Application of mesotrione at different doses in an amended soil: Dissipation and effect on the soil microbial biomass and activity

Role of Soil Microbiota Enzymes in Soil Health and Activity Changes Depending on Climate Change and the Type of Soil Ecosystem

The extracellular enzymes secreted by soil microorganisms play a pivotal role in the decomposition of organic matter and the global cycles of carbon (C), phosphorus (P), and nitrogen (N), also serving as indicators of soil health and fertility. Current research is extensively analyzing these microbial populations and enzyme activities in diverse soil ecosystems and climatic regions, such as forests, grasslands, tropics, arctic regions and deserts. Climate change, global warming, and intensive agriculture are altering soil enzyme activities. Yet, few reviews have thoroughly explored the key enzymes required for soil fertility and the effects of abiotic factors on their functionality. A comprehensive review is thus essential to better understand the role of soil microbial enzymes in C, P, and N cycles, and their response to climate changes, soil ecosystems, organic farming, and fertilization. Studies indicate that the soil temperature, moisture, water content, pH, substrate availability, and average annual temperature and precipitation significantly impact enzyme activities. Additionally, climate change has shown ambiguous effects on these activities, causing both reductions and enhancements in enzyme catalytic functions.

"Structural responses of non-targeted bacterial and hppd communities to the herbicide tembotrione in soil"

Tembotrione (TBT) is a β-triketone herbicide targeting the 4-Hydroxyphenylpyruvate dioxygenase enzyme (4-HPPD) of weeds. This molecule can also affect soil microorganisms, either through both direct and indirect toxic effects for microorganisms expressing 4-HPPD, or by promoting tolerant and/or degrading microbial populations. Our study aimed to characterize the impacts of TBT on the diversity of total- and hppd (coding for 4-HPPD) -soil bacterial communities. Soil microcosms were treated with the active ingredient TBT at the recommended field dose (100 g a.i/ha; D1) or the tenfold dose (D10). Soil samples were collected from 0 to 55 days post-treatment to study: (i) total- and hppd-bacterial diversities using 16SrRNA and hppd amplicons sequencing, respectively; (ii) TBT dissipation in soil. Both total- and hppd-bacterial community composition was not affected by TBT treatments (D1 and D10). However, D10 treatment slightly increased richness and phylogenetic diversity of the total bacterial community while decreasing hppd richness. Overall, the highest dose of TBT seemed to promote TBT-tolerant or TBT-degrading bacterial populations and to deplete TBT-sensitive ones. These effects were transient as TBT was rapidly dissipated with a DT50 of 7 days and 15 days for D1 and D10, respectively. Differential abundance analysis with a Generalized Linear Model allowed the identification of Sphingomonas, Steroidobacter and Lysobacter as genus that were influenced by TBT, and which could be used as a new class of exposure biomarkers.

Changes in vineyard soil parameters after repeated application of organic-inorganic amendments based on spent mushroom substrate

The changes of physicochemical and biochemical parameters of a silty loam (S1) and sandy loam (S2) vineyard soils added with spent mushroom substrate (SMS) or SMS composted with ophite (OF) as rock dust (SMS + OF) were studied. Two doses of SMS or SMS + OF (25 and 100 Mg ha^-1) were applied for two consecutive years (2020-2021) and changes of soil physicochemical parameters, and dehydrogenase activity (DHA), respiration (RES), microbial biomass (BIO), and the phospholipid fatty acids (PLFAs) profile were assayed on a temporal basis. The results showed an increase in soil organic carbon (OC) content, total and mineralised N, P, and K, especially when the highest SMS dose was applied to soils. Repeated application caused OC content over time up to 2.3 times higher than initial content in the silty loam soil. This increase was not observed in sandy soil, possibly due to a higher bioavailability of OC, as indicated by the evolution of extractable humic acid/fulvic acid pools. In both soils, all biochemical parameters increased after amendment, being favoured both by the OC and by the presence of OF. Significant positive correlations were found between DHA, RES and BIO, and OC content especially in the first part and then levelled off after the second dose application. Total bacterial or fungal PLFAs patterns reflected the variation of BIO by SMS application. The higher growth of fungi vs. bacterial community in amended soils was recorded after the first SMS application, although the opposite effect occurred after the second application, with similar results in both soils. The findings indicate that the application of SMS or SMS + OF in vineyard soils could be an appropriate agronomic management practice for maintaining soil sustainability, although doses and application times of these amendments should first be evaluated depending on soil texture.

