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1
Finch, Heather. "The Bromus tectorum-Pyrenophora semeniperda Pathosystem." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/4125.
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Variable mortality of Pyrenophora semeniperda--infected Bromus tectorum seeds has been referred to as a "race for survival", stating that seeds that germinate quickly are more likely to escape pathogen-caused mortality. Dormancy status is not the only variable determining outcomes within the Bromus-Pyrenophora pathosystem. Varying temperature and exposure to water may strongly influence germination outcomes of B. tectorum when in the presence of P. semeniperda. Low water potentials characteristic of semi-arid soils are often over-looked in the context of seed pathogens, and are ecologically relevant- especially for plant species that inhabit intermittently dry environments. To adequately characterize the Bromus tectorum-Pyrenophora semeniperda pathosystem, four studies were conducted to address the following questions: (1) do temperature, water potential, and dormancy status influence germination outcomes in the Bromus-Pyrenophora pathosystem, (2) do repeated wetting-drying scenarios influence germination outcomes of infected B. tectorum seeds following dehydration at low water potentials similar to those found in the field (i.e., -4 through -150 MPa), (3) can we accurately characterize the asexual life cycle of P. semeniperda on a dormant B. tectorum seed, determining when infection takes place, and what occurs during disease development in continuously hydrated conditions, and (4) how does disease development of P. semeniperda influence the B. tectorum seed embryo and endosperm. All studies were conducted using dormant and/or non-dormant B. tectorum seeds and an intermediate strain of P. semeniperda. Study one used varying temperatures (5-20°C), and five water potentials (0, -0.5, -1, -1.5, -2 MPa) (achieved using PEG 8000). Inoculated seeds were exposed to low water potentials at various temperatures for 7, 14, 21, or 28 days then re-hydrated for 28 days. In the second study, seeds were incubated at 20°C at four nominal water potentials (-4, -10, -40, or -150 MPa) following 8 or 24 hours of initial hydration. Seeds were dehydrated for 1, 7, 14, or 21 days, then re-hydrated. In study three, inoculated seeds were chemically fixed between days 0 and 21 and viewed with a scanning electron microscope. In the fourth study, infected seeds were frozen with liquid nitrogen following 3, 8, and 14 days of disease development, then cross sectioned longitudinally and laterally prior to chemical fixation. Results indicate that non-dormant seeds escape death by germinating rapidly under favorable conditions, that incubation at low water potentials greatly increases seed mortality, that -10 MPa is near the threshold for full pathogen activity, and at water potentials lower than -40 MPa, P. semeniperda may successfully survive severe dehydration if previous hydration resulting in infection has occurred. SEM images indicate that mycelia penetration occurs within 8-24 hours, and that mycelium may penetrate all opening in the seed (i.e., stomata, cracks). Development of P. semeniperda is shown to cause significant damage to the endosperm and embryo within 8 days. As starch is consumed, the endosperm collapses leaving a hollow middle. The embryo is more resilient, but gradually deforms and deteriorates.
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Elwood, Heather. "Integrated Management of Downy Brome (Bromus Tectorum L.) Infested Rangeland." DigitalCommons@USU, 2013. https://digitalcommons.usu.edu/etd/2019.
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Invasive weed species are a threat to the health and functionality of many rangeland systems. Downy brome (Bromus tectorum) is an invasive annual grass that affects the productivity of rangelands by decreasing the grazing capacity for livestock as well as altering the wildfire cycle and competing against more desirable vegetation for limited resources.In 2006, an Invasive Plant Management Plan and Environmental Assessment was approved for Dinosaur National Monument, calling for prioritization of invasive species management on high value wildlife habitat, vector areas, and for species with a high ecological impact. The Cub Creek Watershed was identified as a priority for immediate attention due to its high historical, recreational, and environmental significance.This research was another phase of an integrated effort to manage vegetation in the Cub Creek Watershed and surrounding rangelands. Field work at two locations within Dinosaur National Monument was coupled with greenhouse experiments to evaluate chemical and mechanical methods of downy brome seed reduction and control, and to evaluate the response of four weedy grasses to herbicides used in broadleaf weed management practices.
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Fowers, Beth. "Ecologically-Based Manipulation Practices for Managing Bromus tectorum-infested Rangelands." DigitalCommons@USU, 2011. https://digitalcommons.usu.edu/etd/1019.
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Cheatgrass (Bromus tectorum) is an invasive annual grass common in several semiarid plant communities in the western U.S. B. tectorum presence increases fire frequency and size, reducing species diversity, and leading to annual species-dominated systems with inconsistent livestock forage potential and degraded wildlife habitat value. Most efforts to manage B. tectorum-dominated rangelands have focused on controlling the plant itself rather than addressing the causes of vegetation change. An alternative approach, ecologically-based invasive plant management (EBIPM), identifies treatments that can alter factors associated with the causes of succession, leading to a more desirable vegetation state. This study utilized the EBIPM framework to design a large-scale demonstration project, which implemented a series of manipulation treatments (mowing, prescribed fire, imazapic herbicide, and seeding with perennial species) to suppress B. tectorum and promote desirable species. The treatments were implemented at two semiarid shrubland sites in northwestern Utah. Treatments were evaluated by measuring resident vegetation cover, density, aboveground biomass, and litter and soil seed banks. Herbicide was most effective in reducing B. tectorum cover, density, and biomass, while fire was effective in reducing seed density in the litter seed bank. Treatment interactions were rarely significant; however, by combining fire and herbicide, increased B. tectorum control was achieved. Seedlings of seeded perennial grasses emerged in all treatments; however, establishment by the end of the first growing season was greatest in treatments involving fire. The results of this study indicate that using a decision-making framework to select a series of treatments that alter the causes of succession can improve the management of B. tectroum-dominated rangelands.
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Ricks, Nathan Joseph. "A Metagenomic Approach to Understand Stand Failure in Bromus tectorum." BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/8549.
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Bromus tectorum (cheatgrass) is an invasive annual grass that has colonized large portions of the Intermountain west. Cheatgrass stand failures have been observed throughout the invaded region, the cause of which may be related to the presence of several species of pathogenic fungi in the soil or surface litter. In this study, metagenomics was used to better understand and compare the fungal communities between sites that have and have not experienced stand failure. Samples were taken from the soil and surface litter in Winnemucca, Nevada and Skull Valley, Utah. Results show distinct fungal communities between Winnemucca and Skull Valley, as well as between soil and surface litter. In both the Winnemucca and Skull Valley surface litter, there was an elevated abundance of the endophyte Ramimonilia apicalis in samples that had experienced a stand failure. Winnemucca surface litter stand failure samples had increased abundance of the potential pathogen in the genus Comoclathris while the soils had increased abundance of the known cheatgrass pathogen Epicoccum nigrum. Skull Valley surface litter stand failure samples had increased abundance of the known cheatgrass pathogen Clarireedia capillus-albis while the soils had increased abundance of potential pathogens in the genera Olpidium and Monosporascus.
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Myklebust, May Christin. "The Carbon Cycle of a Semi-arid Grass System, Bromus tectorum." DigitalCommons@USU, 2007. https://digitalcommons.usu.edu/etd/6617.
