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1.

Purpose

The present study focuses on a compositional characterization of the humic acid (HA) fraction of several wetland soils using solid-state 13C NMR spectroscopy. The data were analysed using the molecular mixing model (MMM), based on an empirical approach by Nelson and Baldock. The compositional data from HAs obtained with this model were used to obtain a wider assessment of the process of humification from comparison of total soil wetland organic matter composition and HA composition.

Materials and methods

Twenty samples of humic acids (HAs) isolated from a Mediterranean semiarid wetland (‘Tablas de Daimiel’, central Spain) were studied using elemental analysis and cross polarization magic angle spinning (CPMAS)13C nuclear magnetic resonance (NMR) spectroscopy. The NMR data were analysed with the molecular mixing model (MMM) considering up to six generic components (carbohydrate, protein, lignin, lipid, char and ‘carbonyl’). HAs are considered a conceptual mixture of these model components, and the MMM determines the proportions of the characteristic biomolecules contributing to HA composition.

Results and discussion

The composition of the HAs under study depends on local factors such as site vegetation and occurrence of fire. Correlations between the proportions of the six generic components and further comparison with those determined for the unfractionated OM (whole sample, WS), gave information on HA origin and humification mechanisms. In particular, the proportions of char and carbohydrate (R 2 0.637) and contents of lignin and protein (R 2 0.471) in the HAs were negatively correlated (P < 0.05). Significant correlations (R 2 0.439) also existed for char contents in whole sample (WS) compared to HA, and for carbohydrates in WS compared to HA (R 2 0.558). Char proportion grew in HA with respect to the WS, and carbohydrates dropped to a half on average in HA compared to WS.

Conclusions

Two different humification mechanisms could be identified for no-fire and fire areas. In the former, HA-char was preserved selectively from char in the sample, whereas in the latter, char was newly formed by fire effect.
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2.
Humic acid (HA) plays an important role in the migration and transformation of uranium in natural waters. To effectively remove uranium in the presence of HA, a bifunctional polymer, diethylenetriaminepentaacetic acid cross-linked β-cyclodextrin (DTPA-β-CD), was synthesized by polycondensation reaction. The sorption performance of DTPA-β-CD in functions of pH, ionic strength, contact time, initial time, and temperature were explored batch wise. Experimental results showed that DTPA-β-CD could concurrently sorb uranium and HA around pH of 3.0. The sorption strongly depended on pH and on ionic strength, demonstrating outer-sphere surface complex in nature. Two sorption kinetics well followed pseudo-second-order model. Sorption isotherm accorded with Sips model. Increasing temperature facilitated uranium and restrained HA sorption. This work demonstrated that DTPA-β-CD was a promising material for sorbing uranium in the presence of HA.  相似文献   

3.
Color sensor technologies offer opportunities for affordable and rapid assessment of soil organic carbon (SOC) and total nitrogen (TN) in the field, but the applicability of these technologies may vary by soil type. The objective of this study was to use an inexpensive color sensor to develop SOC and TN prediction models for the Russian Chernozem (Haplic Chernozem) in the Kursk region of Russia. Twenty-one dried soil samples were analyzed using a Nix Pro? color sensor that is controlled through a mobile application and Bluetooth to collect CIEL*a*b* (darkness to lightness, green to red, and blue to yellow) color data. Eleven samples were randomly selected to be used to construct prediction models and the remaining ten samples were set aside for cross validation. The root mean squared error (RMSE) was calculated to determine each model’s prediction error. The data from the eleven soil samples were used to develop the natural log of SOC (lnSOC) and TN (lnTN) prediction models using depth, L*, a*, and b* for each sample as predictor variables in regression analyses. Resulting residual plots, root mean square errors (RMSE), mean squared prediction error (MSPE) and coefficients of determination (R2, adjusted R2) were used to assess model fit for each of the SOC and total N prediction models. Final models were fit using all soil samples, which included depth and color variables, for lnSOC (R2 = 0.987, Adj. R2 = 0.981, RMSE = 0.003, p-value < 0.001, MSPE = 0.182) and lnTN (R2 = 0.980 Adj. R2 = 0.972, RMSE = 0.004, p-value < 0.001, MSPE = 0.001). Additionally, final models were fit for all soil samples, which included only color variables, for lnSOC (R2 = 0.959 Adj. R2 = 0.949, RMSE = 0.007, p-value < 0.001, MSPE = 0.536) and lnTN (R2 = 0.912 Adj. R2 = 0.890, RMSE = 0.015, p-value < 0.001, MSPE = 0.001). The results suggest that soil color may be used for rapid assessment of SOC and TN in these agriculturally important soils.  相似文献   