Ecotoxicological implications of residual pesticides to beneficial soil bacteria: A review

Optimization of crop production in recent times has become essential to fulfil food demands of constantly increasing human populations worldwide. To address this formidable challenge, application of agro-chemicals including synthetic pesticides in intensive farm practices has increased alarmingly. The excessive and indiscriminate application of pesticides to foster food production however, leads to its exorbitant deposition in soils. After accumulation in soils beyond threshold limits, pesticides harmfully affect the abundance, diversity and composition and functions of rhizosphere microbiome. Also, the cost of pesticides and emergence of resistance among insect-pests against pesticides are other reasons that require attention. Due to this, loss in soil nutrient pool cause a substantive reduction in agricultural production which warrant the search for newer environmentally friendly technology for sustainable crop production. Rhizosphere microbes, in this context, play vital roles in detoxifying the polluted environment making soil amenable for cultivation through detoxification of pollutants, rhizoremediation, bioremediation, pesticide degradation, and stress alleviation, leading to yield optimization. The response of soil microorganisms to range of chemical pesticides is variable ranging from unfavourable to the death of beneficial microbes. At cellular and biochemical levels, pesticides destruct the morphology, ultrastructure, viability/cellular permeability, and many biochemical reactions including protein profiles of soil bacteria. Several classes of pesticides also disturb the molecular interaction between crops and their symbionts impeding the overall useful biological processes. The harmful impact of pesticides on soil microbes, however, is poorly researched. In this review, the recent findings related with potential effects of synthetic pesticides on a range of soil microbiota is highlighted. Emphasis is given to find and suggest strategies to minimize the chemical pesticides usage in the real field conditions to preserve the viability of soil beneficial bacteria and soil quality for safe and sustainable crop production even in pesticide contaminated soils.

Weed Management and Crop Establishment Methods in Rice (Oryza sativa L.) Influence the Soil Microbial and Enzymatic Activity in Sub-Tropical Environment

Weed management has become the most important and inevitable aspect of crop management for achieving a higher rice yield. Nowadays, chemical herbicide application has become a popular practice for managing weeds in different rice cultures. However, herbicide application can have qualitative and quantitative impacts on soil microorganisms and soil enzymes, particularly in the case of new herbicide molecules and their indiscriminate use for a longer period. Further, different rice establishment methods also play a significant role in soil microbial population dynamics as well as soil biological properties. Keeping these in view, a field experiment was conducted at the Agronomy Main Research Farm, Orissa University of Agriculture and Technology (OUAT), India, during the kharif season of 2016 and 2017, on the impact of crop establishment methods and weed management practices on soil microbial and enzymatic status. The field experiment was laid out in a split-plot design with three replications with four crop establishment methods in the main plot, viz., M₁, Direct Seeded Rice (DSR); M₂, Wet Seeded Rice (WSR); M₃,Unpuddled Transplanted Rice (NPTR); M₄, Puddled Transplanted Rice (PTR), and six weed management practices in the sub-plot, viz., W₁, Weedy check; W₂, Bensulfuron methyl 0.6% + Pretilachlor 6% (pre-emergence (PE)) 0.660 kg ha^-1 + Hand weeding (HW) at 30 days after sowing/transplanting (days after sowing/transplanting (DAS/T)); W₃, Bensulfuron methyl 0.6% + Pretilachlor 6% (PE) 0.495 kg ha^-1 + HW at 30 DAS/T; W₄, Bensulfuron methyl 0.6% + Pretilachlor 6% (PE) 0.495 kg ha^-1 + Bispyribac-Sodium (post-emergence(POE)) 0.025 kg ha^-1 at 15 DAS/T; W₅, Cono weeding (CW) at 15 DAS/T + hand weeding 30 DAS/T, and W₆, Brown manuring/Green manuring. The initial decline in the microbial population was observed due to herbicide application in NPTR and PTR up to 7 DAS/T and then it increased up to 28 DAS/T. There was a reduction in soil microbial and enzymatic status after the application of herbicides Bensulfuron methyl 0.6% + Pretilachlor 6% (PE) and Bispyribac-Sodium (POE) that again followed an upward graph with crop age. Significant variation in enzymatic activity and the microbial count was also observed among treatments involving crop establishment methods. The study revealed that improved microbial population and enzyme activity were noted in unpuddled transplanted rice under organic weed management due to favorable conditions, and chemical weed control initially affected microbial population and activities.

