Responses of soil microbial community to different concentration of fomesafen

Long-term herbicide residues affect soil multifunctionality and the soil microbial community

Residues of herbicides with the extensive applications may impact the soil ecosystem and ultimately threaten agricultural sustainability. However, the effects of long-term herbicide residues on soil multifunctionality and the soil microbial community remain poorly understood. Here, we evaluated relationships between soil multifunctionality and soil microbial communities with residual herbicide concentrations by surveying and analyzing 62 black soil samples collected from an agricultural area in northeastern China. Total residual herbicide concentrations varied from 35 to 568 μg/kg in the soil samples. The response of soil multifunctionality to increasing residual herbicide concentrations exhibited an inverted U-shaped relationship with a peak at approximately 310 μg/kg, with net mineralized organic nitrogen (Nm) and total nitrogen (TN) exhibiting the same trend. Microbial community richness was significantly lower in soil samples with high residual herbicide concentrations (> 310 μg/kg, HG) compared to low residual herbicide concentrations (< 310 μg/kg, LG). In addition, the relative abundances of specific keystone microbial genera differed significantly between LG and HG: norank_f_Acetobacteraceae, norank_f_Caldilineaceae, Candidatus_Alysiosphaera, and Gonytrichum. The relative abundances of these genera were also significantly correlated with soil multifunctionality. Structural equation models (SEMs) further showed that herbicide residues influenced soil multifunctionality by affecting these specific keystone genera. Our study demonstrates that long-term herbicide residues significantly impact the multifunctionality of agricultural black soil, where low concentrations stimulate while high concentrations inhibit, underscoring the need for reasonable application of herbicides to maintain soil ecosystem health.

A review of the impact of herbicides and insecticides on the microbial communities

Enhancing crop yield to accommodate the ever-increasing world population has become critical, and diminishing arable land has pressured current agricultural practices. Intensive farming methods have been using more pesticides and insecticides (biocides), culminating in soil deposition, negatively impacting the microbiome. Hence, a deeper understanding of the interaction and impact of pesticides and insecticides on microbial communities is required for the scientific community. This review highlights the recent findings concerning the possible impacts of biocides on various soil microorganisms and their diversity. This review's bibliometric analysis emphasised the recent developments' statistics based on the Scopus document search. Pesticides and insecticides are reported to degrade microbes' structure, cellular processes, and distinct biochemical reactions at cellular and biochemical levels. Several biocides disrupt the relationship between plants and their microbial symbionts, hindering beneficial biological activities that are widely discussed. Most microbial target sites of or receptors are biomolecules, and biocides bind with the receptor through a ligand-based mechanism. The biomarker action mechanism in response to biocides relies on activating the receptor site by specific biochemical interactions. The production of electrophilic or nucleophilic species, free radicals, and redox-reactive agents are the significant factors of biocide's metabolic reaction. Most studies considered for the review reported the negative impact of biocides on the soil microbial community; hence, technological development is required regarding eco-friendly pesticide and insecticide, which has less or no impact on the soil microbial community.

Development of an immunoassay based on a specific antibody for the detection of diphenyl ether herbicide fomesafen

Fomesafen belongs to the diphenyl ether herbicide, and is widely used in the control of broadleaf weeds in crop fields due to its high efficiency and good selectivity. The residual of fomesafen in soil has a toxic effect on subsequent sensitive crops and the microbial community structure because of its long residual period. Therefore, an efficient method for detecting fomesafen is critical to guide the correct and reasonable use of this herbicide. Rapid and sensitive immunoassay methods for fomesafen is unavailable due to the lack of specific antibody. In this study, a specific antibody for fomesafen was generated based on rational design of haptens and a sensitive immunoassay method was established. The half maximal inhibitory concentration (IC50) of the immunoassay was 39 ng/mL with a linear range (IC10-90) of 1.92-779.8 ng/mL. In addition, the developed assay had a good correlation with the standard UPLC-MS/MS both in the spike-recovery studies and in the detection of real soil samples. Overall, the developed indirect competitive enzyme immunoassay reported here is important for detecting and quantifying fomesafen contamination in soil and other environmental samples with good sensitivity and high reproducibility.

Coupling multifactor dominated the biochemical response and the alterations of intestinal microflora of earthworm Pheretima guillelmi due to typical herbicides

The excessive application of herbicides on farmlands can substantially reduce labor costs and increase crop yields, but can also have undesirable effects on terrestrial ecosystems. To evaluate the ecological toxicity of herbicides, metolachlor and fomesafen, two typical herbicides that are extensively used worldwide were chosen as target pollutants, and the endogeic earthworm Pheretima guillelmi, which is widely distributed in China, was selected as the test organism. A laboratory-scale microcosmic experiment was set, and energy resources, enzymes, and the composition and connections of intestinal microorganisms in earthworms were determined. Both herbicides depleted the energy resources of the earthworms, especially glycogen contents; increased the levels of antioxidant enzymes; and inhibited acetylcholinesterase. Moreover, the richness and diversity of the intestinal bacterial community of the earthworms were suppressed. Additionally, the bacterial composition at the genus level changed greatly and the connections between dominant bacteria increased dramatically. Most interactions among the bacterial genera belonging to the same and different phyla showed mutualism and competition, respectively. Importantly, metolachlor with higher toxicity had a transitory effect on these indicators in earthworms, whereas fomesafen, with lower toxicity but stronger bioaccumulation potential, exerted a sustaining impact on earthworms. Collectively, these results indicate that the toxic effects of herbicides on terrestrial organisms should be comprehensively considered in combination with biological toxicity, persistence, bioaccumulation potential, and other factors.

Ecotoxicity of parathion during its dissipation mirrored by soil enzyme activity, microbial biomass and basal respiration

The application of parathion (PTH) in agriculture can result in its entry into the soil and threaten the soil environment. Monitoring the PTH residues and assessing toxicity on soil health are of paramount importance to the public. Herein, the dissipation of PTH and concomitant influence on microbial activities [FDA hydrolase (FDA‒H), microbial biomass carbon (MBC) and basal respiration (BR)] in coastal solonchaks were investigated. Results showed that the dissipation of PTH in tested soil declined linearly, and the half-lives varied from 5.6 to 56.8 days, depending on pollutant concentrations. The FDA‒H activity and MBC were negatively affected by PTH pollution and exhibited a significantly positive correlation. Two‒way ANOVA analysis demonstrated that microbial activities were affected not only by PTH dose and incubation time but also by their interactions. The integrated biomarker response (IBR/n) index values on day 120 were between 1.02 and 2.89, larger than those on day 1 during PTH dissipation. This implied that the soil quality did not recover though there was no PTH residue in the soil at the end of the experiment. These findings suggested that microbial activities integrated with IBR/n index could elucidate the hazardous impacts of PTH dissipation on biochemical cycling and microorganisms in soil.

Effects of Oxathiapiprolin on the Structure, Diversity and Function of Soil Fungal Community

Pesticides can affect non-target microorganisms in the soil and are directly related to soil microecological health and environmental safety. Oxathiapiprolin is a piperidinyl thiazole isoxazoline fungicide that shows excellent control effect against oomycete fungal diseases, including late blight, downy mildew, root rot, stem rot, and blight. Though it can exist stably in the soil for a long time, its effects on soil microbial structure and diversity are not well investigated. In the present study, the effects of oxathiapiprolin on the abundance and diversity of soil fungal communities in typical farmland were studied. The results show that the abundance and diversity of soil fungi were increased by oxathiapiprolin treatment with differences not significant on the 30th day. Oxathiapiprolin was found to change the structure of soil fungal communities, among which Ascomycota and Mortierellomycota were the most affected. Undefined saprophytic fungi increased in the treatment groups, and the colonization of saprophytic fungi can act as a major contributor to the function of soil microbial communities. This study lays a solid foundation regarding environmental behavior with the use of oxathiapiprolin in soil and details its scientific and rational use.

Effect of different soil water managements on the selectivity of fomesafen in conventional and RR soybean

The study aimed to study the selectivity of the herbicide fomesafen, sprayed at different growth stages of the conventional and RR soybean cultivars, under different soil water managements. Two soybean cultivars were used: MG/BR 46 Conquista (conventional) and BRS Valiosa (RR), submitted to the spraying of fomesafen at two phenological stages (V2-first open trefoil; V4-third open trefoil), under three soil water conditions (-0.03, -0.07, and -0.5 MPa). Under water scarcity conditions, soybean plants have lower visual phytotoxicity when subjected to the spraying of the herbicide fomesafen. There were anatomical differences between the leaf blades of the conventional (MG/BR 46 Conquista) and transgenic (BRS Valiosa - RR) cultivars, and the water scarcity changed the anatomy of the soybean plants. The condition of moderate water shortage (-0.07 MPa) led the conventional cultivar to present a lower development than the transgenic cultivar. The transgenic cultivar had a greater ability to sustain the biological nitrogen fixation under moderate water shortage conditions (-0.07 MPa) than the conventional cultivar.