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Understanding the carbon cycle of major ecosystems is important in predicting feedback responses of the terrestrial biosphere to climate change. Bromus tectorum dominated ecosystems currently cover 7% of the Great Basin and represents a major land cover type for the region. This study looked at the carbon cycle of a near monoculture field of B. tectorum in southeastern Idaho, USA. A major portion of the study was dedicated to measurement validation because of the disagreement among techniques used to measure net ecosystem exchange (NEE) of CO2 between the atmosphere and terrestrial ecosystems . NEE, net photosynthesis, and canopy and soil respiration were quantified for the B. tectorum stand using multiple methods. This allowed for comparisons among measurement techniques and permitted the calculation of a best estimate of NEE. The study found that the eddy covariance technique underestimated NEE at night for the B. tectorum stand and the magnitude of underestimation increased with increasing leaf area index of the plant canopy. Annual NEE estimated by eddy covariance for the year 2005 was over four times lower than the best estimate of -80 g C m-2 yr-1 determined by a combination of methods. Implications are that many studies currently underestimate NEE and productive systems underestimate NEE more than less productive systems.
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Lindon, Heather Lynn. "Genetic variation in Bromus tectorum (L.) (Poaceae) in the Eastern Mediterranean region." Online access for everyone, 2007. http://www.dissertations.wsu.edu/Thesis/Spring2007/H_Lindon_042707.pdf.
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Griffith, Alden B. "Global change in a sagebrush ecosystem : Bromus tectorum invasion and precipitation change /." Diss., Digital Dissertations Database. Restricted to UC campuses, 2008. http://uclibs.org/PID/11984.
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Bair, Necia B. "A hydrothermal after-ripening time model of seed dormancy loss in Bromus tectorum /." Diss., CLICK HERE for online access, 2004. http://contentdm.lib.byu.edu/ETD/image/etd487.pdf.
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Bair, Necia Beck. "A Hydrothermal After-ripening Time Model of Seed Dormancy Loss in Bromus tectorum." BYU ScholarsArchive, 2004. https://scholarsarchive.byu.edu/etd/533.
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After-ripening, the process of seed dormancy loss in dry storage is associated with a decrease in the mean base water potential, one of the parameters of hydrothermal time. The rate of change of the mean base water potential is assumed to be a linear function of temperature above a specific base temperature and as a result can be described by a thermal after-ripening (TAR) time model, an extension of hydrothermal modelling. The thermal requirement for after-ripening is the thermal time necessary for the modelling base water potential of the seed to shift from its original value to its final value. In order to include the effects of water potential on the rate of dormancy loss, a hydrothermal after-ripening (HTAR) time model was developed. Laboratory and field studies were conducted using seeds of Bromus tectorum. These studies identified four important ranges of water potential that influence the rate of dormancy loss. The ranges are identified as follows: seeds experiencing soil water potentials seeds experiencing soil water potentials <-400 MPa do not after-ripen, between -400 MPa and -150 MPa seeds after-ripen as a function of temperature (T) and water potential (Ψ), seeds experiencing water potentials >-150 MPa after-ripen as a linear function of temperature, and somewhere above -40 MPa seeds are too wet to after-ripen. These ranges suggest that specific reaction thresholds associated with non-fully imbibed seeds also apply to the process of after-ripening. The HTAR model for B. tectorum seeds generally improved predictions of dormancy loss in the field under soil conditions that were too dry for TAR alone. Reduced after-ripening rate under extremely dry conditions is ecologically relevant in explaining how seeds may prolong dormancy under high soil temperature conditions.
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Eldon, Desiree Rochelle. "Population Genetic Structure of Bromus tectorum in the American Desert Southwest." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/4273.
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Following its introduction to North America in the late nineteenth century, Bromus tectorum L., an inbreeding invasive winter annual grass, has become dominant on millions of hectares of sagebrush steppe habitat throughout Intermountain Western North America. It appears that within the last 30-40 years, B. tectorum has expanded its range southward into the Mojave Desert and also into more climatically extreme salt desert environments. Previous research using microsatellite markers and experimental studies has suggested that lineages found in desert habitats are genetically distinct from those found in the sagebrush-steppe habitat and possess suites of traits that pre-adapt them to these environments. To provide additional support for our hypothesis that desert habitat-specific haplotypes dominate and are widely distributed across warm and salt desert habitats, we genotyped approximately 20 individuals from each of 39 B. tectorum populations from these habitats and adjacent sagebrush steppe habitats using 71 single nucleotide polymorphic (SNP) markers. Our data clearly demonstrate that populations throughout the Mojave Desert region, as well as in salt desert habitats further north, are dominated by a small number of closely related SNP haplotypes that belong to the desert clade. In contrast, populations from adjacent environments are largely dominated by haplotypes of the common clade, which is widely distributed throughout the North American sagebrush steppe. Populations across all habitats were usually dominated by 1-2 SNP haplotypes. This suggests that inbreeding B. tectorum lineages can often maintain their genetic integrity. It also explains the strong association between marker fingerprints and suites of adaptive traits in this species.
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Merrill, Katherine Temus. "Apparent Competition with Bromus tectorum Through Pyrenophora semeniperda Reduces Establishment of Native Grasses." BYU ScholarsArchive, 2011. https://scholarsarchive.byu.edu/etd/2956.
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Contributing to the success of Bromus tectorum in the Intermountain West may be a mechanism called apparent competition, which occurs when one species increases the pressure of a consumer on a second species. This indirect interaction has been documented only a few times in invasive plant systems, and never in a fungal pathosystem. We examined the effects of the invasive annual Bromus tectorum and predation by the seed pathogen Pyrenophora semeniperda on seedling emergence and survival for two native grasses (Pseudoroegneria spicata and Elymus elymoides), by manipulating B. tectorum densities and P. semeniperda inoculum loads in randomized plots. Identical field studies were conducted in Skull Valley, Utah (xeric site) and Sprague, Washington (mesic site). The addition of inoculum decreased emergence of native grass seedlings at both sites and increased the amount of unemerged native seeds that were killed by P. semeniperda. Higher densities of B. tectorum decreased native grass survival at the mesic site and increased survival at the xeric site probably due to the beneficial effects of B. tectorum litter on soil moisture. At both sites, there were more B. tectorum seeds found in the seed banks in plots with high B. tectorum densities than in low-density plots. This indicates an increase in available prey for P. semeniperda. There was a much lower level of infection in B. tectorum seed bank seeds at the mesic site than at the xeric site. The high level of ungerminated native seeds killed by background levels of P. semeniperda, combined with the increase in available prey for the fungus in high-density B. tectorum plots, shows that apparent competition may play a role, along with direct competition, in the success of B. tectorum. This interaction is important to consider when dealing with control of B. tectorum.
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Williamson, Taryn Lori. "Evaluating Fungal Pathogen Inoculum Loads in Field Seed Banks." BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/8277.
