Historical distribution of DDT residues in pond sediments in an intensive agricultural watershed in the Yangtze-Huaihe region,China

Purpose

The extensive use of chemical pesticides on farmlands during the last several decades in China has led to a rapid deterioration of environmental water quality in recent years. The aims of this study were to: reconstruct the history of pesticide residues, determine the input load and residual load of dichlorodiphenyltrichloroethane (DDT) pesticides, and assess the risk of pesticide residues to aquatic ecosystem and human health.

Materials and methods

Caesium-137 was used to date sediment cores collected from ponds representing four land use types of an agricultural watershed with high-yield grain production and characterized by multipond systems in the Yangtze-Huaihe region of China. These ponds were selected to establish the historic pattern of DDT pesticide residues.

Results and discussion

(1) The mean total concentration of DDT residues including p,?p?′-dichlorodiphenyldichloroethylene (p,p′-DDE), p,?p?′-dichlorodiphenyldichloroethane ( p,p′-DDD), o,p′-DDT, and p,p′-DDT in sediment in the watershed was 82 μg kg^?1, ranging from under the detection limit to 457 μg kg^?1, which was mostly contributed by p,?p′-DDE (57 μg kg^?1 on average). Spatially, total concentrations of DDT residues in farmland pond sediment were the highest, reaching as high as 457 μg kg^?1. Temporally, an inflection point appeared in the 1970s, prior to which DDT contents increased with time, after which concentrations showed a decreasing trend. (2) In total, 323 kg DDT pesticide was applied to the Liuchahe Watershed since 1955. The total retention of four DDT residues in the multipond system was 14 kg (～4 % of the input), and most DDT pesticide was degraded to p,?p?′-DDE. (3) More than 80 % of sediment DDT residues exceeded their interim freshwater sediment quality guidelines, and the percentages of DDT,DDD, and DDE residues exceeding probable effect limit (PEL) values were 57, 29, and 70 %, respectively, which indicated a moderate to high ecological risk of DDT in this watershed.

Conclusions

Our results clearly reveal that the extensive use of pesticides has resulted in significant pesticide residual pollution in this watershed, which could severely deteriorate water quality and threaten aquatic ecosystem and human health in the watershed and, thus, remain a cause for concern.     

Development of a Two-Phase Cosolvent Washing-Fungal Biosorption Process for the Remediation of DDT-Contaminated Soil

A bench scale, two-phase soil washing-biosorption process was developed for the remediation of p,p′-DDT-contaminated soil (containing 990 and 7750 mg kg^-1 of p,p′-DDT). Removal of p,p′-DDT from contaminated soil was achieved by washing the soil with low molecular weight primary alcohols (ethanol or 1-propanol). An improved efficiency of p,p′-DDT removal was observed with increasing C-chain length of the cosolvent and by increasing the cosolvent volume fraction. When 40 or 80% 1-propanol were used, greater than 93% of p,p′-DDT was desorbed from the respective soils. p,p′-DDT was partitioned from the cosolvent solutions using biomass of Cladosporium sp. strain AJR³18,501 as the sorptivematrix. When studies were conducted using a cosolvent-recycling regime (with 80% 1-propanol) greater than 95% of p,p′-DDT was removed from Soil A (990 mg kg^-1 p,p′-DDT) and Soil B (7750 mg kg^-1 p,p′-DDT) with the majority of the desorbed organochlorine repartitioning onto the fungal biomass. Less than 2.4 μg mL^-1 p,p′-DDT was detected in the cosolvent wash solution of Soil A after 80 hr: potentially the cosolvent could be further reused to treat other soil. A higher concentration of p,p′-DDT was detected in the cosolvent wash solution of soil B after 120 hr (13.3 μg mL^-1) indicating that the p,p′-DDT sorption sites on the fungal biomass were fully saturated.     

