Biodegradation of chlorinated phenols in subsurface soils

Microcosm studies were employed to determine the subsurface biodegradation rates of phenol, 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP), and pentachlorophenol (PCP). Soil samples were taken from sites in Pennsylvania and Virginia from depths up to 31 m, and all samples contained significant microbial populations. Soil from both sites readily biodegraded all five compounds. Biodegradation rates increased as initial concentrations increased, and all biodegradation rates appeared to follow first-order kinetics with regard to the initial compound concentrations. Biodegradation rates for the five compounds followed the order: phenol = 2-CP > 2,4,6-TCP > 2,4-DCP. PCP was degraded more slowly than phenol or 2-CP, but similarly to 2,4,6-TCP and 2,4-DCP. Different soils exhibited different degradation rates, and the soil characteristics that may influence the rates are discussed. The data suggest that biological degradation is a significant attenuation mechanism for phenol and its chlorinated derivatives in subsurfaces saturated and unsaturated zones.     

Enzymatic Treatment of Soils Contaminated with Phenol and Chlorophenols Using Soybean Seed Hulls

This study presents the application of soybean seed hulls for the decontamination and/or detoxification of phenol and chlorophenol polluted soils. The effect of soil was examined on both catalytic activity of soybean seed hull peroxidase (SBP) and enzymatic transformation of phenol, 2-chlorophenol, and 2,4-dichlorophenol through the polymerization reaction. The sorption of the enzyme to soil organic matter was found to account for the loss of partial catalytic activity of soybean seed hulls in a soil slurry environment. The organic matter present in loamy soils, rather than other soluble soil constituents and soil micro-organisms, is a factor in SBP inhibition by soil and the corresponding decline in treatment efficiency of phenol and chlorophenols. Under improved conditions, however, soybean seed hulls demonstrated a satisfactory ability to catalyze the polymerization reaction. Over 96% of total phenols were removed using soybean seed hulls in a soil slurry bioreactor, which demonstrates a great potential in use of soybean seed hulls, a readily available and inexpensive source of SBP, for bioremediation of soils contaminated with phenolic compounds.     

Fate of 14C-ring-labeled 2,4-D, 2,4-dichlorophenol and 4-chlorophenol during straw composting

Experiments were carried out to study the transformation of ¹⁴C-ring-labeled 2,4-D and the two related chlorophenols 4-chlorophenol (4-CP) and 2,4-dichlorophenol (4-DCP) during straw composting under controlled laboratory conditions. Incubation under sterile and nonsterile conditions was done to evaluate the relative importance of the biotic and abiotic processes. Pre-composted straw was treated with the three chemicals. The availability of the different chemicals was monitored during incubations as well as their degradation. Under nonsterile conditions, the mineralization of both chlorophenols reached 20% of the applied compounds, whereas it was 52% for 2,4-D. Transitory water-soluble metabolites of 2,4-D and chlorophenols were formed but they disappeared rapidly. After 21 days, 21% of the 2,4-D and 38% of the 2,4-DCP was stabilized as nonextractable (bound) residues under nonsterile conditions. Bound residues of both chemicals were negligible under sterile conditions. Availability of chemicals as estimated by water extraction decreased during incubation proportionally to mineralization and to the formation of bound residues. The increase in immobilization of the chemical residues was stronger under nonsterile conditions than under sterile conditions. Under nonsterile conditions 71% of the 4-CP was recovered as bound residues, whereas under sterile conditions 30% of the applied 4-CP formed bound residues after formaldehyde addition and only 8% with autoclaved straw. Global microbial activity decreased in the presence of the chlorophenols probably due to their toxic effect. These data indicate that the biological activity associated with straw transformation during composting stimulates the depletion of 2,4-D and chlorophenols by mineralization and by formation of bound residues. Received: 6 September 1996     