Cobalt (II) complex as a fluorescent sensing platform for the selective and sensitive detection of triketone HPPD inhibitors

4-Hydroxyphenylpyruvatedioxygenase (HPPD) is a Fe(II)/Co(II)-dependent enzyme which has become one of the most effective herbicide targets. HPPD inhibitors have been developed as efficient herbicides for resistant weed control. Developing a method for efficient and rapid HPPD inhibitors detection is still challenging. N-n-butyl-4-methylhydrazinecarbothioamide-1,8-naphthalimide (NMN) was synthesized and used to detect Co²⁺ efficiently with the limit of detection (LOD) of 7.82 nM with a turn-on fluorescence. Herein a novel fluorescent complex, NMN‒Co²⁺ was employed to determine HPPD inhibitors which performed a turn-off effect in the sensing process based on the competitive coordination between the probe and HPPD with Co²⁺. The LODs for three commercial triketone HPPD inhibitors (mesotrione, tembotrione and NTBC) were 6.60 nM, 7.37 nM and 10.22 nM with good sensitivity and selectivity. Furthermore, the present probe has potentials to quantitatively detect mesotrione and tembotrione in real samples.

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.

Constructing sustained-release herbicide formulations based on poly-3-hydroxybutyrate and natural materials as a degradable matrix

BACKGROUND

The purpose of the present study was to develop ecofriendly herbicide formulations. Its main aim was to develop and investigate slow-release formulations of herbicides (metribuzin, tribenuron-methyl, and fenoxaprop-P-ethyl) of different structure, solubility, and specificity, which were loaded into a degradable matrix of poly-3-hydroxybutyrate (P(3HB)) blended with available natural materials (peat, clay, and wood flour).

RESULTS

Differences in the structure and physicochemical properties of the formulations were studied depending on the type of the matrix. Herbicide release and accumulation in soil were associated with the solubility of the herbicide. Fourier-transform infrared spectroscopy showed that no chemical bonds were formed between the components in the experimental formulations. Degradation of the formulations in agro-transformed soil in laboratory conditions was chiefly influenced by the shape of the specimens (granules or pellets) while the effect of the type of filler (peat, clay, or wood flour) was insignificant. The use of granules enabled more rapid accumulation of the herbicides in soil: their peak concentrations were reached after 3 weeks of incubation while the concentrations of the herbicides released from the pellets were the highest after 5-7 weeks. Loading of the herbicides into the polymer matrix composed of the slowly degraded P(3HB) and natural materials enabled both sustained function of the formulations in soil (lasting between 1.5 and ≥3 months) and stable activity of the otherwise rapidly inactivated herbicides such as tribenuron-methyl and fenoxaprop-P-ethyl.

CONCLUSION

The experimental herbicide formulations enabled slow release of the active ingredients to soil. © 2019 Society of Chemical Industry.

Effects of trichloroethylene stress on the microbiological characteristics of Mollisol

Trichloroethylene (TCE), one of 129 kinds of priority pollutants, is the most common halogenated organic pollutant in the environment. To explore the changes in soil physicochemical properties and biological activities then clarify the effects of these factors on bacterial, fungal and actinomycetes communities in Mollisol under TCE stress is the significance of our research. The results indicated that when TCE concentration was greater than 10 mg kg^-1, soil quality declined and soil decomposition of organic matter and cycling of mineral nutrients were inhibited through an effect on soil microbial biomass. Operational taxonomic units (OTUs) richness of the bacteria in Mollisol was altered by TCE contamination. The S_Chao1 and H_Shannon indices of bacterial communities in Mollisol decreased when 40 mg kg^-1 TCE was applied. Meanwhile, the OTU richness of fungi in Mollisol was altered by TCE contamination. The H_Shannon indices of the fungal communities in Mollisol were inhibited by higher TCE concentrations (20 and 40 mg kg^-1 TCE). TCE altered the content of some bacteria, fungi and actinomycetes involved in soil carbon and nitrogen cycling and metabolism, such as Acidobacteria, Proteobacteria, Planctomycetes, Chytridiomycota, Streptomycetales, Pseudonocardiales, Propionibacteriales and Rhizobiales, and thus influenced nutrient cycling and the process of energy metabolism in Mollisol. In addition, redundancy analysis (RDA) results indicated that physicochemical properties and biological activities under TCE contamination significantly affected soil microbial community composition thus confirming that TCE interfered with the carbon and nitrogen cycling and metabolism of soil microorganisms. The results of this study are of great importance for revealing the effects of TCE stress on the microbiological characteristics of Mollisol, and also provide more useful information for determining the potential ecological risk of organic pollutants in Mollisol.