Response of Bacterial Community to the Occurrence of Clubroot Disease in Chinese Cabbage

Clubroot disease is a common soilborne disease caused by Plasmodiophora brassicas Wor. and widely occurs in Chinese cabbage. Soil microorganisms play vital roles in the occurrence and development of plant diseases. The changes in the soil bacterial community could indicate the severity of plant disease and provide the basis for its control. This study focused on the bacterial community of the clubroot disease-infected soil-root system with different severity aiming to reveal the composition and structure of soil bacteria and identified potential biomarker bacteria of the clubroot disease. In the clubroot disease-infected soil, the bacterial community is mainly composed of Actinobacteria, Gammaproteobacteria, Alphaproteobacteria, Bacilli, Thermolrophilia, Bacteroidia, Gemmatimonadetes, Subgroup_6, Deltaproteobacteria, KD4-96, and some other classes, while the major bacterial classes in the infected roots were Oxyphotobacteria, Gammaproteobacteria, Alphaproteobacteria, Actinobacteria, Bacilli, Bacteroidia, Saccharimonadia, Thermoleophilia, Clostridia, Chloroflexia, and some other classes. The severe clubroot disease soil-root system was found to possess a poorer bacterial richness, evenness, and better coverage. Additionally, a significant difference was observed in the structure of the bacterial community between the high-severity (HR) and healthy (LR) soil-root system. Bacillus asahii and Noccaea caerulescens were identified as the differential bacteria between the LR and HR soil and roots, respectively. pH was demonstrated as a vital factor that was significantly associated with the abundance of B. asahii and N. caerulescens. This study provides novel insight into the relationship between soil bacteria and the pathogen of clubroot disease in Chinese cabbage. The identification of resistant species provides candidates for the monitoring and biocontrol of the clubroot disease.

Effects of thifluzamide on soil fungal microbial ecology

Thifluzamide, a succinate dehydrogenase inhibitor fungicide, has been used extensively for many diseases control and has the risk of accumulation in soil ecology. In order to study the ecotoxicity of thifluzamide to soil fungal communities, typical corn field soils in north (Tai'an) and south (Guoyang) China were treated with thifluzamide (0, 0.1, 1.0 and 10.0 mg/kg) and incubated for 60 days. Thifluzamide exposure promoted soil basal respiration, and significantly reduced the number of soil culturable fungi and the abundance of soil fungi (RT-qPCR) in middle and late treatment period (15, 30, 60 days). Illumina Mi-Seq sequencing revealed that thifluzamide could reduce fungal alpha diversity (Sobs, Shannon, Simpson indexes) and change fungal community structure. FUN Guild analysis showed that the relative abundance of Undefined Saprotroph increased after the thifluzamide treatment, whereas that of Plant Pathogen decreased, and we concluded that exposure to thifluzamide could change the function of soil fungi. This study evaluated the soil ecological risk caused by thifluzamide's release into soil, providing a basis for its rational application.

Growth, respiratory activity and chlorpyrifos biodegradation in cultures of Azotobacter vinelandii ATCC 12837

This study aimed to evaluate the growth, respiratory activity, and biodegradation of chlorpyrifos in cultures of Azotobacter vinelandii ATCC 12837. A strategy based on the modification of culture media and aeration conditions was carried out to increase the cell concentration of A. vinelandii, in order to favor and determine its tolerance to chlorpyrifos and its degradation ability. The culture in shaken flasks, using sucrose as a carbon source, significantly improved the growth compared to media with mannitol. When the strain was cultivated under oxygen-limited (5.5, 11.25 mmol L⁻¹ h⁻¹) and no-oxygen-limited conditions (22 mmol L⁻¹ h⁻¹), the growth parameters were not affected. In cultures in a liquid medium with chlorpyrifos, the bacteria tolerated a high pesticide concentration (500 ppm) and the growth parameters were improved even under conditions with a reduced carbon source (sucrose 2 g L⁻¹). The strain degraded 99.6% of chlorpyrifos at 60 h of cultivation, in co-metabolism with sucrose; notably, A. vinelandii ATCC 12837 reduced by 50% the initial pesticide concentration in only 6 h (DT₅₀).

Exposure to fomesafen alters the gut microbiota and the physiology of the earthworm Pheretima guillelmi

The application of herbicide fomesafen plays a crucial role in ensuring global soybean productivity in modern agriculture, but it results in both adverse effects on soil ecosystems and phytotoxicity to succeeding crops. Soil pollution due to herbicides has raised much concern worldwide. However, there has been little investigations concerning their effects on soil fauna, especially on the gut microbial communities of earthworms. In this study, the soil endogeic earthworm Pheretima guillelmi was incubated for 20 days in natural and fomesafen-polluted soils to investigate the effects of the herbicide on gut bacterial microbiota and the earthworm's physiological indices, including energy resource (protein) and antioxidant enzyme (superoxide dismutase, SOD) of earthworms in the soil ecosystem. A significantly different and smaller microbial community was presented in the earthworm's gut compared with the cast and the surrounding soil, with exposure to fomesafen further reducing the bacterial diversity and altering the gut community composition. This was observed as significant changes in the relative abundance of the phyla Actinobacteria, Firmicutes, and Proteobacteria as well as the genera Bacillus, Microvirga, Blastococcus, Nocardioides, and Gaiella. Moreover, exposure to fomesafen reduced earthworms' energy resources and activated the antioxidant system, with both effects being significantly correlated with the gut microbial diversity. These findings unravel the fact that exposure to the herbicide fomesafen may affect non-target soil fauna via changes in their microbiota and physiological indices, thereby contributing new knowledge regarding the adverse impacts of fomesafen on the terrestrial ecosystem.

Effect of Soil Type and Temperature on Persistence and Dissipation Kinetics of a New Readymix Formulation of Fomesafen + Quizalofop-ethyl

The research portrays the fate of a new herbicide mixture of fomesafen and quizalofop-ethyl. The soil samples viz. red lateritic soil (A), coastal saline soil (B) and black soil (C) were fortified separately for fomesafen and quizalofop-ethyl at 0.5 (T1) and 1.0 mg kg^-1 (T2) doses and incubated at 20, 30 and 40°C. A satisfactory mean recovery, precision and linearity proved that the methods were accurate. Both the herbicides followed first + first order kinetics. Higher persistence of fomesafen was observed in Soil C than Soil B and Soil A with 22.38-53.75 days half-life, whereas quizalofop-ethyl showed higher stability in Soil A than Soils B and C with half-life of 0.93-12.07 days. Both compounds showed faster rates of dissipation at increased temperature, irrespective of soil type. The current study will help to predict the effect of temperature on the dissipation of herbicides in different soil under real field scenario.

Impact of Soil Disinfestation on Fungal and Bacterial Communities in Soil With Cucumber Cultivation

Soil treatment with disinfectants has been used for controlling soilborne phytopathogens. Besides suppressing specific pathogens, how these disinfectants impact soil health, especially soil microbial communities, is yet to be systemically determined. The objectives of this study were to examine the effects of three representative disinfectants, including the dazomet fumigant, fenaminosulf fungicide, and kasugamycin antibiotic on chemical properties, enzymatic activities, and microbial communities in soil for cucumber cultivation. Results showed that 14 days after soil treatment with these chemicals, residual content of dazomet and kasugamycin quickly declined in soil and were undetectable, while fenaminosulf residues were found at 0.48 ± 0.01 mg/kg. Total nitrogen and total carbon increased in soil after dazomet treatment. Urease and sucrase activities were significantly restrained after disinfectant application. The disinfectants did not significantly change the taxon of predominant bacteria and fungi but altered the relative abundance and diversity of soil microbiome, as well as microbial interspecific relationships. Moreover, cucumber cultivation enhanced the overall soil microbial diversity and enzymatic activities, which diminished the difference of soil microbiome among four treatments. The difference in soil microbial diversity among the four treatments became smaller after planting cucumber. Thus, soil microbial communities were affected by soil disinfectants and gradually recovered by cucumber application.