4.
A new method of assessing the effective specific surface area based on the successive thermal desorption of water vapor at different temperature stages of sample drying is analyzed in comparison with the conventional static adsorption method using a representative set of soil samples of different genesis and degree of dispersion. The theory of the method uses the fundamental relationship between the thermodynamic water potential (Ψ) and the absolute temperature of drying (T): Ψ = Q ? aT, where Q is the specific heat of vaporization, and a is the physically based parameter related to the initial temperature and relative humidity of the air in the external thermodynamic reservoir (laboratory). From gravimetric data on the mass fraction of water (W) and the Ψ value, Polyanyi potential curves (W(Ψ)) for the studied samples are plotted. Water sorption isotherms are then calculated, from which the capacity of monolayer and the target effective specific surface area are determined using the BET theory. Comparative analysis shows that the new method well agrees with the conventional estimation of the degree of dispersion by the BET and Kutilek methods in a wide range of specific surface area values between 10 and 250 m2/g.  相似文献   

5.

Purpose

Combined pollution by polycyclic aromatic hydrocarbons (PAHs) and heavy metals are commonly found in industrial soils. This study aims to investigate the effect of the coexistence of heavy metals on the sorption of PAHs to soils. We focused specifically on the relationship of the sorption capacity with the estimation of the binding energy between PAHs and heavy metals.

Materials and methods

The sorption of typical PAHs (naphthalene, phenanthrene, and pyrene) to soils coexisting with heavy metals (Cu(II), Pb(II), and Cr(III)) was characterized in batch sorption experiments. The binding energy between PAHs and heavy metals in aqueous solution was estimated by quantum mechanical (QM) method using density functional theory (DFT) at the M06-2x/def2svp level of theory.

Results and discussion

Sorption capacity and nonlinearity of the PAHs to the soils were enhanced by the coexisting heavy metals. The extent of increment was positively associated with the hydrophobicity of the PAHs and the electronegativity and radius of the metal cations: Cr(III)?>?Pb(II)?>?Cu(II). The cation-π interaction was revealed as an important noncovalent binding force. There was a high correlation between the binding energies of the PAHs and K f ′ (K f adjusted after normalizing the equilibrium concentration (C e) by the aqueous solubility (C s)) (R 2?>?0.906), indicating the significant role of the cation-π interactions to the improved PAH sorption to soils.

Conclusions

In the presence of heavy metals, the sorption capacities of naphthalene, phenanthrene, and pyrene to soils were enhanced by 21.1–107 %. The improved sorption capacity was largely contributed from the potent interactions between PAHs and heavy metals.
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6.
Soil components from different environments (forest (OF), semiarid (SZ), and sand (AS)) were separated from fulvic and humic substances, characterized by DRX, EDS(SEM), and zero-charge points were determined. The sorption of U(VI) by these materials was determined considering contact time, concentration of U(VI), pH, ionic strength, and presence of sodium chloride and humic acids. The time to reach the kinetic sorption equilibrium was ca. 1 min for the components of the SZ and AS soils, whereas those from OF required longer times. The zero-charge points of the materials indicate that in the experimental conditions, the surfaces of the materials are positively charged, as are uranyl ions. The sorption kinetic data were well fitted to the pseudo-second-order model, which indicates chemical sorption. The maximum sorption capacities for U(VI) obtained from data fitted to the Langmuir model of OF and SZ were 49 and 19.8 mg g?1 respectively. Sorption isotherm data for AS were best fitted to the Freundlich model (qe?=?5.4 mg g?1). The maximum values of distribution coefficients (Kd) were 23?±?7 L kg?1, 545?±?64 L kg?1, and 1178?±?229 L kg?1 for AS, SZ, and OF, respectively; these values may depend on pH, contact time, initial concentration of U(VI), and the composition of the materials. Sodium chloride in the aqueous solutions affects U(VI) sorption by the materials SZ and AS. The effect of humic acids depends on pH, only in acid media soluble humate complexes may be formed.  相似文献   

