Multifunctional Interlayer Engineering for Silkworm Excrement-Derived Porous Carbon Enabling High-Energy Lithium Sulfur Batteries.

Lithium-sulfur (Li-S) batteries show advantage of high theoretical capacity. However, the shuttle effect of polysulfides and sluggish sulfur redox kinetics seriously reduce their service life. Inspired by the porous structural features of biomass materials, herein, a functional interlayer is fabricated by silkworm excrement-derived three-dimensional porous carbon accommodating nano sized CoS2 particles (SC@CoS2 ). The porous carbon delivers a high specific surface area, which provides adequate adsorption sites, being responsible for suppressing the shuttle effect of polysulfides. Meanwhile, the porous carbon is favorable for hindering the aggregation of CoS2 and maintaining its high activity during extended cycles, which effectively accelerates the polysulfides conversion kinetics. Moreover, the SC@CoS2 functional interlayer effectively limits the formation of Li dendrites and promotes the uniform deposition of Li on the Li electrode surface. As a result, the CMK-3/S cathode achieves a high initial capacity of 1599.1 mAh g-1 at 0.2 C rate assisted by the polypropylene separator coated with the functional interlayer and 1208.3 mAh g-1 is maintained after the long cycling test. This work provides an insight into the designing of long-lasting catalysts for stable functional interlayer, which encourages the application of biomass-derived porous carbon in high-energy Li-S batteries.

Responses of potential ammonia oxidation and ammonia oxidizers community to arsenic stress in seven types of soil.

Soil arsenic contamination is of great concern because of its toxicity to human, crops, and soil microorganisms. However, the impacts of arsenic on soil ammonia oxidizers communities remain unclear. Seven types of soil spiked with 0 or 100 mg arsenic per kg soil were incubated for 180 days and sampled at days 1, 15, 30, 90 and 180. The changes in the community composition and abundance of ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA) were analyzed by terminal restriction fragment length polymorphism (T-RFLP) analysis, clone library sequencing, and quantitative PCR (qPCR) targeting amoA gene. Results revealed considerable variations in the potential ammonia oxidation (PAO) rates in different soils, but soil PAO was not consistently significantly inhibited by arsenic, probably due to the low bioavailable arsenic contents or the existence of functional redundancy between AOB and AOA. The variations in AOB and AOA communities were closely associated with the changes in arsenic fractionations. The amoA gene abundances of AOA increased after arsenic addition, whereas AOB decreased, which corroborated the notion that AOA and AOB might occupy different niches in arsenic-contaminated soils. Phylogenetic analysis of amoA gene-encoded proteins revealed that all AOB clone sequences belonged to the genus Nitrosospira, among which those belonging to Nitrosospira cluster 3a were dominant. The main AOA sequence detected belonged to Thaumarchaeal Group 1.1b, which was considered to have a high ability to adapt to environmental changes. Our results provide new insights into the impacts of arsenic on the soil nitrogen cycling.

The application of metagenomic next-generation sequencing for detection of pathogens from dialysis effluent in peritoneal dialysis-associated peritonitis .

BACKGROUND: Metagenomic next-generation sequencing (mNGS) can improve pathogen identification in infectious diseases. METHODS: A prospective parallel control study was undertaken to evaluate the clinical significance of mNGS in identifying pathogens in dialysis effluent of patients with peritoneal dialysis-associated peritonitis (peritonitis). Dialysis effluent specimens were detected both by peritoneal dialysis effluent culture and mNGS. The positive rates and coincidence rates of the two methods were compared. RESULTS: From April 2020 to March 2021, 30 patients presenting with peritonitis were enrolled in this study. The positive pathogen detection rate of mNGS was significantly higher than that of the traditional culture method (86.67% vs. 60.00%; p = 0.039). Fifteen specimens were positive for both of the methods, while 11 specimens were negative for culture but positive for mNGS. Three specimens were positive for culture but negative for mNGS; all of them were streptococcus mitis. One specimen was negative for both methods. The culture method detected one type of pathogen in all specimens; however, two or more types of pathogens were detected in eight specimens by mNGS. In addition to common pathogens, additional pathogens detected by mNGS included Coxiella burnetii, human herpesvirus type 5, human herpesvirus type 6B and Mortierella. CONCLUSION: The pathogen detection rate of mNGS in dialysis effluent of peritonitis patients was significantly higher than that of traditional culture. The mNGS is advantageous in diagnosing the pathogens that are difficult to be cultured. However, mNGS did not demonstrate sensitivity to streptococcus mitis. Results from this study show that mNGS, combined with traditional culture, has potential application for detecting pathogens in peritoneal dialysis patients with peritonitis.

