STUDIES ON THE EFFECTS OF THE HERBICIDE SIMAZINE ON MICROFLORA OF FOUR AGRICULTURAL SOILS—Short Communication (original) (raw)
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FEMS Microbiology Ecology, 2011
s-Triazine herbicides are widely used for weed control, and are persistent in soils. Nitrification is an essential process in the global nitrogen cycle in soil, and involves ammonia-oxidizing Bacteria (AOB) and ammonia-oxidizing Archaea (AOA). In this study, we evaluated the effect of the s-triazine herbicide simazine on the nitrification and on the structure of ammonia-oxidizing microbial communities in a fertilized agricultural soil. The effect of simazine on AOB and AOA were studied by PCR-amplification of amoA genes of nitrifying Bacteria and Archaea in soil microcosms and denaturing gradient gel electrophoresis (DGGE) analyses. Simazine [50 lg g À1 dry weight soil (d.w.s)] completely inhibited the nitrification processes in the fertilized agricultural soil. The inhibition by simazine of ammonia oxidation observed was similar to the reduction of ammonia oxidation by the nitrification inhibitor acetylene. The application of simazine-affected AOB community DGGE patterns in the agricultural soil amended with ammonium, whereas no significant changes in the AOA community were observed. The DGGE analyses strongly suggest that simazine inhibited Nitrosobacteria and specifically Nitrosospira species. In conclusion, our results suggest that the s-triazine herbicide not only inhibits the target susceptible plants but also inhibits the ammonia oxidation and the AOB in fertilized soils.
Influence of microorganisms and leaching on simazine attenuation in an agricultural soil
Simazine is an s-triazine herbicide world widely used for the control of broadleaf weeds. The influence of leaching and microorganisms on simazine attenuation in an agricultural soil long-term treated with this herbicide was studied. To elucidate the leaching potential of simazine in this soil, undisturbed soil columns amended with simazine were placed in a specially designed system and an artificial precipitation was simulated. To evaluate the simazine removal by soil microorganisms, three soil microcosm sets were established: i) control soil; ii) soil subjected to gamma irradiation (g-soil) and iii) g-soil inoculated with the simazine-degrading bacterium Pseudomonas sp. strain MHP41. The simazinedegrading microorganisms in soil were estimated using an indicator for respiration combined with MPN enumeration. The simazine removal in soil was monitored by GC-ECD and HPLC. In this agricultural soil the leaching of the applied simazine was negligible. The gamma irradiation decreased in more than one order of magnitude the cultivable heterotrophic bacteria and reduced the simazine-degrading microorganisms. Simazine was almost completely depleted (97%) in control soil by natural attenuation after 23 d, whereas in g-soil only 70% of simazine was removed. The addition of the simazine-degrading strain MHP41 to g-soil restored and upheld high stable simazine catabolic microorganisms as well as increased the simazine removal (87%). The results indicated that simazine is subjected to microbial degradation with negligible leaching in this agricultural soil and pointed out the crucial role of native microbiota in the herbicide removal.
The Role of the Bacterial Community of an Agroecosystem in Simazine Degradation
Italian Journal of Agronomy, 2007
The use of pesticides and fertilizers in agricultural practice is the main source of soil and groundwater contamination. S-Triazines are among the most used herbicides in the world for selective weed control in several types of crops. The homeostatic capability of an agroecosystem to remove a triazinic herbicide, simazine, was assessed in microcosms treated with the herbicide in presence/absence of urea fertilizer. The latter, as well as a fertilizer, is also one of the last by-products before simazine mineralization. The biodegradation, in terms of disappearance of 50% of the initial concentration (DT 50 ), was compared to the degradation and metabolite formation occurring in sterilized soil. Moreover, the bacterial community response was assessed in terms of abundance and community structure by the epifluorescence direct count method and fluorescence in situ hybridization. The results show that the microbial community has a primary role in simazine degradation and that this process is due to the presence of a microbial pool working in succession and of which the metabolism may be modulated by exogenous sources of nitrogen, like urea. The latter influences the degradative pathway with a greater formation and accumulation of the desethyl-simazine metabolite, which is a hazardous contaminant of soil and groundwater ecosystems, as well as its parent compound.
Journal of Applied Microbiology, 2006
To study biological removal of the herbicide simazine in soils with different history of herbicide treatment and to test bioaugmentation with a simazine-degrading bacterial strain. Methods and Results: Simazine removal was studied in microcosms prepared with soils that had been differentially exposed to this herbicide. Simazine removal was much higher in previously exposed soils than in unexposed ones. Terminal restriction fragment length polymorphism analysis and multivariate analysis showed that soils previously exposed to simazine contained bacterial communities that were significantly impacted by simazine but also had an increased resilience. The biodegradation potential was also related to the presence of high levels of the atz-like gene sequences involved in simazine degradation. Bioaugmentation with Pseudomonas sp. ADP resulted in an increased initial rate of simazine removal, but this strain scarcely survived. After 28 days, residual simazine removals were the same in bioaugmented and not bioaugmented microcosms. Conclusions: In soils with a history of simazine treatment bacterial communities were able to overcome subsequent impacts with the herbicide. The success of bioaugmentation was limited by the low survival of the introduced strain. Significance and Impact of the Study: Conclusions from this work provided insights on simazine biodegradation potential of soils and the convenience of bioaugmentation.
