Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 92-103).

Thesis (Ph. D.)--University of Washington, 1988. / Vita. Bibliography: leaves [74]-79.

Little is known of the physiological and biochemical mechanisms underlying competitive interactions between alien invasive grasses and native taxa, and how these are affected by resource supply. Consequently, this study compared photosystem II (PS II) function, photosynthetic gas and water exchange, enzyme and pigment concentrations, flowering and biomass accumulation in an indigenous geophyte, Tritonia crocata (L.) Ker. Gawl., grown in monoculture and admixed with the alien grass, Lolium multiflorum Lam., at different levels of water and nutrient supply. Diminished stomatal conductances were the primary cause of reduced net C02 assimilation rates, and consequent biomass accumulation in T. crocata admixed with L. multiflorum at all levels of water and nutrient supply with one exception. These corresponded with decreased soil water contents induced presumably by more efficient competition for water by L. multiflorum, whose biomass was inversely correlated with soil water content. Biochemical impairments to photosynthesis were also apparent in T. crocata admixed with L. multiflorum at low levels of water and nutrient supply. These included a decline in the density of working photosystems (reaction center per chlorophyll RC/ABS), which corresponded with a decreased leaf chlorophyll a content and a decreased efficiency of conversion of excitation energy to electron transport (¥0 / l-^o), pointing to a reduction in electron transport capacity beyond QA~, a decline in apparent carboxylation efficiency and Rubisco content. At low nutrient levels but high water supply, non-stomatal induced biochemical impairments to photosynthesis (decreased RC/ABS, chlorophyll a and Rubisco content) were apparent in T. crocata admixed with L. multiflorum. These attributed to a reallocation of fixed carbohydrate reserves to floral production which increased significantly in T. crocata under these conditions only and associated with a corresponding reduction in the mass of its underground storage organ (bulb). The results of this study did not support the hypothesis that under conditions of low water and low nutrient supply invasive annual grasses would have a lesser impact on the growth and physiology of native geophytes than under resource enriched conditions that favor growth of these grasses. Unresolved is whether resource limitation and allelopathic mechanisms functioned simultaneously in the inhibition of the native geophyte by the alien grass. / Thesis (M. Environmental Science (Ecological Remediation and Sustainable Utilisation))--North-West University, Potchefstroom Campus, 2008.

Little is known of the physiological and biochemical mechanisms underlying competitive interactions between alien invasive grasses and native taxa, and how these are affected by resource supply. Consequently, this study compared photosystem II (PS II) function, photosynthetic gas and water exchange, enzyme and pigment concentrations, flowering and biomass accumulation in an indigenous geophyte, Tritonia crocata (L.) Ker. Gawl., grown in monoculture and admixed with the alien grass, Lolium multiflorum Lam., at different levels of water and nutrient supply. Diminished stomatal conductances were the primary cause of reduced net C02 assimilation rates, and consequent biomass accumulation in T. crocata admixed with L. multiflorum at all levels of water and nutrient supply with one exception. These corresponded with decreased soil water contents induced presumably by more efficient competition for water by L. multiflorum, whose biomass was inversely correlated with soil water content. Biochemical impairments to photosynthesis were also apparent in T. crocata admixed with L. multiflorum at low levels of water and nutrient supply. These included a decline in the density of working photosystems (reaction center per chlorophyll RC/ABS), which corresponded with a decreased leaf chlorophyll a content and a decreased efficiency of conversion of excitation energy to electron transport (¥0 / l-^o), pointing to a reduction in electron transport capacity beyond QA~, a decline in apparent carboxylation efficiency and Rubisco content. At low nutrient levels but high water supply, non-stomatal induced biochemical impairments to photosynthesis (decreased RC/ABS, chlorophyll a and Rubisco content) were apparent in T. crocata admixed with L. multiflorum. These attributed to a reallocation of fixed carbohydrate reserves to floral production which increased significantly in T. crocata under these conditions only and associated with a corresponding reduction in the mass of its underground storage organ (bulb). The results of this study did not support the hypothesis that under conditions of low water and low nutrient supply invasive annual grasses would have a lesser impact on the growth and physiology of native geophytes than under resource enriched conditions that favor growth of these grasses. Unresolved is whether resource limitation and allelopathic mechanisms functioned simultaneously in the inhibition of the native geophyte by the alien grass. / Thesis (M. Environmental Science (Ecological Remediation and Sustainable Utilisation))--North-West University, Potchefstroom Campus, 2008.