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Quantification of soilborne pathogen inoculum loads is important in both agricultural and wildland settings. Quantitative Polymerase Chain Reaction (qPCR) methods using SYBR Green chemistry have been shown to be useful for quantifying fungal inoculum loads in environmental samples. The purpose of this study was to develop a method to quantify fungal pathogen inoculum loads in soil seed banks using a qPCR method with SYBR Green chemistry. The invasive annual grass Bromus tectorum was chosen for this seed bank study. There were three objectives: 1) to design target-specific primers for three fungal pathogens known to be important in Bromus tectorum seed banks, 2) to develop a procedure for measuring inoculum loads in field samples, including optimization of qPCR standard curves and protocols, for these pathogens, and 3) to perform qPCR using this methodology on a representative set of field samples to quantify pathogen DNA in seed bank soil and surface litter. The three pathogens were chosen for quantification based on their hypothesized roles in Bromus tectorum stand failure: the seed pathogen Pyrenophora semeniperda, an undescribed species of Fusarium seed rot pathogen belonging to the F. tricinctum species group (FTSG), and the newly-described causal agent of bleach blonde syndrome (Clarireedia capillus-albis). Primers designed for each pathogen were shown to be target-specific in tests against each other and 12 other fungal species cultured from B. tectorum seed banks. Subsequently developed standard curves for each pathogen had R2 values > 0.98, efficiencies between 90 and 110 percent, and generally optimal dissociation curves. Inoculum loads were expressed for each pathogen as picograms of DNA per microliter of extracted soil or surface litter. Significant differences in measured inoculum loads were found between the targeted pathogens and between soil and litter samples for each pathogen. The data provided reinforces that the SYBR Green qPCR method provides a potentially useful tool for the study of field seed and seedling diseases across a wide spectrum of both wildland and agronomic applications.
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Orloff, Lesley Noelle. "Understanding ecological interactions to improve management of Bromus tectorum in rangeland and cropland ecosystems." Thesis, Montana State University, 2011. http://etd.lib.montana.edu/etd/2011/orloff/OrloffL1211.pdf.
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Bromus tectorum L. (downy brome or cheatgrass) has been called the most dominant invasive plant species in the western United States. It is a barrier to restoration efforts in degraded lands and a serious weed problem for small grain growers. Investigating ecological interactions that play a mechanistic role in its success is a necessary step towards developing effective ecologically-based management strategies for B. tectorum. We investigated how biotic and abiotic factors impact interactions between B. tectorum and desired vegetation, with implications for restoration of lands dominated by B. tectorum and management of B. tectorum in small-grain cropping systems. Our research objectives were; 1) appraise the impact of relative size and soil nitrogen (N) availability on interactions between B. tectorum and Pseudoroegneria spicata (Pursh) A. Love (bluebunch wheatgrass), a species important in rangeland revegetation, and, 2) determine the impacts of Wheat streak mosaic virus (WSMV), resource availability, and neighborhood characteristics on B. tectorum performance in a winter wheat (Triticum aestivum L.) system. Objective 1 was carried out in a greenhouse experiment with two trials, following an addition series factorial design with four density treatments for each species, three P. spicata size cohort treatments, and two N treatments. Regression analysis indicated that giving P. spicata an initial size advantage over B. tectorum increased its ability to both suppress and avoid suppression by B. tectorum. We also observed that while N availability increased productivity of both species, it did not change their competitive relationship. Objective 2 was explored in two trials of a field experiment using a split-plot design with N availability assigned to main plots, WSMV inoculation assigned to subplots, B. tectorum proximity to the nearest wheat row as a predictor, and neighborhood characteristics as covariates. Regression analysis indicated that in low and high N environments (compared to the recommended N rate), distance from row influenced individual B. tectorum biomass only in disease-free environments, suggesting that healthy wheat suppressed B. tectorum that was closest to the row. Wheat inoculated with WSMV did not suppress B. tectorum. In an intermediate N environment, increased distance from row increased B. tectorum performance only with WSMV inoculation.
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Boguena, Toupta. "Epidemiology of Ustilago bullata Berk. on Bromus tectorum L. and implications for biological control /." Diss., CLICK HERE for online access, 2003. http://contentdm.lib.byu.edu/ETD/image/etd261.pdf.
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Fernelius, Kaitlynn Jane. "Post-fire Interactions Between Soil Water Repellency, Islands of Fertility, and Bromus tectorum Invasibility." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/3850.
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An intrinsic link exists between soil moisture and soil nitrogen. Factors that increase or decrease soil moisture can have a profound effect on soil nitrogen cycling, which may have later repercussions in the plant community. Post-fire soil water repellency is one factor that can limit soil moisture acquisition and may indirectly affect nitrogen cycling and weed invasion in woody islands of fertility. Plots centered on burned Juniperus osteosperma trees were either left untreated or treated with a surfactant to ameliorate water repellency. Two years later, soils were excavated from the untreated and treated field plots. In the greenhouse, half of each soil type received a surfactant treatment while the other half was left untreated. Pots were seeded with either Bromus tectorum or Pseudoroegneria spicata. Analysis of field soil prior to the greenhouse trial showed that untreated, repellent soils had inorganic nitrogen levels an order of magnitude higher than wettable, surfactant-treated soils. Greenhouse pots that had received a surfactant treatment in the field and/or greenhouse had similar soil water content, plant density, and above ground biomass, which were, respectively, 55-101%, 31 to 34 -fold, and 16 to 18 -fold greater than pots without a surfactant treatment. No species effects were found. This study indicates that water repellency can reduce wetting and retention of water in the soil while promoting the retention of high levels of inorganic nitrogen. However, the effects of soil water repellency on inorganic nitrogen appeared to have a minimal effect on plant growth compared to the effect of soil water repellency on water availability.
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Boguena, Toupta. "Epidemiology of Ustilago bullata Berk. on Bromus tectorum L. and Implication for Biological Control." BYU ScholarsArchive, 2003. https://scholarsarchive.byu.edu/etd/1142.
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The seedling-infecting pathogen Ustilago bullata Berk. is a naturally occurring biological control agent for cheatgrass (Bromus tectorum L.). The effects of temperature and nutrients on pathogen teliospore germination behavior and the effects of temperature on host seed germination were examined. The effects of temperature on sporidial proliferation, host infection in a temperature-controlled environment and in a field setting for eight populations were investigated. The infection success of Ustilago bullata on Bromus tectorum in cultivated fields as a function of seeding date, inoculation method, inoculum density, supplemental watering, and litter was also investigated. Teliospores germinated faster on potato dextrose agar than on water agar. Teliospores germinated slowly at temperatures far from the optimum of 15 and 20 C. There were among population variations in teliospore germination and sporidial proliferation, but differences among populations were much more pronounced at temperatures below 15 C. Infection also decreased and varied far from the optimum with almost no infection at 2.5 C in a controlled-environment and in the field for the December-planted seeds. Warmer early fall rather than the colder late fall was suitable for successful infection. This agreed with both laboratory and controlled-environment experiments. Intratetrad mating was observed with teliospores at 2.5 C. Teliospore germination tracked seed germination closely with teliospore germination rate exceeding the host seed germination rate over the range of 10 to 25 C where both were measured. Below 10 C, teliospore germination rate fell below host seed germination. This phenomenon was associated with lower infection percentages, suggesting that teliospore germination needed to be ahead of the seed for maximum infection. Inoculum density was positively correlated with infection rate. Litter significantly increased infection, while supplemental watering significantly increased plant establishment. Since teliospores from different populations showed similar germination patterns at temperatures typical of autumn seedbeds in the Intermountain West, it may not be necessary to use locally-adapted pathogen populations in biological control program. A biocontrol program is most likely to be effective under a scenario where autumn precipitation permits emergence of most of the host seed bank as a fall cohort.
