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

Regulating pathway for bacterial diversities toward improved ecological benefits of thiencarbazone-methyl·isoxaflutole application: A field experiment

Herbicide abuse has a significantly negative impact on soil microflora and further influences the ecological benefit. The regulating measures and corresponding mechanisms mitigating the decreased bacterial diversity due to herbicide use have rarely been studied. A field experiment containing the application gradient of an efficient maize herbicide thiencarbazone-methyl·isoxaflutole was performed. The relationship between soil bacterial community and thiencarbazone-methyl·isoxaflutole use was revealed. Modified attapulgite was added to explore its impacts on soil microflora under the thiencarbazone-methyl·isoxaflutole application. Based on the analytic network process-entropy weighting method-TOPSIS method model, the ecological benefit focusing on microbial responses was quantitatively estimated along with technical effectiveness and economic benefit. The results showed that the diversity indices of soil microflora, especially the Inv_Simpson index, were reduced at the recommended, 5 and 10 times the recommended dosages of thiencarbazone-methyl·isoxaflutole use. The Flavisolibacter bacteria was negatively correlated with the residues in soils based on the random forest model and correlation analysis, indicating a potential degrader of thiencarbazone-methyl·isoxaflutole residues. The structural equation model further confirmed that the high soil water content and soil pH promoted the function of Flavisolibacter bacteria, facilitated the dissipation of thiencarbazone-methyl·isoxaflutole residues and further improved the diversity of soil microflora. In addition, the presence of modified attapulgite was found to increase the soil pH, which may improve bacterial diversity through the regulating pathway. This explained the high ecological benefits of the treatment where the thiencarbazone-methyl·isoxaflutole was applied at the recommended dosage rates in conjunction with modified attapulgite addition. Therefore, the comprehensive benefits of thiencarbazone-methyl·isoxaflutole application with a focus on ecological benefits can be improved by regulating the soil pH with modified attapulgite.

Disturbance mitigation of thiencarbazone-methyl·isoxaflutole on bacterial communities through nitrification inhibitor and attapulgite

There is a knowledge gap in the interaction between the effects of herbicide thiencarbazone-methyl·isoxaflutole on soil microflora and environmental parameters, which leads to a lack of measures in mitigating damage to bacterial communities from the herbicide use. The impacts of thiencarbazone-methyl·isoxaflutole and soil parameters on the diversity, structure and functions of soil bacterial communities were clarified, and the effects and potential mitigation mechanisms of nitrapyrin and modified attapulgite with bacterial function intervention on bacterial communities were explored through incubation and field experiments. The results showed that as thiencarbazone-methyl·isoxaflutole application increased, the stress on soil bacterial community structure and diversity also increased. The relative abundance of bacteria including Aridibacter and GP7 and functional annotations including "nitrate_reduction" were significantly negatively correlated with thiencarbazone-methyl·isoxaflutole residues in soils. The remarkable toxic effects on the Adhaeribacter bacteria were detected at the recommended dose of thiencarbazone-methyl·isoxaflutole application. The residue of isoxaflutole (one of the effective ingredients of thiencarbazone-methyl·isoxaflutole) directly and more strongly affected the diversity of soil bacterial communities than thiencarbazone-methyl. Increasing soil pH was recognised as an important factor in improving the diversity and structure of soil microflora based on the results of the Mantel test and canonical correspondence analysis. Supplemental use of nitrapyrin or modified attapulgite was found to increase soil pH, and further improve the expression of "manganese oxidation" function annotation. This contributed to the increased bacterial diversity (Shannon index). Therefore, the disturbance of soil microflora caused by thiencarbazone-methyl·isoxaflutole application can be mitigated by the use of nitrapyrin and modified attapulgite through raising soil pH.