Keystone taxa-mediated bacteriome response shapes the resilience of the paddy ecosystem to fungicide triadimefon contamination

The increasing input of fungicides has emerged as a global concern for agroecosystem stability and sustainability. Agroecosystem resilience has been linked to microbiome response, however, is not well understood. Focusing on a widespread triazole-class fungicide triadimefon in the paddy ecosystem, we characterized that the soils and sediments were dominant triadimefon reservoirs with the peak level at 195 μg kg^-1 and 31.3 μg kg^-1, respectively, but essential for the resilience of paddy ecosystem to triadimefon. In paddy simulation models, the half-life of triadimefon in soil-sediment was 8.4-28.9 days, while it was prolonged to 86.6-115.5 days after elimination of resident microbial community. Phospholipid fatty acid profiling and high-throughput sequencing showed that the distinctive bacterial community responses contributed to variable degradation of triadimefon in paddy soils and sediments. Sphingomonas and Xanthomonas were identified as positive responders of the keystone taxa in the responsive bacteriome, whereas Enterobacter were negative responders that declined over time. Synthetic assemblages combined with quantitative polymerase chain reaction further validated that Sphingomonas and Xanthomonas were involved in sustaining soil-sediment resilience to triadimefon contamination. Collectively, our results revealed that the shaping of soil and sediment bacteriomes was responsible for the resilience of the paddy agroecosystem to fungicide contamination.

LDPE microplastics affect soil microbial communities and nitrogen cycling

Microplastics (MPs) are a contaminant of increasing concern in the environment. However, the impacts of MPs on soil ecosystems and biogeochemical processes like nitrogen cycle have not been well elucidated. In this study, we designed an indoor microcosm experiment to investigate the effects of exposure to low density polyethylene (LDPE) MPs on soil bacterial community and nitrogen cycling function over a 90-day incubation. Next-generation sequencing of the 16S rRNA genes revealed that both 2% and 7% LDPE MPs exposure slightly affected the soil bacterial diversity. Further analysis at the genus level showed differential tolerance to LDPE MPs, the genera Pedomicrobium, Steroidobacter, Pseudonocardia, Nitrospira and Turicibacter were enriched in the soil with 2% (w/w) LDPE MPs amendment, while the genera Pedomicrobium, Mycobacterium and Hyphomicrobium were significantly enriched in the soil with 7% (w/w) LDPE MPs amendment on days 15 and 30. Co-occurrence network analysis further suggested that LDPE MPs changed bacterial network complexity and modularity and Acidobacteria formed intimate associations with each other in responding to LDPE MPs exposure. Additionally, LDPE MPs in soil increased the abundance of nifH, AOBamoA and nirK genes involved in nitrogen cycling in different incubation phases compared to the control. The abundance of AOAamoA genes decreased on day 15 and then increased. Conversely, the abundance of nirS genes increased during the first 15 days and then decreased. These results suggested that both 2% and 7% LDPE MPs impact soil bacterial network structure and alters functional groups involved in soil nitrogen cycling processing.

Effects of increasing concentrations of fungicide QuadrisR on bacterial functional profiling in loamy sand soil

A mesocosm experiment was conducted to assess the side effects of the fungicide Quadris^R on soil bacterial functioning. Quadris^R was applied to a loamy sand soil at increasing concentrations (0.0-35.0 mg kg^-1 dry soil) calculated according to its active ingredient azoxystrobin (Az). Soil sampling was carried out from the 1st to the 120th day of soil incubation to determine the changes occurred in bacterial catabolism using the technique of community-level physiological profiling (CLPP) via Biolog EcoPlates™. It was found that the field recommended fungicide concentration (2.90 mg kg^-1 dry soil) altered mostly the low-available Biolog carbon sources (< 0.50 optical density (OD)), whereas the fungicide higher concentrations (14.65 and 35.00 mg kg^-1 dry soil) were effective also on medium (0.50-1.00 OD) and highly (> 1.00 OD) utilizable ones. Pearson correlation analysis revealed that the main environmental factors correlated with the utilization rates of Biolog carbon sources (CSs) were soil nutrients and pH. No linear relationships were found between Az soil residues and the use of CSs. We concluded that Quadris^R affects bacterial catabolic profiles in loamy sand soils through soil acidification and altering soil nutrient pool. The study also revealed that CLPP and EcoPlate™ are useful practical tools for testing the fungicide ecotoxicity.

Clomazone improves the interactions between soil microbes and affects C and N cycling functions

Clomazone, a widely used herbicide, is mainly used in soybean fields. We previously found that clomazone alters Proteobacteria and Nitrospirae abundances and also alters urease activity, which result in changes in NH₄⁺ and NO₃^- contents in soil nitrogen cycling. It remains unknown, however, how the co-occurrence patterns of species and functions of soil ecosystems change in response to clomazone applications in soil. We designed a 3-month greenhouse experiment to investigate soil microorganism dynamics in response to clomazone. Clomazone was applied at three doses (e.g., T1, T10, T100), which significantly increased bacterial abundance at days 15 and 60. Fungal abundance was stimulated at day 30 in T10-treated soils, whereas fungal abundances decreased in T100-treated soils at day 15. Clomazone altered bacterial and fungal community structures. Network analyses showed more complex and highly connected microbial communities in clomazone-treated soils. Moreover, an Acidobacteria-dominated cluster was identified within each network of clomazone-treated soils. Clomazone applied at the recommended rate decreased the functional groups that were associated with denitrification and hydrogen oxidation at days 15 and 60, and enhanced photoheterotrophy from days 30 to 60. High clomazone inputs increased trophic types (e.g., chemoheterotrophy, phototrophy, photoautotrophy and cyanobacteria) and C cycling functional groups (e.g., fermentation and cellulolysis). The half-life of clomazone ranged from 40.1 to 93.5 days in three cases. Our results provide important information for use of this herbicide.

The effect of the pesticide delivery method on the microbial community of field soil

The study deals with the effects of herbicides (metribuzin, tribenuron-methyl, fenoxaprop-P-ethyl) and fungicides (tebuconazole, epoxiconazole, azoxystrobin) applied to soil as free pesticides or as slow release formulations embedded in a biodegradable composite matrix on the structure of the soil microbial community. The matrix consisted of a natural biopolymer poly-3-hydroxybutyrate [P(3HB)] and a filler-one of the natural materials (peat, clay, and wood flour). The soil microbial community was characterized, including the major eco-trophic groups of bacteria, dominant taxa of bacteria and fungi, and primary P(3HB)-degrading microorganisms, such as Pseudomonas, Bacillus, Pseudarthrobacter, Streptomyces, Penicillium, and Talaromyces. The addition of free pesticides adversely affected the abundance of soil microorganisms; the decrease varied from 1.4 to 56.0 times for different types of pesticides. The slow release pesticide formulations, in contrast to the free pesticides, exerted a much weaker effect on soil microorganisms, no significant inhibition in the abundance of saprotrophic bacteria was observed, partly due to the positive effects of the composite matrix (polymer/natural material), which was a supplementary substrate for microorganisms. The slow release fungicide formulations, like the free fungicides, reduced the total abundance of fungi and inhibited the development of the phytopathogens Fusarium and Alternaria. Thus, slow release formulations of pesticides preserve the bioremediation potential of soil microorganisms, which are the main factor of removing xenobiotics from the biosphere.

Soil Enzyme Activity and Microbial Metabolic Function Diversity in Soda Saline–Alkali Rice Paddy Fields of Northeast China

Western Jilin province has the most serious area of soda salinization in Northeast China, which affects and restricts the sustainable development of agriculture. The effects of physico-chemical properties of rhizosphere and non-rhizosphere soil on soil microbial diversity and enzyme activities (polyphenol oxidase, catalase, invertase, amylase) were evaluated in typical soda saline-alkali paddy field. Community-level physiological profile (CLPP) based on Biolog-ECO plates was used to assess the functional diversity of soil microorganisms. Exchangeable sodium percentage (ESP) and pH were negative correlated with the microbial activity (AWCD), soil enzyme activities (amylase, sucrose, and catalase, except for polyphenol oxidase) in rice rhizosphere and non-rhizosphere soil (P < 0.05). The indexes of microbial diversity in rice rhizosphere soil were significantly higher than that of non-rhizosphere soil. The utilization of amino acids by rice rhizosphere microorganisms was relatively high, while non-rhizosphere soil had relatively high utilization of carboxylic acid, phenolic acid, and amine. Among the selected physico-chemical properties, soil organic carbon (SOC) and soil water content (SWC) had the greatest influence on the variation of microbial diversity indexes and enzyme activities in rhizosphere soil. ESP and pH showed a significant positive correlation with carbon source utilization, especially for amine (AM) and phenolic acid (PA) carbon source utilization (P < 0.05) by means of RDA, and the utilization rate of AM and PA carbon sources by rice rhizosphere and non-root soil microorganisms was P1 < P2 < P3.

