Entity

Time filter

Source Type

DeWitt, IA, United States

Newman M.M.,Auburn University | Hoilett N.,Northwest Missouri State University | Lorenz N.,Ohio State University | Dick R.P.,Ohio State University | And 3 more authors.
Science of the Total Environment | Year: 2016

Glyphosate is one of the most widely used herbicides in agriculture with predictions that 1.35. million. metric tons will be used annually by 2017. With the advent of glyphosate tolerant (GT) cropping more than 10. years ago, there is now concern for non-target effects on soil microbial communities that has potential to negatively affect soil functions, plant health, and crop productivity. Although extensive research has been done on short-term response to glyphosate, relatively little information is available on long-term effects. Therefore, the overall objective was to investigate shifts in the rhizosphere bacterial community following long-term glyphosate application on GT corn and soybean in the greenhouse. In this study, rhizosphere soil was sampled from rhizoboxes following 4 growth periods, and bacterial community composition was compared between glyphosate treated and untreated rhizospheres using next-generation barcoded sequencing. In the presence or absence of glyphosate, corn and soybean rhizospheres were dominated by members of the phyla Proteobacteria, Acidobacteria, and Actinobacteria. Proteobacteria (particularly gammaproteobacteria) increased in relative abundance for both crops following glyphosate exposure, and the relative abundance of Acidobacteria decreased in response to glyphosate exposure. Given that some members of the Acidobacteria are involved in biogeochemical processes, a decrease in their abundance could lead to significant changes in nutrient status of the rhizosphere. Our results also highlight the need for applying culture-independent approaches in studying the effects of pesticides on the soil and rhizosphere microbial community. © 2015. Source


Lane M.,Ohio State University | Lorenz N.,Ohio State University | Saxena J.,Ohio State University | Ramsier C.,Ag Spectrum | Dick R.P.,Ohio State University
Pedobiologia | Year: 2012

The herbicide, glyphosate [N-(phosphonomethyl) glycine] is extensively used worldwide. Long-term use of glyphosate can cause micronutrient deficiency but little is known about potassium (K) interactions with glyphosate. The repeated use of glyphosate may create a selection pressure in soil microbial communities that could affect the nutrient dynamics such as K. The objective of this study was to determine the effect of single or repeated glyphosate applications on microbial and K properties of soils. A 54 day incubation study (Exp I) had a 3 × 5 factorial design with 3 soils (silt loam: fine, illitic, mesic Aeric Epiaqualf) of similar physical and chemical characteristics, that varied in long-term glyphosate applications (no, low, and high glyphosate field treatments) and five glyphosate rates (0, 0.5×, 1×, 2×, and 3× recommended field rates applied once at time zero). A second 6 month incubation study (Exp II) had a 3 × 3 factorial design with three soils (as described above) and three rates of glyphosate (0, 1×, and 2× recommended field application rates applied monthly). For each study microbial properties [respiration; community structure measured by ester linked fatty acid methyl ester (EL-FAME) analysis and microbial biomass K] and K fractions (exchangeable and non-exchangeable) were measured periodically. For Exp I, glyphosate significantly increased microbial respiration that was closely related to glyphosate application rate, most notably in soils with a history of receiving glyphosate. For Exp II, there was no significant effect of repeated glyphosate application on soil microbial structure (EL-FAME) or biomass K. We conclude that glyphosate: (1) stimulates microbial respiration particularly on soils with a history of glyphosate application; (2) has no significant effect on functional diversity (EL-FAME) or microbial biomass K; and (3) does not reduce the exchangeable K (putatively available to plants) or affect non-exchangeable K. The respiration response in soils with a long-term glyphosate response would suggest there was a shift in the microbial community that could readily degrade glyphosate but this shift was not detected by EL-FAME. © 2012 Elsevier GmbH. Source


Lorenz N.,Ohio State University | Verdell K.,Ohio State University | Ramsier C.,Ag Spectrum | Dick R.P.,Ohio State University
Soil Science Society of America Journal | Year: 2010

Various assays for microbial biomass C (Cmic) and other elements in the soil are available but there are none for microbial biomass K (K mic). Our objective was to develop a rapid chloroform-fumigation extraction (CFE) assay to estimate Kmic. The extractants ammonium acetate (CH3COONH4) and sodium hydrogen carbonate (NaHCO3) wete tested at three molarities on a Hoytville clay. A 1 mol L-1 CH3COONH4 yielded the highest levels of extractable K. To calibrate the CFE efficiency fot Kmic, bactetia and fungi isolated from soils were cultuted, suspended, and mixed with three soils of different texture: a fine sand, a silt loam, or a clay. The known concentrations of Kmic in the inoculum served as a basis co calculate the microbial biomass K conversion factors (kEK) for the thtee soils tested. Soils from corn (Zea mays L.) fields in Ohio under no-till, minimum tillage, and plow tillage had Kmic values tanging from 68 to 179 mg Kkg-1. The Kmic value was highest in the silt loam under no-till and in the clay soil under minimum tillage. Soil exchangeable K (K exch) and nonexchangeable K (Knexch) did not correlate with Kmic, but with total C. On average, Kexch was 2.7 and Knexch 8.3 times higher than Kmic. The data presented in this study are based on an initial study, and more soils and ecosystems need to be evaluated before the method can be generally adopted for soil samples. Out study shows, however, that Kmic is a significant K pool in soils that has been overlooked in the past. © Soil Science Society of America, All rights reserved. Source