Dissipation of chlorantraniliprole in contrasting soils and its effect on soil microbes and enzymes

An experiment was set up to determine the rate of dissipation of chlorantraniliprole (CTP) from two soils with contrasting properties. The other objective of the study was to find out the effect of CTP on soil microorganisms (population, microbial biomass carbon and soil enzymes) under controlled environment. CTP residues when applied at recommended dose ((RD) (at 40 g a.i./ha)) could not be recovered either from alluvial soil or red soil at 60 days post application of CTP in a microcosm study. Higher clay content led to higher half-life in alluvial soil compared to red soil. CTP could not be recovered from RD treatment at 30 days after pesticide application under controlled environment. Faster dissipation of CTP was observed in rice rhizosphere soil with 23.89 and 34.65 days dissipation half-lives for RD and double the recommended dose (DRD) treatments, respectively. Different doses of chlorantraniliprole did not have considerable negative effect on actinomycetes, fungi, biological nitrogen fixers and phospahte solubilising bacteria except the bacteria population. Among the treatments, DRD recorded the lowest activity of dehyrodeganse, fluoresein diacetate hydrolase, acid and alkaline phosphatases followed by RD treatment. Microbial biomass carbon, β -glycosidase and urease did not vary significantly among the different doses of CTP. In general, RD did not have negative effcts on soil microbes. Hence, CTP can be recommeded in rice pest managment maintaining existing soil microbes and soil enzymes activity.

Dynamic Effect of Fresh and Aged Biochar on the Behavior of the Herbicide Mesotrione in Soils

In this study, we assessed the sorption, dissipation, and leaching of the herbicide mesotrione in soil amended with fresh and field-aged biochars, when added to the soil. The aging process was performed by burying the fresh biochar at 10 cm depth in three soils located in different points across the USA [Wisconsin (ABC_WI), Idaho (ABC_ID), and South Carolina (ABC_SC)] for six months. ABC_ID and ABC_SC slightly increased the sorption of mesotrione in soils, whereas ABC_WI removed greater amounts of herbicide from the solution. This was attributed to differences in water-soluble components and metal content of this aged biochar. Consequently, the persistence of the herbicide in the amended soils with fresh biochar and ABC_ID and ABC_SC were similar to that in unamended soils, while ABC_WI slightly increased mesotrione half-life. Differences between treatments were detected in leaching studies although no direct relationship with the dissipation batch studies was observed. Mesotrione leaching could not be detected in soil columns amended with ABC_WI and was high for the rest of treatments. The outcomes from this work demonstrate that temporal variability of biochar sorption capacities due to soil exposure can occur altering mesotrione's behavior in biochar-amended soils.

Constructing Slow-Release Fungicide Formulations Based on Poly(3-hydroxybutyrate) and Natural Materials as a Degradable Matrix

Slow-release fungicide formulations (azoxystrobin, epoxiconazole, and tebuconazole) shaped as pellets and granules in a matrix of biodegradable poly(3-hydroxybutyrate) and natural fillers (clay, wood flour, and peat) were constructed. Infrared spectroscopy showed no formation of chemical bonds between components in the experimental formulations. The formulations of pesticides had antifungal activity against Fusarium verticillioides in vitro. A study of biodegradation of the experimental fungicide formulations in the soil showed that the degradation process was mainly influenced by the type of formulation without significant influence of the type of filler. More active destruction of the granules led to a more rapid accumulation of fungicides in the soil. The content of fungicides present in the soil as a result of degradation of the formulations and fungicide release was determined by their solubility. Thus, all formulations are able to function in the soil for a long time, ensuring gradual and sustained delivery of fungicides.

Effects of biochar on the earthworm (Eisenia foetida) in soil contaminated with and/or without pesticide mesotrione

The plant-derived biochars act as soil conditioners, and thus may influence biological interactions in the soil environment. However, their unintended negative and positive effects on soil organisms remain largely understudied. Therefore, we investigated the effect of 0, 1, 3, and 10% of wheat straw-derived biochar amendments on earthworm (Eisenia foetida) activity in the soil contaminated with and/or without pesticide mesotrione (10 mg/kg dry soil) after 28 days of incubation. The pesticide mesotrione did not affect earthworm growth or reproduction; however, it induced oxidative stress and DNA damage. Although biochar application significantly decreased the concentration of mesotrione in earthworms, it delayed the degradation of pesticide in the soil environment. Compared to zero amendment, the amendment of 1 and 3% of biochar significantly increased (P < 0.05) the earthworm weight and reduced the toxicity effects of mesotrione on earthworms. However, the application of 10% biochar significantly decreased (P < 0.05) earthworm growth and caused DNA damage even in the absence of mesotrione. This study suggests that it is necessary to investigate the effects of different levels of biochar amendments on earthworms and other soil organisms in agricultural fields to develop a broader understanding about the use of biochar and its consequences on soil health.