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Hawkins, Katie Karen. "Secondary Dormancy and Summer Conditions Influence Outcomes in the Pyrenophora semeniperda - Bromus tectorum Pathosystem." BYU ScholarsArchive, 2014. https://scholarsarchive.byu.edu/etd/4207.
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Variable mortality of Pyrenophora semeniperda–infected Bromus tectorum seeds has been referred to as a “race for survival.” Dormant seeds are highly susceptible to P. semeniperda infection. While much is known about primary dormancy little is known about secondary dormancy in B. tectorum seeds. Dormancy status is not the only variable determining outcomes within the Bromus - Pyrenophora pathosystem. Varying temperature and intermittent hydration may strongly influence germination outcomes of B. tectorum in the presence of P. semeniperda. While it has long been assumed that B. tectorum seeds are infected by P. semeniperda in the fall it was recently suggested that seeds may be infected in the summer; however, there is little evidence to support this. To further characterize the Pyrenophora semeniperda - Bromus tectorum pathosystem two studies were conducted to address the following: (1) characterization of secondary dormancy in B. tectorum seeds and (2) summer interactions between host and pathogen after summer inoculation. Studies were conducted using dormant and/or non-dormant B. tectorum (along with B. rubens in one study) seeds and two strains of P. semeniperda. Study one used laboratory and field experiments to characterize secondary dormancy in B. tectorum seeds in terms of temperature (0.5-20°C), and water potential (-2.0-0 MPa). Data was used in repeated probit regression analysis to determine hydrothermal parameters (ψb(50), σψb, θHT) for secondary dormancy induction and loss. In the second study seeds were inoculated with one of two strains of P. semeniperda then exposed to intermittent hydration or dry storage at warm temperatures (30-60°C). After treatment seeds were rehydrated and outcomes observed. Optimum conditions for secondary dormancy induction were incubation at -1.0 MPa at 5°C. Seeds were likely to enter secondary dormancy through the cold winter months indicated by an increase or more positive ψb(50), while a decrease or more negative ψb(50) is associated with dormancy loss which is generally observed in the hot, dry summer months. When seeds were inoculated in the summer they only escaped death when summer conditions were ideal for after-ripening which allowed them to germinate rapidly under favorable autumn conditions. However, the pathogen caused high seed mortality no matter the treatment when disease progression advanced enough to inhibit seed germination. Thus this research shows that in areas with frequent summer rain storms, it would be highly advantageous to apply P. semeniperda as a biocontrol on seeds at maturity.
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Hohnhorst, Amanda Kay. "The effects of suppressive bacteria on the germination and growth of cheatgrass (Bromus tectorum L.)." Pullman, Wash. : Washington State University, 2009. http://www.dissertations.wsu.edu/Thesis/Summer2009/a_hohnhorst_062509.pdf.
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Thesis (M.S. in natural resource sciences)--Washington State University, August 2009.Title from PDF title page (viewed on Aug. 5, 2009). "Department of Natural Resource Sciences." Includes bibliographical references (p. 12-15).
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Embry, Saundra J. "Mycorrhization patterns in Bromus tectorum from salt desert and sagebrush habitats of the Great Basin, Nevada." abstract and full text PDF (free order & download UNR users only), 2004. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1433384.
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Huttanus, Temsha D. "Introduction and spread of Bromus tectorum (cheatgrass) into midwestern United States : population genetic and evolutionary consequences /." [Boise, Idaho] : Boise State University, 2009. http://scholarworks.boisestate.edu/td/52/.
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Franke, JanaLynn. "Identification of the Infection Route of a Fusarium Seed Pathogen into Non-Dormant Bromus tectorum Seeds." BYU ScholarsArchive, 2014. https://scholarsarchive.byu.edu/etd/4318.
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The genus Fusarium has a wide host range and causes many different forms of plant disease. These include seed rot and seedling blight diseases of cultivated plants. The Fusarium-caused diseases of wild plants are less well-known. In this study we examined Fusarium sp. n-caused disease development on non-dormant seeds of the important rangeland weed Bromus tectorum as part of broader studies of the phenomenon of stand failure or ‘die-off’ in this annual grass. We previously isolated an undescribed species in the Fusarium tricinctum species complex from die-off soils and showed that it is pathogenic on seeds. It can cause high mortality of non-dormant B. tectorum seeds, especially under conditions of water stress, but rarely attacks dormant seeds. In this study, we used scanning electron microscopy (SEM) to investigate the mode of attack used by this pathogen. Non-dormant B. tectorum seeds (i.e., florets containing caryopses) were inoculated with isolate Skull C1 macroconidia. Seeds were then exposed to water stress conditions (-1.5MPa) for 7 d, then transferred to free water. Time lapse SEM photographs of healthy vs. infected seeds revealed that hyphae under water stress conditions grew toward and culminated their attack at the abscission layer of the floret attachment scar. A prominent infection cushion, apparent macroscopically as a white tuft of mycelium at the radicle end of the seed, developed within 48 hours after inoculation. Seeds which lacked an infection cushion completed germination upon transfer to free water, whereas seeds with an infection cushion were almost always killed. In addition, hyphae on seeds that did not initiate germination lacked directional growth and did not develop the infection cushion. This strongly suggests that the fungal attack is triggered by seed exudates released through the floret attachment scar at the initiation of germination. Images of cross-sections of infected seeds showed that the fungal hyphae first penetrated the caryposis wall, then entered the embryo, and later ramified throughout the endosperm, completely destroying the seed.
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Jensen, Alexa Lunt. "Evaluating Nitrogen and Carbon Differences in Standing Litter from Normal and Prematurely Senesced Bromus tectorum Plants." BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/8265.
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Bromus tectorum, an invasive winter annual, has displaced native vegetation throughout the western United States. Bromus tectorum litter influences nutrient cycling near the soil surface as well as plant establishment. Failed seed production of B. tectorum occasionally occurs in the field, with plants exhibiting weak flowering culms that turn straw-colored in spring when normal plants are green or purple in color. Because annual grasses transport most soluble carbon (C) and nitrogen (N) to reproductive organs, seed production failure results in significantly different fates for these nutrients compared with normal plants. As part of larger efforts to understand events leading to large-scale seedling emergence failure (termed die-offs), occasionally observed in near mono-cultures of B. tectorum, we here test the hypothesis that prematurely senesced litter associated with seed production failure has higher soluble C and N than normal litter. C and N concentrations of aboveground biomass were compared for normal and prematurely senesced B. tectorum plants. Two methods were used to cause premature senescence: fungal pathogen infection with Clarireedia capillus-albis and glyphosate herbicide application. In a related experiment, field sampling of normal and prematurely senesced plants under natural conditions was conducted to compare C and N levels in-situ. Herbicide-induced senescence resulted in 1.5 to 2 times greater soluble C concentrations, but fungal infection had no effect on soluble C under experiment conditions. Prematurely senesced litter had increased total N concentrations, resulting in lower C:N ratios. The C:N ratio for prematurely senesced plants (averaged across all studies) was 68:1, whereas mature normal plants averaged 243:1. These findings illustrate failed seed production associated with premature senescence results in B. tectorum litter with significantly higher N concentrations and can result in increased soluble C concentrations. Altered nutrient status may contribute to changes in soil microbial activity, including activity of soilborne pathogens found in die-offs.
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Eddington, Daniel Blaine. "Effects of Cheatgrass Control on Wyoming Big Sagebrush in Southeastern Utah." BYU ScholarsArchive, 2006. https://scholarsarchive.byu.edu/etd/826.