Oxidation of Chlorophenols in Aqueous Solution by Excess Potassium Permanganate

A simple spectrophotometric method was developed to quantify chlorophenol (CP) concentrations after reaction with potassium permanganate and quenching with sodium sulfite. Other quenching agents (peroxide, sodium thiosulfate and hydroxylamine hydrochloride) were found to create absorbance in the spectral range required for CP quantification. Analysis at pH 12 gave greater absorption and sensitivity for the method compared with pH 5.6. The calibration curves of the proposed methods were linear in the concentration ranges 0.0061–0.61 and 0.0078–0.78 mM with detection limit of 0.0006 and 0.0008 mM for dichlorophenols and monochlorophenols, respectively. The oxidation kinetics of five chlorophenols in aqueous solution with excess potassium permanganate were evaluated using the analytical method. The pseudo-first-order reaction rates were found to be relatively rapid 1.42 × 10⁻³ to 0.024 s⁻¹ and followed the sequence 2-chlorophenol (2-CP) > 2,6-dichlorophenol (2,6-DCP) > 4-chlorophenol (4-CP) > 2,4-dichlorophenol (2, 4-DCP) > 3-chlorophenol (3-CP). The apparent second-order rate constant was calculated from the measured pseudo-first-order rate constant with respect to CP with initial KMnO₄ concentration (1.5 mM) and follows the same sequence of pseudo-first-order rate constant. This shows that chlorine atoms in the structure of chlorophenol had a significant influence on the oxidation of chlorophenols by potassium permanganate. Permanganate can be used for the treatment of chlorophenol-contaminated soil and groundwater.     

Sonochemical Degradation of Chlorinated Phenolic Compounds in Water: Effects of Physicochemical Properties of the Compounds on Degradation

This study examined a comparative degradation of various chlorinated phenolic compounds including phenol, 4-chlorophenol (4-CP), 2,6-dichlorophenol (2,6-DCP), 2,4,6-trichlorophenol (2,4,6-TCP), 2,3,4,6-tetrachlorophenol (2,3,4,6-TeCP), and pentachlorophenol (PCP) using 28, 580, and 1,000 kHz ultrasonic reactors. The concentration of hydrogen peroxide was also determined in order to investigate the efficacy of different sonochemical reactors for hydroxyl radical production. Clearly, it was observed that the 580 kHz sonochemical reactor had maximum efficacy for hydroxyl radical production. The degradation of all the compounds followed the order; 580 kHz (91?C93%) > 1,000 kHz (84?C86%) > 28 kHz (17?C34%) with an initial concentration of 2.5 mg L^?1 at a reaction time of 40 min with ultrasonic power of 200 ± 3 W and aqueous temperature of 20 ± 1°C in each experiment. Overall, the degradation of those phenolic compounds followed the order, PCP > 2,3,4,6-TeCP > 2,4,6-TCP > 2,6-DCP > 4-CP > phenol at various frequencies in the presence/absence of a radical scavenger (tert-butyl alcohol). It was revealed that the correlations between the compound degradation rates and the physicochemical parameters, R ² = 0.99 for octanol?Cwater partition coefficient, R ² = 0.95 for water solubility, R ² = 0.94 for vapor pressure, and R ² = 0.88 for Henry??s law constant, excluding PCP, were very good in the entire range of each parameter.     

Enhanced Phenol and Chlorinated Phenols Removal by Combining Ozonation and Biodegradation

Water treatment for wastewater containing phenols and their chlorinated variations has attracted important research efforts. Phenol??s high toxicity makes them a good model to test possible water treatment based on biological and/or chemical methods. High concentrations of phenols may be treated by pure biological schemes. However, chlorinated phenols are very toxic for many microorganisms. Therefore, mixed treatment trains can be proposed to solve the treatment of this class of organics. In this study, the ozonation was used as pretreatment to decompose chlorinated phenols. Besides, this study describes how the microbial consortiums were adapted to handle ozonation by-products. The biodegradation of different phenol concentrations from 50 to 1,500?mg/L was evaluated using preadapted microbial consortia in batch and in a trickling packed-bed reactor (TPBR). Under batch conditions, phenol was efficiently removed up to 500?mg/L. For every phenol concentration evaluated, higher degradation rates were obtained in TPBR. The chlorophenols were found to be poorly degraded by the pure biological treatment, 4-CPh was not degraded during the biological process and 2,4-DCPh was only 40?% degraded after 250?h of culture. By combining the chemical (as pretreatment) and the biological processes, 85?% of 4-CPh was removed, while the degradation of the 2,4-DCPh was enhanced from 40 to 87?%. The predominant bacteria found in the preadapted cultures were Xanthomonas sp., Ancylobacter sp., and Rhodopseudomonas. Total treatment period was reduced from several weeks to some days. This information reflects the benefits offered by the mixed water treatment train proposed in this paper.     