The performance and mechanism of cadmium availability mitigation by biochars differ among soils with different pH: Hints for the reasonable choice of passivators.

The performances of passivation materials mitigating Cadmium (Cd) bioavailability considerably vary with the pH condition of Cd-contaminated soils. However, less information was available for the method of improving Cd passivation efficiency taking into account the pH of the targeted soil. Furthermore, the underlying mechanism of Cd availability mitigation in soils with different pH has not been clearly explored. In this study, cotton straw biochar (CSB) and its modified products using NaOH (CSB-NaOH) were prepared and applied in two kinds of Cd-contaminated soils with different pH. It was found that CSB-NaOH was more effective than CSB in regulating the Cd bioavailability in the acid soil, while the opposite tendency was observed in alkaline soil. The difference of the Cd passivation efficiency is correlated with contributions of various Cd-biochar binding mechanisms, which cation exchange mechanism is largely eliminated for CSB-NaOH. The interaction of Cd with CSB/CSB-NaOH was further evidenced through characterization results of Scan Electron Microscopy (SEM), X-Ray Diffraction (XRD), Fourier-transformed infrared spectroscopy (FTIR) and X-ray Photoelectron spectroscopy (XPS). Characterization results proved that carboxyl, hydroxyl and ethyl groups were the key functional groups involved in Cd passivation. XPS results showed that Cd binding methods varied between CSB and CSB-NaOH, which Cd2+ and Cd-O were the main form of Cd binding to CSB while Cd-O was the main form on CSB-NaOH. In this work, it was demonstrated that in acid soil, pH change caused by biochar plays a more significant role in controlling the Cd bioavailability, while in alkaline soil, the strength of the Cd-biochar interaction is more decisive for the Cd passivation efficiency. This work provides information on how to select the suitable passivator to decrease the Cd bioavailability in terms of different soil pH and property.

Soil ridge cultivation maintains grain As and Cd at low levels and inhibits As methylation by changing arsM-harboring bacterial communities in paddy soils.

The simultaneous mitigation of toxic arsenic (As) and cadmium (Cd) in rice grain remains a global challenge. The over-accumulation of husk dimethylarsinic acid (DMAs) induces the rice straight-head disease, which threatens rice production worldwide. In this study, we investigated various soil ridge height treatments with Eh ranging from - 225-87 mV and pH ranging from 6.3 to 4.1. Soil ridge cultivation can maintain grain As and Cd at low levels for slightly co-contaminated paddy soils, especially when the ridge height is 11 cm (Eh of 43 mV and pH of 4.6), where grain inorganic As decreased-at maximum-by 48% and DMAs by 55%. Grain Cd (0.14 mg kg-1) increased but was still below the limit (0.2 mg kg-1) in China, and the cost of ridging is acceptable. There were definite correlations among porewater As, Cd, Fe, S, and Mn contents across various Eh and pH values. Soil ridge cultivation significantly (P < 0.05) diminished the copy number of As-reducing (harboring arsC and arrA), As-methylating (harboring arsM), and sulfate-reducing (harboring dsrA) bacteria. Moreover, soil ridge cultivation shifted the arsM-harboring microbiota. In response to ridge height increase, the abundance of the bacterial biomarker phylum Euryachaeota declined and the families Halorubrum and Planctomyces were gradually replaced by Sandaracinus in paddy soil.

Contradictory tendency of As(V) releasing from Fe-As complexes: Influence of organic and inorganic anions.

The strong ability of ferrihydrite and its aged minerals for fixing arsenate is a key factor in remediating arsenate-polluted environments. It is therefore crucial to clarify the stability of Fe-As complexes and the release conditions for As(V). The As(V) release amount was evaluated and compared in the presence of six representative anions, namely, phosphate, silicate, sulfate, inositol hexaphosphate, citrate, and oxalate. It was found that the As(V) release amount changed with the aging time of ferrihydrite and that this tendency generally followed two rules. These are, longer aging time leads to lower As(V) release (Rule 1), and longer aging time leads to higher As(V) release (Rule 2). Whether Rule 1 or Rule 2 dominated As release depended on the number of surface groups, size of competing anions, and contribution of As(V) re-adsorption. Characterization results using X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) provided evidence for the predicted mechanisms of As(V) release under various circumstances. In this work, it was demonstrated that when inorganic anions such as sulfate and silicate are present, ferrihydrite with longer aging time led to decreased As(V) release. When organic anions are present, ferrihydrite with less aging time results in reduced As(V) leaching. For anions such as phosphate, the As(V) release amount in relation to the ferrihydrite aging time depends on the concentration of phosphate ions. Nevertheless, the ligand concentration and As(V) loading rate on ferrihydrite should be simultaneously considered for the rule governing As(V) releasing.

