| My dissertation research focused on the physiological impacts of interspecific competition on seed protein and oil composition and its implication for consumer and industrial use. A two-year field study was conducted at the Agronomy Research Center at Southern Illinois University, Carbondale to investigate the response of five cultivars to three weed competition levels in terms of seed yield, quality, and reproductive development. Greater competition intensity resulted in decreased pod production, pod abortion, seed produced per plant, and total yield. In general, a significant increase in seed protein was evident with increasing competition levels whereas seed oil decreased with competition. By altering the relative proportion of protein and oil, the selling potential of the seed is changed.;Physiological and biochemical markers were used to evaluate the intensity of competition at pre-flowering (V7), flowering (R2), and post-flowering (R6). The markers included: trigonelline (TRG, an osmoprotectant), Fv/Fm (chlorophyll a fluorescence), relative water content (RWC), and foliar micronutrients (Mn, Fe, Cu, Zn). The parameters not affected by competition included Fv/Fm and RWC, but they did differ by stage of development. The foliar micronutrients and TRG, however, were most responsive to competition. Furthermore, competition altered the relative proportions of foliar micronutrients and it is suggested that this was through a combination of resource competition and allelopathy. The foliar micronutrients and their proportions may affect seed quality.;A greenhouse experiment was conducted using differing levels of Mn supply. This experiment did not work as many of the plants died from several factors such as insect infestation and low lighting. Of the plants that did survive, more Mn was found in the roots of canola and the shoots of soybean.;To investigate resource competition for Mn, a growth chamber experiment was conducted that examined the effect of competition level, competitor species, and Mn supply on soybean resource allocation. Under low competition, biomass allocation to roots increased but was not affected by competitor species or Mn supply. Micronutrient partitioning between root and shoot in response to high competition level was significantly different for Mn, but also for Zn, Fe, and Cu. Competitor species impacted root Fe levels. The results suggest that resource partitioning (in terms of biomass and micronutrients) in response to competition for micronutrients is similar to that for competition for macronutrients. More biomass and micronutrients are allocated to tissues used to capture the limiting resource as stress increases.;A field study was conducted to determine whether the soil micronutrient pools were altered when competitors were grown with soybean. In general, there were no interactions between competition level and soil type for R2 and seed quality parameters. Competition did not alter soil micronutrient levels but did impact foliar micronutrient concentrations at R2 and seed quality. The effect of soil type also impacted the selected parameters, which may also be related to environmental factors since selected plots were at different geographic locations. The results from this study further support the observation that competition leads to increased protein in seed as seen in Chapter 3. |
