Evaluation of allelopathy as a mechanism by which buckwheat suppresses Canada thistle and its mycorrhizae Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/zp38wg225

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  • Experiments were conducted to determine if allelopathy is a mechanism by which buckwheat interferes with a) the growth of Canada thistle and/or b) mycorrhizae colonization in Canada thistle roots. In a competition experiment, buckwheat plant biomass was only affected by the intraspecific competition from other buckwheat plants and not by the interspecific competition from Canada thistle plants. Canada thistle plant biomass was only affected by the interspecific competition from buckwheat and not the intraspecific competition from other Canada thistle plants. Since one of the interspecific competition components was missing (Canada thistle did not affect buckwheat), the value for niche differentiation is greater than unity, indicating that buckwheat and Canada thistle are not exploiting the same resources. A niche differentiation value less than unity would have indicated that not all available resources were being used. Allelopathy is one mechanism that prevents use of all available resources. In root-shoot isolation experiments, Canada thistle biomass was significantly affected by buckwheat when growing only in the presence of buckwheat roots (shoots trained away). When growing under buckwheat's canopy, Canada thistle biomass was greater when Canada thistle roots were isolated from the buckwheat roots than when roots were not isolated. In both cases, plants were irrigated with water containing a soluble 20-20-20 (nitrogen (N)-phosphorous-potassium) fertilizer at an N concentration of 100 parts/million (wt/vol) to reduce or eliminate competition for nutrients and water. Canada thistle biomass, when both Canada thistle roots and shoots were separated from buckwheat roots and shoots, was reduced when exposed to leachates from buckwheat's root system. A 10% Hoagland's solution was circulated between buckwheat's and Canada thistle's root systems to reduce or eliminate competition for light, water, and nutrients. Results from the root-shoot isolation experiments suggest that allelopathy may be a mechanism by which buckwheat interferes with Canada thistle. Results from mycorrhizae experiments indicate that buckwheat did not become mycorrhizal possibly because of extensive root hair development. Also, results suggest that buckwheat suppressed the colonization and growth of mycorrhizae in Canada thistle roots because of the low light condition created by buckwheat's canopy and not because of allelopathy.
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