运用红边参数估算叶片叶绿素含量

Soil samples collected from several sites along an altitudinal transect on the eastern slope of the Tibetan Plateau were analyzed for hexachlorobenzenes(HCHs) and dichlorodiphenyltrichloroethanes(DDTs).The results showed that HCHs and DDTs were found in the soil samples from the remote high altitude areas away from source regions,which confirmed the long-range atmospheric transport phenomenon of these organochlorine pesticides(OCPs) insecticides.The OCP concentrations in the soils had a significant negative correlation with altitude;they showed a trend to increase with decreasing altitude,but the increase was not continuous,being interrupted at some moderate-altitude sites on the transect.The distances from the source region,landforms,soil properties,and physical-chemical properties of OCPs were more important than total organic carbon content to the distribution of OCPs in soils disturbed by human activities.An analysis of the compositions of HCH isomers and DDTs revealed predominantly low ratios of α-HCH to γ-HCH,ranging from 0.06 to 4.79,which suggested current lindane inputs.On the other hand,low p,p-DDT/p,p-DDE and o,p-DDT/p,p-DDT ratios were observed,indicating mainly aged historical DDT residues in the study area.     

采用白腐菌对难降解有机污染物的生物净化

白腐菌对难降解污染物的生物降解作用已引起世界范围内的普遍关注，它可通过其分泌的特殊的降解酶系或其他机制将各种难降解的有机污染物彻底降解为CO₂和H₂O。该文介绍了白腐真菌的生物学特性及其分泌的酶系，阐述了白腐菌所分泌的酶在降解各种难降解有机物中的作用机制，分析了提高白腐菌降解能力的方法，总结了白腐菌在治理环境污染方面的应用现状与研究进展，探讨了白腐菌在实际应用方面的不足以及今后的研究方向，对白腐菌在解决环境污染方面的问题具有实际意义。     

Biological control of onion white rot

Six bacteria and one fungus isolated from sclerotia of Sclerotium cepivorum, the causal agent of white rot of onions, produced diffusible antibiotics antagonistic to growth of S. cepivorum on potato dextrose agar. Three of the bacterial isolates applied as seed treatments to onions grown in non-sterile muck soil in a controlled environment chamber reduced the proportion of infections by S. cepivorum. Antagonists were further evaluated as seed treatments for field control of white rot on two onion cultivars grown on muck soil containing high levels of natural inoculum. Four of the bacterial isolates provided significant season-long protection on the partially-resistant cultivar Festival, and the best of these also provided significant protection on the susceptible cultivar Autumn Spice. The fungal antagonist has been identified as Penicillium nigricans, and all bacterial isolates appear to be Bacillus subtilis. The levels of protection provided by some of these latter isolates were comparable to those provided by chemical treatments and represent practical potential for field control of white rot.     

Resistance of microbial populations in DDT-contaminated and uncontaminated soils

One DDT-contaminated soil and two uncontaminated soils were used to enumerate DDT-resistant microbes (bacteria, actinomycetes and fungi) by using soil dilution agar plates in media either with 150 μg DDT ml⁻¹ or without DDT at different temperatures (25, 37 and 55°C). Microbial populations in this study were significantly (p<0.001) affected by DDT in the growth medium. However, the numbers of microbes in long-term contaminated and uncontaminated soils were similar, presumably indicating that DDT-resistant microbes had developed over a long time exposure. The tolerance of isolated soil microbes to DDT varied in the order fungi>actinomycetes>bacteria. Bacteria from contaminated soil were more resistant to DDT than bacteria from uncontaminated soils. Microbes isolated at different temperatures also demonstrated varying degrees of DDT resistance. For example, bacteria and actinomycetes isolated at all incubation temperatures were sensitive to DDT. Conversely fungi isolated at all temperatures were unaffected by DDT.     

Transformation and form of dichlorodiphenyltrichloroethane (DDT) applied to Moscow soils

The transformation rate and direction of dichlorodiphenyltrichloroethane (DDT) and its forms entering the surface layers of Moscow soils have been analyzed. The DDT transformation rate into metabolites—dichlorodiphenyldichloroethylene (DDE) and dichlor diphenyl dichloroethane (DDD)—is small. In 75% of soils, less than half the initial pesticide is transformed. In 67.5% of soils, formation of DDD predominates in the DDE formation. In soils of the entire area of Moscow, 16% of DDT was transformed into DDE and 23% into DDD. The о,n′-DDT to n,n′-DDT ratio is <0.3 for 95% of soils, and the mean ratio is 0.1, which is typical for application of DDT as a technical product.     

