The differentiation of plant vascular tissue is regulated by plant hormones and transcription factors. One of the key plant hormones involved in this process is auxin. Auxin signals are mediated by auxin response factor transcription factors (ARFs). These transcription factors are involved in the perception of auxin signals and the subsequent activation or deactivation of suites of downstream genes. Based on its mutant phenotype, one of the most interesting members of this family is the ARF MONOPTEROS (MP). This thesis investigates the role played by MP in secondary vascular differentiation, as well as taking a look at other molecular aspects of secondary vascular differentiation, with a focus on the model plants Arabidopsis thaliana and poplar (Populus trichocarpa and hybrid poplar). A dexamethasone inducible RNAi silencing strategy was developed, and transgenic Arabidopsis lines produced. When silencing was induced in these lines from germination, a phenotype closely resembling the mp mutant was observed. When MP silencing was induced in bolting stems, early senescence, as well as a dramatic reduction in interfascicular fibre production was observed, and these stems were thinner and less rigid than empty vector controls. RNA from these stems was isolated and used in a global transcript profiling microarray experiment. This experiment showed that several auxin-related genes, as well as several transcription factors, were differentially regulated in response to MP silencing. Because Arabidopsis is not a typical woody plant, further investigation into the role played by MP in wood formation was done using the model tree poplar. A BLAST search of a poplar xylem EST database identified a single promising partial sequence. Based on this sequence information, a poplar MP homolog was isolated and named PopMP1. The full-length sequence of this gene demonstrated remarkable structural conservation when compared with that of Arabidopsis. Subsequent complete sequencing of the poplar genome revealed a second copy of the MP gene in poplar and named PopMP2. Expression profiling across a range of tissues suggests that subfunctionalization has occurred between the two copies. Overexpression transgenic lines for PoptrMP1 were developed. AtHB8 is known to be regulated by MP in Arabidopsis, and a poplar HB8 homolog was upregulated in the transgenic lines. However, no obvious physical phenotype in these lines was apparent. To investigate the transcriptome-wide changes associated with initiation of cambium formation in poplar stems, a global transcript profiling experiment was performed. Out of 15400 genes tested, 2320 met an arbitrary cutoff of >1.3 fold and p-value <0.05 and were labeled differentially expressed (DE). These included several transcription factors and showed remarkable similarity to analogous data from Arabidopsis. The conclusions drawn from this thesis support the hypothesis that MP plays roles in later development, and do not rule out the possibility that MP is directly involved in wood development. The data reported also offer a large number of candidate for further investigation into the genetic control of wood development.

I examined the effects of hydrologic gradients and upland timber harvesting with different streamside management zone widths on yellow-poplar (Liriodendron tulipifera) processing and the associated macroinvertebrate community structure in the Cumberland Plateau ecophysic region, U.S.A. Prior to upland timber harvesting, 5.0 ± 0.1 g yellow-poplar leaf packs were constructed, zip-tied to gutter nails, and placed into 7 perennial and 6 temporary stream reaches with similar physiochemical and geomorphic characteristics. From December 2007 to May 2008, 3–5 leaf packs were collected per reach monthly. I found significant differences in the functional feeding group composition. Temporary reaches contained higher shredder, gathering-collector, predator, and total macroinvertebrate abundances. Shredder and total macroinvertebrate biomass was also higher in the temporary stream reaches. Gathering-collector biomass along one measurement was higher in the temporary streams. Perennial and temporary stream reaches contained similar macroinvertebrate diversity. Logging operations occurred from May 2008–December 2008. After logging operations ended, yellow-poplar leaf packs were placed into the perennial and temporary reaches of 3 control and 3 treatment streams (2 with same SMZ width, 1 different). From December 2008–May 2009. Leaf packs were collected monthly. Within the temporary and perennial stream reaches, no significant differences were detected between control and treatment yellow-poplar processing rates. No significant differences were detected between the control and treatment functional feeding group composition in abundance and biomass. Post-harvest, taxon richness increased in both the perennial control and treatment streams, while richness declined in the temporary control and increased in the temporary treatment. My findings indicate that when water is present, organic matter processing will function similarly to downstream reaches that have continual water flow. During seasonal flow patterns, macroinvertebrate communities associated with organic matter are present in temporary streams and may exceed perennial stream reaches in their density and biomass. This indicates that temporary streams are physically suitable habitats for macroinvertebrate fauna and contribute to a stream’s form and function. Overall, no observed distinct response in yellow-poplar processing rates or the associated macroinvertebrate community structure was detected within the perennial or temporary streams. Macroinvertebrate community structure varied spatially and temporally. On the taxonomic level, increases in taxa-specific abundance and biomass remain to be explained. Future research assessing interactions on the taxonomic level might help explain increases or decreases in abundance and biomass in relation to treatment effects. This study documented the response of organic matter breakdown and associated macroinvertebrate community structure during the 1st 5 months after logging. Thus, it is only a snapshot of stream ecosystem response to disturbance. Long-term studies are needed to evaluate full ecosystem response and recovery. Due to uncontrollable factors, I was not able to evaluate the success of different SMZ widths. Results documented should be treated with hesitancy, until full ecosystem response has been documented.