Exogenous fulvic acid enhances stability of mineral-associated soil organic matter better than manure.

Mineral-associated soil organic matter (MAOM) is seen as the key to soil carbon sequestration, but its stability often varies with types of exogenous organic materials. Fulvic acid and manure are ones of the exogenous organic materials used for the improvement of degraded soil. However, little is known about if and how fulvic acid and manure affect the stability of MAOM. Using a field experiment of four fertilization treatments (no fertilization, mineral fertilizers, fulvic acid, and manure) and a comprehensive meta-analysis using relevant studies published prior to January 2020, we investigated effects of exogenous fulvic acid and manure applications on four MAOM stability indexes: association intensity, humus stabilization index, iron oxide complex coefficient, and aluminum oxide complex coefficient. Exogenous fulvic acid and manure applications increased soil organic carbon fractions by 26.04-48.47%, MAOM stability by 12.26-387.41%, and complexed iron/aluminum contents by 16.12-20.01%. Fulvic acid application increased MAOM stability by promoting mineral oxide complexation by 20.33% and manure application improved MAOM stability via increasing humus stabilization by 21-25%. Association intensity was positively correlated with contents of soil carbon fractions and the metal oxide complex coefficients were positively correlated with iron/aluminum oxide contents. Moreover, stable-humus exerted significantly positive direct and indirect effects on association intensity and humus stabilization index, while amorphous iron/aluminum content had significantly negative influences on metal oxide complex coefficients. The meta-analysis verified that long-term fulvic acid application improved MAOM stability more so than manure application in acidic soils. We recommend that strategies aiming to prevent land degradation should focus on the potential of fulvic acid as a soil amendment because it can significantly increase MAOM stability.

Effects of green manure planted in winter and straw returning on soil aggregates and organic matter functional groups in double cropping rice area.

To explore the mechanism of exogenous organic materials enhancing soil organic carbon and soil fertility, based on a long-term experiment located in Hengyang Red Soil Experimental Station, we examined the effects of winter green manure and straw returning patterns (CK, winter fallow; MV, winter Chinese milk vetch; S, early-season rice straw total returning; DS, early-season and late-season rice straw total returning; SMV, winter Chinese milk vetch + early-season rice straw total returning; DSMV, winter Chinese milk vetch + early-season and late-season rice straw total returning) on soil aggregates and organic functional groups. The results showed that the proportion of super aggregates (>2 mm) and macroaggregates (0.25-2 mm) in double cropping rice soil was the highest with a ratio of about 72.1%-81.8%, and the organic carbon content in the two kinds of aggregates was as high as 12.1-20.7 g·kg-1, accounting for 22.7%-59.0% of the total organic carbon. The main organic functional group in paddy soil was polysaccharides, followed by aliphatic carbon and aromatic carbon. The abundance of all those groups was affected by winter Chinese milk vetch growing and straw returning. Compared with other treatments, DSMV significantly increased the proportion of super aggregates (>2 mm) and macroaggregates (0.25-2 mm) and favored the accumulation of inert carbon such as aromatic carbon in the two kinds of aggregates. DSMV could enhance the stability of soil aggregates and organic matter, which had high potential in the real agricultural production.

Investigating the Mechanism of Metabolic Resistance to Tribenuron-Methyl in Capsella bursa-pastoris (L.) Medik. by Full-Length Transcriptome Assembly Combined with RNA-Seq.