Structural Influence on Photooxidative Degradation of Halogenated Phenols

The influence of structure on degradation of five halogenated phenols (XPs) by UV/H₂O₂ process was investigated. The combined influence of type or number of substituents and UV/H₂O₂ process parameters (pH and [H₂O₂]) on the degradation kinetics of 2-fluorophenol (2-FP), 2-chlorophenol (2-CP), 2-bromophenol (2-BP), 2,4-dichlorophenol (2,4-DCP), and 2,4,6-trichlorophenol (2,4,6-TCP) was studied using modified miscellaneous 3³ full factorial design and response surface modeling (RSM). Studied XPs obey first-order degradation kinetics within the investigated range of process parameters. Determined degradation rate constants (k _obs) were correlated with process and structural parameters by the quadratic polynomial models. Analysis of variance (ANOVA) demonstrated RSM models’ accuracy and showed that, in addition to pH and [H₂O₂], model terms related with the pollutant structure are highly influential. k _obs of mono-XPs follow the decreasing order 2-FP, 2-CP, and 2-BP, while CPs follow the decreasing order 2-CP, 2,4-DCP, and 2,4,6-TCP. Biodegradability (biochemical oxygen demand (BOD)₅/chemical oxygen demand (COD)) and toxicity (TU) were evaluated prior to the treatment and at the reference time intervals. The observed differences are correlated with the structural characteristics of studied XPs.     

Atrazine and metolachlor degradation in subsoils

Degradation of atrazine [2-chloro-4-etylamino-6-isopropylamino-1,3,5-triazine] and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)-acetamide] in sterile and non-sterile soil samples collected at two different soil depths (0-20 and 80-110 cm) and incubated under aerobic and anaerobic conditions was studied. Under aerobic conditions, the half-life of atrazine in non-sterile surface soil was 49 days. In non-sterile subsoil, the half-life of atrazine (119 days) was increased by 2.5 times compared in surface soils and was not statistically different from half-lives in sterile soils (115 and 110 days in surface soil and subsoil, respectively). Metolachlor degradation occurred only in non-sterile surface soil, with a half-life of 37 days. Under anaerobic conditions, atrazine degradation was markedly slower than under aerobic conditions, with a half-life of 124 and 407 days in non-sterile surface soil and non-sterile subsoil, respectively. No significant difference was found in atrazine degradation in both sterile surface soil (693 days) and subsoil (770 days). Under anaerobic conditions, degradation of metolachlor was observed only in non-sterile surface soil. Results suggest that atrazine degraded both chemically and biologically, while metolachlor degraded only biologically. In addition, observed Eh values of soil samples incubated under anaerobic conditions suggest a significant involvement of soil microorganisms in the overall degradation process of atrazine under anaerobic conditions.     

Metabolic fate of [14C] chlorophenols in radish (Raphanus sativus), lettuce (Lactuca sativa), and spinach (Spinacia oleracea)

Chlorophenols are potentially harmful pollutants that are found in numerous natural and agricultural systems. Plants are a sink for xenobiotics, which occur either intentionally or not, as they are unable to eliminate them although they generally metabolize them into less toxic compounds. The metabolic fate of [ (14)C] 4-chlorophenol (4-CP), [ (14)C] 2,4-dichlorophenol (2,4-DCP), and [ (14)C] 2,4,5-trichlorophenol (2,4,5-TCP) was investigated in lettuce, spinach, and radish to locate putative toxic metabolites that could become bioavailable to food chains. Radish plants were grown on sand for four weeks before roots were dipped in a solution of radiolabeled chlorophenol. The leaves of six-week old lettuce and spinach were treated. Three weeks after treatments, metabolites from edible plant parts were extracted and analyzed by high performance liquid chromatography (HPLC) and characterized by mass spectrometry (MS), and nuclear magnetic resonance spectroscopy (NMR). Characterization of compounds highlighted the presence of complex glycosides. Upon hydrolysis in the digestive tract of animals or humans, these conjugates could return to the toxic parent compound, and this should be kept in mind for registration studies.     