Potential application of Pistia stratiotes for the phytoremediation of mesotrione and its degradation products from water

The aim of the present work is to estimate remediation potential of Pistia stratiotes, its ability to uptake mesotrione (MES) - one of the most frequently used herbicides, and its main degradation products: 2-amino-4-methylsulfonyl benzoic acid (AMBA) and 4-methylsulfonyl-2-nitrobenzoic acid (MNBA). This research focuses on model experiments performed under laboratory conditions. The results show that Pistia stratiotes can uptake up to 75% of degradation products from 1 L of surface water samples polluted with 0.4 µg/L of each analyte during 7 days without significant phytotoxic effect. Under the same experimental conditions, the effectiveness of mesotrione sorption is in the range of 42-58%. The phytotoxicity of this compound is higher in comparison to its degradation products (decrease of chlorophyll concentration in plant tissues exposed to MES 27-32% vs 4-13% in case of exposition to AMBA and MNBA). The adequate nutrition of the plants is crucial to their well-being and thus the sorption of pollutants.

Effects of the herbicide mesotrione on soil enzyme activity and microbial communities

Mesotrione (2-[4-(methylsulfonyl)-2-nithobenzoyl]-1, 3-cyclohexanedione) is a selective triketone herbicide that has been widely used in corn production for the past 15 years. However, its potential for risk to soil ecosystems is poorly documented. The present study investigated the soil enzyme activity and soil microbial community responses to a 20 days' mesotrione exposure at doses of 0.1, 1.0 and 5.0 mg/kg. On days 2, 5, 10 and 20, activities of soil β-glucosidase, urease and acid phosphatase, soil microbe abundances, soil microbial community structure and abundance of the AOA-amoA and AOB-amoA genes were measured. Results showed that activities of urease and acid phosphatase were relatively stable, with no difference found between the mesotrione-treated group and control at the end of exposure. But β-glucosidase activity was reduced in the 5.0 mg/kg mesotrione treatment. In the 1.0 and 5.0 mg/kg mesotrione-treated soil, abundance of bacteria, fungi and actinomycetes all were reduced. In the 0.1 mg/kg mesotrione-treated soil, only fungi abundance was reduced by the end of the exposure. The analysis of terminal restriction fragment length polymorphism (T-RFLP) revealed soil microbial community structure could be affected by mesotrione at all experimental doses, and microbial diversity declined slightly after mesotrione exposure. Abundance of AOA-amoA and AOB-amoA genes were reduced markedly in 1.0 and 5.0 mg/kg mesotrione-treated soil. The present study suggests that mesotrione at higher doses might induce negative impacts on soil microbes, a finding which merits additional research and which should be accounted for when application of this herbicide is considered.

Dissipation of herbicides after repeated application in soils amended with green compost and sewage sludge

Certain agricultural practices, such as the repeated application of herbicides or organic amendments to soil, can influence herbicide dissipation. This research has studied the effects of two repeated applications of mesotrione, pethoxamid, and triasulfuron on their dissipation rates in unamended soil (S) and soil amended with green compost (S+GC) or sewage sludge (S+SS). The dissipation experiment has also included an evaluation of the adsorption of the three herbicides by soils and of changes in soil dehydrogenase activity (DHA). The adsorption of the three herbicides by amended soils (Kf range 0.83-2.98) was higher than by unamended soil (Kf range 0.20-0.64). The adsorption coefficients (Kd) of mesotrione and triasulfuron were higher for S+SS, while that of pethoxamid was higher for S+GC, but no relationship between values for the time to 50% degradation (DT₅₀) and adsorption coefficients could be determined. The repeated application of mesotrione decreased its dissipation rate in unamended soil (DT₅₀ increased from 4.75 to 8.15 days) and amended soils (DT₅₀ increased from 11.7 to 28.2 days in S+GC and from 17.7 to 37.9 in S+SS), whereas the repeated application of pethoxamid increased its dissipation rate in all the treatments, and the rate for triasulfuron increased only in amended soils. The highest DT₅₀ values for pethoxamid (12.3 days) and triasulfuron (57.1 days) were in S+GC, and the lowest in S+SS (8.35 and 24.7 days). Soil DHA was stimulated by the presence of GC in the soil and by the first application of mesotrione. The second application of mesotrione and pethoxamid positively affected soil DHA, but this did not occur for triasulfuron. The repeated applications of herbicides and soil organic amendments have different effects on herbicide dissipation, adsorption, and soil DHA, and they should be taken into account when assessing soil quality and other potential environmental implications of pesticide use.