7.
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8.
Environmental pollution with chromium is due to residues of several industrial processes. Bioremediation is an alternative actually considered to remove Cr (VI) from the environment, using adapted organisms that grow in contaminated places. Have been conducted studies with fungi mechanisms of interaction with chromium, most of which have focused on processes biosorption, characterized it by passive binding of metal components of the cell surface, and bioaccumulation, wherein the metal entry to cells occurs with energy expenditure. The paper presents the results of studies carried out on sorption of chromium (VI) ions from aqueous solutions by Fusarium sp. and Myrothecium sp. Both biomasses have the ability to take up hexavalent chromium during the stationary phase of growth and as well inactive conditions. Fusarium sp. showed 26% of biosorption with active biomass and 64% in inactive biomass; meanwhile, Myrothecium sp. obtained 97 and 82%, respectively. Both fungi showed adjust to pseudo-second-order model in active (Fusarium sp. R 2 = 0.99; Myrothecium sp. R 2 = 0.96) and inactive biomass assay (Fusarium sp. R 2 = 0.99; Myrothecium sp. R 2 = 0.99). The data of the active biomass test also confirmed to the intraparticle diffusion model (Fusarium sp. R 2 = 0.98; Myrothecium sp. R 2 = 0.93). The results obtained through this investigation indicate the possibility of treating waste effluents containing hexavalent chromium using Fusarium sp. and Myrothecium sp.  相似文献   

9.
The effect of humic acids (HAs) on physiological processes (photosynthesis, respiration, and abundance) of green microalga Chlorella vulgaris has been studied, and the relationships between the physiological activity of HAs and their structural parameters have been investigated. It has been found that the optimum range of HA concentrations for the growth of C. vulgaris is 0.01–0.03%. In this range, the highest positive effect on total photosynthesis increment is due to hydrophilic HA preparations from fallow soddypodzolic soil (Albic Retisol) and virgin gray soil (Luvic Greyzemic Phaeozem). The minimum stimulation of respiration is noted for all HA preparations in the region of the maximum photosynthesis stimulation. At concentrations above 0.003%, all HA preparations have a negative effect: the rate of photosynthesis in C. vulgaris cells decreases, and their respiration is strongly enhanced. The abundance of C. vulgaris under the effect of all of the studied preparations under illumination increases more rapidly than in the dark. A high positive coefficient of correlation is found between the hydrophilicity of HAs calculated from 13C NMR data and the photosynthesis rate in C. vulgaris.  相似文献   

10.

Purpose

Irrigation and fertilization can change soil environment, which thereby influence soil microbial metabolic activity (MMA). How to alleviate the adverse effects by taking judicious saline water irrigation and fertilization regimes is mainly concerned in this research.

Materials and methods

Here, we conducted a field orthogonal designed test under different saline water irrigation amount, water salinity, and nitrogen fertilizer application. The metabolic profiles of soil microbial communities were analyzed by using the Biolog method.

Results and discussion

The results demonstrated that irrigation amount and fertilizer application could significantly change MMA while irrigation water salinity had no significant effect on it. Medium irrigation amount (30 mm), least (50 kg ha?1) or medium (350 kg ha?1) N fertilizer application, and whatever irrigation water salinity could obtain the optimal MMA. Different utilization rates of carbohydrates, amino acids, carboxylic acids, and polymers by soil microbial communities caused the differences of the effects, and D-galactonic acid γ-lactone, L-arginine, L-asparagine, D-glucosaminic acid, Tween 80, L-threonine, and D-galacturonic acid were the indicator for distinguishing the effects.