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Critical mule deer (Odocoileus hemionus) winter ranges in southeastern Utah dominated by Wyoming big sagebrush (Artemisia tridentata var. wyomingensis [Beetle and A. Young] Welsh) have developed dense cheatgrass (Bromus tectorum L.) understories. These communities are currently characterized by predominately mature to decadent stands of sagebrush with few perennial grasses and forbs. Sagebrush seedlings and perennial grasses compete for limited resources with annual grasses and forbs. To determine the affects of cheatgrass control on sagebrush growth and reproductive characteristics, imazapic (PLATEAU®, AC 263,222) herbicide was sprayed at 438.5 ml/ha with water and methylated seed oil during active fall growth of cheatgrass in 2002. Sagebrush growth and reproductive variables were measured on browsed and unbrowsed (caged) plants on sprayed and non-sprayed paired plots on 6 sites. Cheatgrass and other annual forb pretreatment cover was reduced from 23% to less than 3% the first year after the herbicide treatement and only increased to 4% the second year. Soil moisture on the treated plots was available at 15, 30, and 60 cm for several days to several weeks longer than on the control plots depending on the depth in the soil and year. Annual leader growth and flowering seedstalk length were similar on unbrowsed and browsed shrubs, but the number of seedstalks per plant was decreased by browsing. The number of sagebrush flowering seedstalks was significantly reduced by the herbicide the first year after the treatment, but recovered by the second year. The decrease in flowering seedstalks per sagebrush reduced the number of sagebrush seedlings observed the second year after the treatment (control = 81,800 seedlings/ha and treated = 16,700 seedlings/ha). Both seedstalk length (treated = 13.4 cm and control = 11.2 cm) and annual leader growth (treated = 6.2 cm and control = 5.3 cm) were greater on treated plots than control plots. Overall, imazapic can provide a window of cheatgrass and annual forb control to allow big sagebrush seedlings and perennial grasses and forbs to establish.
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Stewart, Thomas E. "The Grass Seed Pathogen Pyrenophora semeniperda as a Biocontrol Agent for Annual Brome Grasses." BYU ScholarsArchive, 2009. https://scholarsarchive.byu.edu/etd/2267.
Full textAbstract:
Bromus tectorum and other annual brome grasses have invaded many ecosystems of the western United States, and because of an annual-grass influenced alteration of the natural fire cycle on arid western range lands near monocultures are created and conditions in which the native vegetation cannot compete are established. Each year thousands of hectares become near monocultures of annual brome grasses. Pyrenophora semeniperda, a generalist seed pathogen of annual grasses, shows major potential as a possible mycoherbicide that could help in reducing the monocultures created by annual grasses. The purpose of this research was to identify the requirements for isolating cultures of P. semeniperda, search for a hypervirulent strain, and evaluate its effect in the field. The techniques for isolating the fungus have evolved and become more efficient. The first two years of working with P. semeniperda resulted in 11 isolates. During the third year of this study, we developed a single spore isolation technique that resulted in 480 additional isolates. Virulence screening resulted in detection of a range of isolate ability to kill non-dormant B. tectorum seeds. Ninety-two isolates represented a range of virulence from 0-44%. The variation in virulence was expressed mostly within populations rather than between populations. Similarly, virulence varied significantly within Internal Transcribed Spacer (ITS) genotypes and habitats but not between them. When conidial inoculum was applied in the field there was no observed difference in disease incidence between different levels of inoculum. This is thought to have been due to applying the inoculum under conditions in which most in situ seeds were infected and killed by already high field inoculum loads. While additional field trials are needed to optimize the inoculum effectiveness, the overall results of this research provide a good foundation for using P. semeniperda as a biological control for seed banks of annual brome grasses.
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Mann, Rebecca K. "Intraspecific Variation in the Response of Elymus Elymoides to Competition from Bromus Tectorum." DigitalCommons@USU, 2016. https://digitalcommons.usu.edu/etd/4749.
Full textAbstract:
Native plant materials are often seeded to restore biodiversity and ecosystem function in areas overtaken by exotic weeds. Plant materials are evaluated on intraspecific differences in productivity and expression of traits advantageous to establishment (e.g., phenology, seed mass, and growth rate); some investigations also consider population-level adaptation to exotic species. However, there is a lack of studies that broadly evaluate response to competition from exotic species at multiple scales within a species.
In a greenhouse experiment, we used analysis of variance to assess the growth response of a perennial grass native to the Intermountain West, (Elymus elymoides), to competition from a common invasive species, (Bromus tectorum), at three levels of intraspecific differentiation: subspecies, lineage (wild vs. domestic germplasm), and population. We used regression analysis to assess whether E. elymoides populations from highly invaded areas were less affected by B. tectorum competition. Finally, we explored the relationship between growth traits and competitive response using random forest regression. We found significant differences among E. elymoides subspecies in their response to B. tectorum competition, no difference between wild and domestic lineages, and no population-level differentiation within subspecies. Field abundance of B. tectorum had a significant positive relationship with E. elymoides biomass, but not competitive response, suggesting that E. elymoides has not adapted to the invader. Elymus elymoides plants which were less affected by competition were smaller, allocated more biomass to leaves, and had fewer fine roots, suggesting that light interception and tissue retention were prioritized by seedlings in this competitive greenhouse environment.
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Nicholson, Joshua Alan. "Cheatgrass Die-Off Phenomena: What are the Short and Long Term Recovery Factors of Bromus tectorum Stand Failure?" BYU ScholarsArchive, 2014. https://scholarsarchive.byu.edu/etd/4311.
Full textAbstract:
Observations of Bromus tectorum L. (cheatgrass or downy brome) monocultures have shown that populations are susceptible to stand die-off or replacement failures. Die-offs, where the seed bank from the previous year fails to emerge, occurs in cheatgrass stands and it is unclear the trigger or cause. The fungus Fusarium has been identified in plant and seed samples from die-offs and may drive die-off activity through pathogenicity. Die-off recovery may take several years but cheatgrass populations eventually reestablish. The purpose of our study was to determine whether Fusarium is a potential player in a die-off, and understand how die-offs recover after multiple years of stand failure. Our objectives were to determine: 1- litter and water effects on die-off activity; 2- if fungal pathogens, such as Fusarium, decrease the proportion of cheatgrass emergence in a die-off; and 3- whether direct or broadcast seeding, water, and litter treatments increase establishment in recovering die-offs. Litter absent plots had significantly (P < 0.0001 and P < 0.001) more emergence at 49.2% and 41% compared to litter present plots 21.3% and 23.7%. The litter absent plots significantly (P = 0.0003 and P = 0.001) increased survival (82% and 52%) compared to litter present plots (70% and 41%). Direct planted versus broadcast seeding had significantly (P < 0.0001) more emergence, 36% to 11.9%. The addition of Fusarium inoculum to field plots did not effectively replicate anticipated disease levels. The fungicide treatment did not have a significant influence at either site. The results from the study indicate that nothing inhibits cheatgrass from establishing following a persistent die-off disturbance. A unique window may be available for land managers to revegetate natives in invasive populations as large quantities of cheatgrass seeds fail to emerge during die-off events.