In situ Remediation of DDT-contaminated Soil Using a Two-Phase Cosolvent Flushing-Fungal Biosorption Process

The effectiveness of cosolvent soil flushing and fungal biosorption for the remediation of p,p′-DDT-contaminated soil was evaluated usingpacked soil columns in order to simulate an in situ soil flushing technique. Greater than 95% of p,p′-DDT (940 mg kg^-1) was desorbed from the soil by flushing with 40 or 80% 1-propanol. Increasing the cosolvent volume fraction increased the rate of p,p′-DDT removal from the soil, however, the extent of p,p′-DDT removal was not enhanced. A further enhancement in therate of p,p′-DDT removal was achieved by increasing the cosolventflow rate from 6 ml hr^-1 to 12 ml hr^-1 (pore water velocity from 18.9 to 37.8 cm hr^-1). The desorbed p,p′-DDT was removed from cosolvent wash solutions by partitioning onto fungal biomass. Biosorption of p,p′-DDT resulted in low concentrations of the organochlorine (3.3 μg ml^-1) remaining in thecosolvent effluent indicating that the cosolvent could be reused for further p,p′-DDT desorption. Using this technique, between 53 and 95 pore volumes were required to reduce p,p′-DDT concentrationsfrom 990 mg kg^-1 to below Australian and New Zealand Environmentaland Conservation Council (ANZECC) guidelines (50 mg kg^-1).     

Kocuria rosea HN01, a newly alkaliphilic humus-reducing bacterium isolated from cassava dreg compost

Purpose

The aims of this study were to isolate an alkaliphilic humus-reducing bacterium, investigate the fastest microbial reduction of humus analog as affected by different cultivation, and examine its ability for iron(III) oxide reduction and organochlorine pollutants (OCPs) degradation.

Materials and methods

A strain of pure culture, designated as HN01, was isolated from cassava dreg compost using anaerobic enrichment procedure with glucose as the electron donor and anthraquinone-2,6-disulphonate (AQDS) as the sole terminal electron acceptor. The isolate strain was identified using phenotypic and phylogenetic analysis. Iron(III) oxides and OCPs were chosen as potential electron acceptors. Strict anaerobic techniques and sterile conditions were applied throughout the incubation experiments, purged with O₂-free N₂ for 15 min. The concentration of reduced AQDS and Fe(II) was then quantified using a UV–vis spectrophotometer. The concentration of OCPs was analyzed by gas chromatography with a micro-electron capture detector. Cell number was determined by direct plate counting on aerobic Luria–Bertani medium agar medium at pH 9.

Results and discussion

(1) Strain HN01 was identified as Kocuria rosea, and the AQDS reduction by HN01 was observed in NaCl concentrations below 12 % (w/v) (optimum, 10 %) and pH ranges of 6.0–10.0 (optimum, 9.0) with sucrose as electron donor at 30 °C; (2) glucose, sucrose, methanol, ethanol, glycerol, and acetate were the favorable electron donors for AQDS reduction by strain HN01; (3) the strain had the ability of reducing iron(III) oxides in the presence of sucrose at pH 9.0 and its Fe(III)-reducing capacity ranked as goethite (α-FeOOH) > lepidocrocite (γ-FeOOH) > haematite(α-Fe₂O₃); and (4) the strain could effectively dechlorinate p,p′-DDT (1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane), and the dechlorination rate reached 71.3 %.

Conclusions

This is the first report of a strain of K. rosea capable of reducing AQDS, iron (III) oxides, and p,p′-DDT, which extends the diversity of the alkaliphilic and halotolerant humus/Fe(III)-reducing bacterium associated with dechlorination. The strain may have the potential to be used for bioremediation of an anoxic alkaline wastewater or site contaminated with OCPs.     

Vinasse irrigation: effects on soil fertility and arbuscular mycorrhizal fungi population

Purpose

The aim of this research was to determine the vinasse irrigation effects on the arbuscular mycorrhizal fungi (AMF) population (total spore abundance (TSA), richness, relative abundance, and diversity indices) and soil parameters and nutrients at high doses. The irrigation of soil with vinasses derived from sugarcane, beet, or alcohol production is a common practice around the world. Little is known about how this affects the AMF community and soil nutrients.

Materials and methods

The spider plant (Chlorophytum comosum, (Thunb.) Jacques), a mycorrhizable plant, was used to investigate the effect of 4 months of frequent vinasse irrigation (0, 25, 50, 75, and 100% vinasse concentration) on AMF and soil characteristics, e.g., electrical conductivity (EC), pH, mineral N, available P, Na⁺, K⁺, Ca²⁺, and Mg²⁺.