Little is known of the physiological and biochemical mechanisms underlying competitive interactions between alien invasive grasses and native taxa, and how these are affected by resource supply. Consequently, this study compared photosystem II (PS II) function, photosynthetic gas and water exchange, enzyme and pigment concentrations, flowering and biomass accumulation in an indigenous geophyte, Tritonia crocata (L.) Ker. Gawl., grown in monoculture and admixed with the alien grass, Lolium multiflorum Lam., at different levels of water and nutrient supply. Diminished stomatal conductances were the primary cause of reduced net C02 assimilation rates, and consequent biomass accumulation in T. crocata admixed with L. multiflorum at all levels of water and nutrient supply with one exception. These corresponded with decreased soil water contents induced presumably by more efficient competition for water by L. multiflorum, whose biomass was inversely correlated with soil water content. Biochemical impairments to photosynthesis were also apparent in T. crocata admixed with L. multiflorum at low levels of water and nutrient supply. These included a decline in the density of working photosystems (reaction center per chlorophyll RC/ABS), which corresponded with a decreased leaf chlorophyll a content and a decreased efficiency of conversion of excitation energy to electron transport (¥0 / l-^o), pointing to a reduction in electron transport capacity beyond QA~, a decline in apparent carboxylation efficiency and Rubisco content. At low nutrient levels but high water supply, non-stomatal induced biochemical impairments to photosynthesis (decreased RC/ABS, chlorophyll a and Rubisco content) were apparent in T. crocata admixed with L. multiflorum. These attributed to a reallocation of fixed carbohydrate reserves to floral production which increased significantly in T. crocata under these conditions only and associated with a corresponding reduction in the mass of its underground storage organ (bulb). The results of this study did not support the hypothesis that under conditions of low water and low nutrient supply invasive annual grasses would have a lesser impact on the growth and physiology of native geophytes than under resource enriched conditions that favor growth of these grasses. Unresolved is whether resource limitation and allelopathic mechanisms functioned simultaneously in the inhibition of the native geophyte by the alien grass. / Thesis (M. Environmental Science (Ecological Remediation and Sustainable Utilisation))--North-West University, Potchefstroom Campus, 2008.