Effect of fomesafen on the embryonic development of zebrafish

Fomesafen is widely used in agriculture and can be detected in the environment and agricultural products. Research on the developmental toxicity of fomesafen in animals is currently very limited. Here, we used zebrafish as an animal model to evaluate the toxicity of fomesafen in developing aquatic vertebrates and higher animals. From 6h to 72h following fertilization, exposure of zebrafish embryos to 5, 10 and 20 mg/L of fomesafen resulted in pericardial edema, a reduction in heart rate, shortening of body length, and yolk sac edema. Fomesafen reduced the number of immune cells such as neutrophils and macrophages, increased the expression of a number of inflammatory factors, induced the up-regulation of the oxidative stress response and apoptosis, and disrupted the activity of enzymes related to nerve development, which affected the motility of the embryos. In conclusion, the results provide new evidence for the comprehensive assessment of fomesafen toxicity in aquatic vertebrates.

Impact of a synthetic fungicide (fosetyl-Al and propamocarb-hydrochloride) and a biopesticide (Clonostachys rosea) on soil bacterial, fungal, and protist communities

The use of synthetic pesticides in agriculture is increasingly debated. However, few studies have compared the impact of synthetic pesticides and alternative biopesticides on non-target soil microorganisms playing a central role in soil functioning. We conducted a mesocosm experiment and used high-throughput amplicon sequencing to test the impact of a fungal biopesticide and a synthetic fungicide on the diversity, the taxonomic and functional compositions, and co-occurrence patterns of soil bacterial, fungal and protist communities. Neither the synthetic pesticide nor the biopesticide had a significant effect on microbial α-diversity. However, both types of pesticides decreased the complexity of the soil microbial network. The two pesticides had contrasting impacts on the composition of microbial communities and the identity of key taxa as revealed by microbial network analyses. The biopesticide impacted keystone taxa that structured the soil microbial network. The synthetic pesticide modified biotic interactions favouring taxa that are less efficient at degrading organic compounds. This suggests that the biopesticides and the synthetic pesticide have different impact on soil functioning. Altogether, our study shows that pest management products may have functionally significant impacts on the soil microbiome even if microbial α-diversity is unaffected. It also illustrates the potential of high-throughput sequencing analyses to improve the ecotoxicological risk assessment of pesticides on non-target soil microorganisms.

Influence of the herbicide haloxyfop-R-methyl on bacterial diversity in rhizosphere soil of Spartina alterniflora

Haloxyfop-R-methyl (haloxyfop) can efficiently control Spartina alterniflora in coastal ecosystems, but its effect on soil microbial communities is not known. In the present study, the impact of the haloxyfop on rhizosphere soil bacterial communities of S. alterniflora over the dissipation process of the herbicide has been studied in a coastal wetland. The response of the bacterial community in the rhizoplane (iron plaque) of S. alterniflora subjected to haloxyfop treatment was also investigated. Results showed that the persistence of haloxyfop in the rhizosphere soil followed an exponential decay with a half-life of 2.6-4.9 days, and almost all of the haloxyfop dissipated on Day 30. The diversity of rhizosphere soil bacteria was decreased at the early stages (Days 1, 3 & 7) and recovered at late stages (Days 15 & 30) of the haloxyfop treatment. Application of haloxyfop treatment increased the relative abundance of the genera Pseudomonas, Acinetobacter, Pontibacter, Shewanella and Aeromonas. Strains isolated from these genera can degrade herbicides efficiently, which possibly played a role in the degradation of haloxyfop. The rhizoplane bacterial diversity was reduced on Day 15 while being vastly enhanced on Day 30. Soil variables, including the electric conductivity, redox potential, and soil moisture, along with the soil haloxyfop residue, jointly shape the bacterial community in rhizosphere soil.

Fomesafen impacts bacterial communities and enzyme activities in the rhizosphere

Fomesafen, a long-lived protoporphyrinogen-oxidase inhibitor, specially developed for post-emergence control of broad-leaf weeds, is used widely in soybean fields in northern China (Dayan and Duke, 2010). The impact of fomesafen on microbial communities in rhizosphere soils, however, is unknown. In this study we examined fomesafen degradation as well as its effects in the rhizosphere of soybean plants grown in a greenhouse. Fomesafen had shorter half-life in rhizosphere soil than previously reported for bulk soil from the same location (87 vs 120 days). The enzyme activity of soil extracts and the microbial community composition of 16S rRNA genes (16S) amplified from soil DNA were also investigated. Although not immediately apparent, both the high (37.5 mg kg-1) and low (18.75 mg kg-1) doses of fomesafen significantly decreased urease and invertase activities in the rhizosphere soil from days 30 and 45 respectively until the end of the experiment (90 days). Analysis of 16S amplicons demonstrated that fomesafen had a dose dependent effect, decreasing alpha diversity and altering beta diversity. Significant phylum level decreases were observed in five of the ten phyla that were most abundant in the control. Proteobacteria was the only phylum whose relative abundance increased in the presence of fomesafen, driven by increases in the genera Methylophilacaea, Dyella, and Sphingomonas. The functional implications of changes in 16S abundance as predicted using PICRUSt suggested that fomesafen enriched for enzymes involved in xenobiotic metabolism and detoxification (cytochrome P450s and glutathione metabolism). Our data suggest that, despite being degraded more rapidly in the rhizosphere than in bulk soil, fomesafen had long-lasting functional impacts on the soil microbial community.

Enhanced remediation of bispyribac sodium by wheat (Triticum aestivum) and a bispyribac sodium degrading bacterial consortium (BDAM)

The use of plant-bacterial association is a promising approach for the enhanced remediation of pesticides. Generally, both rhizo- and endosphere bacteria assist their host plants to survive in the contaminated environment. In this work, we have studied the individual and combined effects of wheat (Triticum aestivum) and a previously optimized bispyribac sodium (BS) degrading bacterial consortium (BDAM) on the degradation of BS and plant biomass production. Results showed that the bacterial strains of the BDAM have successfully survived in the plant rhizo-as well as endosphere and enhanced degradation of BS and plant biomass. In soil spiked with 2 mg/kg and 5 mg/kg of BS and was planted and inoculated with BDAM (P_I) showed 100% degradation of BS both in rhizosphere soil and endosphere of the plant. However, during the same period (45 days) the degradation of BS was 96 and 90%, and 93 and 84% in inoculated but un-planted (I_UP) and planted but un-inoculated (P_UI) soils spiked with 2 and 5 mg/kg, respectively. Liquid chromatography-mass spectrometry (LC-MS) analysis of the treated samples showed novel degradation products of BS. Based on the results, we concluded that plant-bacterial association is an efficient tool for enhanced remediation of BS contaminated soil and herbicide free crop production.

In vitro investigation to explore the toxicity of different groups of pesticides for an agronomically important rhizosphere isolate Azotobacter vinelandii

In this work, an attempt was made to evaluate the effect of pesticides on growth pattern, surface morphology, cell viability and growth regulators of nitrogen fixing soil bacterium. Pesticide tolerant Azotobacter vinelandii strain AZ6 (Accession no. MG028654) was found to tolerate maximum level of pesticide and displayed multifarious PGP activities. At higher concentrations, pesticides triggered cellular/structural damage and reduced the cell viability as clearly shown under SEM and CLSM. With increase in concentration, pesticides exhibited a significant (p < 0.05) decrease in PGP traits of strain AZ6. Among all three groups of pesticides, herbicides glyphosate and atrazine were most toxic. Kitazin, hexaconazole, metalaxyl, glyphosate, quizalofop, atrazine, fipronil, monocrotophos and imidacloprid at 2400, 1800, 1500, 900, 1200, 900, 1800, 2100 and 2700 μg mL^-1, respectively, decreased the production of IAA by 19.5 ± 1.9 (61%), 18.1 ± 1.2 (64%), 36.4 ± 3.4 (28%), 13.1 ± 0.8 (74%), 15.6 ± 1.0 (69%), 7.6 ± 0.5 (83%), 11.9 ± 0.8 (76%), 24.7 ± 1.7 (51%) and 32 ± 2.3 (37%) μg mL^-1, respectively, over control (50.7 ± 3.6 μg mL^-1). A maximum reduction of 8.4 ± 1.2 (46%), 5.8 ± 0.6 (62%) and 4 ± 0.2 (74%) μg mL^-1 in 2, 3-DHBA at 300 (1×), 600 (2×) and 900 (3×) μg mL^-1 glyphosate, respectively, While, 32.8 ± 2.7 (19%), 27.2 ± 2 (33%) and 21.5 ± 1.3 (47%) μg mL^-1, respectively in the production of SA was observed at 300 (1×), 600 (2×) and 900 (3×) μg mL^-1 atrazine, respectively. Likewise, with increase in concentration of pesticides, decrease in P solubilization ability and change in pH of broth was detected. The order of pesticide toxicity to PSE (percent decline over control) at highest concentration was: atrazine (45) > kitazin (44) > metalaxyl (43) > monocrotophos (43) > glyphosate (41) > hexaconazole (39) > quizalofop (33) > imidacloprid (31) > fipronil (25). The present study undoubtedly suggests that even at higher doses of pesticides, A. vinelandii maintained secreting plant growth regulators and this property makes this strain agronomically important microbe for enhancing the growth of plants.