Results and discussion

The vinasse irrigation decreased the TSA, AMF richness and diversity after 4 months, regardless of vinasse concentration. The vinasse irrigation did not acidify the soil, but the EC, mineral N and available P increased. The biomass of C. comosum decreased (77–81%) after vinasse irrigation for 4 months.

Conclusions

Frequent irrigation with vinasse at concentrations ≥50% increases EC, K⁺, Na⁺, Mg²⁺, Ca²⁺ and available P in the soil, and decreases the amount of AMF spores, richness and diversity, which is not desirable in agricultural soils.

     

Influence of soil type and indigenous pathogenic fungi on bean hypocotyl rot caused by Rhizoctonia solani AG4 HGI in Cuba

Calcisol, ferralsol and vertisol soils, representative of different bean production areas of Villa Clara province in Cuba, were selected to determine the impact of soil type on bean hypocotyl rot severity caused by Rhizoctonia solani AG4 HGI (isolate CuVC-Rs7). In inoculated autoclaved soil, hypocotyl rot was most severe in calcisol soil, followed by ferralsol soils and then vertisol soils. In inoculated natural soils, disease severity was lower in vertisol and calcisol soils and higher in ferralsol soil, indicating that biological factors are suppressing or stimulating the pathogenic efficiency of R. solani. Native binucleate Rhizoctonia AGF, Sclerotium rolfsii and R. solani AG 4 HGI were isolated from bean plants grown in natural calcisol, vertisol and ferralsol soils, respectively. Subsequent studies about the interaction between these fungi and R. solani indicated that they were involved in the variability of disease severity caused by R. solani. The addition of R. solani AG4 HGI (isolate CuVC-Rs7) into each autoclaved soil inoculated with binucleate Rhizoctonia or S. rolfsii resulted in a reduction of disease severity caused by this pathogen while in soils inoculated with native R. solani AG4 HGI, disease severity increased. Irrespective of fungal interactions, calcisol was always the most disease conducive soil and vertisol the most disease repressive soil. The mechanisms by which native pathogenic fungi could influence disease severity caused by R. solani are discussed.     

Accumulation and metabolism of DDT and its metabolites byTetrahymena

Tetrahymena pyriformis readily accumulated DDT and its metabolites from the medium initially containing 1 ppm of each compound. These compounds were accumulated in a decreasing order of DDD, DDE, o,p′-DDT, DDMU, and p,p′-DDT. DDT was metabolized to DDE, o,p′-DDT, and DDMU. DDD was metabolized to DDMU whereas o,p′-DDT, DDE and DDMU were not metabolized. When the organisms were transferred to toxicant free medium excretion of p,p′-DDT and its metabolite occurred in two phases: (a) rapid phase of elimination which was completed during the first 3 h and (b) slow phase of elimination which continued for another 21 h. The implications of these results are discussed.     

Effects of vermicompost amendment as a basal fertilizer on soil properties and cucumber yield and quality under continuous cropping conditions in a greenhouse

Purpose

We examined the effects of vermicompost application as a basal fertilizer on the properties of a sandy loam soil used for growing cucumbers under continuous cropping conditions when compared to inorganic or organic fertilizers.

Materials and methods

A commercial cucumber (Cucumis sativus L.) variety was grown on sandy loam soil under four soil amendment conditions: inorganic compound fertilizer (750 kg/ha,), replacement of 150 kg/ha of inorganic compound fertilizer with 3000 kg/ha of organic fertilizer or vermicompost, and untreated control. Experiments were conducted in a greenhouse for 4 years, and continuous planting resulted in seven cucumber crops. The yield and quality of cucumber fruits, basic physical and chemical properties of soil, soil nutrient characteristics, and the soil fungal community structure were measured and evaluated.

Results and discussion

Continuous cucumber cropping decreased soil pH and increased electrical conductivity. However, application of vermicompost significantly improved several soil characteristics and induced a significant change in the rhizosphere soil fungal community compared to the other treatments. Notably, the vermicompost amendments resulted in an increase in the relative abundance of Ascomycota, Chytridiomycota, Sordariomycetes, Eurotiomycetes, and Saccharomycetes, and a decrease in Glomeromycota, Zygomycota, Dothideomycetes, Agaricomycetes, and Incertae sedis. Compared to the organic fertilizer treatment, vermicompost amendment increased the relative abundance of beneficial fungi and decreased those of pathogenic fungi. Cucumber fruit yield decreased yearly under continuous cropping conditions, but both inorganic and organic fertilizer amendments increased yields. Vermicompost amendment maintained higher fruit yield and quality under continuous cropping conditions.