Capsella bursa-pastoris (L.) Medik. has evolved resistance to ALS-inhibiting herbicides on a large scale. Previous studies primarily focused on the target-site resistance (TSR), and the non-TSR (NTSR) is not well characterized. In this study, pre-treatment with the cytochrome P450 monooxygenase (P450) inhibitor malathion clearly reduced the tribenuron-methyl resistance in the resistant (R) population. After tribenuron-methyl treatment, the glutathione S-transferase (GST) activity of R plants was significantly higher than that of susceptible (S) plants. The higher tribenuron-methyl metabolism in R plants was also confirmed by using LC-MS/MS analysis. Isoform sequencing (Iso-Seq) combined with RNA sequencing (RNA-Seq) was used to identify candidate genes involved in non-target metabolic resistance in this population. A total of 37 differentially expressed genes were identified, 11 of them constitutively upregulated in R plants, including three P450s, one GST, two glycosyltransferases, two ATP-binding cassette transporters, one oxidase, and two peroxidases. This study confirmed the metabolic tribenuron-methyl resistance in C. bursa-pastoris, and the transcriptome data obtained by Iso-Seq combined with RNA-Seq provide gene resources for understanding the molecular mechanism of NTSR in C. bursa-pastoris.

Seeking for an optimal strategy to avoid arsenic and cadmium over-accumulation in crops: Soil management vs cultivar selection in a case study with maize.

Soil management and cultivar selection are two strategies to reduce the accumulation risk of heavy metals in crops. However, it is still an open question which of these two strategies is more efficient for the safe utilization of contaminated soil. In this study, the available bio-concentration factors (aBCF) of arsenic (As) and cadmium (Cd) among 39 maize cultivars were determined through a field experiment. The effect of soil management was mimicked by choosing diverse sampling sites having different soil available contents of As and Cd. The aBCF of As and Cd in grain ranged from 0.02 to 0.13 and 1.17 to 42.2, respectively. The accumulation ability of As and Cd was classified among different maize cultivars. Soil pH and total As controlled the level of available As in soils, while soil pH dominated available Cd in soil. A soil pH of 6.5 was recommended to simultaneously minimize soil available As and Cd by managing soil conditions. The quantitative effects of cultivar and soil management on grain As and Cd were expressed as Q [Grain As] = 0.746Q [Cultivar]-0.126Q [pH]+0.276Q [Asavailable] (R2 = 0.648, P = 1.00 × 10-37) and Q [Grain Cd] = 0.913Q [Cultivar]-0.192Q [pH]+0.071Q [SOC] (R2 = 0.782, P = 1.00 × 10-37), respectively. Cultivar selection contributed stronger than soil management to decrease the As and Cd levels in maize grains. A feasible method to seek for a more efficient strategy was proposed for the safe utilization of contaminated soil.

Stability of Fe-As composites formed with As(V) and aged ferrihydrite.

During the aging process, ferrihydrite was transformed into mineral mixtures composed of different proportions of ferrihydrite, goethite, lepidocrocite and hematite. Such a transformation may affect the fixed ability of arsenic. In this study, the stability of Fe-As composites formed with As(V) and the minerals aged for 0, 1, 4, 10 and 30 days of ferrihydrite were systematically examined, and the effects of molar of ratios Fe/As were also clarified using kinetic methods combined with multiple spectroscopic techniques. The results indicated that As(V) was rapidly adsorbed on minerals during the initial polymerization process, which delayed both the ferrihydrite conversion and the hematite formation. When the Fe/As molar ratio was 1.875 and 5.66, the As(V) adsorbed by ferrihydrite began to release after 6 hr and 12 hr, respectively. The corresponding release amounts of As(V) were 0.55 g/L and 0.07 g/L, and the adsorption rates were 92.43% and 97.50% at 60 days, respectively. However, the As(V) adsorbed by the transformation products aged for 30 days of ferrihydrite began to release after adsorbed 30 days. The corresponding release amounts of As(V) were 0.25 g/L and 0.03 g/L, and the adsorption rates were 84.23% and 92.18% after adsorbed 60 days, for the Fe/As=1.875 and 5.66, respectively. Overall, the combination of As(V) with ferrihydrite and aged products transformed from a thermodynamically metastable phase to a dynamically stable state within a certain duration. Moreover, the aging process of ferrihydrite reduced the sorption ability of arsenate by iron (hydr)oxide but enhanced the stability of the Fe-As composites.