Effects of the herbicide alachlor on soil microbial activities
Ecotoxicology, 1994
A study was made of the effects of one selected acetanilide herbicide, alachlor, at concentrations of 2.0-10.0 kg ha-' on bacterial populations, fungi, dinitrogen fixation bacteria, denitrifying bacteria, nitrifying bacteria, nitrogenase activity, acid and alkaline phosphatases, arylsulfatase and deshydrogenase. The presence of 2.0-10.0 kg ha-' of alachlor in the soil increased the total number of bacteria and fungi. The population of denitrifying bacteria increased significantly at concentrations of 5.0-10.0 kg ha-'. However, aerobic dinitrogen fixing bacteria and nitrogenase activity decreased at alachlor concentrations of 3.5-10.0 kg ha-'. Acid and alkaline phosphatases, arylsulfatase and dehydrogenase activity decreased significantly initially at concentrations of 5.0-10.0 kg ha-', but recovered to levels similar to those in the control. Nitrifying bacteria were not affected as a consequence of the addition of the herbicide to agricultural soil.
Simazine biodegradation in soil: analysis of bacterial community structure byin situ hybridization
Pest Management Science, 2005
Pesticide and nitrate contamination of soil and groundwater from agriculture is an environmental and public health concern worldwide. Simazine, 6-chloro-N 2 ,N 4 -diethyl-1,3,5-triazine-2,4-diamine, is a triazine herbicide used in agriculture for selective weed control with several types of crops and it is frequently applied to soils receiving N-fertilizers. Degradation experiments were performed in the laboratory to assess whether the biodegradation of simazine in soil may be influenced by the presence of urea. Simazine degradation rates under different experimental conditions (presence/absence of urea, microbiologically active/sterilized soil) were assessed together with the formation, degradation and transformation of its main metabolites in soil. Simazine degradation was affected by the presence of urea, in terms both of a smaller half-life (t 1/2 ) and of a higher amount of desethyl-simazine formed. The soil bacterial community was also studied. Microbial abundances were determined by epifluorescence direct counting. Moreover in situ hybridization with rRNA-targeted fluorescent oligonucleotide probes was used to analyze the bacterial community structure. Fluorescent in situ hybridization (FISH) was used to detect specific groups of bacteria such as the α,β,γ -subdivisions of Proteobacteria, Gram-positive bacteria with a high G + C DNA content, Planctomycetes, Betaproteobacterial ammonia-oxidizing bacteria and nitrifying bacteria. The presence of the herbicide and/or urea affected the bacterial community structure, showing that FISH is a valuable tool for determining the response of bacterial populations to different environmental conditions.
Effect of Some Commonly Used Herbicides on Soil Microbial Population
Journal of environment and earth science, 2016
Herbicide application has become an integral part of vibrant agricultural productivity in the whole world since its benefit has been overwhelming over the years. However, its toxic impact on the non-target soil microorganisms which play roles in degrading organic matter, nitrogen and nutrient recycling and decomposition needs to be considered. In the present study, the effect of four (4) most commonly used herbicides in Ghana; Atrazine, 2, 4-D amine, Glyphosate and Paraquat on soil microorganisms was assessed over a period of fifteen continuous days (exposure period). The herbicide treatments were the normal recommended field rate, (6.67 mg active ingredient per gram of soil for Atrazine, 6.17 mg for 2, 4-D amine, 5.56 mg for Glyphosate, and 2.46 mg for Paraquat), half and double of the recommended field rate. Bacterial and Fungal populations were then determined at a five-day interval up to the 15 th day after treatment. The data gathered from bacterial enumeration was logarithmic...
Alachlor and Metribuzin Herbicide on N2-fixing Bacteria in a Sandy Loam soil
International Journal of Bio-resource and Stress Management, 2016
Herbicides interact with soil organisms and their metabolic activities and may alter the physiological and biochemical behavior of soil microbes. Some microbial groups are capable of using applied pesticide as a source of energy and nutrients to multiply, whereas the pesticide may be toxic to other organisms. Laboratory experiment was conducted to investigate the effect of two selective systemic herbicides viz., alachlor and metribuzin, at their recommended field rates (2.0 and 0.4 kg a.i. ha-1 , respectively) on the growth and activities of non symbiotic N 2-fixing bacteria in relation to mineralization and availability of nitrogen in a sandy loam soil of India. Both the herbicides, either singly or in a combination, stimulated the growth and activities of N 2-fixing bacteria resulting in higher mineralization and availability of nitrogen in soil. The single application of alachlor increased the proliferation of aerobic non-symbiotic N 2-fixing bacteria to the highest extent while that of metribuzin exerted maximum stimulation to their N 2-fixing capacity in soil. Both the herbicides, either alone or in a combination, did not have any significant difference in the stimulation of total nitrogen content and availability of exchangeable NH 4 + in soil while the solubility of NO 3 − was highly manifested when the herbicides were applied separately in soil. The effect of combined application of the herbicides was more or less at par with their single application.