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Schmelzer, Lee. "Reducing fuel load of key cheatgrass (Bromus tectorum L.) dominated range sites by the use of fall cattle grazing." abstract and full text PDF (UNR users only), 2009. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1464424.
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Merrill, Keith R. "Usage and Development of Molecular Markers for Investigation of the Population and Ecological Genetics of Bromus tectorum L." BYU ScholarsArchive, 2011. https://scholarsarchive.byu.edu/etd/2955.
Full textAbstract:
This thesis includes two studies: The first examined patterns of neutral genetic diversity within Bromus tectorum L. across the IMW region, and uses patterns of microsatellite (SSR) genotype distribution to make inferences about the respective roles of adaptively significant genetic variation, adaptive phenotypic plasticity, and facultative outcrossing in the ongoing invasion and recent range expansion of B. tectorum. It has been previously demonstrated that, due to extremely low outcrossing rates, it is possible to characterize individual genotypes of this species using four SSR loci. We sampled 20 individuals from each of 96 B. tectorum populations (classified by region and habitat) from throughout the IMW and used these SSR markers to characterize each individual. We found 131 four-locus SSR genotypes; however, the 14 most common genotypes collectively accounted for 79.2% of the individuals sampled. Individuals with certain SSR genotypes sorted strongly into warm or salt desert habitats (stringent habitats) and flowered earlier than individuals with genotypes from more mesic habitats, providing evidence of adaptively significant genetic variation associated with these genotypes. Other SSR genotypes were found across a wide range of habitats though they tended to be less prevalent in stringent habitats, providing evidence that adaptive phenotypic plasticity may be important for the distribution of some common genotypes. We observed very few heterozygous individuals, consistent with the highly inbreeding reproductive strategy of B. tectorum. Because specialist genotypes dominating recently invaded areas within the IMW region contained unique alleles, they are not likely to have resulted from recombination, leading us to doubt the role of facultative outcrossing as a significant mechanism facilitating the current range expansion of B. tectorum in the IMW.Previous research investigating the population and ecological genetics of Bromus tectorum L. in the North American invaded range has relied on either allozyme or microsatellite (SSR) genetic analyses, both of which have proven to have shortcomings. In order to overcome the issues associated with these other marker types, in the second study of this thesis we developed single nucleotide polymorphism (SNP) markers for B. tectorum by 1) obtaining normalized cDNA, 2) sequencing normalized cDNA using 454 sequencing, 3) aligning resultant contigs and looking for SNPs, 4) designing assays for SNP validation and genotyping using KASPar, 5) converting working KASPar assays for use with the Fluidigm EP1 platform using the 96.96 Dynamic ArrayTM IFC. Sequencing resulted in 1258041 reads, which assembled into 65486 contigs (20782 large contigs exceeding 500 base pairs). Using selection criteria of at least 10x coverage and 30% of the minor allele, 3333 putative SNPs were identified. We developed KASP assays for 255 putative SNPs, which resulted in 101 working polymorphic assays. Ninety-six assays were then successfully converted for use with KASP on the Fluidigm EP1 genotyping platform using 96.96 dynamic arrays.
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Summerhays, Jan C. R. "Effects of Non‐Surface‐Disturbing Treatments for Native Grass Revegetation on Cheatgrass (Bromus tectorum L.) Metrics and Soil Ion Availabilities." DigitalCommons@USU, 2011. https://digitalcommons.usu.edu/etd/1024.
Full textAbstract:
Several restoration methods intended to increase the success of aerially‐seeded perennial grasses were assessed to determine their effects on cheatgrass metrics and soil nutrient bioavailabilities. These methods were: 1) imazapic herbicide application (140 g ai ∙ ha‐1, 210 g ai ∙ ha‐1, and no application [control]), 2) vegetation manipulation treatments (50% sagebrush overstory thinning, 100% sagebrush overstory thinning, sagebrush overstory and/or vegetative thatch burning, and no manipulation [control]), and 3) alternative seeding treatments (aerial seeding with raking, aerial seeding with activated carbon [AC] addition, aerial seeding with sucrose addition, and regular aerial seeding [control]). Treatments were arranged in 3‐way factorial designs, which allowed main effects and interactions between treatments to be assessed. Responses were followed for two growing seasons following treatment.
Main effects of treatments and their interactions on cheatgrass metrics are described in Chapter 2. Herbicide reduced cheatgrass weights and tiller and spikelet numbers in 2009, but these variables were greater than in no‐herbicide plots in 2010. Burning decreased cheatgrass densities but increased weights and tiller and spikelet numbers in both years. One hundred percent sagebrush thinning resulted in greater cheatgrass weights and tiller and spikelet numbers in both years and greater densities in 2010. Sucrose addition decreased cheatgrass weights and tiller and spikelet numbers in 2009, but increased these variables in 2010. An interaction between AC and herbicide treatment was observed, with AC potentially sequestering and lessening the negative effect of herbicide on cheatgrass. Aerial seeding with raking and 50% sagebrush thinning treatments were not found to significantly affect cheatgrass either year.
The effects of treatments (herbicide, 50% sagebrush thinning, aerial seeding on snow, and aerial seeding with raking treatments omitted) on soil nutrient availabilities are described in Chapter 3. We used ion exchange resin (IER) membrane probes to measure extractable quantities of 15 ions over three time periods following treatment applications. Burning resulted in short‐term increases in many soil nutrient availabilities, including nitrate (NO3 ‐), phosphate (H2PO4 ‐), and sulfate (SO4 2‐). Sucrose addition reduced availabilities of NO3 ‐ and H2PO4 ‐ during the first winter and growing season. No changes were detected with AC addition or 100% sagebrush thinning during any sampling time.
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Diamond, Joel M. "Effects of Targeted Grazing and Prescribed Burning on Fire Behavior and Community Dynamics of a Cheatgrass (Bromus tectorum) Dominated Landscape." DigitalCommons@USU, 2009. https://digitalcommons.usu.edu/etd/257.
Full textAbstract:
Studies were conducted to determine the effectiveness of using targeted grazing and prescribed burning as tools to reduce fire hazards and cheatgrass (Bromus tectorum) dominance on rangelands in the northern Great Basin. A field study, with four grazing-burning treatments (graze and no-burn, graze and burn, no-graze and burn, and no-graze and no-burn), was conducted on a B. tectorum-dominated site near McDermitt, Nevada from 2005-2007. Cattle removed 80-90% of standing biomass in grazed plots in May 2005 and 2006 when B. tectorum was in the boot (phenological) stage. Grazed and ungrazed plots were burned in October 2005 and 2006. Targeted grazing in May 2005 reduced B. tectorum biomass and cover, which resulted in reductions in flame length and rate of spread when plots were burned in October 2005. When grazing treatments were repeated on the same plots in May 2006, B. tectorum biomass and cover were reduced to the point that fires did not carry in grazed plots in October 2006. Fuel characteristics of the October 2005 burns were used to parameterize dry climate grass models in BehavePlus 3.0, and simulation modeling indicated that grazing in spring (May) would reduce the potential for catastrophic fires during the peak fire season (July-August). The graze-and-burn treatment was more effective than grazing alone (graze and no-burn treatment) and burning alone (no-graze and burn treatment) in reducing B. tectorum cover, biomass, plant density, and seed density, and in shifting species composition from a community dominated by B. tectorum to one composed of a suite of species [including tumble mustard (Sisymbrium altissimum), clasping pepperweed (Lepidium perfoliatum), and Sandberg bluegrass (Poa secunda)], with B. tectorum as a component rather than a dominant.