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To acquire a feasible method for a rapid comparison of the cadmium (Cd) accumulation capacities of different leafy vegetables, using substrate cultivation with different contents of Cd and cultivation time, we compared the observed Cd accumulation capacity with these obtained in the field. The results showed that the Cd content and bio-concentration factors (BCFs) value in the aboveground tissue of leafy vegetable varied significantly with Cd content and cultivation time. Multi-factor analysis of variance showed that vegetable variety, cultivation time, Cd content in substrate and their interaction had significant effects on BCFs of Cd in leafy vegetable. Leafy vegetable variety was the dominant factor affecting BCFs of Cd in leafy vegetable and controlled its absolute level. When Cd content in the substrate reached 1.0 mg·kg-1 with a cultivation of 10 days, the correlation coefficient of Cd BCFs between the substrate cultivation and field experiments was the highest, with a R2 value of 0.90. The results of cluster analysis and one-way ANOVA had the highest consistence with the field results. Comparatively, the substrate cultivation with Cd content of 1.0 mg·kg-1 and a cultivation of 10 days showed a good reproducibility and stability in reflecting the difference in Cd accumulation capacities of different leafy vegetable varieties. The Cd-rich substrate cultivation could be used to screen the vegetables with low Cd accumulation and also would promote the field application of the vegetables with low Cd accumulation in the Cd-contaminated area of China.

Isolation and expression of acetolactate synthase genes that have a rare mutation in shepherd's purse (Capsella bursa-pastoris (L.) Medik.).

Acetolactate synthase (ALS) inhibitor-resistant biotypes are the fastest growing class of herbicide-resistant weeds. Shepherd's purse (Capsella bursa-pastoris (L.) Medik.), a tetraploid species and one of the most troublesome weeds in wheat production, has evolved ALS inhibitor resistance. To confirm and characterize the resistance of shepherd's purse populations to ALS-inhibiting herbicides, whole-plant bioassays were conducted. To investigate the molecular basis of resistance in shepherd's purse, the ALS gene was sequenced and compared between susceptible (S) and resistant (R) biotypes. Two partial intronless ALS genes (ALS-1 and ALS-2) were identified, and two heterozygous mutations (CCT to TCT in ALS-1 and CCT to CAT in ALS-2) at position 197 (Pro197Ser and Pro197His) providing resistance were simultaneously found in a single plant in a resistant population. Our results confirmed that the resistant shepherd's purse population showed high-level resistance to tribenuron-methyl (RI = 59.8), pyroxsulam (RI = 38.7) and flucarbazone-Na (RI = 88.0). Quantitative reverse transcription-polymerase chain reaction (RT-qPCR) results suggested that the difference in ALS gene expression was small between S and R populations, which may be insufficient to cause herbicide resistance, and according to the results of in vitro ALS activity, insensitivity of ALS may be the main mechanism of high resistance to tribenuron-methyl in resistant populations.

[Accumulation Characteristics of Heavy Metals in Greenhouse Soil and Vegetables in Siping City, Jilin Province].

Based on the typical greenhouse vegetable production system in Siping City, Jilin Province, 124 soil samples were collected from greenhouse soils growing vegetables (GSGV), fields growing maize (FGM), and forest soil (FS) under different land utilization patterns. In addition, other samples including greenhouse vegetables (81), fertilizers (50), and irrigation water (10) were also collected in the studied region. To illustrate the accumulation characteristics of heavy metals in GSGV and greenhouse vegetables, the heavy metal content of different samples was measured using inductively coupled plasma mass spectrometry (ICP-MS) technology. The results indicated that the heavy metal content in GSGV was much higher than that in FGM and FS except for lead (Pb). Heavy metals including cadmium (Cd), copper (Cu), chromium (Cr), nickel (Ni), and zinc (Zn) in GSGV presented with various degrees of accumulation. The mean value of Cd content in the soils in the investigation region was 0.45 mg·kg-1, with about 42.8% of all the soil samples exceeding the Cd content criterion of the Environmental Quality Evaluation Standard for Farmland in Greenhouse Vegetable Production (HJ 333-2006). The content of the other heavy metals was in the normal range, and all met the regulations of the standard. In comparison with different vegetable categories, leafy vegetables showed much higher heavy metal concentrations (Cd 0.033 mg·kg-1 fresh weight) than did fruity ones. In total, about 2.5% and 1.2% of vegetable samples exceeded the regulated values of Cd and Pb recommended by the Standard of Food limits, respectively. With the cultivation time prolonged, heavy metal concentration in soils and vegetables all increased synchronously as the pH value decreased. The content of heavy metals in greenhouse vegetables was significantly influenced by soil pH and organic matter. It can be concluded that the health risk of greenhouse vegetables increased with GSGV accumulating more heavy metals due to the substantial application of chemical fertilizer and manure containing high level of heavy metals.