Conclusions

The results presented here demonstrated that by regulating irrigation water amount and fertilizer application, the effects of irrigation salinity on MMA could be alleviated, which offered an efficient approach for guiding saline water irrigation.
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11.
The use of biochar (BC) has been suggested for remediation of contaminated soils. This study aims to investigate the role of microorganisms in sorption of PAH to BC-amended soils. Fungi, especially the wood and litter-degrading fungi, have shown the ability for humification and to degrade recalcitrant molecules, and are thus suitable model organisms. Haplic Arenosol with high organic matter content was chosen to highlight the importance of soil organic matter (SOM) in PAH sorption, possibly to form non-extractable residue. Basidiomycetous fungi Agrocybe praecox and Phanerochaete velutina grown on pine bark were inoculated in organic matter (OM)-rich Haplic Arenosol and OM-poor sandy loam with either BC or chemically activated BC (ABC) and 14C-labelled pyrene for 60 days. Fungi did not mineralize pyrene, but increased sorption up to 47–56% in BC-amended Haplic Arenosol in comparison with controls (13–25%) without a fungus irrespective of the presence of an adsorbent. In OM-poor sandy loam, only 9–12% of pyrene was sorbed to amended soil in the presence of fungus and adsorbent. The results suggest that BC and fungal amendment increased sorption of pyrene, especially to Haplic Arenosol more than by either BC or fungi alone.  相似文献   

12.
New methodological approaches and an algorithm for the quantitative assessment of accumulating a substance by a plant (C p ) with due regard for its concentration in the soil (C n ) are proposed. The first approach is the approximation of concentration curves by the functions C p = f(C n ) and their parameters. The second one is the standardization of the coefficients of biological sorption (K b ) of a substance upon its stable concentration in the soil using the function K b = f(C n ). As compared to the variation-statistical values of the mean and extreme concentrations, or the coefficients K b , the proposed parameters are characterized by a higher accuracy and sensitivity. They may be successfully used for quantitative studies of the mechanism and the intensity of the absorption of substances by plants, for the prediction of the accumulation of substances in the trophic chain, and the assessment of soil self-purification (detoxification) and comparative ratings.  相似文献   

13.
The adsorption of copper (Cu(II)) from aqueous solutions by activated Luffa cylindrica biochar fibres has been investigated by means of batch equilibrium experiments and FTIR spectroscopy. The effect of various physicochemical parameters, such as pH, initial metal concentration, ionic strength, mass of the adsorbent, contact time and temperature, has been evaluated by means of batch type adsorption experiments. FTIR spectroscopy, as well as acid-base titrations, was used for the characterization of the material and the surface species formed. According to the experimental results even at pH 3, the relative sorption is above 85% and the adsorption capacity of the activated biochar fibres for Cu(II) is q max = 248 g kg?1. Moreover, the interaction between the surface carboxylic moieties and Cu(II) results in the formation of very stable inner-sphere complexes (?G o = ?11.2 kJ mol?1 at pH 3 and ?22.4 kJ mol?1 at pH 5.5).  相似文献   

14.

Purpose

Soil organic carbon (SOC) and its labile fractions are strong determinants of physical, chemical and biological properties. The objective of the present work was to evaluate the effects of organic amendments (technosol made of wastes and biochar) and Brassica juncea L. on the soil C fractions in a reclaimed mine soil.

Materials and methods

The studied soil was from a former copper mine that was subsequently partially reclaimed with vegetation and wastes. A greenhouse experiment was carried out to amend the mine soil with different proportions of technosol and biochar mixture and planting B. juncea. B. juncea plants can tolerate high levels of metals and can produce a large amount of biomass in relatively short periods of time.

Results and discussion

The results showed that with the addition of biochar and wastes, soil pH increased from 2.7 to 6.18, SOC from undetectable to 105 g kg?1 and soil total nitrogen (TN) from undetectable to 11.4 g kg?1. Amending with wastes and biochar also increased dissolved organic carbon (DOC) from undetectable to 5.82 g kg?1, carbon in the free organic matter (FOM) from undetectable to 30.42 g kg?1, FAP (carbon in fulvic acids removed with phosphoric acid) from undetectable to 24.14 g kg?1 and also increased the humification ratio, the humification index, the polymerisation rate and the organic carbon in the humified fractions (humic acids, fulvic acids and humin). Soils amended and vegetated with B. juncea showed lower FOM values and higher humification index values than the soils amended only with biochar and wastes.