A simulation study was designed to compare the cost-effectiveness of using cattle grazing and herbicide to create fuel breaks on B. tectorum-dominated landscapes in the northern Great Basin. Fuel characteristics from this targeted grazing study and from a Plateau® (Imazapic) herbicide study near Kuna, Idaho were used to parameterize fire behavior models and simulate flame lengths and rates of spread for the two fuel reduction treatments under peak fire conditions using BEHAVE Plus. Targeted grazing and Plateau® had similar reductions in flame length and rate of spread. Cattle grazing had high fixed costs (primarily fencing), and was more cost-effective than applications of Plateau® under five fuel loading scenarios except for three consecutive years of low fuel loads.
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Agbalog, Rose E. Medler Michael. "Effects of fire on cheatgrass (Bromus tectorum) : a case study of fire restoration in the Lake Chelan National Recreation Area, Washington /." Online version, 2010. http://content.wwu.edu/cdm4/item_viewer.php?CISOROOT=/theses&CISOPTR=350&CISOBOX=1&REC=16.
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Kelrick, Michael Ira. "Factors Affecting Seeds in a Sagebrush-Steppe Ecosystem and Implications for the Dispersion of an Annual Plant Species, Cheatgrass (Bromus Tectorum L.)." DigitalCommons@USU, 1991. https://digitalcommons.usu.edu/etd/2152.
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I investigated how shrub-induced spatial heterogeneity influenced and was manifested by a representative ground-story plant species at a sagebrush-steppe site in southwestern Wyoming. The dispersion of cheatgrass (Bromus tectorum) reflected differences between undershrub (higher plant densities) and interspace (between shrubs, supporting lower densities) microenvironments, hence the population ecology of this annual species served as a biological probe of shrub-associated patch structure in this community. Since cheatgrass is an annual, factors affecting the seed portion of its life cycle were of special interest. First, attributes of the above- and below-ground seed pool were characterized. The environment-wide seed depositional pattern was assessed using seed traps of several designs, and the legacy of seed incorporation into the soil was examined by separating seeds from soil samples. For both components of the seed pool, annuals' seeds predominated. Seeds at the surface were subject to substantial redistribution, moving readilythrough interspace, and their deposition was related to both the interaction of wind and shrub canopies and the presence of litter. More annuals' seeds were encountered in undershrub than in interspace soils; seeds of cheatgrass were restricted to the soil surface. Second, a manipulative experiment tested effects of granivoryfherbivory and presence/absence of a replicate shrub's canopy upon success of cheatgrass plants arising from known numbers of seeds introduced into undershrub versus interspace microenvironments. While biomass of plants in treatments accessible to herbivores was less than that of protected plants, consumers did not affect plant densities, and herbivore effects were not microenvironment-specific . Shrub canopy removal had no effect on plant success, and, contrary to expectations based on the dispersion of indigenous plants, interspace plants fared better than undershrub counterparts. Finally, demographic fates of individually marked seeds were observed, to disentangle effects of microenvironment from effects of microenvironment-specific surface types on determining safe sites. Littered microsites were strongly associated with undershrub microenvironments, and on these surfaces, cheatgrass seeds were less likely to move and to suffer depredation, and more likely to become favorably positioned for subsequent germination and establishment, than on bare ground surfaces typifying interspace. \
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Compagnoni, Aldo. "Climate change and plant demography in the sagebrush steppe." DigitalCommons@USU, 2013. https://digitalcommons.usu.edu/etd/1748.
Full textAbstract:
We used demographic methods to address one of the main challenges facing ecological science: forecasting the effect of climate change on plant communities. Ecological forecasts will be crucial to inform long-term planning in wildland management and demographic methods are ideal to quantify changes in plant abundance. We carried out our research in the sagebrush steppe, one of the most extensive plant ecosystems of Western North America. Our research intended to inform ecological forecasts on an exotic invader, cheatgrass (Bromus tectorum). Moreover, we investigated the general question asking: to what degree competition among plants influences the outcome of ecological forecasts on the effect of climate change? We carried out two field experiments to test the hypothesis that warming will increase cheatgrass abundance in the sagebrush steppe. This hypothesis was strongly supported by both experiments. Warming increased cheatgrass abundance regardless of elevation, neighboring vegetation or cheatgrass genotype. Moreover, we found cheatgrass was hindered by snow cover. Therefore, warming increases cheatgrass growth directly by increasing temperature, and indirectly by decreasing or removing snow cover. In our last experiment, we tested whether forecasts of climate change effects on rare species can ignore competition from neighbors. This should occur because rare species should have little niche overlap with other species. The lower the niche overlap, the less competition with other species. To test this hypothesis, we used a long-term data set from an Idaho sagebrush steppe. We built population models that reproduced the dynamics of the system by simulating climate and competition. Model simulations supported our hypothesis: rare species have little niche overlap and little competitive interactions with neighbor species.
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Lucero, Jacob Elias. "Cheatgrass (Bromus tectorum), Native Grasses, and Small Mammals in the Great Basin: a Test of the Apparent Competition Hypothesis Facilitated by a Novel Method of Decanting Seeds from a Flotation Solution." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3405.
Full textAbstract:
The effect of shared enemies between invasive and native species has been argued to facilitate biological invasions (i.e., the apparent competition hypothesis or ACH). This study investigated a previously untested possibility: whether granivorous small mammals facilitate cheatgrass (Bromus tectorum) invasion by driving food-mediated apparent competition between cheatgrass and native grasses. Specifically, we tested three predictions that must be true if such apparent competition occurs. First, cheatgrass invasion augments total seeds available to granivorous small mammals. Second, density of granivorous small mammals increases in response to increased seed availability (simulated with experimental additions of cheatgrass seeds). Third, granivorous small mammals prefer seeds from native grasses over cheatgrass seeds. We tested these predictions in the Great Basin Desert of Utah, USA. Cheatgrass invasion augmented total yearly seed production. Granivorous small mammals preferred native seeds over cheatgrass seeds. However, neither abundance, richness, nor diversity of granivorous small mammals increased in response to experimental additions of cheatgrass seed. We therefore conclude that granivorous small mammals did not drive food-mediated apparent competition during the study period. The lack of support for the ACH in this study may suggest that the role of small mammal-driven apparent competition is either unimportant in the Great Basin, or that the appropriate indirect interactions between small mammals, cheatgrass, and native grasses have yet to be evaluated. Testing the third prediction required the separation of seeds from the soil matrix. We employed a chemical flotation methodology to recover target seeds from soil, and developed a novel method of decanting target material from the flotation solution. We compared the utility of the novel method to that of a traditional decantation method. Specifically, we compared effectiveness (the proportion of seeds recovered from a known sample), rapidity (the time required to decant that sample), efficiency (the number of seeds decanted per second), and recovery bias (the effect of relative density on seed recovery) between methods. Our proposed method was more effective, more rapid, more efficient, and less biased than the traditional method. Therefore, any future work relying on flotation to analyze seed banks should clearly describe how samples are decanted and should consider the proposed method as a potential means of enhancing the efficiency of chemical flotation.
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Bone, Elizabeth. "Post-introduction evolution in invasive Bromus tectorum." 2007. https://scholarworks.umass.edu/dissertations/AAI3254960.