Soil Retention Capacity of Phenols from Biologically Pre-Treated Kraft Mill Wastewater

Allophanic soil, natural and activated by acidification or calcination was used to adsorb organic recalcitrant compounds (lignin and chlorophenols) from biologically pre-treated kraft mill effluent. A synthetic non crystalline aluminosilicate like allophane coated with iron oxide (Al-Si-Fe) was used as control for comparison purposes. It was observed that the adsorption capacity of the allophanic soil increased at higher solid/solution ratio, and at lower pH values. The highest total phenolic compounds removal was obtained between pH 4.0 and 4.5 for natural and activated soil using a solid/solution ratio of 1:5, and for synthetic aluminosilicate using 300 mg in 30 mL of effluent solution. Soil activated by calcination procedure presented the highest total phenolic compounds adsorption capacity (71–85%) for untreated and aerobic or anaerobic pre-treated effluent. The specific chlorophenols analysis indicated that pentachlorophenol (PCP) was almost completely adsorbed onto the allophanic soil (> 99%), and that over 79% of the 2,3,4,6-tetrachlorophenol (TeCP) was adsorbed, independent of the biological pre-treatment type and the soil activation procedure. On the other hand, 2,4-dichlorophenol (DCP) coming from both aerobic and anaerobic treated effluent was poorly removed (24–30%) when natural soil was used for adsorption; whereas in calcinated and acidified soil DCP removal was more than 71%.     

Microbial Degradation of Fipronil in Clay Loam Soil

Fipronil, (±)-5-amino-1-(2,6-dichloro-∝,∝,∝-trifluoro-p-tolyl)-4-trifluoromethysulfinylpyrazole-3-carbonitrile, is used as an effective insecticide for the control of rice pests in China. Although many studies examining the fate of fipronil in the soilenvironment have been conducted, there are no studies on the microbial degradation of fipronil in the soil environment. Fipronil was degradedby microorganisms in the non-sterile clay loam soil, which resulted in the formation of metabolite, MB45950. The degradation of fipronil in non-sterile clay loam soil was mainly influenced by the soil microbes. The half-lives in non-sterile clay loam soil were 9.72 and 8.78 d at 25 and 35 °C, respectively compared to 33.51 and 32.07 d at 25 and 35 °C, respectively in the sterile soil. The microbial viability test showed that non-sterile clay loam soil had viable microorganisms throughout the experiment. Fipronil did not adversely affect the microbes once soil microbes adapted to the presence of fipronil in the clay loam soil.     

Multi-Step Competitive Sorption and Desorption of Chlorophenols in Surfactant Modified Montmorillonite

Single- and bi-solute sorption and desorption of 2,4-dichlorophenol (2,4-DCP) and 2,4,5-trichlorophenol (2,4,5-TCP) in montmorillonite modified with hexadecyltrimethylammonium (HDTMA) were investigated using multi-step sorption and desorption procedure. Effect of pH on the multi-step sorption and desorption was investigated. As expected by the magnitude of octanol-water partition coefficient, K _ow , both sorption and desorption affinity of 2,4,5-TCP was higher than that of 2,4-DCP at pH 4.85 and 9.15. For both chlorophenols, the protonated speciation (at pH 4.85) exhibited a higher affinity in both sorption and desorption than the predominant deprotonated speciation (about 95% and 99% of 2,4-dichlorophenolate and 2,4,5-trichlophenolate anions at pH 9.15, respectively). Desorption of chlorinated phenols was strongly dependent on the current pH regardless of their speciation in the previous sorption stage. Freundlich model was used to analyze the single-solute sorption and desorption data. No appreciable desorption-resistant (or non-desorbing) fraction was observed in organoclays after several multi-step desorptions. This indicates that sorption of phenols in organoclay mainly occurs via partitioning into the core of the pseudo-organic medium, thereby causing desorption nearly reversible. In bisolute competitive systems, sorption (or desorption) affinity of both chlorophenols was reduced compared to that in its single-solute system due to the competition between the solutes. The ideal adsorbed solution theory (IAST) coupled to the single-solute Freundlich model successfully predicted bisolute multi-step competitive sorption and desorption equilibria.     

