Theses and Dissertations at Montana State University (MSU)
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Item Pest management challenges and climate change in water limited winter wheat agroecosystems in southwestern Montana(Montana State University - Bozeman, College of Agriculture, 2020) Nixon, Madison Grace; Chairperson, Graduate Committee: Fabian D. MenalledDryland winter wheat production is influenced by many environmental factors including climate, disease, and resource availability. In Montana, Bromus tectorum (cheatgrass) and Fusarium pseudograminearum (a fungus causing root crown rot) are major winter wheat pests; reducing yield and grain quality. However, little is known how climate change and resource availability impact winter wheat, B. tectorum, and F. pseudograminearum individually as well as their multi-trophic interactions. Thus, this research aimed to 1) Determine the susceptibility of B. tectorum to F. pseudograminearum and assess how CO 2 and nitrogen impact their growth, and 2) Evaluate how elevated temperature, reduced precipitation, and plant competition impact winter wheat and B. tectorum growth and reproduction. Utilizing growth chambers, high and low nitrogen treatments, fungal inoculated and uninoculated treatments, and ambient and elevated CO 2 treatments, Bromus tectorum was found to be a host of F. pseudograminearum, and the fungus significantly reduced root, shoot and total biomass, as well as primary physiological processes of B. tectorum. Fusarium pseudograminearum infection was not impacted by nitrogen or CO 2 level. Low nitrogen increased emergence and root production early on, while high nitrogen increased shoot production at later growth stages. Low nitrogen also improved stomatal conductance and transpiration rate. High CO 2 increased B. tectorum root, shoot, and biomass production, as well as intercellular CO 2. An interaction between ambient CO 2 and low nitrogen resulted in the greatest shoot relative growth rate between the first and second harvest. Field tests, using three climate treatments (ambient, increased temperature, reduced precipitation with increased temperature) and three plant competition levels (monoculture winter wheat, monoculture B. tectorum, and biculture of the two), found that for both winter wheat and B. tectorum monocultures, ambient and warmer climates produced similar yields and biomass, respectively, whereas the drier with warmer treatment reduced these factors. Additionally, B. tectorum presence increased winter wheat grain protein. A quadratic interaction model of winter wheat yield as a function of B. tectorum biomass by climate treatment suggests that at low to moderate B. tectorum biomass levels, winter wheat yield was negatively impacted by the warmer and drier treatment, whereas ambient and warmer treatment results were similar.Item Belowground competition and response to defoliation of Centaurea maculosa and two native grasses(Montana State University - Bozeman, College of Agriculture, 2005) Sartor, Karla Anne; Chairperson, Graduate Committee: Catherine A. Zabinski.Invasion of native rangelands in the western United States has serious ecological and economic effects. Understanding the mechanisms behind invasion of Centaurea maculosa (spotted knapweed) is necessary to effectively manage this species. Arbuscular mycorrhizae (AM), which are a type of plant fungal symbiosis, are ubiquitous in grasslands. My research explores the role of AM for increasing the competitive ability of C. maculosa. A greenhouse experiment tested the effects of AM fungi and neighbor species on growth of C. maculosa, Festuca idahoensis (Idaho fescue) and Pseudoroegneria spicata (bluebunch wheatgrass). A mesh barrier permeable to AM hyphae allowed comparison of species interactions by either roots and/or AM hyphae in pots without a barrier or by AM hyphae alone in pots with a barrier. Centaurea maculosa plants had high AM colonization levels within roots and ERH (extraradical hyphae), and may have increased AM colonization of neighboring plants. I found no evidence, however, that ERH affected competition, as C. maculosa neighbors had the greatest effect on native grass neighbors there was the potential for root contact. Additionally, plants grown with AM fungi were always smaller than non-mycorrhizal plants. In the second experiment, I investigated growth response after herbivory (simulated by clipping), with different neighboring species and AM fungi. Centaurea maculosa, F. idahoensis and P. spicata were grown in the greenhouse with a C. maculosa neighbor, with or without AM fungi, and with one of three clipping treatments (no clipping, focal plant clipped or neighbor plant clipped to remove 75% of aboveground biomass). Compensatory growth was dependent on AM fungi and neighbor species. Centaurea maculosa compensated for herbivory only when grown with a conspecific and with AM fungi, or with a F. idahoensis neighbor and no AM fungi. Clipping decreased AM colonization in F. idahoensis only, and colonization also decreased in F. idahoensis when C. maculosa neighbors were clipped. This research suggests that AM fungal effects vary between species in the grassland system, and is important for determining plant species response to herbivory. I also find that high levels of herbivory may reduce C. maculosa biomass enough to be a method for weed control, but neighbor species is important to determining plant response to herbivory.