Studies on the effects of variable terbutryne concentrations and temperatures on some physiological responses of 'Elodea Canadensis Michx.'

Abstract

Effects of different concentrations of terbutryne on photosynthesis, respiration, chlorophyll concentration and dry matter accumulation of Blodea canadensis Michx. over a wide range of temperature, under natural and artificial light climates have been described in this thesis. At a given temperature, effects of terbutryne increased with increased concentration, and at a given concentration phototoxicity increased with rising temperature. There was a highly significant concentration x temperature interaction of terbutryne activity. The difference in the metabolic and physiological responses of B. canadensis to terbutryne treatment under the two light climates were not wide. At all concentrations and temperatures the maximum inhibitory effects on net photosynthesis were expressed by the second day and on dark respiration by the third day of treatment. Fifty percent inhibition (I₅₀) in net photosynthesis occurred at the lowest concentration of 0.0125 mgL⁻¹ and temperature 10°C and dark respiration at a concentration of 0.025 mgL⁻¹ and temperature 20 C. Complete suppression of net photosynthesis (100% inhibition) occurred at the highest concentration of 0.05 mgL⁻¹ at temperatures 20° and 25°C, under natural light conditions, while it did not occur under artificial light conditions at the same concentration and temperature. Complete suppression of dark respiration never occurred at any concentration and temperature. Recovery from photosynthetic inhibition of terbutryne started from third day of treatment in all concentrations at most of the temperatures. Recovery was higher at lower concentrations and temperatures. Recovery from respiratory inhibition never occurred.at any concentration and temperature. Dry weight of the treated plants decreased at all concentrations and temperatures. The general trend was for the dry weight to decrease most with increasing concentration of terbutryne. Despite some variation, the chlorophyll (a+b) concentration in the tissues of the treated plants remained more or less unaffected and the plants suffered no visible physical damage due to terbutryne treatment over the experimental period. The relevance of these findings to aquatic weed control in tropical conditions of Bangladesh (i.e. at the equivalent high ambient temperatures) is discussed.