Photocatalytic Degradation of Chlorophenol Compounds using Poly Aromatic Star Copolymer

This study investigated the encapsulation and photocatalysis of chlorophenol compounds in water using porphyrin-(polystyrene-b-2-dimethylaminoethyl acrylate) star polymer. The chloride ions generated during photocatalytic process were identified and quantified. 2,4,6-Trichlorophenol, pentachlorophenol, and 2,4-dichlorophenol were satisfactorily decomposed in the photoreactor using porphyrin-(polystyrene-b-2-dimethylaminoethyl acrylate) star polymer, with removal efficiencies of 2,454, 498, and 760 mg/g of porphyrin-(polystyrene-b-2-dimethylaminoethyl acrylate) star polymer. The half-life times reached around 30 min, with the exception of that for 2,4-dichlorophenol. The star polymer-impregnated porphyrin is a promising photocatalyst for the removal of chlorophenols.     

Effects of soil temperature and anaerobiosis on degradation of biodegradable plastics in soil and their degrading microorganisms

The bioplastic PHB/HV (copolymer of 3-hydroxybutyrate and 3-hydroxyvalerate) underwent a faster degradation at 30°C than at 52°C in soil under aerobic conditions, while there was no remarkable difference between 30°C and 52°C in the degradation rate of PCL [poly(ε-caprolactone)], PBSA (polybutylene succinate and agipate), and PBS (polybutylene succinate). PHB showed the fastest degree of degradation among the four plastics at 30°C and PBSA the fastest at 52°C. Degradation of all the four plastics was nor observed both at 30°C and 52°C under anaerobic conditions for 50 d. Microorganisms on the degrading plastics appeared to be diverse at 30"C, including bacteria and fungi. However, among the several to ca. 10 kinds of bacterial and fungal strains isolated from the degradation sites of each plastic at 30°C, only one or two fungal strains were able to degrade the respective plastics in vitro. The degraders were identified as Mucor sp. (PHB), Paecilomyces sp. (PCL), Aspergillus sp. (PBSA), and Cunninghamella sp. (PBSA). In contrast, only a single type of fungus was observed at the degradation sites of PCL and PBSA at 52°C. The fungus isolated from PCL and PBSA was identified as Thermomyces sp. This study demonstrated that soil temperature and anaerobiosis exerted significant effects on the degradation of the plastics, and that fungi were mainly responsible for the degradation of the plastics in soil.     

Phenoxy herbicide degradation in soils: Quantitative studies of 2,4-D- and MCPA-degrading microbial populations

Microbial populations able to degrade 2,4-D (2,4-dichlorophenoxyacetate) and MCPA (4-chloro-2-methylphenoxyacetate) were enumerated by means of a most probable number (MPN) procedure in eight Natal soils not previously treated with these herbicides. Estimated 2,4-D-degrading populations ranged from 1.26 to 245.2 and MCPA-degrading populations from 0.34 to 1377 g^?1 dry soil; in seven of the soils the populations of these organisms were less than 40 and 30 g^?1, respectively. Such counts indicate that for the successful isolation of 2,4-D- or MCPA-degrading microorganisms from soil, at least 1 g dry weight of soil should be used for enrichment cultures. The 2,4-D-degrading organisms occurred among the aerobic soil bacteria detectable by plate count, at frequencies of only 1 in 30 × 10³ to 1 in 36 × 10⁶ and the MCPA-degrading organisms at frequencies of 1 in 5 × 10³ to 1 in 133 × 10⁶; the ease with which the herbicide-degrading organisms can be isolated from enriched soil cultures treated with 2,4-D or MCPA is evidence of their massive preferential proliferation in response to the herbicides.Log 2,4-D- and MCPA-degrading populations did not differ significantly in four soil samples, but in the others either the 2,4-D- or the MCPA-degrading population was dominant. The longer persistence of MCPA compared with that of 2,4-D could therefore not be ascribed to quantitative differences in the populations of MCPA- and 2,4-D-degrading soil microorganisms.No relationship was evident between the soil populations of 2,4-D- or MCPA-degrading microorganisms and aerobic soil bacteria, and variations of the three populations among the soil samples were not associated in any obvious way with the soil physical and chemical characteristics, except perhaps an association of the highest counts of herbicide-degrading organisms with a sugar cane soil of sandy texture and high C: N ratio.     