Reduced arsenic availability and plant uptake and improved soil microbial diversity through combined addition of ferrihydrite and Trichoderma asperellum SM-12F1.

Arsenic (As) accumulation in agricultural soils is prone to crop uptake, posing risk to human health. Passivation shows potential to inactivate soil labile As and lower crop As uptake but often contributes little to improving the microbiota in As-contaminated soils. Here, the combined addition of ferrihydrite and Trichoderma asperellum SM-12F1 as a potential future application for remediation of As-contaminated soil was studied via pot experiments. The results indicated that, compared with the control treatment, the combined addition of ferrihydrite and T. asperellum SM-12F1 significantly increased water spinach shoot and root biomass by 134 and 138%, respectively, and lowered As content in shoot and root by 37 and 34%, respectively. Soil available As decreased by 40% after the combined addition. The variances in soil pH and As fractionation and speciation were responsible for the changes in soil As availability. Importantly, the combined addition greatly increased the total phospholipid fatty acids (PLFAs) and gram-positive (G+), gram-negative (G-), actinobacterial, bacterial, fungal PLFAs by 114, 68, 276, 292, 133, and 626%, respectively, compared with the control treatment. Correspondingly, the soil enzyme activities closely associated with carbon, nitrogen, and phosphorus mineralization and antioxidant activity were improved. The combination of ferrihydrite and T. asperellum SM-12F1 in soils did not reduce their independent effects.

Arsenic availability and uptake by edible rape (Brassica campestris L.) grown in contaminated soils spiked with carboxymethyl cellulose-stabilized ferrihydrite nanoparticles.

This study investigated arsenic (As) availability and uptake by rape (Brassica campestris L.) during two harvest periods of carboxymethyl cellulose (CMC)-stabilized ferrihydrite (HFO) nanoparticles for in situ treatment As-contaminated soil. Application of modified HFO nanoparticles in soils not only provided a larger specific surface area but also markedly improved stability against aggregation and recrystallization. For 90-day incubation, bare HFO particles were gradually converted to the crystalline Fe(III) oxide form, although this was not observed for the 0.5% CMC-HFO nanoparticles. CMC-modified HFO nanoparticles could be more effective in lowering the As uptake by rape and available As in soils than bare HFO particles. Compared the control without amendments, As contents in rape and available As in soils decreased 69.7 and 59.0%, respectively, during the second harvest when soils were amended with 0.5% HFO nanoparticles. And the soil-solution distribution coefficient (K d ) increased by 2.6 and 2.8 times for the first and second harvest. Furthermore, the ratio of amorphous and free Fe-oxides (Feo/Fed) showed significant negative linear correlations with Asplant (P < 0.01), available As (P < 0.05), and nonspecifically sorbed As in soil (P < 0.01). In contrast, Feo/Fed was positively correlated with K d and amorphous crystalline Fe/Al oxide-sorbed As, which suggests that a larger amount of As is associated with Fe(hydr)oxide in the amorphous phase or smaller particles.

Tribenuron-methyl resistance and mutation diversity of the AHAS gene in shepherd's purse (Capsella bursa-pastoris (L.) Medik.) in Henan Province, China.

Shepherd's purse is a troublesome dicot weed that occurs in the major wheat-producing areas in China. Twenty-eight shepherd's purse populations were collected from winter wheat-planting areas in Henan Province and used to evaluate tribenuron-methyl resistance and acetohydroxyacid synthase (AHAS) gene-mutation diversity. The results indicate that all 28 shepherd's purse populations were resistant to tribenuron-methyl at different levels compared with the susceptible population. Mutation of the 197 codon (CCT) changed proline (Pro) into tyrosine (Tyr), histidine (His), leucine (Leu), serine (Ser), arginine (Arg), alanine (Ala) and threonine (Thr), whereas mutation of the 574 codon (TGG) changed tryptophan (Trp) into leucine (Leu). Among these amino acid changes, a co-concurrence of Pro197Leu and Trp574Leu substitutions was identified for the first time in resistant weed species. Furthermore, Pro197Tyr, Pro197Arg and Pro197Ala substitutions have not been previously reported in shepherd's purse. The results of the in vitro AHAS assay suggest that an insensitive AHAS is likely involved in the resistance to tribenuron-methyl in the R populations with AHAS gene mutations, and the non-target-site based resistance might exist in some populations.