Conclusions

Continuous cropping decreased cucumber yield in a greenhouse, but basic fertilizer amendment reduced this decline. Moreover, basal fertilizer amendment decreased beneficial and pathogenic fungi, and the use of vermicompost amendment in the basic fertilizer had a positive effect on the health of the soil fungal community.

     

Taxon-specific responses of soil microbial communities to different soil priming effects induced by addition of plant residues and their biochars

Purpose

This work investigated changes in priming effects and the taxonomy of soil microbial communities after being amended with plant feedstock and its corresponding biochar.

Materials and methods

A soil incubation was conducted for 180 days to monitor the mineralization and evolution of soil-primed C after addition of maize and its biochar pyrolysed at 450 °C. Responses of individual microbial taxa were identified and compared using the next-generation sequencing method.

Results and discussion

Cumulative CO₂ showed similar trends but different magnitudes in soil supplied with feedstock and its biochar. Feedstock addition resulted in a positive priming effect of 1999 mg C kg^?1 soil (+253.7 %) while biochar gave negative primed C of ?872.1 mg C kg^?1 soil (?254.3 %). Linear relationships between mineralized material and mineralized soil C were detected. Most priming occurred in the first 15 days, indicating co-metabolism. Differences in priming may be explained by differences in properties of plant material, especially the water-extractable organic C. Predominant phyla were affiliated to Acidobacteria, Actinobacteria, Chloroflexi, Gemmatimonadetes, Firmicutes, Planctomycetes, Proteobacteria, Verrucomicrobia, Ascomycota, Basidiomycota, Blastocladiomycota, Chytridiomycota, Zygomycota, Euryarchaeota, and Thaumarchaeota during decomposition. Cluster analysis resulted in separate phylogenetic grouping of feedstock and biochar. Bacteria (Acidobacteria, Firmicutes, Gemmatimonadetes, Planctomycetes), fungi (Ascomycota), and archaea (Euryarchaeota) were closely correlated to primed soil C (R ²?=??0.98, ?0.99, 0.84, 0.81, 0.91, and 0.91, respectively).

Conclusions

Quality of plant materials (especially labile C) shifted microbial community (specific microbial taxa) responses, resulting in a distinctive priming intensity, giving a better understanding of the functional role of soil microbial community as an important driver of priming effect.

     

Influence of mixtures of acenaphthylene and benzo[a]anthracene on their degradation by Pleurotus ostreatus in sandy soil

Purpose

Polycyclic aromatic hydrocarbons (PAHs) are a class of organic compounds commonly found as soil contaminants. Fungal degradation is considered as an environmentally friendly and cost-effective approach to remove PAHs from soil. Acenaphthylene (Ace) and Benzo[a]anthracene (BaA) are two PAHs that can coexist in soils; however, the influence of the presence of each other on their biodegradation has not been studied. The biodegradation of Ace and BaA, alone and in mixtures, by the white rot fungus Pleurotus ostreatus was studied in a sandy soil.

Materials and methods

Experimental microcosms containing soil spiked with different concentrations of Ace and BaA were inoculated with P. ostreatus. Initial (t ₀) and final (after 15 days of incubation) soil concentrations of Ace and BaA were determined after extraction of the PAHs.

Results and discussion

P. ostreatus was able to degrade 57.7% of the Ace in soil spiked at 30 mg kg^?1 dry soil and 65.8% of Ace in soil spiked at 60 mg kg^?1 dry soil. The degradation efficiency of BaA by P. ostreatus was 86.7 and 77.4% in soil spiked with Ace at 30 and 60 mg kg^?1 dry soil, respectively. After 15 days of incubation, there were no significant differences in Ace concentration between soil spiked with Ace and soil spiked with Ace + BaA, irrespective of the initial soil concentration of both PAHs. There were also no differences in BaA concentration between soil spiked with BaA and soil spiked with BaA + Ace.

Conclusions

The results indicate that the fungal degradation of Ace and BaA was not influenced by the presence of each other’s PAH in sandy soil. Bioremediation of soils contaminated with Ace and BaA using P. ostreatus is a promising approach to eliminate these PAHs from the environment.     