Efficiency and ecological safety of herbicide haloxyfop-R-methyl on removal of coastal invasive plant Spartina alterniflora

Spartina alterniflora is a global invasive plant and has caused considerable damage to coastal wetland ecosystem. This study evaluated the efficiency and ecological safety of herbicide haloxyfop-R-methyl (HPME) in removing S alterniflora in Laizhou Bay. The results showed that the density of regenerated S. alterniflora after 10 months of application of 0.01, 0.02 and 0.03 g/m2 HPME decreased by 86.67 %, 99.16 % and 99.31 %, respectively. Moreover, seed abortion rates were 62.25 %, 92.24 % and 94.82 %, and weight of roots in HPME groups were 56.63 %, 59.99 %, and 40.10 % of those in the control group. After 4 days of application, HPME could not be detected in S. alterniflora and sediments. In addition, HPME did not change sediment physicochemical properties, macrozoobenthos community and microbial community structure during 16 days, but increased the density of native macrozoobenthos after 1 year. Therefore, HPME might be an effective and ecologically safe chemical for the eradication of S. alterniflora.

Performance of atrazine adsorption behavior and microbial community structure in Mollisol aggregate fraction

Owing to complex pore systems and chemical substances, soil aggregates provide a spatially heterogeneous microenvironment for adsorption capacity and microbial survival. As the widely used pesticide in farmlands, atrazine environmental behavior is not well known at the aggregate scale. In this study, Mollisol soil samples were sieved into four aggregate-size classes: large macroaggregates (>2 mm, LMa), small macroaggregates (1-2 mm, SMa), microaggregates (0.25-1 mm, Mia) and primary particles (<0.25 mm, P). The pore characteristics of each aggregate fraction was visualized by non-invasive X-ray three-dimensional microscopic computed tomography (3D-CT) combined with pore network extraction. The adsorption kinetics of atrazine in each aggregate-size fraction can be described well by a pseudo-second-order kinetic model. The adsorption isothermal process of atrazine can be better fitted by the Langmuir isotherm model than Freundlich isotherm model. There was an obvious linear correlation between the maximum atrazine adsorption capacity and aggregate SOC content as well as TN. In addition, the abundance of bacteria, actinomycetes and anaerobic bacteria in P was totally higher than those in SMa and Mia. Although pH is strongly linked to the bacterial community in the aggregate fraction, aggregate particle size explained 18 % for shaping the microbial community. Therefore, chemical properties and pore characteristics of each soil aggregate fraction both contributed to performance of atrazine adsorption behavior and microbial community.

Effects of above ground pathogen infection and fungicide application on the root-associated microbiota of apple saplings

BACKGROUND

The root-associated microbiome has been of keen research interest especially in the last decade due to the large potential for increasing overall plant performance in agricultural systems. Knowledge about the impact of above ground plant disturbances on the root-associated microbiome remains limited. We addressed this by focusing on two potential impacts, foliar pathogen infection alone and in combination with the application of a plant health protecting product. We hypothesized that these lead to plant-mediated responses in the rhizosphere microbiota.

RESULTS

The effects of an infection of greenhouse grown apple saplings with either Venturia inaequalis or Podosphaera leucotricha as foliar pathogen, as well as the combined effect of P. leucotricha infection and foliar application of the synthetic plant health protecting product Aliette (active ingredient: fosetyl-aluminum), were studied on the root-associated microbiota. The bacterial community structure of rhizospheric soil and endospheric root material was characterized post-infection, using 16S rRNA gene amplicon sequencing. With increasing disease severity both pathogens led to changes in the rhizosphere and endosphere bacterial communities in comparison to uninfected plants (explained variance up to 17.7%). While the preventive application of Aliette on healthy plants two weeks prior inoculation did not induce changes in the root-associated microbiota, a second later application on the diseased plants decreased disease severity and resulted in differences of the rhizosphere bacterial community between infected and several of the cured plants, though differences were overall not statistically significant.

