 570°C) phenols/lignin monomers, lipids and alkylaromatics between years 19 and 34 in compost fertilized soils. This was a result of enhanced losses of compounds that are considered easily metabolized by microorganisms (e.g. carbohydrates) after compost addition as derived from Py-GC/MS and Py-FIMS. In summary, long-term application of mature compost was shown to have a positive, long lasting effect on the organic carbon sequestration in agricultural soils.  相似文献   

10.
A combination of solid‐state CPMAS‐13C‐NMR and TMAH thermochemolysis‐GC/MS was applied to investigate the molecular composition of particulate organic matter (POM) separated from a Chinese paddy soil, from the Tai Lake region, under a long‐term field experiment with different fertilizer treatments. The treatments were: (i) no fertilizer application (NF), (ii) chemical fertilizers only (CF), (iii) chemical fertilizer plus pig manure (CFM) and (iv) chemical fertilizer plus crop straw (CFS). CPMAS‐13C‐NMR spectra showed that POM from all treated plots was rich in O‐alkyl‐C compounds, followed by alkyl‐C and aromatic‐C compounds. However, as compared with a control (NF), POM under CFM and CFS treatments exhibited a smaller relative O‐alkyl‐C content and a larger contribution of aromatic‐C and alkyl‐C, thus increasing both aromaticity and hydrophobicity and, hence, recalcitrance of POM samples. Thermochemolysis of POM from all treatments demonstrated a dominance of aliphatic and lignin‐derived compounds. However, the distribution of lignin monomers (p‐hydroxyphenyl, P, guaiacyl, G, and syringyl, S) revealed significant differences among the treatments. The relative distribution of lignin P, G and S monomers in NF, CF and CFS indicated a preferential contribution of annual crops and maize straw, as compared with that found for CFM. Concomitantly, a larger content of aliphatic thermochemolysis derivatives was found for CFS and CFM. The relative increase of aliphatic molecules in CFS was attributed to hydrophobic polyesters from higher plants. In the CF and CFM systems, the presence of aliphatic components of microbial origin suggested a greater microbial activity in comparison with NF and CFS. The combined application of solid state CPMAS‐13C‐NMR and TMAH thermochemolysis‐GC/MS can be used to assess effectively the accumulation of recalcitrant organic compounds in soil POM under long‐term fertilizer application with organic biomass. It is thus inferred that soil organic matter stabilization by molecular recalcitrance contributes to carbon sequestration in Chinese paddy soils under long‐term managements.  相似文献   

11.
We have sought to understand the molecular mechanisms by which dissolved organic matter (DOM) forms and soil organic matter (SOM) degrades in upland peaty gley soil under grass. Pyrolysis mass spectrometry (Py-MS) and pyrolysis gas chromatography mass spectrometry (Py-GC/MS) were applied to characterize the DOM collected from lysimeters and its parent SOM. The macromolecular organic matter in the litter and fermentation (Lf) horizon of the soil consists primarily of little decomposed lignocellulose from grass, whereas the humus (Oh) horizon is characterized by an accumulation of selectively decomposed lignocellulose material, microbial metabolites and bound fatty acids. The mineral horizon produced a relative enrichment of furan structures derived from microbial reworking of plant polysaccharides but virtually no lignin signals. A series of exceptional long chain C43 to C53 fatty acids with odd over even predominance, probably derived from mycobacteria, were also identified in the Oh horizon. Side-chain oxidation and shortening, increase of carboxyl functionality and selective removal of syringyl (S) > guaiacyl (G) > p-hydroxyphenyl (P) lignin units were the main reactions when lignin degraded. Compared with SOM, the DOM shows a large accumulation of more oxidized lignin and aromatic structures, especially those containing carboxylic and dicarboxylic acid functionalities and with shorter side-chain length. The polysaccharide-type compounds in the DOM were more modified (greater abundance of furan structures in pyrolysis products), and had significantly lower molecular weight and more diverse polymeric structures than did those in soils. Increased temperature and rainfall appeared to result in greater relative abundance of lignin degradation products and aromatic compounds in DOM.  相似文献   

12.
A comprehensive lignin structure analysis of ten industrially relevant hardwood species is presented. Milled wood lignin (MWL) was isolated from each species using a modified protocol and all milled wood lignin preparations were analyzed through quantitative (13)C NMR spectroscopy, elemental analysis, methoxyl analysis, sugar analysis, and nitrobenzene oxidation. Nitrobenzene oxidation and ozonation were carried out on extractive-free wood, alkali-extracted wood, milled wood lignin, and alkali-extracted lignin. Milled wood lignin isolated by the modified protocol was found to be representative of the total lignin in alkali-extracted wood. Significant variations in lignin structures, such as syringylpropane/guaiacylpropane ratio (S/G ratio), arylglycerol-β-aryl ether (β-O-4), degree of condensation, and elemental and methoxyl contents, were found among the hardwood species studied. These structural variations among species appear to be correlated to a single factor, the syringyl/guaiacyl ratio. A new method to predict the S/G ratio of total lignin in wood was developed, using a calibration line established by the syringaldehyde/vanillin (S/V) ratio (nitrobenzene oxidation) and the S/G ratio ((13)C NMR) of milled wood lignin (MWL).  相似文献   