Newman M.M.,Auburn University | Lorenz N.,Ohio State University | Hoilett N.,Northwest Missouri State University | Lee N.R.,Ohio State University | And 4 more authors.
Science of the Total Environment | Year: 2016

In commercial agriculture, populations and interactions of rhizosphere microflora are potentially affected by the use of specific agrichemicals, possibly by affecting gene expression in these organisms. To investigate this, we examined changes in bacterial gene expression within the rhizosphere of glyphosate-tolerant corn (Zea mays) and soybean (Glycine max) in response to long-term glyphosate (PowerMAX™, Monsanto Company, MO, USA) treatment. A long-term glyphosate application study was carried out using rhizoboxes under greenhouse conditions with soil previously having no history of glyphosate exposure. Rhizosphere soil was collected from the rhizoboxes after four growing periods. Soil microbial community composition was analyzed using microbial phospholipid fatty acid (PLFA) analysis. Total RNA was extracted from rhizosphere soil, and samples were analyzed using RNA-Seq analysis. A total of 20-28 million bacterial sequences were obtained for each sample. Transcript abundance was compared between control and glyphosate-treated samples using edgeR. Overall rhizosphere bacterial metatranscriptomes were dominated by transcripts related to RNA and carbohydrate metabolism. We identified 67 differentially expressed bacterial transcripts from the rhizosphere. Transcripts downregulated following glyphosate treatment involved carbohydrate and amino acid metabolism, and upregulated transcripts involved protein metabolism and respiration. Additionally, bacterial transcripts involving nutrients, including iron, nitrogen, phosphorus, and potassium, were also affected by long-term glyphosate application. Overall, most bacterial and all fungal PLFA biomarkers decreased after glyphosate treatment compared to the control. These results demonstrate that long-term glyphosate use can affect rhizosphere bacterial activities and potentially shift bacterial community composition favoring more glyphosate-tolerant bacteria. © 2016 The Authors. Source


Lane M.,Ohio State University | Lorenz N.,Ohio State University | Saxena J.,Ohio State University | Ramsier C.,Ag Spectrum | Dick R.P.,Ohio State University
Pedobiologia | Year: 2012

With the advent of glyphosate [N-(phosphonomethyl)glycine] tolerant crops, soils have now been receiving repeated applications of the herbicide for over 10 years in the Midwestern USA. There is evidence that long-term use of glyphosate can cause micronutrient deficiency but little is known about plant potassium (K) uptake interactions with glyphosate. The repeated use of glyphosate may create a selection pressure in soil microbial communities that could affect soil K dynamics and ultimately K availability for crops. Therefore, the objectives of this study were to characterize the effect of foliar glyphosate applied to GR (glyphosate resistant) soybeans on: (1) rhizosphere microbial community profiles using ester linked fatty acid methyl ester (EL-FAME) biomarkers, (2) exchangeable, non-exchangeable, and microbial K in the rhizosphere soil, and (3) concentrations of soybean leaf K. A greenhouse study was conducted in a 2×2×3 factorial design with two soil treatments (with or without long-term field applications of glyphosate), two plant treatments (presence and absence of soybean plants), and three rates of glyphosate treatments (0×, 1× at 0.87, and 2× at 1.74kg aeha -1, the recommended field rate). After each glyphosate application, rhizosphere soils were sampled and analyzed for microbial community structure using ester linked fatty acid methyl ester biomarkers (EL-FAME), and exchangeable, plant tissue and microbial biomass K. Glyphosate application caused a significant decrease in the total microbial biomass in soybean rhizosphere soil that had no previous exposure to glyphosate, at 7 days after glyphosate application. However, no significant changes were observed in the overall microbial community structure. In conclusion, the glyphosate application lowered the total microbial biomass in the GR soybean rhizosphere soil that had no previous exposure to glyphosate, at 7 days after glyphosate application; caused no changes in the microbial community structure; and did not reduce the plant available K (soil exchangeable or plant tissue K). © 2012 Elsevier GmbH. Source

Discover hidden collaborations