Memoria para optar al título profesional de Ingeniera Agrónoma / La presente investigación tuvo por objetivo evaluar el efecto de dos alternancias de temperaturas en la germinación y emergencia de tres géneros de interés forrajero, simuladas en dos momentos de inicio del ciclo de crecimiento de la pradera anual de clima mediterráneo. Este estudio se llevó a cabo en el Laboratorio de Manejo de Praderas del Departamento de Producción Animal y el material de estudio fué recolectado en la Estación Experimental Germán Greve Silva ubicada en Rinconada de Maipú, ambos sitios pertenecientes a la Facultad de Ciencias Agronómicas de la Universidad de Chile. Para el ensayo de germinación, se trabajó con semillas de Bromus, Erodium y Vulpia, cosechadas en campo directamente desde las plantas, las cuales una vez en laboratorio, fueron sometidas a prueba de germinación y viabilidad. Los tratamientos fueron el resultado de la combinación de los tres géneros en estudio con las dos alternancias de temperaturas (16ºC/8ºC - temperaturas otoñales, 12ºC/4ºC - temperaturas invernales), obteniendo 6 tratamientos. Las semillas se dispusieron sobre papel filtro en placas petri, en cámara de crecimiento, con humedad constante y un fotoperiodo de 12 horas de luz y 12 horas de oscuridad. Las variables a medir fueron porcentaje de germinación y tasa de germinación por placa petri.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1960. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Large populations of controlled hybrids are essential to the most rapid progress in many phases of plant breeding programs. Plant species vary in the ease with which they may be hybridized. Hand hybridization of forage grasses is usually slow and laborious, and the minuteness of the floral parts of most of the species which have perfect flowers renders their hybridization by hand especially difficult and tedious. This difficulty limits the use that forage grass breeders are making of the significant principles of hybridization and thereby retards progress in this phase of plant breeding. Any dependable, rapid technique of hybridization which would eliminate many of the present hand operations, that is "bulk" hybridization, would make possible more rapid progress in the breeding of forage grasses. The study herein reported was designed to estimate the feasibility of applying various methods of bulk emasculation and bulk pollination to forage grasses. In limiting the scope of the study, smooth bromegrass (Bromus inermis) was selected to receive the greatest attention because of its importance among forage grasses and the wide range of self-fertility among individual plants of the species, a characteristic which proved very helpful in the study.

The social, economic, and ecological costs of plant invasions are vast, through their ability to alter ecosystem structure and function. Invasive annual grasses are a nuisance in the American Southwest through promotion of the grass-fire cycle. Annual grasses such as Bromus rubens, Bromus tectorum, Schismus barbatus, and Schismus arabicus have invaded the Mojave Desert and increased fire occurrence, thus it is important to identify and characterize the areas where persistent invasion has occurred and subsequently fire risk is increased by understanding the distribution of these invasive grasses. Previous plot and landscape-scale research has revealed anthropogenic and biophysical correlates with the establishment and dominance of invasive annual grasses in the Mojave Desert. However, these previous studies have been limited in spatial and temporal scales. Here we use a remote sensing framework to map persistent and productive populations of invasive annual grass, called hot spots, in the entire Mojave Desert ecoregion over 12 years, identify important variables for predicting hot spot distribution, and identify the most invaded subregions. Hot spots were identified in over 5% of the Mojave Desert, and invasive grasses were detected in over 90% of the desert at least once. Our results indicate that soil texture, aspect, winter precipitation, and elevation are the most important predictive variables of invasive grass hot spots, while anthropogenic variables were the least useful. The most invaded subregions of the Mojave Desert were western Mojave basins, eastern Mojave mountain woodland and shrubland, western Mojave low ranges and arid footslopes, eastern Mojave basins, and eastern Mojave low ranges and footslopes.

Exotic plant invasions represent a significant threat to the integrity of native grasslands. Across the Northern Great Plains, grasslands invaded by smooth brome (Bromus inermis Leyss) support lower plant diversity, potentially resulting in important consequences for ecosystem function. Previous research on smooth brome has primarily focused on aboveground changes in plant communities, but there is growing evidence that the soil ecosystem can be significantly altered with invasion. The two objectives of this thesis were to examine whether smooth brome invasion alters soil nitrogen cycling, and to determine if changes in plant community diversity or productivity influence soil bacterial communities. Relationships between smooth brome and the soil ecosystem were assessed using data collected from a Festuca hallii Vasey (Piper) (plains rough fescue) grassland located near Macrorie, SK. Gross rates of nitrogen cycling and community productivity from smooth brome invaded and native grassland sites were compared to determine the potential influence of smooth brome invasion on the soil nitrogen cycle. The relationship between increasing smooth brome abundance and soil bacterial structure and composition was also studied. Gross mineralization rates and total soil nitrogen were significantly higher in smooth brome-invaded areas relative to native grassland. Bacterial and archaeal amoA, used as indicators of ammonia-oxidizer population sizes, were altered by smooth brome cover. Higher gross mineralization rates were likely due to stimulated microbial activity caused by increased litter and root production in areas invaded by smooth brome. Smooth brome decreased plant species richness through increased litter production, but had the opposite effect on bacterial communities. Bacterial communities had higher species richness and evenness in soils invaded by smooth brome, and smooth brome invasion was also associated with bacteria important for soil nitrogen cycling. As bacteria dominate microbial biomass and are important for decomposition processes, a more even bacterial community may have supported increased mineralization rates in smooth brome-invaded soils. Specifically, a more even bacterial community may have increased mineralization rates through greater resource utilization and niche partitioning. The responses observed in these studies suggest that belowground changes with smooth brome invasion have the potential to have important consequences for ecosystem processes.

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.

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.

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.

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.

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.