13.
Six alkali soluble lignin fractions were extracted from the cell wall materials of oil palm trunk and empty fruit-bunch (EFB) fibers with 5% NaOH, 10% NaOH, and 24% KOH/2% H(3)BO(3). All of the lignin fractions contained rather low amounts of associated neutral sugars (0.8-1.2%) and uronic acids (1.1-2.0%). The lignin fractions isolated with 5% NaOH from the lignified palm trunk and EFB fibers gave a relatively higher degree of polymerization as shown by weight-average molecular weights ranging between 2620 and 2840, whereas the lignin fractions isolated with 10% NaOH and 24% KOH/2% H(3)BO(3) from the partially delignified palm trunk and EFB fibers showed a relatively lower degree of polymerization, as shown by weight-average molecular weights ranging between 1750 and 1980. The results obtained by alkaline nitrobenzene oxidation showed that all of the lignin preparations contained a high proportion of noncondensed syringyl units with small amounts of noncondensed guaiacyl and fewer p-hydroxyphenyl units. The lignin fraction extracted with 5% NaOH from the lignified EFB fiber was mainly composed of beta-O-4 ether-linked units. Small amounts of 5-5', beta-5, and beta-beta' carbon-carbon linkages were also found to be present between the lignin structural units. Further studies showed that uronic, p-hydroxybenzoic, and ferulic acids in the cell walls of palm fibers were esterified to lignin.  相似文献   

14.
To analyze the accuracy of the Klason lignin method as applied for the determination of lignin contents in plant based-food products, Klason lignin preparations from curly kale, pears, whole wheat grains, and corn bran were chemically characterized. Characterization included routine ash and protein determinations and the extraction of fat/waxes as well as cutin/suberin depolymerization and extraction of the liberated monomers. Fat/wax and cutin/suberin amounts in the Klason lignin preparations were determined gravimetrically, and their compositions were analyzed by using GC-MS. Typical fat, wax, and cutin (and suberin) constituents such as saturated and unsaturated fatty acids, hydroxy and/or epoxy fatty acids, and phenolic acids were identified in all samples, whereas the detection of long-chain hydrocarbons, alcohols, and ketones, sterols, stanols, and dioic acids was dependent on the sample analyzed. Estimation of the contribution of non-lignin compounds to the Klason lignin contents reduced the noncorrected Klason lignin contents of the insoluble fibers from 28.7% (kale), 22.8% (pear), 14.8% (wheat), and 9.9% (corn) to maximum lignin contents of 6.5% (kale), 16.4% (pear), 4.9% (wheat), and 2.3% (corn). These data demonstrate that certain commonly used statements such as "cereal brans are highly lignified" need to be revised.  相似文献   

15.
Stem tissues of tall fescue (Festuca arundinacea Schreb.) were sampled at three elongation stages and three reproductive stages. Anatomical analysis showed the deposition of guaiacyl (G) and syringyl (S) lignin during plant development and the formation of a lignified sclerenchyma ring. A dramatic increase in Klason lignin content was found from elongation stage to reproductive stage. Lignin composition analyzed by gas chromatography-mass spectrometry revealed that S lignin content and S/G ratio increased with stem development, but contents of p-hydroxyphenyl (H) and G lignins decreased during the same period. S lignin content and S/G ratio also increased from the younger upper internode down to the older basal internode of the stem, but G and H lignin decreased in parallel. Relative O-methyltransferase activities increased during stem development and in parallel with the lignification process of stem. The pattern of enzyme activity during development varied with the choice of substrate, with highest activities seen when substrates were caffeoylaldehyde and 5-hydroxyferulic acid, and lowest activities were seen when caffeic acid and 5-hydroxyconiferyl alcohol were used as substrates. The expression of caffeic acid O-methyltransferase and cinnamyl alcohol dehydrogenase genes increased during the stem elongation stage and remained at high levels during the reproductive stages. The changes at anatomical, metabolic, and molecular levels during plant development were closely associated with lignification and degradability. This study provides an integrated picture of the molecular and chemical events that accompany changes in lignin deposition and ruminal degradability.  相似文献   