Conclusions

This study concludes that the combined addition of wastes and biochar has a greater potential for both increasing and improving organic carbon fractions in mine soils. The authors recommend the application of biochar and technosol made of wastes as a soil amendment combined with B. juncea on soils that are deficient in organic matter, since they increased all of the SOC fractions in the studied copper mine soil.
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15.
DNA sequences of nuclear gene Got2 was studied in 60 accessions of Aegilops tauschii, 29 of subsp. tauschii and 31 of subsp. strangulata. It was found that Got2 allozyme polymorphism in Ae. tauschii is due to a single, unique, mutation which led to replacement of glutamic acid by isoleucine in residue 256 of the enzyme molecule, encoded by Got2. As revealed by Got2 DNA sequences variation, initially in its history Ae. tauschii was presented by subsp. strangulata, and among phylogenetic lineages of subsp. strangulata, the lineage “t-91s” (TauL3) is the most ancient, a relict one. Subspecies tauschii is relatively “young”. Initially it was presented by the lineage marked by combination of allozyme alleles Got2 105 and Acph1 100. In the past it inhabited the Continental area from Caucasia to Pakistan, but later on it was forced out by newly originated, now—a major lineage of subsp. tauschii, marked by Got2 100. This lineage extended the Continental area of the species up to Kirgizstan, but actually failed to penetrate into pre-Caspian area, occupied by subsp. strangulata. These results essentially differ from those obtained previously, using chloroplast DNA (cpDNA) sequences polymorphism. As revealed by cpDNA, the major, “usual”, subsp. strangulata (TauL2) is “younger” than subsp. tauschii, which resided on phylogenetic tree between relict lineage “t-91s”of subsp. strangulata—and major subsp. strangulata. But both cpDNA and Got2 DNA sequences indicate that the level of genetic variation in subsp. tauschii is much lower than in subsp. strangulata. According to Got2 DNA sequences variation, it was Ae. tauschii subsp. strangulata lineage “k-109″ which donated genome D to Triticum aestivum L. This lineage includes accessions: k-109 from South-Eastern Precaspian Azerbaijan; KU-2105, KU-2159 from Western Precaspian Iran; KU-2080 from Eastern Precaspian Iran.  相似文献   

16.
Fertilization is an important factor influencing the chemical structure of soil organic carbon (SOC) and soil microbial communities; however, whether any connection exists between the two under different fertilization regimes remains unclear. Soils from a 27-year field experiment were used to explore potential associations between SOC functional groups and specific bacterial taxa, using quantitative multiple cross-polarization magic-angle spinning 13C nuclear magnetic resonance and 16S rRNA gene sequencing. Treatments included balanced fertilization with organic materials (OM) and with nitrogen (N), phosphorus (P), and potassium (K) mineral fertilizers (NPK); unbalanced fertilization without one of the major elements (NP, PK, or NK); and an unamended control. These treatments were divided into four distinct groups, namely OM, NPK, NP plus PK, and NK plus control, according to their bacterial community composition and SOC chemical structure. Soil total P, available P, and SOC contents were the major determinants of bacterial community composition after long-term fertilization. Compared to NPK, the OM treatment generated a higher aromatic C–O and OCH3 and lower alkyl C and OCH abundance, which were associated with the enhanced abundance of members of the Acidobacteria subgroups 6 and 5, Cytophagaceae, Chitinophagaceae, and Bacillus sp.; NP plus PK treatments resulted in a higher OCH and lower aromatic C–C abundance, which showed a close association with the enrichment of unclassified Chloracidobacteria, Syntrophobacteraceae, and Anaerolineae and depletion of Bacillales; and NK plus control treatments resulted in a higher abundance of aromatic C–C, which was associated with the enhanced abundance of Bacillales. Our results indicate that different fertilization regimes changed the SOC chemical structure and bacterial community composition in different patterns. The results also suggest that fertilization-induced variations in SOC chemical structure were strongly associated with shifts in specific microbial taxa which, in turn, may be affected by changes in soil properties.  相似文献   

