Off-campus UNL users: To download campus access dissertations, please use the following link to log into our proxy server with your NU ID and password. When you are done browsing please remember to return to this page and log out.
Non-UNL users: Please talk to your librarian about requesting this dissertation through interlibrary loan.
CANADA THISTLE (CIRSIUM ARVENSE) ROOT BUD INITIATION, BIOLOGY, AND TRANSLOCATION OF CARBON-14 LABELED GLYPHOSATE AS INFLUENCED BY NITROGEN, TEMPERATURE, PHOTOPERIOD, AND GROWTH STAGE
Abstract
Effects of nitrogen levels, temperature, photoperiod, and source of nitrogen on root bud initiation and growth of Canada thistle {Cirsium arvense (L.) Scop.} were examined in greenhouse and growth chamber experiments. Translocation of ('14)C-glyphosate {N-(phosphonomethyl)glycine} as influenced by growth stage and simulated frost was also investigated. Root-to-shoot ratios decreased as nitrogen levels increased under both soil and hydroponic culture. Top-growth dry-weight was increased when supplemental nitrogen at 84 ppm was added to plants (two weeks prior to harvest) already growing under soil culture at 8, 42, or 84 ppm nitrogen. Canada thistle growth and development was not influenced by nitrogen levels supplied as NO(,3) or NH(,4)NO(,3) under hydroponic culture. Levels of nitrogen used in this investigation did not consistently stimulate root bud initiation under either soil or hydroponic culture. Growth was generally better under high nitrogen (84, 168 ppm), but injury occurred at higher levels. It is doubtful improved control can be achieved with foliar applied, translocated herbicides by the addition of nitrogen to stimulate root bud growth under field conditions. A temperature regime (gradual temperature changes) of 25/15 C day/night produced more vigorous plants (two ecotypes observed) than temperature regimes of 15/5 or 30/22 C under either 13- or 15-h photoperiod. Neither ecotype flowered at 13-h photoperiod after 13 weeks growth, but flowering at 15-h photoperiod occurred first at the highest temperature regime. Plant dry weight was greater when root temperature was allowed to fluctuate with air temperature. Plants grew very well under 15/5 C air temperature and 17 C root temperature regime (simulates fall conditions in Nebraska), but grew poorly under conditions of 15/5 C air temperature and unregulated root temperature. Nitrogen supplied as either NO(,3) or NH(,4)NO(,3) did not greatly influence growth of Canada thistle under 15/5 C air temperature at 17 C or unregulated root temperature. Field observations of several Nebraska ecotypes showed spring shoot emergence to begin about 22 March, while flowering began about 1 June. Metabolism of ('14)C-glyphosate by Canada thistle after 42 days under greenhouse conditions was found to be insignificant. More herbicide was absorbed and translocated to roots when leaves were treated with ('14)C-glyphosate at the vegetative-stage (shoot elongation) versus the flower-bud-stage under growth chamber conditions. Simulated frost one day after plants (initially grown at 25/15 C air temperature) were treated with ('14)C-glyphosate significantly reduced translocation of glyphosate to root shoots and roots when compared to simulated frost one day prior to treatment or to a no frost treatment. Translocation was not altered by simulated frost, however, in plants which were hardened for 1 week under 15/5 C air temperature and 15 C root temperature. Treatments which resulted in the greatest glyphosate translocation to root shoots and roots also resulted in the greatest root shoot growth, indicating herbicide translocation was increased through sinks created by actively growing root shoots.
Subject Area
Botany
Recommended Citation
HOEFER, RAYMOND HENRY, "CANADA THISTLE (CIRSIUM ARVENSE) ROOT BUD INITIATION, BIOLOGY, AND TRANSLOCATION OF CARBON-14 LABELED GLYPHOSATE AS INFLUENCED BY NITROGEN, TEMPERATURE, PHOTOPERIOD, AND GROWTH STAGE" (1981). ETD collection for University of Nebraska-Lincoln. AAI8203217.
https://digitalcommons.unl.edu/dissertations/AAI8203217