16.
  【目的】  探讨丘陵山区乡村不同土壤景观表土有机质积累的团聚体分布及其化学组成的变化,为认识自然条件和人为利用下土壤有机质的空间变化特点提供新视角。  【方法】  选取江苏省南京市溧水区芳山小流域内保护林地、园地、旱地和稻田等景观样地,采集0—20 cm土壤样品,分析有机碳(SOC)总量。将土壤样品通过湿筛法分出宏团聚体(2000～250 μm)、微团聚体(250～53μm)和粉黏粒(<53 μm) 3个粒径组,测定其中有机碳含量,计算土壤中各团聚体结合态碳的比例。再者,对土壤样品依次进行总溶剂(TSE)提取,碱水解(BHY) 提取和氧化铜氧化(CUO)提取,分别主要得到游离脂、结合态脂和木质素酚,采用气相色谱–质谱联用仪(GC-MS)测定各组分中生物标志物有机分子丰度,计算分子多样性指数。  【结果】  与林地相比,园地、旱地和稻田表土本体有机碳含量分别降低70%、57%和51%,其中宏团聚体结合有机碳的含量分别降低了85%、81%和71%,微团聚体结合有机碳分别降低了74%、79%和67%,粉黏粒结合有机碳则分别降低了48%、18%和3%。表土中提取得到游离态脂类、结合态脂类和木质素酚类的有机分子丰度分别介于2.24～6.74、4.81～14.87和3.51～6.16 mg/g SOC;不同土壤景观间,这些提取态生物标志物分子丰度的变化趋势均表现为林地>稻田>园地>旱地。而木质素酚类丰度表现为林地和稻田相近。相对于林地,园地、旱地和稻田的脂肪酸丰度、烷醇、甾类及萜类等生物标志物分子丰度显著降低,但烷烃分子丰度明显增加,同时微生物来源有机质对土壤有机质的贡献提高;林地及园地土壤中结合态脂类组分以羟基酸丰度较高,而旱地和稻田则以烷酸为主。通过计算的生物标志物分子多样性指数的变化,发现游离态脂类和结合态脂类是林地和稻田高于旱地和园地,而木质素酚是稻田高于旱地,旱地又高于园地和林地。  【结论】  自然林地和农用地土壤的有机碳含量和团聚体结构具有较大差异,在提取态有机分子的组成上也具有不同的组成特征。林地土壤有机碳含量高,宏团聚体、微团聚体和粉黏粒比例均衡,有机碳的团聚体分配也均衡,而且有机质主要以植物源有机碳为主,具有碳链长、分子多样性高等特点。因之,稳定性也高。相反,园地、旱地的有机碳总量低,宏团聚体和微团聚体趋于分解,团聚体结合态有机碳显著减少,而且结合态和游离态脂类有机分子的多样性均显著降低,微生物来源有机碳对土壤有机碳的贡献更高。而稻田土壤有机碳和分子多样性均高于旱地及园地。因此,合理的土壤管理特别是有机物料的投入是提高农地土壤健康程度的重要途径。  相似文献   

17.
《Geoderma》2006,130(1-2):141-156
Sixteen Orthic Chernozemic surface soil samples, one half from virgin prairie and one half from adjacent cultivated prairie (cultivated for 31 to 94 years), were collected from eight sites throughout Southern Saskatchewan, Canada. Samples were analyzed for total organic C and a number of other chemical and physical properties. The virgin and cultivated soils at site No. 4 were selected for more detailed analysis by CP-MAS 13C NMR, Curie-point-pyrolysis-gas chromatography/mass spectrometry (Cp-Py-GC/MS), and by pyrolysis-field ionization mass spectrometry (Py-FIMS). Long-term cultivation resulted in large significant decreases in total SOM (soil organic matter), as represented by total soil organic C. There were significant increases in aromaticity of the SOM as a result of long-term cultivation as indicated by CP-MAS 13C NMR spectroscopy. This was mainly attributable to the result of cultivation-enhanced degradation of aliphatic C relative to aromatic C. Organic compounds identified in the Cp-Py-GC/MS spectra of the virgin and cultivated soils at site No. 4 consisted of n-alkanes (ranging from C11 to C22) and alkenes (ranging from C7:1 to C21:1), with the virgin soil being richer in alkenes than the cultivated soil. Other components identified were cyclic aromatics, carbocyclics, N-containing aromatics, N-heterocyclics, benzene and substituted benzenes, phenols and substituted phenols and substituted furans. The compounds identified appeared to originate from long-chain aliphatics, lignins, polyphenols, aromatics, polysaccharides, and N-containing compounds in the two soils. While qualitatively similar compounds were identified by Py-FIMS in the two soils, the total ion intensity (TII) of the virgin soil was almost 2.5 times as high as that of the cultivated soil. This suggests that cultivation made the organic matter less volatile, either by favouring the formation of higher molecular weight organic matter or by promoting the formation of non-volatile metal-organic matter complexes. The Py-FIMS spectra showed that the virgin soil contained relatively more lignin dimers, lipids, sterols, and n-C16 to n-C34 fatty acids than the cultivated soil. Thus, conversely, the cultivated soil was richer in carbohydrates, phenols and lignin monomers, alkyl aromatics and N-containing compounds, including peptides, than the virgin soil.  相似文献   