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.

Oxidative stress and DNA damage in common carp (Cyprinus carpio) exposed to the herbicide mesotrione

The present study was undertaken to investigate the oxidative stress and genotoxic effects of the herbicide mesotrione in a common freshwater fish, Cyprinus carpio. These fish were exposed to environmentally relevant concentrations of mesotrione (1.8, 18 and 180 μg L^-1) for 7, 14 and 28 days. Levels of reactive oxygen species (ROS), malondialdehyde (MDA), reduced glutathione (GSH), activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione reductase (GR) were measured in the gill, liver and muscle, together with levels of DNA damage that occurred. After 28 days exposure, significant increases in SOD and CAT activity and ROS content were observed in all three tissues but only at the highest concentration of exposure (180 μg L^-1). No obvious changes in MDA, GSH, GPx or GR were observed in all treatments during the experiment. Comet assays revealed that the highest concentration of mesotrione induced DNA damage to different tissues in the common carp, especially the liver after chronic exposure occurred. These results provide evidence that the oxidant-antioxidant and comet assay could be integrated into monitoring programs determining the toxicity of water pollutants.

Influence of Herbicide Triasulfuron on Soil Microbial Community in an Unamended Soil and a Soil Amended with Organic Residues

The effect of organic amendments and pesticides on a soil microbial community has garnered considerable interest due to the involvement of microorganisms in numerous soil conservation and maintenance reactions. The aim of this work was to assess the influence on a soil microbial community of the simultaneous application of the herbicide triasulfuron at three doses (2, 10, and 50 mg kg-1), with an organic amendment [sewage sludge (SS) or green compost (GC)]. Dissipation kinetics, soil microbial biomass, dehydrogenase activity (DHA) and respiration, and the profile of phospholipid fatty acids (PLFAs) extracted from the soil, were determined in unamended (S) soil and amended (S+SS and S+GC) ones. Triasulfuron dissipation followed the single first-order kinetics model. Half-life (DT50) values were higher in the amended soils than in the unamended one for the 10 and 50 mg kg-1 doses. The dissipation rates were lower in the S+GC soil for the three herbicide doses applied. In general, soil biomass, DHA and respiration values increased in SS- and GC-amended soils compared to the unamended one. DHA values decreased (S and S+SS) or increased (S+GC) with the incubation time of soil with herbicide at the different doses applied. Respiration values increased with the herbicide doses applied and decreased with the incubation time, although maximum values were obtained for soils treated with the highest dose after 70 days of incubation. PLFA analysis indicated different effects of triasulfuron on the soil microbial community structure depending on the organic amendments. While the increasing triasulfuron doses resulted in deeper alterations in the S soil, the time after triasulfuron application was the most important variation in the S+SS and S+GC soils. The overall results indicate that the soil amendment has an effect on herbicide dissipation rate and the soil microbial community. Initially, a high dose of triasulfuron had detrimental effects on the soil microbial community, which is important in the case of the long-term use of this compound.

Fate and ecotoxicological impact of new generation herbicides from the triketone family: An overview to assess the environmental risks

Triketones, derived chemically from a natural phytotoxin (leptospermone), are a good example of allelochemicals as lead molecules for the development of new herbicides. Targeting a new and key enzyme involved in carotenoid biosynthesis, these latest-generation herbicides (sulcotrione, mesotrione and tembotrione) were designed to be eco-friendly and commercialized fifteen-twenty years ago. The mechanisms controlling their fate in different ecological niches as well as their toxicity and impact on different organisms or ecosystems are still under investigation. This review combines an overview of the results published in the literature on β-triketones and more specifically, on the commercially-available herbicides and includes new results obtained in our interdisciplinary study aiming to understand all the processes involved (i) in their transfer from the soil to the connected aquatic compartments, (ii) in their transformation by photochemical and biological mechanisms but also to evaluate (iii) the impacts of the parent molecules and their transformation products on various target and non-target organisms (aquatic microorganisms, plants, soil microbial communities). Analysis of all the data on the fate and impact of these molecules, used pure, as formulation or in cocktails, give an overall guide for the assessment of their environmental risks.

