Skip to Main Content
 

Global Search Box

 
 
 
 

Files

File List


N.Lee_Thesis_FINAL_Rev5_05_07_18.pdf (1.57 MB)

ETD Abstract Container

Abstract Header

Long Term Glyphosate Effects on Roundup Ready Soybean Rhizosphere Microorganisms

Lee, Nathan Robert William
http://rave.ohiolink.edu/etdc/view?acc_num=osu1525689141453883

Abstract Details

2018, Master of Science, Ohio State University, Environment and Natural Resources.
The herbicide glyphosate (N-(phosphonomethyl) glycine) was first introduced in 1974 as a non-selective, broad spectrum, post-emergent agrochemical, branded under the trade name Roundup® and intended to control weed competition in agricultural farming. It gained large popularity and increased usage in 1996 with the introduction of glyphosate resistant soybean (Glycine max) cultivars and again in 1998 with resistant corn (Zea mays) cultivars. Its widespread usage has increased the concern of unknown long-term effects on the soil rhizosphere microbial community. In the same long-term context there is also increased concern over glyphosate’s toxicity and accumulation of degradation products, notably aminomethylphosphponic acid (AMPA), which accounts for the majority of detected metabolites in the soil. Chapter one of this thesis will review the current literature on the toxicity and degradability of glyphosate and AMPA in the soil. In chapter two of this thesis a long-term glyphosate greenhouse experiment was designed with two main objectives, (1) determine the effects of long-term glyphosate application for three different glyphosate formulations on glyphosate resistant (GR) soybean rhizosphere microbial communities of two different soil managements, one with and one without a history of glyphosate exposure, and (2) use stable isotope probing (SIP) to identify possible glyphosate degrading microbial functional groups in these two soil managements. The objective of chapter three was to expand on chapter two by investigating the accumulation of glyphosate and AMPA in both the rhizosphere and bulk soil of the same long-term glyphosate greenhouse experiment. Research from a greenhouse study showed that repeated application of glyphosate increased the abundance of gram-negative microorganisms relative to a single application as detected by FAMEs. Likewise a field study also showed that repeated application of glyphosate increased Fusarium fungal colonization on both corn and soybean root systems over multiple growing seasons. Another study demonstrated that a glyphosate infused medium drastically reduced the abundance of arbuscular michorizae colonies. Additionally, the literature reveals that both glyphosate and AMPA have a higher absorption potential within the soil matrix than most other herbicides, and that microbial communities are mostly responsible for their degradation. AMPA is also found to persist longer in the soil matrix than glyphosate and can be used by some organisms as a source of phosphate. These studies suggest: (1) that long-term glyphosate application could upset the delicate balance between beneficial and non-beneficial microorganisms in the glyphosate resistant soybean rhizosphere by increasing the abundance of gram-negative and fungal microbial communities; (2) glyphosate resistant plants may have an increased risk of fungal disease and mycotoxicity stress from Fusarium fungal species; (3) fungal and gram-negative microorganisms may be major players in the degradation of glyphosate and; (4) accumulation of glyphosate and its metabolites is likely more pronounced in areas of the soil with less microbial activity. The major findings of this thesis indicate that glyphosate induces changes in the rhizosphere microbial communities of a soil that has never received glyphosate application and likely adapts to use glyphosate as a substrate, most notably by fungus. Additionally, glyphosate and its degradation product AMPA accumulate heavily in the bulk soil, and greater microbial biomass in the rhizosphere soil is associated with low levels of GLY and AMPA.
Richard Dick (Advisor)
119 p.
Agricultural Chemicals; Agriculture; Microbiology; Soil Sciences
Rhizosphere; Glyphosate; Microbial Community; AMPA; PLFA;

Recommended Citations

Citations

  • Lee, N. R. W. (2018). Long Term Glyphosate Effects on Roundup Ready Soybean Rhizosphere Microorganisms [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1525689141453883

    APA Style (7th edition)

  • Lee, Nathan. Long Term Glyphosate Effects on Roundup Ready Soybean Rhizosphere Microorganisms . 2018. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1525689141453883.

    MLA Style (8th edition)

  • Lee, Nathan. "Long Term Glyphosate Effects on Roundup Ready Soybean Rhizosphere Microorganisms ." Master's thesis, Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1525689141453883

    Chicago Manual of Style (17th edition)

osu1525689141453883
445
© 2018, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.