Soil-applied biochar increases microbial diversity and wheat plant performance under herbicide fomesafen stress

The herbicide "fomesafen" causes phytotoxicity to the rotational wheat crop and may reduce its yield. Considering that biochar may improve remediation and biophysical conditions of the contaminated soil environments to benefit plant growth. Here, we investigated the impacts of three levels of the wheat straw-derived biochar (1%, 2%, and 4% (w/w)) on growth, physiological properties, and rhizosphere microbial communities of the wheat (Triticum aestivum) seedlings under the fomesafen stress using high-throughput sequencing. The results showed that biochar amended into soil significantly reduced the uptake of wheat to fomesafen and thereby eliminate its toxicity to wheat seedlings. Moreover, biochar increased the abundance and diversity of plant beneficial bacterial and fungal taxa in the rhizosphere of wheat seedlings. Compared with the three addition amounts, amendment with 2% of biochar has the best effects to reduce the toxicity of fomesafen on wheat seedlings and maintain the balance of soil microbial community structure in soil contaminated with fomesafen (1.0 mg kg^-1). Overall, our results suggest that the level of biochar application influences the structure and diversity of soil microbiome (and mycobiome) and plant performance under abiotic stress conditions.

Soil aggregate-associated bacterial metabolic activity and community structure in different aged tea plantations

Revealing the dynamics of soil aggregate-associated microbial (particularly bacterial) metabolic activity and community structure is of great importance to maintain the soil health and microbial community stability in tea plantation ecosystems. In this study, the bacterial metabolic activity (as measured by Biolog Eco MicroPlates) and community structure (as measured by high-throughput sequencing) were analyzed in soil aggregates, which were collected at the 0-20 cm depth in four tea plantations with different ages (16, 23, 31, and 53 yrs.) in the areas of Western Sichuan, China. A dry-sieving procedure was adopted to separate soil aggregates into four fractions, including >2, 2-1, 1-0.25, and <0.25 mm. In all the tea plantations, the highest levels of soil bacterial metabolic activity (as indicated by average well color development, AWCD) and community diversity (as indicated by Chao 1 and Shannon indices) appeared in the >2 mm fractions, which indicated that these aggregate fractions with complex bacterial communities not only provided biological buffering, but also prevented the dominance of individual microorganisms through predation or competition. Soil aggregates with >2 mm were concentrated in the 23 yrs. tea plantation, implying that this tea plantation possessed the relatively suitable soil environments to the growth and proliferation of soil bacteria, thus increasing their metabolic activity and community diversity. After 23 yrs. of tea planting, the reduction of the >2 mm fractions in the whole-soil accounted for the degradation of soil bacterial communities to some extent. In the meanwhile, soil microbial quotient (the ratio of soil microbial biomass C to organic C) and pH were also important drivers of the variations in soil bacterial communities during tea planting. This study underscored the requirement for sustainable soil managements which could maintain the soil health and bacterial community stability after 23 yrs. of tea planting in the areas of Western Sichuan, China.

Changes in the abundance and community composition of different nitrogen cycling groups in response to fumigation with 1,3-dichloropropene

The fumigant 1,3-dichloropropene (1,3-D) is widely-used to control pathogenic bacteria, fungi, nematodes and insects in soil before a crop is planted. Although fumigants in general have been reported to have a 'fertilizer effect' in the soil by increasing nitrogen availability, little is known of how a specific fumigant such as 1,3-D affects available nitrogen. This study used real-time quantitative PCR (qPCR) and 16S rRNA gene amplicon sequencing techniques to investigate the effects of 1,3-D on microorganisms involved in nitrogen cycling that were present in 2 soils: Jiangxi lateritic red soil and Beijing fluvo-aquic soil. The fumigant 1,3-D temporarily decreased the abundance of 11 functional genes involved in nitrogen-fixing, nitrification and denitrification in both soil types. Different nitrogen cycling groups recovered to the unfumigated level in various incubation phases. Microorganisms containing nifH, nxrB, napA and qnorB genes were most vulnerable to 1,3-D fumigation. However, a stronger and longer inhibition effect of 1,3-D on these 11 functional genes was observed in Jiangxi soil than in Beijing soil. At the same time, the abundance of nifH, AOBamoA, nirS, qnorB and cnorB genes was significantly increased 59 days after 1,3-D fumigation. Fumigation with 1,3-D significantly reduced the nitrogen-fixing bacteria Azospirillum and Paenibacillus; the nitrifiers Nitrosomonas and Nitrospira; and the denitrifiers Pseudomonas, Paracoccus and Sphingomonas. Conversely, fumigation with 1,3-D increased the nitrogen-fixing bacteria Bradyrhizobium and Rhizobium; the nitrification bacteria Nitrosospira and Nitrolancea; and the denitrification bacteria Sphingobium, Alcanivorax, Bacillus, Streptomyces and Aeromonas. Fumigation with 1,3-D therefore caused significant shifts in the species composition and number of microbes directly involved in nitrogen cycling in the short-term. These results contribute toward a better understanding of the impact of 1,3-D fumigation on various types of soil nitrogen-cycling groups.

Influence of different agricultural management practices on soil microbial community over dissipation time of two herbicides

Soil microbiology could be affected by the presence of pesticide residues during intensive farming, potentially threatening the soil environment. The aim here was to assess the dissipation of the herbicides triasulfuron and prosulfocarb, applied as a combined commercial formulation, and the changes in soil microbial communities (through the profile of phospholipid fatty acids (PLFAs) extracted from the soil) during the dissipation time of the herbicides under field conditions. The dissipation of herbicides and the soil microbial structure were assessed under different agricultural practices, such as the repeated application of herbicides (twice), in unamended and amended soils with two organic amendments derived from green compost (GC1 and GC2) and with non-irrigation and irrigation regimes. The results obtained indicate slower dissipation for triasulfuron than for prosulfocarb. The 50% dissipation time (DT₅₀) decreased under all conditions for the second application of triasulfuron, although not for prosulfocarb. The DT₅₀ values for both herbicides increased in the GC2 amended soil with the highest organic carbon (OC) content. The DT₅₀ values decreased for prosulfocarb with irrigation, but not for triasulfuron, despite its higher water solubility. The herbicides did not have any significant effects on the relative population of Gram-negative and Gram-positive bacteria during the assay, but the relative abundance of Actinobacteria increased in all the soils with herbicides. At the end of the assay (215 days), the negative effects of herbicides on fungi abundance were significant (p < 0.05) for all the treatments. These microbiological changes were detected in non-irrigated and irrigated soils, and were more noticeable after the second application of herbicides. Actinobacteria could be responsible for the modification of herbicide degradation rates, which tend to be faster after the second application. This study makes a useful contribution to the evaluation of the soil environment and microbiological risks due to the long-term repeated application of herbicides under different agricultural management practices.

Clomazone influence soil microbial community and soil nitrogen cycling

We designed an indoor mesocosm experiment to investigate the long-term effects of exposure to clomazone, a widely used herbicide, on soil microbial communities and their nitrogen (N) cycling functions. Clomazone was applied to two typical soils from China at three concentrations: 0.8 (the recommended dosage), 8 and 80 mg kg^-1 soil dry weight, and the mix was incubated for 90 days. Samples were removed periodically for assay with several techniques. The half-lives of clomazone in this experiment were 11-126 d. Results were significant only for the highest clomazone concentration. Next-generation sequencing of the 16S and 18S rDNA genes revealed that bacterial diversity significantly decreased whereas fungal abundance increased after day 60 but with no detectable effect on the microbial community. Hierarchical cluster and principal coordinates analysis revealed that the bacterial community structure was negatively impacted. Linear discriminant analysis of effect size identified Sphingomonas and Arthrobacter as the predominant bacterial species. Finally, we measured soil NH₄⁺ and NO₃^- concentrations and used real-time PCR to analyze the abundance of the N-cycling genes, nifH and amoA. In the first 30 days, the NO₃^--N content and the number of ammonia-oxidizing bacteria increased. N₂-fixing bacteria were inhibited after 60 days, but the NH₄⁺-N concentration remained unchanged and was likely provided by ammoniation.