17.
Aromatic rice (Oryza sativa L.) cultivated in Japan is regionally differentiated by geographical distribution and characteristics. We aimed to characterize the lineage of Japanese aromatic rice using DNA markers. Based on analyses with nuclear SSR markers, we found that Japanese aromatic rice cultivars belong, with one exception, to japonica but showed some differences from authentic japonica and were divided into two clades that were distributed in western and eastern Japan, respectively. Further analyses with organelle markers showed that most of the cultivars in eastern Japan had cytoplasm characterized by tropical japonica, whereas most of those in western Japan had cytoplasm characterized by temperate japonica. We postulate that the ancestor of the cultivars in eastern Japan differs from those of the cultivars in western Japan, and that the two groups may have been separately introduced from Taiwan into Japan. The cytoplasm of aromatic rice cultivars in western Japan may have originated from tropical japonica and been substituted into the cytoplasm of temperate japonica through hybridization between tropical japonica as a male parent and temperate japonica as a female parent.  相似文献   

18.

Purpose

The dynamics and uncertainties in wetland methane budgets affected by the introduction of Alnus trabeculosa H. necessitate research on production of methane by methanogenic archaea and consumption by methane-oxidizing microorganisms simultaneously.

Materials and methods

This study investigated methane emission in situ by the closed chamber method, and methanogenic and methanotrophic communities using denatured gradient gel electrophoresis (DGGE) and quantitative PCR based on mcrA (methyl coenzyme M reductase), pmoA (particulate methane monooxygenase) genes in the rhizosphere and non-rhizosphere soils in the indigenous pure Phragmites australis T., and A. trabeculosa–P. australis mixed communities in Chongxi wetland.

Results and discussion

Methane flux rate from the pure P. australis community was 2.4 times larger than that of A. trabeculosa–P. australis mixed community in the rhizosphere and 1.7 times larger in the non-rhizosphere, respectively. The abundance of methanogens was lower in the mixed community soils (3.56?×?103–6.90?×?103 copies g?1 dry soil) compared with the P. australis community (1.47?×?104–1.89?×?104 copies g?1 dry soil), whereas the methanotrophs showed an opposite trend (2.08?×?106–1.39?×?106 copies g?1 dry soil for P. australis and 6.20?×?106–1.99?×?106 copies g?1 dry soil for mixed community soil). A liner relationship between methane emission rates against pmoA/mcrA ratios (R 2?=?0.5818, p?<?0.05, n?=?15) was observed. The community structures of the methane-cycling microorganism based on mcrA and pmoA suggested that acetoclastic methanogens belonging to Methanosarcinaceae and a particular type II methanotroph, Methylocystis, were dominant in these two plant communities.

Conclusions

The introduction of A. trabeculosa would promote the proliferation of methanotrophs, especially the dominant Methylocystis, but not methanogens, ultimately diminishing methane emission in the wetland.
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19.
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20.
Low molecular weight carbohydrates of seeds of 10 species of Vicia, namely: V. angustifolia, V. articulata, V. cordata, V. ervilia, V. johannis, V. macrocarpa, V. monantha, V. narbonensis, V. pannonica and V. sativa were analyzed by the high resolution gas chromatography method. Seeds of the investigated species contain common (glucose, fructose, myo-inositol, sucrose, galactinol, di-galactosyl myo-inositol and raffinose family oligosaccharides—RFOs) and species-specific carbohydrates (d-pinitol and its α-d-galactosides—in V. articulata, V. monantha and V. pannonica or d-ononitol and its galactoside—in V. ervilia). Among the species containing in seeds RFOs as the main α-d-galactosides (V. angustifolia, V. cordata, V. johanensis, V. macrocarpa, V. narbonensis and V. sativa), an additional subgroup can be separated, which contains a set of unknown compounds (found in V. angustifolia, V. cordata and V. macrocarpa). Moreover, several other unidentified carbohydrate-containing compounds were detected exclusively in seeds of V. ervilia. The concentrations of total soluble carbohydrates (TSCs), including sugars, RFOs, cyclitols and galactosyl cyclitols and unknown compounds, in seeds differ significantly (P < 0.05) among the species. RFOs and sucrose are the main fractions in TSCs, with the exception of V. pannonica seeds, containing more galactosyl pinitols, and V. ervilia, in which unknown compounds account for 50% of TSCs. In V. ervilia RFOs occur at the lowest concentration (9.32 mg g?1 seeds), and the concentration of DGMI (di-galactosyl myo-inositol) is comparable with that of RFOs, which is unusual among all the investigated Vicia species.  相似文献   

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