Thesis (Ph. D.)--Oregon State University, 2007. / Printout. Includes bibliographical references. Also available on the World Wide Web.

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Understanding the mechanisms of invasion is critical in order to control an invasive species. Poa pratensis L. (Kentucky bluegrass) is an invasive species that has been present in the northern Great Plains (NGP) for over 100 years, but has become a dominant species in the mixed grass region recently. My dissertation seeks to answer one critical question—why has P. pratensis become such a successful invasive species in the NGP? I first asked if the invasion was caused by adaptation and/or propagule pressure. I screened the genetic fingerprint of invasive P. pratensis in the NGP along with measuring the genomic content of wild plants and compared them to common cultivars. I found virtually no overlap between lawn cultivars and invasive P. pratensis populations. This was further supported by a narrow range of genomic content in wild individuals compared to the lawn cultivars. I also found no evidence of geographical patterning which is consistent with the hypothesis that local adaptation is not pervasive in P. pratensis. I then asked whether P. pratensis was a strong competitor compared to dominant plant species native to the tallgrass prairie. I studied competitive effect between Poa pratensis, Nassella viridula, Pascopyrum smithii, and Bouteloua gracilis through a species-pair competition experiment. Based on the relative interaction indices, P. smithii and P. pratensis were competitive against B. gracilis, and P. smithii was competitive against N. viridula. Additionally, P. pratensis was facilitated by all three species in the experiment. This study indicates that P. pratensis may be somewhat competitive. Finally, I asked whether the increase in the frequency of P. pratensis in the NGP may be attributed to environmental factors. In order to understand long-term correlations between P. pratensis invasion and environmental variables, I resampled plots that were previously sampled for species composition in 1978, 1979, and 1999. I found that P. pratensis levels did increase across plots and was corrrelated with higher levels of precipitation. My research indicates that increased precipitation in the NGP as a result of climate change is correlated with P. pratensis invasion in the NGP. / United States Fish and Wildlife Service (FWS-R6-POAPRATENSISGENETICS) / North Dakota State University. Department of Biological Sciences / North Dakota State University. Department of Natural Resource Management / North Dakota State University. Graduate School / Cross Ranch Fellowship

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Field experiments were established on September 7, 1968, and Hay 13 and July 16, 1969, by seeding three rates (on pure live seed basis [PLS]) of several companion grasses with a constant rate of Kentucky bluegrass (Poa pratensis L.). Mixtures were irrigated and clipped to 1- and 2-in. sod residues. Objectives were to determine which mixture or mixtures could provide rapid initial establishment. with subsequent high quality, permanent turf. The improved perennial ryegrasses (Lolium perenne L.) (NK-100 and Pelo) were no more competitive in the seedling stage toward Kentucky bluegrass (Poa pratensis L.) than annual ryegrass (Lolium multiflorum L.), but they provided as rapid initial cover. However, their persistence provides a means for bluegrass encroachment during the seedling year. Seedling competition was not due to any excretions from ryegrass seeds or seedlings. Turf quality of the improved perennials was superior to annual ryegrass, but slightly lower than pure bluegrass, because of frayed leaf tips. Redtop (Agrostis alba L.) and creeping red fescue (Festuca rubra L.) were less competitive to bluegrass than the ryegrasses, but they provided little advantage in ground cover; however, turf quality was similar to pure bluegrass. It was concluded that mixtures should be designed to obtain designated populations of companion and other seedlings that are needed for sufficient initial cover. The 5% PLS in this study was higher than normally recommended on a weight basis; therefore there was no advantage from higher seeding rates. Fall seeded mixtures generally contained the most Kentucky bluegrass, and the summer seedings had the least. Low clipping reduced competition from companion grasses, especially the improved perennial ryegrasses, which allowed a uniform transition toward bluegrass dominance with turf of average quality. Sod strength was best for the pure bluegrass turf, but root development of the improved perennial ryegrasses was best. / Master of Science

A series of studies were conducted to examine morphological and physiological responses of Kentucky bluegrass (Poa prazensis L.) following foliar applications of chelated iron phosphate citrate (Fe), the synthetic cytokinin benzyladenine (BA), the systemic triazole fungicides propiconazole and triadimefon, and MZ63 cold water seaweed extract. Applications of Fe at 112 mg m⁻², BA at 6 mg m⁻², propiconazole and triadimefon at 42 and 150 mg m⁻², respectively, and MZ63 seaweed extract at 0.32 ml m⁻² enhanced root and shoot growth and development of seedling Kentucky bluegrass. Repeated applications of BA, the triazoles, or MZ63 in late summer or fall and spring tended to slightly increase post-transplant rooting and sod strength of Kentucky bluegrass as compared to single applications. Repeated applications of Fe applied alone in late summer or fall and spring increased Kentucky bluegrass rooting as compared to single applications of Fe. However, the potential for reduced sod strength and post-transplant rooting was also indicated following single summer applications of chelated Fe at 112 mg m⁻². Kentucky bluegrass growth from various combinations of BA, the triazoles, MZ63 seaweed extract and Fe were highly variable. The nature of the responses indicated the possibility of an adverse interaction between the growth promoting activities of chelated Fe and the other materials. Kentucky bluegrass seedlings treated with Fe, BA, the triazoles, or MZ63 seaweed extract had increased photosynthetic rates on a land area basis, but not on a per gram shoot dry weight basis. These results suggested the larger photosynthetic rates were probably in response to an increased leaf area resulting from stimulation of leaf and lateral bud initiation. Benzyladenine was the most active material in delaying the senescence-like response of excised Kentucky bluegrass leaves as measured by carbon dioxide exchange, percent chlorophyll fluorescence decay, and leaf color ratings. Applications of Fe or propiconazole also delayed excision-induced senescence of Kentucky bluegrass leaves, while the anti-senescence activity of triadimefon was highly variable. Combinations of Fe with BA or the triazoles did not further promote a delay in excision-induced senescence. / Ph. D.

Thesis (Ph. D.)--Rutgers University, 2008. / "Graduate Program in Plant Biology." Includes bibliographical references.

Thesis (Ph. D.) -- University of Tennessee, Knoxville, 2006. / Title from title page screen (viewed on June 7, 2006). Thesis advisor: Thomas C. Mueller. Vita. Includes bibliographical references.

Thesis (Ph. D., Environmental Science)--University of Idaho, June 2009. / Major professor: J.D. Wulfhorst. Includes bibliographical references. Also available online (PDF file) by subscription or by purchasing the individual file.