CONCLUSIONS

Foliar pathogen infections can induce plant-mediated changes in the root-associated microbiota, indicating that above ground disturbances are reflected in the below-ground microbiome, even though these become evident only upon severe leaf infection. The application of the fungicide Aliette on healthy plants itself did not induce any changes, but the application to diseased plants helped the plant to regain the microbiota of a healthy plant. These findings indicate that above ground agronomic management practices have implications for the root-associated microbiome, which should be considered in the context of microbiome management strategies.

Impact of pyroxasulfone on sugarcane rhizosphere microbiome and functioning during field degradation

Pyroxasulfone (PYR) is a widely used herbicide, but its effects on non-target organisms, particularly microorganisms, are largely unknown. Herein, we investigated the effects of various doses of PYR on the sugarcane rhizosphere microbiome by using amplicon sequencing of rRNA genes and quantitative PCR techniques. Correlation analyses indicated that several bacterial phyla (Verrucomicrobia and Rhodothermaeota) and genera (Streptomyces and Ignavibacteria) strongly responded to PYR application. Additionally, we found that both bacterial diversity and composition were significantly altered after 30 days, indicating a prolonged effect of the herbicide. Moreover, co-occurrence analyses of the bacterial community showed that the network complexity was significantly decreased by PYR at day 45. Furthermore, FAPROTAX analysis suggested that some functions with implications for carbon cycling groups were significantly altered after 30 days. Overall, we provide the first indications that PYR may not pose a significant risk for altering microbial communities in the short term (less than 30 days). However, its potential negative effects on bacterial communities in the middle and late stages of degradation deserve further attention. To our knowledge, this is the first study to provide insight into the effects of PYR on the rhizosphere microbiome, providing an extended basis for future risk assessments.

The Effects of Atrazine, Diuron, Fluazifop-P-butyl, Haloxyfop-P-methyl, and Pendimethalin on Soil Microbial Activity and Diversity

Understanding the impacts of herbicides on soil microbial communities is important, as these organisms mediate a wide range of ecosystem services. Here, we investigated whether the diversity and function of soil microbial communities were significantly influenced by one-off applications of atrazine, diuron, fluazifop-P-butyl, haloxyfop-P-methyl and pendimethalin as pure compounds at their recommended doses over multiple time points (1, 3, 7, 14, 30 and 60 days). Phylogenetic marker gene sequencing revealed that none of the herbicides influenced the numbers of bacterial and archaeal taxa or the evenness of their abundances. Similarly, none of the herbicides influenced the composition of bacterial and archaeal communities, except for diuron, fluazifop-P-methyl and pendimethalin, which were associated with larger relative abundances of a small number of OTUs on day 30 only. Functionally, none of the herbicides significantly influenced fluorescein diacetate hydrolysis (FDA) and beta-glucosidase activities or the induced respiratory responses of soil microbial communities to a range of substrates. These data indicate that the active herbicide ingredients tested may have minimal non-target effects when applied once at their recommended dose. Given their frequent use, it is important to next consider whether these herbicides have more pronounced effects at higher doses and application frequencies.

The Adsorption and Degradation of 2, 4-D Affected by Soil Organic Carbon and Clay

More has yet to be indicated on the adsorption and degradation processes, determining herbicides recycling in the environment. The sorption and degradation of 2, 4-D, affected by organic carbon (1.92-2.81%), soil clay (20-30%) and pH of the citrus orchards of Mazandaran province, Iran was investigated using HPLC equipped with UV detector for the identification and quantification of soil 2, 4-D. The adsorption (k_d) and degradation (K_deg) coefficients were determined using Freundlich and the first-degree kinetic equations. Gardens C (2.45 mL g^-1), and B (0.3 mL g^-1), with the highest (8.2 g day^-1) and least (2.7 g day^-1) degradation coefficients, had the highest and lowest K_d values. K_d variations with pH indicated higher adsorption of 2, 4-D in acidic pH. Due to the high presence of functional groups and soil biological activities, organic carbon affected the adsorption and degradation rates more effectively, which is of economic and environmental significance.