Biodegradability and ecological safety assessment of Stenotrophomonas sp. DDT-1 in the DDT-contaminated soil

The biodegradability and ecological safety assessment of the previously isolated DDT-degrading bacterial strain Stenotrophomonas sp. DDT-1 were investigated in the DDT-contaminated soil under laboratory and field conditions. Under laboratory conditions, the degradation rates of fresh p,p'-DDT in soil were enhanced by 2.0-3.0-fold with the introduction of the strain DDT-1 compared to those of the control treatments. A similar enhancement in the dissipation of DDTs (p,p'-DDT, p,p'-DDE, p,p'-DDD, and o,p'-DDT) in the aged DDT-contaminated field plot soils resulted from the inoculation with this strain. Meanwhile, the degradation rates of DDTs increased by 2.9-5.5- and 2.8-7.6-fold in the inoculated greenhouse and open field soils, respectively, after field demonstration application of strain DDT-1 preparation. Moreover, no significant differences in the soil enzyme activity, microbial functional diversity, and bacterial community structure were observed between the inoculated and un-inoculated field soils, but several soil microbial genera exhibited some fluctuations in abundance. It is concluded that strain DDT-1 could accelerate the removal of DDTs residues in field soils, and furthermore, its inoculation was ecologically safe.

Effects of trifluralin on the soil microbial community and functional groups involved in nitrogen cycling

Large amounts of trifluralin are applied each year for weed control; however, its effects on soil microbial communities and functions are unknown. Two agricultural soils, one silty loam and one silty clay were spiked with TFL (0, 0.84, 8.4, and 84 mg kg^-1) and studied the effects using a laboratory microcosm approach. The half-lives were 44.19-61.83 d in all cases. Bacterial abundance increased 1.12-5.56 times by TFL, but the diversity decreased. From the next-generation sequencing results, TFL altered the bacterial community structure, which initially diverged from the control community structure, then recovered, and then diverged again. Linear discriminant analysis effect size indicated that Sphingomonas and Xanthomonadaceae were the predominant species on day 7 and 15 in TFL treatments. N₂-fixing bacteria were initially increased, then decreased, and then recovered, and it was positively correlated with NH₄⁺-N content. Compared with the control, ammonia-oxidizing bacteria were decreased by 25.51-92.63%, ammonia-oxidizing archaea were decreased by 17.12-85.21% (except day 7), and the NO₃^--N concentration was also inhibited. In contrast to bacteria, fungal abundance was inhibited without any observable effects on fungal diversity or community structure. These results suggest that TFL impacts soil bacterial community and alters functional microorganisms involved in soil N processing.

Rational dose of insecticide chlorantraniliprole displays a transient impact on the microbial metabolic functions and bacterial community in a silty-loam paddy soil

Chlorantraniliprole (CAP) is a newly developed insecticide widely used in rice fields in China. There have been few studies regarding its effects on soil microbial functional diversity and bacterial community composition. An 85-day microcosm experiment was performed to reveal the dissipation dynamics of CAP under different application doses in a silty-loam paddy soil in subtropical China. The half-life of CAP was 51.3 and 62.5d for low (1mgkg^-1) and high (10mgkg^-1) application dose, respectively. We used a combination of community level physiological profile (CLPP) and 16S rRNA gene sequencing analysis to get insights into the soil microbial features responded to CAP during the experiment. Non-metric multidimensional scaling (NMDS) performed on CLPP and the sequence results indicated that the soil microbial functional diversity and bacterial community composition were significantly changed by CAP application at day 14, and recovered to the similar level as no CAP treatment (CK) under low dose of CAP at day 36. However, high dose of CAP imposed longer effect on these soil microbial features, and was still significantly different from CK at day 36. Mcrobial taxa analysis at phylum level showed that high dose of CAP decreased the relative abundance of Nitrospirae at day 14, while increased Bacteroidetes and decreased Actinobacteria, Nitrospirae, and Firmicutes at day 36 in relative to CK. Low dose of CAP only increased Crenarchaeota and decreased Nitrospirae at day 14. The response ratio (RR) analysis was used to quantify significant responses of OTUs to different doses of CAP and found that CAP significantly affected the microbes involving the N transformation. This study provides a basic information to aid in the development of application regulations regarding the safe use of CAP in soil and inspire us to apply CAP at rational dose to minimize its ecotoxicity on soil microbes.

Microbial degradation of fomesafen and detoxification of fomesafen-contaminated soil by the newly isolated strain Bacillus sp. FE-1 via a proposed biochemical degradation pathway

Fomesafen is a long residual herbicide and poses a potential risk to environmental safety, leading to an increasing need to find eco-friendly and cost-effective techniques to remediate fomesafen-contaminated soils. In this article, a novel strain of Bacillus sp., FE-1 was isolated from paddy field soil. This strain was found to degrade fomesafen both in liquid medium and in soil. >82.9% of fomesafen, at concentrations of 0.5, 1 and 10mgL^-1, was degraded by Bacillus sp. FE-1 in liquid medium within 14h. The optimal pH and temperature for degradation were 7.0 and 35°C, respectively. Soil samples inoculated with strain FE-1 showed significantly increased rates of fomesafen degradation. Two metabolites of fomesafen degradation were detected and identified as amino-fomesafen and 5-[2-chloro-4-(trifluoromethyl) phenoxy]-2-amino-benzoic acid. This is the first report of a novel fomesafen biodegradation pathway involving the reduction of a nitro group followed by the hydrolysis of an amide bond. The excellent remediation capability of the isolate FE-1 to detoxify fomesafen-contaminated soil was shown by bioassay of the sensitive aftercrop corn. The results indicate that Bacillus sp. FE-1 has potential for use in the bioremediation of fomesafen-contaminated soil.

Impact of fomesafen on the soil microbial communities in soybean fields in Northeastern China

Fomesafen, a widely adopted residual herbicide, is used throughout the soybean region of northern China for the spring planting. However, the ecological risks of using fomesafen in soil remain unknown. The aim of this work was to evaluate the impact of fomesafen on the microbial community structure of soil using laboratory and field experiments. Under laboratory conditions, the application of fomesafen at concentrations of 3.75 and 37.5mg/kg decreased the basal respiration (RB) and microbial biomass carbon (MBC). In contrast, treatment with 375mg/kg of fomesafen resulted in a significant decrease in the RB, MBC, abundance of both Gram+ and Gram- bacteria, and fungal biomass. Analysis of variance showed that the treatment accounted for most of the variance (38.3%) observed in the soil microbial communities. Furthermore, the field experiment showed that long-term fomesafen application in continuously cropped soybean fields affected the soil bacterial community composition by increasing the relative average abundance of Proteobacteria and Actinobacteria species and decreasing the abundance of Verrucomicrobia species. In addition, Acidobacteria and Chloroflexi species showed a pattern of activation-inhibition. Taken together, our results suggest that the application of fomesafen can affect the community structure of soil bacteria in the spring planting soybean region of northern China.

Effects of hexaconazole application on soil microbes community and nitrogen transformations in paddy soils

The ecological risks of widely used hexaconazole on soil microbes remain obscure. Thus, a 3-month-long experiment using two typical paddy soils in China (red soil and black soil) was conducted to assess the effects of hexaconazole (0.6 (T1) and 6 (T10) mgkg^-1 soil) on the overall microbial biomass, respiratory activity, bacterial abundance and community structure, and nitrogen transformations. Soil was sampled after 7, 15, 30, 60, and 90days of incubation. The half-lives of the two doses of hexaconazole varied from 122 to 135d in the black soil and from 270 to 845d in the red soil. Both dosages of hexaconazole did not affect NH⁺₄-N content, N₂-fixing bacterial populations, total bacterial diversity, and community structure, but transitorily decreased the populations of total bacteria in both soil types. In the black soil, T10 negatively affected microbial biomass carbon (MBC) and soil basal respiration (R_B), but transitorily increased NO^-₃-N concentration and ammonia-oxidizing bacteria populations, while T1 had almost no effect on most of the indicators. As for red soil, both concentrations of fungicide significantly, but transitorily, inhibited MBC and R_B, while only T10 had a relatively long stimulatory effect on NO^-₃-N concentration and ammonia-oxidizing archaea populations. This study showed that over application of hexaconazole is indeed harmful to soil microorganisms and may reduce soil quality and increase the risk of nitrogen loss in paddy soils.

