Coxson, Darwyn S.

Glyphosate is a broad-spectrum herbicide commonly used in Canadian forests to control competitive vegetation. The non target plant species are exposed to a sublethal dose of glyphosate-based herbicides (GBH) due to aerial applications that cause deformities along with other potentially unknown effects. The efficiency and degradation of glyphosate to its metabolic by-products, including amino-methyl phosphonic acid (AMPA), are based on environmental conditions and the genetic capabilities of the plant or exposed organism. Glyphosate enters the plant through foliage and blocks the production of aromatic amino acids such as tryptophan by inhibiting the plant enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). Interestingly, the amino acid tryptophan acts as the precursor of the plant stress response hormone called melatonin. Whenever a plant is exposed to biotic or abiotic stress, the level of melatonin increases to protect the plant. The production of melatonin also tends to change depending on the environmental conditions. Glyphosate-based herbicides may act as a chemical stress, and the plants may respond to it by increasing melatonin concentration. The objectives of this research were: 1)To find out how environment, in this case, measured by the effects of the combination of temperature and photoperiod, affect plant stress responses to GBH application, and to determine which combination of temperature and lightsupported the faster degradation of glyphosate to its secondary metabolite AMPA; 2) To determine the effects of changing environmental conditions and GBH application on a plant’s melatonin production. I used wild strawberries (Fragaria virginiana) as my experimental species as they are a common understory species grown in the forest areas of British Columbia, Canada, where GBH is sprayed, and are also of importance as food to humans and wildlife. I used 1080 g/m2 of GBH treatments in my experiment to replicate the sublethal dose received by the non-target plants in industrial operations. Several plant stress responses were observed during the measurement period in three different trials. Trial 1 had different temperatures with constant photoperiod, trial 2 had different photoperiods with constant temperature, and trial 3 combined variation in temperature and photoperiod. At the end of experiment, I found that GBH were highly effective at 20°C with 18 hours of photoperiod as it affected several plant morphological features. The degradation of GBH were maximum at 20°C with 24 hours of photoperiod as suggested by the degradation ratio of glyphosate and AMPA. The new leaves produced by the plants after GBH application were more sensitive to glyphosate as leaf area and photosynthetic capacity by the new leaves were severely affected compared to the previously emerged leaves. Melatonin levels were altered by temperature, week of sample collection and slightly by photoperiod. The production was not affected by GBH application. These results suggest that wild strawberries grown in forest areas with warmer temperatures are most highly affected by glyphosate applications and when warm temperatures are accompanied by longer duration of sunlight, faster degradation of glyphosate is facilitated in tissues.