Optimization of <Emphasis Type="Italic">o</Emphasis>-Chlorophenol Biodegradation by Combined Mycelial Pellets Using Response Surface Methodology

In the present study, the immobilizing fermentation characteristics and o-chlorophenol biodegradation of Rhodopseudomonas palustris using mycelial pellets as a biomass carrier were investigated. To improve the o-chlorophenol degradation efficiency of the combined mycelial pellets, eight cultivation variables including glucose concentration, yeast extract concentration, spore inoculum size, pH, and agitation speed were optimized with an integrated strategy involving a combination of statistical designs. First, Plackett-Burman experiments identified glucose, yeast extract, and spore inoculum size as three statistically significant factors important for o-chlorophenol removal. Then, the steepest ascent method was used to access the optimal region of these significant factors. Finally, response surface methodology by Box-Behnken optimization was used to examine the mutual interactions among these three variables to determine their optimal levels. The ideal culture conditions for maximum o-chlorophenol removal according to a second-order polynomial model were as follows: 15.60 g/L glucose, 3.09 g/L yeast extract, and 9% (v/v) spore inoculum size, resulting in an expected o-chlorophenol removal rate of 92.60% with an o-chlorophenol initial concentration of 50 mg/L and 96-h culture time. The correlation coefficient (R ² = 0.9933) indicated excellent agreement between the experimental and predicted values, whereas a fair association was observed between the predicted model values and those obtained from subsequent experimentation at the optimized conditions.     

The millimetre-scale distribution of 2,4-D and its degraders drives the fate of 2,4-D at the soil core scale

The biodegradation of organic compounds in soil is a key process that has major implications for different ecosystem services such as soil fertility, air and water quality, and climate regulation. Due to the complexity of soil, the distributions of organic compounds and microorganisms are heterogeneous on sub-cm scales, and biodegradation is therefore partly controlled by the respective localizations of organic substrates and degraders. If they are not co-localized, transfer processes become crucial for the accessibility and availability of the substrate to degraders. This spatial interaction is still poorly understood, leading to poor predictions of organic compound dynamics in soils. The objectives of this work were to better understand how the mm-scale distribution of a model pesticide, 2,4-dichlorophenoxyacetic acid (2,4-D), and its degraders drives the fate of 2,4-D at the cm soil core scale. We constructed cm-scale soil cores combining sterilized and “natural” soil aggregates in which we controlled the initial distributions of 2,4-D and soil microorganisms with the following spatial distributions: i) a homogeneous distribution of microorganisms and 2,4-D at the core-scale, ii) a co-localized distribution of microorganisms and 2,4-D in a single spot (360 mm³) and iii) a disjoint localization of microorganisms and 2,4-D in 2 soil spots (360 mm³) separated by 2 cm. Two sets of experiments were performed: one used radiolabeled ¹⁴C-2,4-D to study the fate of 2,4-D, and the other used ¹²C-2,4-D to follow the dynamics of degraders. Microcosms were incubated at 20 °C and at field capacity (−31.6 kPa). At the core scale, we followed 2,4-D mineralization over time. On three dates, soil cores with microorganisms and 2,4-D localized in soil spots, were cut out in slices and then in 360 mm³ soil cubes. The individual soil cubes were then independently analysed for extractable and non-extractable ¹⁴C and for degraders (quantitative PCR of tfdA genes). Knowing the initial position of each soil cube allowed us to establish 3D maps of 2,4-D residues and degraders in soil. The results indicated that microorganisms and pesticide localizations in soil are major driving factors of i) pesticide biodegradation, by regulating the accessibility of 2,4-D to degrading microorganisms (by diffusion); and ii) the formation of non-extractable residues (NER). These results also emphasized the dominant role of microorganisms in the formation and localization of biogenic NER at a mm-scale. To conclude, these results demonstrate the importance of considering micro-scale processes to better understand the fate of pesticides and more generally of soil organic substrates at upper scales in soil and suggest that such spatial heterogeneity should not be neglected when predicting the fate of organic compounds in soils.     