Catalase and Phosphatase Activities During Hydrocarbon Removal from Oil-Contaminated Soil Amended with Agro-Industrial By-products and Macronutrients

Microbiological activities are essential in the bioremediation of polluted soils. The enzymatic activities of microorganisms are usually used as a biological indicator of soil health. The aim of this work was to observe the catalase, acid phosphatase (AcP), and alkaline phosphatase (AlP) activities in soil that was amended with agro-industrial by-products and macronutrients during the process of total petroleum hydrocarbon (TPH) removal. To this end, microcosm tests were performed with soil and agro-industrial by-products ratios of 100:2:2, for soil:sugarcane bagasse pith:filter cake mud (SSF); 100:2, for both soil:sugarcane bagasse pith (SS); and for soil filter cake mud (SF). The macronutrients—carbon, nitrogen, and phosphorus—in the experimental treatments were adjusted to 100:10:1 with a solution of NH₄NO₃ and K₂HPO₄. The best TPH removal (51.4%) was obtained with SSF at 15 days. In addition, a significant correlation was observed between TPH removal and AlP as well as AcP (r = 0.74, p < 0.0001; r = 0.70, p < 0.0107, respectively). Fungi growth was also correlated with both AlP (r = 0.97, p < 0.0001) and AcP (r = 0.95, p < 0.0001) activities. Besides, bacterial and fungi growth showed a correlation with TPH (r = 0.86, p < 0.001; r = 0.77, p < 0.0034, respectively). It could be said that the agro-industrial by-products and macronutrients contributed to pollutant removal from the oil-polluted soil at relatively short amount of time. In addition, the enzymatic activities were increased after the treatment; in this study, the high sensitivity enzyme was AlP, and it could be used as an indirect indicator of oil pollutant removal.     

Desorption of DDT from a Contaminated Soil using Cosolvent and Surfactant Washing in Batch Experiments

1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane (p,p′-DDT) is a recalcitrant organic compound that is difficult to remove from contaminated soil due to its low solubility. In this study we investigated the effectiveness of both cosolvents and surfactants in enhancing the solubility of p,p′-DDT from a soil that has been contaminated with DDT for nearly 40 yr. The presence of selected surfactants removed less than 1 to 11% of p,p′-DDT compared to cosolvents, which removed less than 1 to 77% of p,p′-DDT from the same soil. The low solubility of p,p′-DDT in the presence of surfactants was attributed to the decreased surfactant concentration to below critical micelle concentrationfollowing sorption by soil surfaces. Enhanced solubility of p,p′-DDT was achieved with the use of cosolvents that releasedup to 77% of p,p′-DDT from a contaminated soil. Increasing the solution concentration and hydrophobicity of the cosolvent increased the amount of p,p′-DDT desorbed. For example, the amount of p,p′-DDT desorbed increased in the order 5% 1-propanol << 50% ethanol << 50% 1-propanol. Repeated washing of the soil with various cosolvents, in all but two cases, markedly increased the total amount of p,p′-DDT desorbed from the soil. For example, repeated washing of the soil with 50% ethanol increased the amount of p,p′-DDT removed by 42% while repeated washings of the soil with 50% 1-propanol had little effect on the amount of p,p′-DDT desorbed. Increasing the soil-solution ratio from 1:2 to 1:10 in the presence of 40% 1-propanol increased the amount of p,p′-DDT desorbed by 100%; suggesting that the soil-solution ratio was an important parameterin controlling the amount of p,p′-DDT desorbed.     

Diversity and vertical distribution of indigenous arbuscular mycorrhizal fungi under two soybean rotational systems

To evaluate the importance of arbuscular mycorrhizal fungi (AMF) to crop production, it is imperative to move beyond the plow layer to include the full soil profile impacted by plant roots. To illustrate this, we investigated the vertical distribution of AMF biomass and community structure within the top 100 cm of soil in soybean (Glycine max (L.) Merr., cv: Enrei) rotational systems cropped to wheat (Triticuma estivum L. cv: Bandowase) or left fallow using fatty acid methyl ester (FAME) biomarkers and molecular analysis, respectively. AMF biomass, as measured by concentration of C16:1cis11, declined during fallow and with increasing soil depth. Greater than 50 % of the stored AMF biomass was found at depths below 35 cm. Phylogenetic analysis revealed 16 AMF phylotypes, including nine Glomus, two Gigaspora, two Scutellospora, and one each of Diversispora, Paraglomus, and an unknown glomeromycete, at different sampling depths in this study. Cluster analysis based on the number and abundance of each AMF phylotype formed two distinct clusters separating wheat from fallow rotations. There was no distinct relationship with soil depth beyond clustering AMF communities above and below 20 cm under wheat. Redundancy analysis (RDA) and hierarchical cluster analysis demonstrated that AMF communities by soil depth within each rotation were not significantly different. However, AMF communities were clearly influenced by crop rotation, where the distribution of specific AMF phylotypes responded to the presence of the wheat crop.     

