Electronic Theses and Dissertations





Date of Award


Document Type


Degree Name

Doctor of Philosophy



Committee Chair

Reza Pezeshki

Committee Member

Randall Bayer

Committee Member

Shirlean Goodwin

Committee Member

Corinna Ethington


Hundreds of thousands of hectares of agricultural lands are drained by edge-of-field ditches that flow into surface waters. Vegetation within agricultural ditches is subject to the effects of agrochemicals in runoff. Glyphosate, the world's most widely used herbicide, has been detected in agricultural runoff where it may interact with plant roots. Laboratory and greenhouse experiments were conducted to evaluate the effects of root-zone glyphosate exposure on plant functioning including growth, physiology, morphology, and survival. Investigations included identifying a sublethal concentration of root-zone glyphosate exposure for use in subsequent experiments, quantifying the physiological effects of a range of sublethal glyphosate exposures, determining the effects of exposure duration and repeated exposure, and exploring the effects of clonal plant physiological integration with respect to spatial heterogeneity of root-zone glyphosate exposure. The effects of root zone glyphosate exposure were investigated over a wide range of concentrations and showed, through various endpoints, dose-dependent adverse effects on physiology and growth of exposed plants. The effects of two important variables related to glyphosate exposure were studied, exposure duration and repeated applications. It was demonstrated that repeated applications of root zone glyphosate affected the physiology of plants but not growth, and exposure duration did not affect plants at all. Finally, the effects of physiological integration and spatial heterogeneity of root zone glyphosate exposure were investigated in order to explain how the effect of such exposure may depend on the root density of the exposed ramet. It was discovered that root-zone glyphosate exposure could alter the morphology of exposed low density ramets. Root zone glyphosate exposure was found to adversely affect nontarget plants commonly found in agricultural ditches under a range of conditions. Collectively, the data generated and the resulting findings have practical field applications for land managers seeking to ameliorate the effects of glyphosate runoff from agricultural fields.Employing vegetated buffer strips, allowing ditch vegetation to persist, and promoting the growth of glyphosate-tolerant species are ways in which land managers can apply these findings. In addition, these findings promote an increased awareness that adverse effects do in fact exist for glyphosate runoff, contrary to conventional wisdom.


Data is provided by the student.

Library Comment

dissertation or thesis originally submitted to the local University of Memphis Electronic Theses & dissertation (ETD) Repository.