Ecotoxicological assessment of pesticides and their combination on rhizospheric microbial community structure and function of Vigna radiata

India is one of the leading countries in production and indiscriminate consumption of pesticides. Owing to their xenobiotic nature, pesticides affect soil microorganisms that serve as mediators in plant growth promotion. Our study aimed to deliver a comprehensive picture, by comparing the effects of synthetic pesticides (chlorpyriphos, cypermethrin, and a combination of both) with a biopesticide (azadirachtin) at their recommended field application level (L), and three times the recommended dosage (H) on structure and function of microbial community in rhizosphere of Vigna radiata. Effect on culturable fraction was assessed by enumeration on selective media, while PCR-denaturing gradient gel electrophoresis (DGGE) was employed to capture total bacterial community diversity. This was followed by a metabolic sketch using community-level physiological profiling (CLPP), to obtain a broader picture of the non-target effects on rhizospheric microbial community. Although plant parameters were not significantly affected by pesticide application, the microbial community structure experienced an undesirable impact as compared to control devoid of pesticide treatment. Examination of DGGE banding patterns through cluster analysis revealed that microbial community structure of pesticide-treated soils had only 70% resemblance to control rhizospheric soil even at 45 days post application. Drastic changes in the metabolic profiles of pesticide-treated soils were also detected in terms of substrate utilization, rhizospheric diversity, and evenness. It is noteworthy that the effects exacerbated by biopesticide were comparable to that of synthetic pesticides, thus emphasizing the significance of ecotoxicological assessments before tagging biopesticides as "safe alternatives."

Effects of aging process on adsorption-desorption and bioavailability of fomesafen in an agricultural soil amended with rice hull biochar

Biochar has been introduced as an acceptable soil amendment due to its environmental benefits such as sequestering soil contaminants. However, the aging process in biochar amended soil probably decreases the adsorption capacity of biochar through changing its physico-chemical properties. Adsorption, leaching and bioavailability of fomesafen to corn in a Chinese soil amended by rice hull biochar after 0, 30, 90 and 180days were investigated. Results showed that the addition of 0.5%-2% fresh biochar significantly increases the adsorption of fomesafen 4-26 times compare to unamended soil due to higher SSA of biochar. Biochar amendment also decreases fomesafen concentration in soil pore water by 5%-23% resulting lower risk of the herbicide for cultivated plants. However, the aging process decreased the adsorption capacity of biochar since the adsorption coefficient values which was 1.9-12.4 in 0.5%-2% fresh biochar amended soil, declined to 1.36-4.16, 1.13-2.78 and 0.95-2.31 in 1, 3 and 6-month aged treatments, respectively. Consequently, higher desorption, leaching and bioavailable fraction of fomesafen belonged to 6-month aged treatment. Nevertheless, rice hull biochar was effective for sequestering fomesafen as the adsorption capacity of biochar amended soil after 6months of aging was still 2.5-5 times higher compared to that of unamended soil.

Successive chlorothalonil applications inhibit soil nitrification and discrepantly affect abundances of functional genes in soil nitrogen cycling

Broad-spectrum fungicide chlorothalonil (CTN) is successively applied into intensive agriculture soil. However, the impacts of successive CTN applications on soil nitrification and related microorganisms remain poorly understood. A microcosm study was conducted to reveal the effects of successive CTN applications on soil nitrification and functional genes involved in soil nitrogen (N) cycling. The CTN at the dosages of 5 mg kg^-1 dry soil (RD) and 25 mg kg^-1 dry soil (5RD) was successively applied into the test soil at 7-day intervals which resulted in the accumulations of CTN residues. After 28 days of incubation, CTN residues in the RD and 5RD treatments were 3.14 and 69.7 mg kg^-1 dry soil respectively. Net nitrification rates in the RD and 5RD treatments were lower than that obtained from the blank control (CK). Real-time PCR analysis revealed that AOA and AOB amoA gene abundances were significantly decreased by CTN applications. Moreover, CTN applications also discrepantly decreased the abundances of functional genes involved in soil denitrification, with the exception of nosZ gene. Principal component analysis further supported the observation that successive CTN applications could result in enhanced ecological toxicity.

Impact of Imidacloprid Seed Dressing Treatment on Soil Microorganisms and Enzyme Activities in the Maize Rhizosphere

Under the field conditions, effects of imidacloprid seed dressing treatment on soil culturable microorganisms and enzyme activities in maize rhizosphere were studied. The results showed that the microbial populations for bacteria, actinomycetes and fungi in maize rhizosphere after imidacloprid treatments were lower than control. The bacteria and actinomycetes populations showed a trend of decreasing after increasing with the maize growth from the seedling stage to the maturity stage, and the fungi populations decreased with the maize growth. The urease activities of maize rhizosphere soil from different treatments showed a trend of initially increasing after decreasing, then decreasing. The invertase activities of maize rhizosphere soil from different treatments showed a trend of decreasing after increasing, and the peak value occurred at flowering stage. With the imidacloprid application, the invertase activities had been stimulated. The results may provide theoretical basis for rational seed dressing treatment.

Response of enzyme activities and microbial communities to soil amendment with sugar alcohols

Changes in microbial community structure are widely known to occur after soil amendment with low-molecular-weight organic compounds; however, there is little information on concurrent changes in soil microbial functional diversity and enzyme activities, especially following sorbitol and mannitol amendment. Soil microbial functional diversity and enzyme activities can be impacted by sorbitol and mannitol, which in turn can alter soil fertility and quality. The objective of this study was to investigate the effects of sorbitol and mannitol addition on microbial functional diversity and enzyme activities. The results demonstrated that sorbitol and mannitol addition altered the soil microbial community structure and improved enzyme activities. Specifically, the addition of sorbitol enhanced the community-level physiological profile (CLPP) compared with the control, whereas the CLPP was significantly inhibited by the addition of mannitol. The results of a varimax rotated component matrix demonstrated that carbohydrates, polymers, and carboxylic acids affected the soil microbial functional structure. Additionally, we found that enzyme activities were affected by both the concentration and type of inputs. In the presence of high concentrations of sorbitol, the urease, catalase, alkaline phosphatase, β-glucosidase, and N-acetyl-β-d-glucosaminidase activities were significantly increased, while invertase activity was decreased. Similarly, this increase in invertase, catalase, and alkaline phosphatase and N-acetyl-β-d-glucosaminidase activities was especially evident after mannitol addition, and urease activity was only slightly affected. In contrast, β-glucosidase activity was suppressed at the highest concentration. These results indicate that microbial community diversity and enzyme activities are significantly affected by soil amendment with sorbitol and mannitol.

Non-target impact of fungicide tetraconazole on microbial communities in soils with different agricultural management

Effect of the fungicide tetraconazole on microbial community in silt loam soils from orchard with long history of triazole application and from grassland with no known history of fungicide usage was investigated. Triazole tetraconazole that had never been used on these soils before was applied at the field rate and at tenfold the FR. Response of microbial communities to tetraconazole was investigated during 28-day laboratory experiment by determination of changes in their biomass and structure (phospholipid fatty acids method-PLFA), activity (fluorescein diacetate hydrolysis-FDA) as well as changes in genetic (DGGE) and functional (Biolog) diversity. Obtained results indicated that the response of soil microorganisms to tetraconazole depended on the management of the soils. DGGE patterns revealed that both dosages of fungicide affected the structure of bacterial community and the impact on genetic diversity and richness was more prominent in orchard soil. Values of stress indices-the saturated/monounsaturated PLFAs ratio and the cyclo/monounsaturated precursors ratio, were almost twice as high and the Gram-negative/Gram-positive ratio was significantly lower in the orchard soil compared with the grassland soil. Results of principal component analysis of PLFA and Biolog profiles revealed significant impact of tetraconazole in orchard soil on day 28, whereas changes in these profiles obtained for grassland soil were insignificant or transient. Obtained results indicated that orchards soil seems to be more vulnerable to tetraconazole application compared to grassland soil. History of pesticide application and agricultural management should be taken into account in assessing of environmental impact of studied pesticides.