Quantification of the fate of mesotrione applied alone or in a herbicide mixture in two Brazilian arable soils

The effects of mesotrione, S-metolachlor, and terbuthylazine, applied in mixture, on soil biodegradation remain insufficiently researched. However, herbicide mixtures have been a common practice in agricultural systems in the last years. Understanding the fate of soil-applied herbicides may help on planning weed management tactics towards more sustainable and efficient weed control. Therefore, this study evaluated the fate of mesotrione alone and in mixture with S-metolachlor and terbuthylazine when applied to two contrasting arable Brazilian soils. Mineralization and degradation experiments were conducted using ¹⁴C-mesotrione alone or in mixture. From the 49-day laboratory incubation data, increased mineralization half-life of mesotrione was observed for the mixture of herbicides, ranging from a 4-day increase for the sandy loam soil to a 1-day increase in the sandy clay texture soils. Mesotrione degradation rate had a twofold increase in the sandy loam compared to the sandy clay soil. Two metabolites can be identified from mesotrione degradation, 4-methyl-sulfonyl-2-nitrobenzoic acid (MNBA) and 2-amino-4-methylsulfonyl benzoic acid (AMBA). Indices for the score of ubiquity in groundwater indicated mesotrione possesses leaching potential for both soils. Applying mesotrione alone or in mixture did not influence the amount of bound residues from mesotrione. However, mesotrione degradation rate was influenced by soil texture regardless if applied alone or in mixture. Mesotrione biotransformation was relatively quick, indicating that this herbicide has low persistence and, consequently, low residual effect on crops and weeds when present in similar soils to this present study.

Bioremediation of diuron contaminated soils by a novel degrading microbial consortium

Diuron is a biologically active pollutant present in soil, water and sediments. It is persistent in soil, water and groundwater and slightly toxic to mammals and birds as well as moderately toxic to aquatic invertebrates. Its principal product of biodegradation, 3,4-dichloroaniline, exhibits a higher toxicity than diuron and is also persistent in the environment. On this basis, the objective of the study was to determine the potential capacity of a proposed novel diuron-degrading microbial consortium (DMC) for achieving not only diuron degradation, but its mineralisation both in solution as well as in soils with different properties. The consortium was tested in a soil solution where diuron was the only carbon source, and more than 98.8% of the diuron initially added was mineralised after only a few days. The consortium was composed of three diuron-degrading strains, Arthrobacter sulfonivorans, Variovorax soli and Advenella sp. JRO, the latter had been isolated in our laboratory from a highly contaminated industrial site. This work shows for the first time the potential capacity of a member of the genus Advenella to remediate pesticide-contaminated soils. However, neither of the three strains separately achieved mineralisation (ring-¹⁴C) of diuron in a mineral medium (MSM) with a trace nutrient solution (NS); combined in pairs, they mineralised 40% of diuron in solution, but the most relevant result was obtained in the presence of the three-member consortium, where complete diuron mineralisation was achieved after only a few days. In the presence of the investigated soils in suspension, the capacity of the consortium to mineralise diuron was evaluated, achieving mineralisation of a wide range of herbicides from 22.9 to 69.0%.

Response of microorganisms and enzymes to soil contamination with a mixture of terbuthylazine, mesotrione, and S-metolachlor

The research objective has been to evaluate the effect, unexplored yet, of a mixture of three active ingredients of the herbicide Lumax 537.5 SE: terbuthylazine (T), mesotrione (M), and S-metolachlor (S) on counts of soil microorganisms, structure of microbial communities, activity of soil enzymes as well as the growth and development of maize. The research was based on a pot experiment established on sandy soil with pHKCl 7.0. The herbicide was applied to soil once, in the form of liquid emulsion dosed as follows: 0.67, 13.4, 26.9, 53.8, 108, 215, and 430 mg kg-1 of soil, converted per active substance (M + T + S). The control sample consisted of soil untreated with herbicide. The results showed that the mixture of the above active substances caused changes in values of the colony development (CD) indices of organotrophic bacteria, actinomycetes, and fungi and ecophysiological diversity (EP) indices of fungi. Changes in the ecophysiological diversity index of organotrophic bacteria and actinomycetes were small. The M + T + S mixture was a strong inhibitor of dehydrogenases, to a less degree catalase, urease, β-glucosidase, and arylsulfatase, while being a weak inhibitor of phosphatases. The actual impact was correlated with the dosage. The M + T + S mixture inhibited the growth and development of maize. The herbicide Lumax 537.5 SE should be applied strictly in line with the regime that defines its optimum dosage. Should its application adhere to the manufacturer's instructions, the herbicide would not cause any serious disturbance in soil homeostasis. However, its excessive quantities (from 13.442 to 430.144 mg kg-1 DM of soil) proved to be harmful to the soil environment.