尕海湿地植被退化过程中土壤碳矿化特征研究

以甘南尕海4种不同退化程度的湿地(未退化(UD)、轻度退化(LD)、中度退化(MD)及重度退化(HD))为研究对象,采用室内5 ℃、15 ℃、25 ℃、35 ℃ 培养法,测定不同土层 SOC 矿化速率和累积矿化量,运用一级动力学方程对土壤的半矿化分解时间(T_1/2)、有机碳矿化潜势(C₀)等参数进行拟合,分析温度、土壤深度和退化程度对土壤碳矿化过程的影响。结果表明：(1)在不同土层、不同温度下,各植被退化程度湿地土壤有机碳 CO₂ 释放量在整个培养期间大致可以分三个阶段,0-4 d快速生成 CO₂ 阶段,4-27 d缓慢生成 CO₂ 阶段,27-41 d平稳阶段;0-10 cm 土层各培养温度下,土壤有机碳矿化速率表现为UD＞LD＞MD＞HD。(2)培养期间,不同退化湿地土壤有机碳矿化速率均随土层加深而降低,表层 0-10 cm的矿化速率(1.14~16.23 mg/(g?d))均显著高于10-20 cm(1.05~2.85 mg/(g?d))和20-40 cm(0.94~1.26 mg/(g?d))土层。(3)整个培养期内,不同退化湿地土壤有机碳总累积矿化量排序为5 ℃(34.54 mg/g)、15 ℃(46.67 mg/g)、25 ℃(58.28 mg/g)和35 ℃(86.46 mg/g)。(4)双库一级动力学方程的C₀值随退化程度增加呈递减趋势,而C₀/SOC随着温度的升高而降低。     

Degradation products of chlomethoxynil (X-52) in soil

The degradation of unlabelled and ^l4C-labelled chlomethoxynil (2,4-dichlorophenyl 3′-methoxy-4′-nitrophenyl ether) in a flooded soil was studied in the laboratory, using thin-layer chromatography (TLC) and combined gas chromatography-mass spectrometry (GC-MS).

Chlomethoxynil was rapidly degraded, and labelled chlomethoxynil was largely transformed into substances which were unextractable with organic solvents. Moreover, most of the radioactive substances extracted with organic solvents were not “free” compounds but complexes. The degradation products identified were the amino derivative (2,4-dichlorophenyl 4′-amino-3-methoxyphenyl ether), the demethyl derivative (2,4-dichlorophenyl 3′-hydroxy-4′-nitrophenyl ether), the formylamino derivative (2,4-dichlorophenyl 4-formylamino-3′-methoxyphenyl ether), the acetylamino derivative (2,4-dichlorophenyl 3-methoxy-4′-acetylaminophenyl ether), thepropionylamino derivative (2,4-dichlorophenyl 4-propionylaminophenyl ether), 2,4-dichlorophenol, and several other minor compounds.     

Growth of Gaeumannomyces graminis var. tritici in soil: Effects of temperature and water potential

The effects of temperature and water on the growth of the take-all fungus, Gaeumannomyces graminis var. tritici (Ggt), were examined in two factorial experiments. The first examined the effects of temperature and water potential on the growth of two isolates of Ggt on agar media, using osmotically-adjusted water potentials. The second experiment was concerned with the growth of the Ggt isolates in one sterile and two natural soils at two water regimes in the absence of a living host. Three temperatures (10, 18 and 26°C) were used in these experiments. A third experiment determined growth through soil.Growth was greatest at high temperatures and low water potential in axenic culture, but in unsterile soil growth at different temperatures and water potentials was strongly influenced by competition from the soil biota. The best temperature for growth in unsterile soil was 18°C. Growth at 26°C in unsterile soil was greatly reduced, this being attributed to more intense microbial competition. In sterile soil Ggt grew equally well at 18 and 26°C. At 10°C, both isolates of Ggt grew better in unsterile soil than in sterile soil.Under suitable conditions Ggt grew out readily from infected straw into unsterile soil (up to 5 cm in 10 days) in the absence of a host plant, forming melanized, hyaline and branched hyphae. These hyphae were infectious after dry storage for 5 months in the laboratory. Ggt thus appears to be a more successful soil inhabitant than is widely believed. Our experiments could explain many of the host-based concepts related to field expression of disease.The technique presented here could be of value for testing the suppressiveness or conduciveness of soils by measuring fungal growth in soil.