Südafrikanische Iridaceae enthalten viele Gattungen mit hohem Potential als neue Zierpflanzen. Von Anfang 2005 bis 2007 fanden Untersuchungen an vier geophytischen Arten aus dem Kapländischen Florenreich statt. Den Gattungen Freesia, Sparaxis und Tritonia angehörend, wachsen diese auf der Südhemisphäre während des Winters heran und blühen im Frühjahr. Bei einer Anzucht im europäischen Herbst bzw. Winter könnten ihre niedrigen Temperaturansprüche für den zukünftigen Produzenten eine energiegünstige alternative Kultur bedeuten. Folgende Untersuchungsziele standen im Mittelpunkt: Export während der Dormanz der Knollen, Lagerbedingungen nach dem Export, Pflanzsätze zu verschiedenen Jahreszeiten in Deutschland und allgemeine Ansprüche an die Wachstumsfaktoren. Die Ergebnisse wurden durch regelmäßige Bonitur der Entwicklung der Knollen bzw. Pflanzen gewonnen. Das Nachvollziehen der Infloreszenzanlage erfolgte durch mikroskopische Untersuchungen des Apikalmeristems während des Wachstums. Der Export der Knollen war unkompliziert und ihre Dormanz konnte durch eine Lagerung bei über 20 °C weiter aufrechterhalten werden. Für eine erfolgreiche Blüte nach der Pflanzung stellte die Temperatur den entscheidenden Faktor dar. Die Arten zeigten sich unterschiedlich empfindlich, doch war eine Kulturtemperatur von 13 °C nachts notwendig, wenn die Temperaturen tags über 17 °C lagen. Während der Sommermonate wurden auf Grund der hohen Temperaturen die Infloreszenzen erst gar nicht angelegt oder abortiert. Die vorherrschenden niedrigen Lichtintensitäten der Wintermonate führten ebenfalls zu einem Infloreszenzabort oder einer verspäteten Anthese. Durch spezielle Lagerbehandlungen der Knollen konnte bei der Anzucht eine Reduzierung der Pflanzenhöhe und eine verbesserte Blühleistung erzielt werden. Zusammenfassend lässt sich ein großes Potential der untersuchten Arten für eine energiegünstige Produktion und eine Erweiterung des Herbst-/Wintersortiments an Topfpflanzen in Europa feststellen. / South African Iridaceae contain many genera with a high potential for new floricultural crops. From the beginning of 2005 until 2007, investigations on four geophytic species native to the Cape Floral Region were conducted. Belonging to the genera Freesia, Sparaxis and Tritonia, they are winter growing/spring flowering in the Southern Hemisphere. If forced as pot plants for the European autumn/winter months, their low temperature requirements during cultivation could represent substantial energy savings for the future grower. The investigations focused on the following aspects: export during the corm dormancy, storage conditions after export, forcing experiments in different seasons in Germany and general cultivation requirements. Results were obtained by regularly monitoring the corms and the plant development. Inflorescence initiation was determined by microscopic examination of the shoot apical meristem during the growing season. - The export of dormant corms was uncomplicated and their dormancy could be further maintained in subsequent storage in Berlin at temperatures above 20°C. Temperature was found to be the main criterion to successfully realise flowering after planting. The species varied in their sensitivity, but generally cultivation at 13°C at night was essential, with temperatures of 17°C and above possible during the day. During the Central European summer months, inflorescences in the terminal bud failed to completely develop or flower primordia were aborted due to the high temperatures present. Furthermore, the naturally low light intensities during the Central European winter months also led to inflorescence abortion or a delay in flowering of three species. A reduction in plant height and enhanced flowering could be achieved for some species by specific storage regimes. In conclusion, the investigated species displayed a great potential for an energy saving production system as well as for enriching the autumn/winter pot plant assortment in Europe.

These studies compare neurotransmitter localization and the behavioral functions of homologous neurons in nudibranch molluscs to determine the types of changes that might underlie the evolution of species-specific behaviors. Serotonin (5-HT) immunohistochemistry in eleven nudibranch species indicated that certain groups of 5 HT-immunoreactive neurons, such as the Cerebral Serotonergic Posterior (CeSP) cluster, are present in all species. However, the locations and numbers of many other 5 HT-immunoreactive neurons were variable. Thus, particular parts of the serotonergic system have changed during the evolution of nudibranchs. To test whether the functions of homologous neurons are phylogenetically variable, comparisons were made in species with divergent behaviors. In Tritonia diomedea, which crawls and also swims via dorsal-ventral body flexions, the CeSP cluster includes the Dorsal Swim Interneurons (DSIs). It was previously shown that the DSIs are members of the swim central pattern generator (CPG); they are rhythmically active during swimming and, along with their neurotransmitter 5-HT, are necessary and sufficient for swimming. It was also known that the DSIs excite efferent neurons used in crawling. DSI homologues, the CeSP-A neurons, were identified in six species that do not exhibit dorsal-ventral swimming. Many physiological characteristics, including excitation of putative crawling neurons were conserved, but the CeSP A neurons were not rhythmically active in any of the six species. In the lateral flexion swimmer, Melibe leonina, the CeSP-A neurons and 5-HT, were sufficient, but not necessary, for swimming. Thus, homologous neurons, and their neurotransmitter, have functionally diverged in species with different behaviors. Homologous neurons in species with similar behaviors also exhibited functional divergence. Like Melibe, Dendronotus iris is a lateral flexion swimmer. Swim interneuron 1 (Si1) is in the Melibe swim CPG. However, its putative homologue in Dendronotus, the Cerebral Posterior ipsilateral Pedal (CPiP) neuron, was not rhythmically active during swim-like motor patterns, but could initiate such a motor pattern. Together, these studies suggest that neurons have changed their functional relationships to neural circuits during the evolution of species-specific behaviors and have functionally diverged even in species that exhibit similar behaviors.