Behaviour of mesotrione in maize and soil system and its influence on soil dehydrogenase activity

The aim of this study was to investigate the dissipation of mesotrione and effect on dehydrogenase activity (DHA) in maize and soil system. The paper for the first time describes behaviour of this herbicide applied at various doses (separately or in mixture with other herbicide) in acidic and alkaline environment. The experiments were conducted using the method randomized blocks in four repetition cycles. Chemical application in seven variants at recommended doses of herbicide were performed. The sample preparation was performed by a modified QuEChERS method and the concentrations of mesotrione in maize and soil were determined by the liquid chromatography with tandem mass spectrometry (LC-MS/MS). The limit of detection was 0.0005mgkg(-1) and quantification 0.001mgkg(-1). The dissipation of mesotrione were described according to first-order (FO) kinetics equation with R(2) were between 0.8794 and 0.9934. The initial deposit of herbicide in soil and maize was higher in an acidic environment (0.06-0.18mgkg(-1)). A positive correlation between an alkaline pH and the rate of dissipation in soil was observed. The results showed that the time after which 50% (DT50) of substance has been degraded was different for both plant and soil. DT50 for soil was within the range 3.2-6.0days and 2.9-4.4days, for the maize 3.9-4.8days and 3.4-4.5days in an alkaline and an acidic environment, respectively. Concentration of mesotrione at applicable MRL level of 0.05mgkg(-1) in maize was achieved at 0.5-5.9days and at proposed MRL of 0.01mgkg(-1) at 8.8-15.8days. The results indicate that the application of mesotrione affected on DHA in the soil. One day after application this herbicide, concentration of DHA in soil was lower than in control plots, but after 21days was observed trend of increasing DHA.

Effect of different rates of spent mushroom substrate on the dissipation and bioavailability of cymoxanil and tebuconazole in an agricultural soil

Physicochemical methods to immobilize pesticides in vulnerable soils are currently being developed to prevent water contamination. Some of these methods include the use of different organic residues to modify soils because they could limit the transport of pesticides and/or facilitate their dissipation. Spent mushroom substrate (SMS) may be used for these purposes. Accordingly a study was conducted under laboratory conditions to know the dissipation and bioavailability of the fungicides cymoxanil and tebuconazole over time in a vineyard soil amended with two rates of spent mushroom substrate (SMS) (5% and 50% (w/w)), selected to prevent the diffuse or point pollution of soil. The dissipation of cymoxanil was more rapid than that of tebuconazole in the different soils studied. The dissipation rate was higher in the amended soil than in the unamended one for both compounds, while no significant differences were observed between the amended soils in either case. An apparent dissipation occurred in the amended soil due to the formation of non-extractable residues. Bound residues increased with incubation time for tebuconazole, although a proportion of this fungicide was bioavailable after 303days. The major proportion of cymoxanil was tightly bound to the amended soil from the start, although an increasing fraction of bound fungicide was bioavailable for mineralization. Soil dehydrogenase activity was significantly affected by SMS application and incubation time; however, it was not significantly modified by fungicide application. The significance of this research suggests that SMS applied at a low or high rate to agricultural soil can be used to prevent both the diffuse or point pollution of soil through the formation of non-extractable residues, although more research is needed to discover the time that fungicides remain adsorbed into the soil decreasing either bioavailability (tebuconazole) or mineralization (cymoxanil) in SMS-amended soils.

454-Pyrosequencing Reveals Variable Fungal Diversity Across Farming Systems

Oasis farming system is common in some parts of the world, especially in the Arabian Peninsula and several African countries. In Oman, the farming system in the majority of farms follows a semi-oasis farming (SOF) system, which is characterized by growing multiple crops mainly for home consumption, but also for local market. This study was conducted to investigate fungal diversity using pyrosequencing approach in soils from a farm utilizing a SOF system which is cultivated with date palms, acid limes and cucumbers. Fungal diversity from this farm was compared to that from an organic farm (OR) growing cucumbers and tomatoes. Fungal diversity was found to be variable among different crops in the same farm. The observed OTUs, Chao1 richness estimates and Shannon diversity values indicated that soils from date palms and acid limes have higher fungal diversity compared to soil from cucumbers (SOF). In addition, they also indicated that the level of fungal diversity is higher in the rhizosphere of cucumbers grown in OR compared to SOF. Ascomycota was the most dominant phylum in most of the samples from the OR and SOF farms. Other dominant phyla are Microsporidia, Chytridiomycota, and Basidiomycota. The differential level of fungal diversity within the SOF could be related to the variation in the cultural practices employed for each crop.

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.