蔬菜不同部位对DDTs的富集与分配作用

在可控条件下研究了人为污染土壤中DDT类污染物在蔬菜（菠菜和胡萝卜）不同部位的富集与分配规律。结果表明,DDT类污染物在菠菜和胡萝卜叶部和根部均有一定富集,其中菠菜叶面富集量占富集总量的68.6%～92.2%之间;而胡萝卜叶部富集占富集总量的34.9%～41.6%之间。不同DDTs在菠菜和胡萝卜体内的生物富集量呈：p,p＇-DDE〉p,p＇-DDT〉p,p＇-DDD〉o,p＇-DDE〉o,p＇-DDT的规律。DDTs通过不同途径在菠菜和胡萝卜内的生物富集系数表现如下规律：BCF大气－菠菜〉BCF大气－胡萝卜〉BCF土壤－胡萝卜〉BCF土壤－菠菜。不同DDTs在蔬菜体内的生物富集系数表现为：BCFp,p＇-DDE〉BCFo,p＇-DDE〉BCFp,p＇-DDD〉BCFp,p＇-DDT〉BCFo,p＇-DDT。由于DDTs在蔬菜体内富集后,可沿食物链传递和放大,对农产品质量和人体健康构成直接威胁。     

Arbuscular mycorrhizal fungal diversity, external mycelium length, and glomalin-related soil protein content in response to long-term fertilizer management

Purpose

Arbuscular mycorrhizal (AM) fungi are crucial for ecosystem functioning and can contribute to the formation and maintenance of soil aggregates through the exudation of glomalin by extraradical hyphae. Monitoring fertilization effects on AM fungi may help us to develop sound management strategies. The objectives of this study were to investigate the impacts of long-term fertilization on AM fungal parameters and to find out the key factor that affects the diversity and function of AM fungi.

Materials and methods

A long-term fertilization experiment established in a sandy loam soil at northern China has received continuous fertilization treatments for 21 years, including control; mineral fertilizers of NK, PK, NP, and NPK; organic manure (OM); and half organic manure N plus half mineral fertilizer N (1/2 OMN). Top soil samples (0–15 cm) from three individual plots per treatment were collected for the analysis of chemical properties and fungal parameters. The population size of soil AM fungi was determined by real-time PCR, and the community composition was analyzed using PCR-denature gradient gel electrophoresis (DGGE), cloning, and sequencing techniques. The external mycelium of AM fungi was assessed using the grid-line intersect method, and the glomalin-related soil protein (GRSP) was extracted with citrate solution using bovine serum albumin as a standard.

Results and discussion

Long-term fertilization significantly increased (P?<?0.05) soil organic C content, AM fungal population, species richness (R), Shannon–Wiener index (H), and GRSP content, except for the P-deficiency (NK) fertilization treatment. OM had a significantly greater (P?<?0.05) impact on AM fungal population and GRSP content compared to mineral fertilizers but significantly decreased the length of external mycelium compared to the control (P?<?0.05). Fertilization also changed the community composition of AM fungi, and the P-deficiency treatment again had the slightest influence. In addition, most species recovered from the DGGE profiles belonged to three genera, Glomus, Diversispora, and Archaeospora. Redundancy analysis showed that the population size and species richness of AM fungi and the GRSP content all significantly correlated to soil organic C content (P?<?0.05).

Conclusions

Long-term P-containing fertilization, especially the application of OM, greatly increased the population size, species richness, and species diversity of AM fungi, as well as the contents of GRSP and soil organic C, but tended to decrease the length of external mycelium, while the P-deficiency fertilization had no such effect, suggesting that P was the key factor to maintain soil fertility as well as soil AM fungal diversity in this sandy loam soil.