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Evidence for rapid evolutionary change in plants in response to changing environmental conditions is widespread in the literature. The first objective of this research was to estimate rates of evolution for previously published studies to begin a foundation for comparison and to examine trends and rates of microevolution in plants and to demonstrate how estimated rates could be used to address specific microevolutionary questions. The remainder of the research in this paper focused on invasion as a stimulus for microevolution using a major invasive grass, Bromus tectorum . Identification of pairs of European, source and North American, introduced population pairs of B. tectorum provided an ideal opportunity to test for post-introduction increase in invasiveness because parallel change involving multiple introduction events suggests a non-random process. This research tested to see if B. tectorum evolved to be more invasive by becoming larger and more fecund, more competitive, and more phenotypically plastic in its invasive range than its source range. All B. tectorum experiments were done in common garden or greenhouse settings to control environmental differences, and comparisons were made between morphological characteristics of introduced and source B. tectorum populations. The experiments showed that introduced B. tectorum was taller and had higher reproductive output than source B. tectorum, but the populations did not differ in aboveground biomass. Contrary to predictions, North American B. tectorum had less competitive effect than European B. tectorum on one of the native bunchgrasses, with no other differences in competitive ability. All of the B. tectorum populations show plasticity for the traits measured in this study, however there was no strong trend to suggest that there has been a change in the level of plasticity in introduced populations. Overall, these results suggest that B. tectorum may have evolved to be more ruderal to capitalize on characteristics that increase its ability to spread in its new environment while not focusing as many resources on competitive ability. As for plasticity, it is likely that the same strategy of phenotypic plasticity from its native range could be a key to the success of B. tectorum in its invaded range with similar levels of selection for plasticity in both ranges.
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Hendrickson, Paul E. "Response of downy brome (Bromus tectorum) and Kentucky bluegrass (Pao pratensis) to primisulfuron." Thesis, 1998. http://hdl.handle.net/1957/33607.
Full textAbstract:
Glasshouse and growth-chamber experiments were conducted to evaluate
primisulfuron phytotoxicity and the influence of adjuvants on downy brome and Kentucky bluegrass. GR₅₀ (50% growth reduction) values were 0.97 ± 0.57 and 8.07 ± 1.85 g/ha for downy brome and Kentucky bluegrass, respectively. Primisulfuron was applied to downy brome and Kentucky bluegrass at 3 placement sites; foliar, soil, and foliar plus soil. Foliar or foliar plus soil applications were more effective at reducing downy brome dry weights than the soil application of primisulfuron, while Kentucky bluegrass was injured more from the soil or foliar plus soil applications than from the foliar application of primisulfuron. Primisulfuron at 5 g/ha applied alone reduced downy brome dry weights by 5%, whereas, when an adjuvant was added, dry weights were reduced by 52 to 83%. Primisulfuron was more phytotoxic to downy brome at alternating temperatures of 8-16 C and 16-24 C than at 0-8 C. Phytotoxicity of
primisulfuron was less when downy brome plants were stressed for soil moisture after herbicide treatments than when the plants were not stressed or only stressed before treatment.Graduation date: 1999
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Sheley, Roger Leslie. "Life-history, growth and interference of cheatgrass (Bromus tectorum L.) and yellow starthistle (Centaurea solstitialis L.) /." 1993. http://hdl.handle.net/1957/10103.
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MacNaughton, Carleton James. "Invasive plant influence on the native grass community of the White Lake Basin, British Columbia." 2012. http://hdl.handle.net/10170/487.
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Invasive plants can have significant ecological effects. Cheatgrass (Bromus tectorum) is of particular concern in North America, where its competitive nature can seriously degrade natural grasslands. This study, conducted in the White Lake Basin region of British Columbia, investigated the impact of cheatgrass on native plant diversity and the relationship between diffuse knapweed (Centaurea diffusa) and introduced grass cover. The study also analysed the association of cheatgrass with other grass species to provide insight in selecting grass seed composition for seeding after habitat disturbance. Results indicated higher native grass diversity in plots without cheatgrass and in plots containing bluebunch wheatgrass (Pseudoregneria spicata). While diffuse knapweed decreased during the study period, due to biological control, invasive grasses increased. Native grass species positively associated with cheatgrass include needle and thread grass (Hesperostipa comata), Sandberg bluegrass (Poa secunda), and sixweeks fescue (Vulpia octoflora), indicating potential for seeding in disturbed areas prone to cheatgrass.
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Park, Kee-Woong. "ALS-inhibitor resistant downy brome (Bromus tectorum L.) biotypes in Oregon : mechanism of resistance, fitness, and competition." Thesis, 2003. http://hdl.handle.net/1957/30435.
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"Effects of targeted grazing and prescribed burning on fire behavior and community dynamics of a cheatgrass (Bromus tectorum)-dominated landscape." UTAH STATE UNIVERSITY, 2009. http://pqdtopen.proquest.com/#viewpdf?dispub=3349573.
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Nasri, Mohamed. "Effect of temperature and competition on shoot and root growth of cheatgrass (Bromus tectorum L.) and 5 collections of Idaho fescue (Festua idahoensis. Elmer)." Thesis, 1993. http://hdl.handle.net/1957/36226.
Full textAbstract:
This research was conducted to determine the effects of
temperature and competition on seedling root and shoot growth of
cheatgrass (Bromus tectorum L.) and 5 collections of Idaho fescue
(Festuca idahoensis. Elmer). For the temperature study, seedlings
were grown in environmental chambers with 16 hours day/8 hours night, at
temperatures of 5, 10 and l5°C. Root depth was weekly recorded during 9
weeks growth period. Seedlings were destructively harvested after 63 days
and evaluated for root and shoot characteristics. At all temperatures,
cheatgrass exhibited greater above and below-ground biomass, root depth,
total root length, daily root depth rate and shoot height than Idaho
fescue. Seedlings of the 5 Idaho fescue collections produced fewer roots
and grew slower than seedlings of cheatgrass. As a group, the Idaho
fescue collections showed similar root and shoot growth and produced more
tillers than cheatgrass, except at 5°C. As temperature increased from 10
to 15 °C, shoot growth of Idaho fescue increased while that of cheatgrass
was similar.
For the competition study, seedlings were grown in pots in a
greenhouse with planting ratios of Idaho fescue to cheatgrass of 1:0, 1:5
and 1:10, and under 2 watering regimes. Seedlings of Idaho fescue were
established from transplants grown two months ahead of cheatgrass. Shoot
height, tiller and leaf number were weekly recorded. Seedlings were
harvested after 49 days and evaluated for aboveground dry weight.
Competition from cheatgrass depleted soil moisture and reduced growth of
Idaho fescue. Cheatgrass had greater aboveground dry weight and shoot
height than Idaho fescue. However, Idaho fescue had greater tiller and
leaf number than cheatgrass. In addition, when competing with cheatgrass,
remnant Idaho fescue plants were less adversely affected in aboveground
dry weight and shoot height than Idaho fescue plants from pristine areas.
These results indicated that remnant Idaho fescue plants may be a
different ecotype occurring in response to competition and may better
tolerate the effect of the interference from cheatgrass. This information
may serve as a basis for reestablishment of Idaho fescue in Central Oregon
rangelands.Graduation date: 1993