18.
Humic acids (HAs) from four soils were fractionated by size exclusion chromatography (SEC) on Sephadex G-75. Three fractions were obtained in all humic acids, collected and assayed by Polyacrylamide gel electrophoresis (PAGE). The unfractionated HA from each soil was used as reference. Each chromatographic fraction formed one electrophoretic zone corresponding closely to one band of the reference sample with some admixture of the fractions preceding or following. The results indicate that fractionation of HAs by tandem SEC-PAGE can be successfully used for obtaining fractions of reduced polydispersity and different electrophoretic mobilities. Pyrolysis/methylation-gas chromatography-mass spectrometry of the full size preparations of HA and fractions with exactly defined molecular size and electrophoretic mobility showed a different distribution in humic components, mainly lipids, lignin derivatives and N-containing compounds.  相似文献   

19.
Analysis of soil lipids may contribute to an improved understanding of atmosphere to soil carbon fluxes, soil organic matter source differentiation and pollutant accumulation. Soil lipids, mostly originating from plants and microorganisms, have traditionally been analysed by non‐automated extraction and separation methods, which produce several lipid fractions, operationally defined by polarity. Here we present a combination of fast, automated and reproducible techniques, adopted from organic geochemical studies, for preparative separation of individual soil lipid fractions with increasing polarity. These techniques involve commercially available instruments, including accelerated solvent extraction and a two‐step automated medium‐pressure liquid chromatography procedure. The method yields eight lipid fractions consisting of five fractions fully amenable to gas chromatography/mass spectrometry (GC/MS) (aliphatic hydrocarbons, aromatic hydrocarbons, ketones, alcohols, carboxylic acids), and three fractions of highly polar or high molecular weight compounds (bases, very long‐chain wax esters (C40+), high polarity compounds) that were not measurable with GC/MS under standard conditions. We tested the method on five agricultural soils. Results show that (i) mass recoveries for the individual fractions are reproducible, (ii) within individual fractions compound distribution patterns are reproducible, as demonstrated for alkanes and carboxylic acids, and (iii) individual fractions represent distinct and clean compound classes, free of interfering substances detectable by GC/MS. Thus, automated separation can be a fast, effective and reproducible procedure for fractionation of complex mixtures of soil lipids into clean compound classes, directly suitable for a variety of molecular (e.g. GC/MS) and isotopic characterizations (e.g. gas chromatography coupled with isotope ratio monitoring mass spectrometry or accelerator mass spectrometry).  相似文献   

20.
Rhizodeposition is an important pathway of atmospheric C-input to soil, however, quantity and quality of plant rhizodeposition are insufficiently known. Therefore, the composition and diurnal dynamics of water-soluble root-derived substances and products of their interaction with sandy soil were investigated in maize plants (Zea mays L.) by pyrolysis-field ionization mass spectrometry (Py-FIMS). In both night- and day-rhizodeposits the C, N and S concentrations were larger by factors ranging from 3.0 to 9.7 than the samples from non-cropped soil. The rhizodeposition was larger during the day than during the night-time and the composition of these deposits was different. The largest differences in the Py-FI mass spectra resulted from signals assigned to amino acids (aspartic acid, asparagine, glutamic acid, leucine, isoleucine, hydroxyproline and phenylalanine) and carbohydrates, in particular pentoses, which were exuded in the photosynthetic period. Marker signals in the Py-FI mass spectra and the curves of their thermal volatilization provided unequivocal evidence for the occurrence of free amino acids in the day-rhizodeposits. Other compounds detected in the Py-FI mass spectra were interpreted as constituents of rhizodeposits (lipids, suberin, fatty acids) or products of the interaction of rhizodeposits and microbial metabolites with stable soil organic matter (lignin dimers and alkylaromatics). It was concluded that the diurnal dynamics in the molecular-chemical composition between day- and night-rhizodeposits resulted from the exudation carbohydrates and amino acids during the photosynthetic period, the deposition of other root-derived compounds such as lipids, suberin and fatty acids, and the microbial metabolism of all available organic compounds in the rhizosphere. Furthermore, applications of the presented approach in C-turnover and phytoremediation research, and for risk assessment of genetically modified crops are proposed.  相似文献   

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