Dynamic arsenic aging processes and their mechanisms in nine types of Chinese soils.

Although specific soil properties controlling the arsenic (As) aging process have been studied extensively, few investigations have attempted to determine how soil types influence As bioavailability and fractionations in soils. Nine types of soil were selected from typical grain producing areas in China, and the bioavailability and fractionations of As during aging were measured. Results showed that available As in all soils rapidly decreased in the first 30 days and slowly declined thereafter. In spiked soils, As easily became less available and less toxic in low pH soils compared to high pH soils, demonstrating the importance of soil pH on As availability. Results from fitting kinetic equations revealed that the pseudo-second-order model described the As aging processes well in all soils (R2 = 0.945-0.999, P < 0.01, SE = 0.09-4.25), implying that the mechanism for As aging combined adsorption, external diffusion, and internal diffusion. Fe oxides were more important than Al oxides for determining the As aging rate (|k|). Based on these results, we are the first to propose the approximate aging equilibrium time (T) for As, which was mainly influenced by soil clay content. The shortest time for approximate stabilization of As aging was 28 d in latosol soils (LS), while the longest approximate equilibrium time was 169 d in cinnamon soils (CS). Individual soil properties controlling the variation in different As fractionations further confirmed that the influences of soil types on As aging were the result of the combined effects of soil properties and a time-consuming redistribution process.

As(V) Resistance and Reduction by Bacteria and Their Performances in As Removal from As-Contaminated Soils.

Bacteria capable of arsenate [As(V)] reduction can be used for remediation of As-contaminated soils via bio-extraction. In this study, As-resistant bacteria were isolated and their abilities to resist and reduce As(V) as well as As bio-extracted from soils naturally contaminated with As were studied. The results indicated that three isolates (2-2, 4-3, and 8-5) showed greater abilities to resist As(V) than other isolates. When the isolates were exposed to 10 mg L-1 As(V), As(V) contents decreased, while arsenite [As(III)] increased over time. In comparison, isolates 2-2 and 4-3 completely reduced As(V) into As(III) within 6 h. According to phylogenetic analysis of the 16S rRNA gene, isolates 2-2, 4-3, and 8-5 were most closely related to Pseudomonas taiwanensis, P. monteilii, and Pseudomonas sp., respectively. Total As contents in soils significantly (P < 0.05) decreased after bacterial extraction. The maximum As removal of 21.6% was observed following inoculation of isolate 2-2 into soil-1. Bacterial extraction weakened the binding between As and the soil solid phase, resulting in As removal from the soil.

Inoculating chlamydospores of Trichoderma asperellum SM-12F1 changes arsenic availability and enzyme activity in soils and improves water spinach growth.

Arsenic (As)-contaminated agricultural soils threaten crop yields and pose a human health risk. Augmentation of exogenous microorganisms exhibiting plant-growth promoting and As speciation changing shows potential to improve crop growth and change soil As availability. Trichoderma asperellum SM-12F1 exhibiting both traits was developed into chlamydospores to improve its persistence in contaminated soils. After inoculation, As availability and enzyme activity in two types of soils and the growth as well as As uptake of water spinach (Ipomoea aquatic Forsk.) were investigated. The results indicated that inoculation significantly improved water spinach growth in both soils. Inoculating chlamydospores at 5% significantly increased As concentration (139%), bioconcentration factor (150%), and translocation factor (150%) in water spinach grown in Chenzhou (CZ) soils, while no significant change for these in Shimen (SM) soils. Inoculating chlamydospores at 5% caused a significant increase (16%) of available As content in CZ soils, while a significant decrease (13%) in SM soils. Inoculation significantly caused As methylation in both soils, while significant As reduction merely observed in CZ soils. The differential changes in available As contents in both soils were attributed to the soil pH, As fractionations and speciation characteristics. Furthermore, Inoculating chlamydospores at 5% significantly improved the activities of ß-glucosidase (155%), chitinase (211%), and phosphatase (108%) in SM soils, while significant decreases in ß-glucosidase (81%), phosphatase (54%), aminopeptidase (60%), and catalase (67%) in CZ soils. Bioaugmentation and As availability change were responsible for this result. These observations will be helpful for the application of fungal chlamydospores in the future bioremediation.