Effects of myclobutanil on soil microbial biomass, respiration, and soil nitrogen transformations

A 3-month-long experiment was conducted to ascertain the effects of different concentrations of myclobutanil (0.4 mg kg(-1) soil [T1]; 1.2 mg kg(-1) soil [T3]; and 4 mg kg(-1) soil [T10]) on soil microbial biomass, respiration, and soil nitrogen transformations using two typical agricultural soils (Henan fluvo-aquic soil and Shanxi cinnamon soil). Soil was sampled after 7, 15, 30, 60, and 90 days of incubation to determine myclobutanil concentration and microbial parameters: soil basal respiration (RB), microbial biomass carbon (MBC) and nitrogen (MBN), NO(-)3-N and NH(+)4-N concentrations, and gene abundance of total bacteria, N2-fixing bacteria, fungi, ammonia-oxidizing archaea (AOA), and ammonia-oxidizing bacteria (AOB). The half-lives of the different doses of myclobutanil varied from 20.3 to 69.3 d in the Henan soil and from 99 to 138.6 d in the Shanxi soil. In the Henan soil, the three treatments caused different degrees of short-term inhibition of RB and MBC, NH(+)4-N, and gene abundance of total bacteria, fungi, N2-fixing bacteria, AOA, and AOB, with the exception of a brief increase in NO(-)3-N content during the T10 treatment. The MBN (immobilized nitrogen) was not affected. In the Shanxi soil, MBC, the populations of total bacteria, fungi, and N2-fixing bacteria, and NH(+)4-N concentration were not significantly affected by myclobutanil. The RB and MBN were decreased transitorily in the T10 treatment. The NO(-)3-N concentrations and the abundance of both AOA and AOB were erratically stimulated by myclobutanil. Regardless of whether stimulation or suppression occurred, the effects of myclobutanil on the two soil types were short term. In summary, myclobutanil had no long-term negative effects on the soil microbial biomass, respiration, and soil nitrogen transformations in the two types of soil, even at 10-fold the recommended dosage.

Nontarget effects of chemical pesticides and biological pesticide on rhizospheric microbial community structure and function in Vigna radiata

Intensive agriculture has resulted in an indiscriminate use of pesticides, which demands in-depth analysis of their impact on indigenous rhizospheric microbial community structure and function. Hence, the objective of the present work was to study the impact of two chemical pesticides (chlorpyrifos and cypermethrin) and one biological pesticide (azadirachtin) at two dosages on the microbial community structure using cultivation-dependent approach and on rhizospheric bacterial communities involved in nitrogen cycle in Vigna radiata rhizosphere through cultivation-independent technique of real-time PCR. Cultivation-dependent study highlighted the adverse effects of both chemical pesticide and biopesticide on rhizospheric bacterial and fungal communities at different plant growth stages. Also, an adverse effect on number of genes and transcripts of nifH (nitrogen fixation); amoA (nitrification); and narG, nirK, and nirS (denitrification) was observed. The results from the present study highlighted two points, firstly that nontarget effects of pesticides are significantly detrimental to soil microflora, and despite being of biological origin, azadirachtin exerted negative impact on rhizospheric microbial community of V. radiata behaving similar to chemical pesticides. Hence, such nontarget effects of chemical pesticide and biopesticide in plants' rhizosphere, which bring out the larger picture in terms of their ecotoxicological effect, demand a proper risk assessment before application of pesticides as agricultural amendments.

Reduced mobility of fomesafen through enhanced adsorption in biochar-amended soil

The residual soil material resulting from biomass thermochemical transformation during carbon separation, known as biochar, has been introduced as a soil amendment because of its numerous environmental benefits, including uses for contaminated land management. Adsorption and leaching of fomesafen in soils amended with 3 different rates of rice hull biochar (0.5%, 1%, and 2% w/w) under laboratory conditions were investigated, and studies were performed following a batch equilibration adsorption-desorption procedure and a column experiment for leaching. Adsorption-desorption data fit with the Freundlich equation well. The adsorption coefficient of fomesafen sharply increased from 0.59 to 0.99 to 8.02 to 22.23 when the amount of biochar amendment in the soil increased from 0% to 2% (w/w). In addition, a strong correlation was found between the amount of adsorbed fomesafen and the rate of amended biochar (r > 0.992, p < 0.01). Furthermore, biochar amendments reduced the desorption percentage of fomesafen in the soils. The outcomes of the leaching experiment also illustrated that the lowest fomesafen concentration in the leachate (21.4%) occurred in the soil amended with 2% (w/w) biochar. Moreover, the adsorption coefficients (K(f)(ads)) of the soil were positively correlated with the total amount of adsorbed fomesafen in the corresponding soil columns (r = 0.990, p < 0.01) and negatively correlated with the leachate percentage (r = 0.987, p < 0.05). The results of the present study suggest that biochar amendments in agricultural soils likely alter the fate of herbicides by decreasing their transport through enhanced adsorption.

Impacts of dimethyl phthalate on the bacterial community and functions in black soils

Dimethyl phthalate (DMP), a known endocrine disruptor and one of the phthalate esters (PAEs), is a ubiquitous pollutant. Its impacts on living organisms have aroused great concern. In this study, the impacts of DMP contamination on bacterial communities and functions were tested by using microcosm model in black soils. The results showed that the operational taxonomic unit (OTUs) richness and bacterial diversity were reduced by DMP contamination. The relative percentages of some genera associated with nitrogen metabolism were increased by DMP contamination, while the relative percentages of some other genera that were extremely beneficial to soil health were decreased by DMP contamination. Further, the relative percentages of some genera that possessed the capability to degrade DMP were increased by the DMP treatment at low concentrations (5, 10, and 20 mg/kg), but were decreased by the high concentration DMP treatment (40 mg/kg). Clearly, DMP contamination changed the bacterial community structure and disturbed the metabolic activity and functional diversity of the microbes in black soils. Our results suggest that DMP pollution can alter the metabolism and biodiversity of black soil microorganisms, thereby directly impact fertility and ecosystem functions.

Exploring bacterial community structure and function associated with atrazine biodegradation in repeatedly treated soils

Substantial application of the herbicide atrazine in agriculture leads to persistent contamination, which may damage the succeeding crops and pose potential threats to soil ecology and environmental health. Here, the degradation characteristics of atrazine and dynamic change of soil bacterial community structure and function as well as their relations were studied during three repeated treatments at the recommended, double, and five-fold doses. The results showed that the degradation half-life of atrazine obviously decreased with increased treatment frequency. Soil microbial functional diversity displayed a variation trend of suppression-recovery-stimulation, which was associated with increased degradation rate of atrazine. 16S amplicon sequencing was conducted to explore bacterial community structure and correlate the genus to potential atrazine degradation. A total of seven potentially atrazine-degrading bacterial genera were found including Nocardioides, Arthrobacter, Bradyrhizobium, Burkholderia, Methylobacterium, Mycobacterium, and Clostridium. These bacterial genera showed almost complete atrazine degradation pathways including dechlorination, dealkylation, hydroxylation, and ring cleavage. Furthermore, the relative abundance of four of them (i.e., Nocardioides, Arthrobacter, Methylobacterium, and Bradyrhizobium) increased with treatment frequency and atrazine concentration, suggesting that they may participate in atrazine degradation during repeated treatments. Our findings reveal the potential relationship between atrazine degradation and soil bacterial community structure in repeatedly treated soils.

Soil microbial community toxic response to atrazine and its residues under atrazine and lead contamination

Intensive use of atrazine and extensive dispersal of lead (Pb) have occurred in farmland with chemical agriculture development. However, the toxicological effect of their presence on soil microorganism remains unknown. The objective of this study was to investigate the impacts of atrazine or Pb on the soil microbiota, soil net nitrogen mineralization, and atrazine residues over a 28-day microcosm incubation. The Shannon-Wiener diversity index, typical microbe species, and a Neighbor-joining tree of typical species from sequencing denaturing gradient gel electrophoresis (DGGE) bands were determined across periodical sampling times. The results showed that the existence of atrazine or Pb (especially high concentration) in soils reduced microbial diversity (the lowest H value is 2.23) compared to the control (H = 2.59) after a 28-day incubation. The species richness reduced little (from 17~19 species to 16~17 species) over the research time. But soil microbial community was significantly affected by the incubation time after the exposure to atrazine or Pb. The combination of atrazine and Pb had a significant inhibition effect on soil net nitrogen nitrification. Atrazine and Pb significantly stimulated soil cumulative net nitrogen mineralization and nitrification. Pb (300 and 600 mg kg(-1)) accelerated the level of atrazine dissipation. The exposure might stimulate the significant growth of the autochthonous soil degraders which may use atrazine as C source and accelerate the dissipation of atrazine in soils.