Success of hybrid poplar plantations will rely on the efficient management of nutrients and weeds. Relatively little is known about the root uptake characteristics of hybrid poplar and weeds, their belowground interactions and particularly, the quantitative understanding of nutrient uptake using mechanistic models under weed-competing conditions. Therefore, the objectives of this study were to investigate the effects of dandelion and quackgrass on the growth of hybrid poplar, to establish their root uptake characteristics and to quantify their nutrient uptake using the soil supply and nutrient demand (SSAND) model. In a pot study, hybrid poplar stem height, root collar diameter, shoot and root biomass, root length, and N, P and K uptake significantly decreased in the presence of dandelion and quackgrass weeds. Similar weed competition effects on growth of hybrid poplar were also observed in the field at the Pasture and Alfalfa sites where hybrid poplar was grown with and without weeds for 50, 79 and 100 days. In a hydroponic experiment, Imax values for NH4-N, NO3-N, P and K varied significantly among hybrid poplar seedlings and dandelion and quackgrass weed species and was greatest for dandelion followed by hybrid poplar and then quackgrass. The Km values were lowest for quackgrass compared to the other plant species for all of the nutrients. Simulation results from the SSAND model for the pot study showed that N uptake was underpredicted in hybrid poplar by 58 to 73%, depending upon soil type and weed treatment. Incorporation of N mineralization as a model input improve the hybrid poplar N uptake predictions by 24 and 67% in the Pasture and Alfalfa soil, respectively, when grown without weeds. SSAND model underestimated P uptake by 84-89% and overestimated K uptake by 28 to 59% for hybrid poplar depending upon the soil type and weed treatment. In the field, N uptake by hybrid poplar was in close agreement to measured N uptake in the control treatment. N uptake was greatly underestimated for both hybrid poplar and weeds in the weed treatment. Including changing water content greatly improves the N uptake by hybrid poplar and weeds in weed treatments. Results from this study suggest weed control is an essential practice to establish successful hybrid poplar plantations. Also, SSAND model can be an effective tool for predicting the nutrient uptake under two plant species competing environment if all the processes of nutrient supply are adequately described in the model.

As a result of predicted climate change, environmental conditions may make woody plant species such as poplars (Populus spp.) vulnerable unless they are sufficiently adaptable to the new environment. This greenhouse study examined the responses of Hill, Northwest, Okanese and Walker hybrid poplar clones to drought, a potential outcome of a changing climate. Plants were grown from cuttings and subjected to two soil moisture treatments; a well-watered treatment and a drought conditioning treatment in which plants were subjected to cycles of soil moisture deficit. The first study examined growth and gas exchange following treatments, while the second study examined concurrent changes in leaf water potential and gas exchange during a period of increasing soil moisture deficit, following treatments.<p> Hill and Okanese plants had reduced shoot:root ratios, possibly leading to more positive plant moisture balances compared to Northwest and Walker plants. Stomatal characteristics related to steady state gas exchange with Okanese plants having stomata predominantly on lower leaf surfaces, and lower stomatal conductance and Northwest plants having relatively large stomata and increased stomatal conductance. Hill and Okanese plants had the most responsive stomata, which began to close at much higher levels of leaf water potential (-0.45 and -0.54 MPa) than Northwest or Walker plants (-1.03 and -0.88 MPa); however, closure was more gradual in Okanese plants. Drought preconditioning resulted in stomatal closure occurring at higher leaf water potentials in droughted Northwest and Walker plants compared to well-watered plants. Regardless of soil moisture treatment, WUE was highest in Okanese and Walker plants. The drought treatment did however lead to increased WUE in Hill and Northwest plants.<p> Overall, Okanese plants appear to be the best adapted to conditions of reduced soil moisture based on growth and physiological traits, while Northwest and Hill seem better suited to areas where moisture deficits are likely to be less frequent or less severe. Results indicate that variability exists in adaptability of hybrid poplar clones to drought, suggesting that there may also be other hybrid clones that are adaptable to reduced soil moisture conditions, which may merit further investigation.

Recently, the use of biomass to produce energy has resulted in evaluating each potential biomass species individually, and primarily in terms of yield potentials. However, discrepancies between species yield caused by varying site conditions and varying fertilization regimes between studies do exist. Therefore, this study attempts to address some of these discrepancies by growing multiple species simultaneously on marginal land with zero fertilization. The yield and fuel characteristics of the four most commonly used biomass feedstocks (Miscanthus, switchgrass, willow and poplar) in southern Ontario, along with one herbaceous polyculture, were investigated. Species' influence on microclimatic modifications was quantified during the 2010 and 2011 growing seasons in order to understand its impact on biomass yields. Yield data was gathered for each species treatment for both growing seasons. Few significant differences were found between species during establishment. Fuel characteristics analyses including, gross calorific value, ash (%), and an elemental ash analysis were completed during 2010 and 2011. The differences between the combustion properties of the grass species and the woody species were obvious, but neither could be conclusively determined as universally better than the other. Yield and fuel characteristics change as plants mature, therefore research should be continued in future years once plots are fully established to determine which species are best suited for bioenergy production in Southern Ontario. This will help growers and energy producers focus on crops that have the most potential in achieving environmental sustainability and economic viability. / OMAFRA

Plant-wide communication between tissues and cells is organized, in part, by a suite of compounds called hormones. I have chosen to focus on the effects of one plant hormone, ethylene; how its synthesis is controlled and how its perception is mediated to differentially control cell development and response to pathogens. In the production of ethylene, one level of control is by modulating the levels of the immediate precursor to ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC). I characterize here a plant encoded gene homologous to bacterial ACC Deaminases, AtACD1, and show through up- and down-regulation of the gene that it can modulate the plants sensitivity to exogenous ACC. Once ethylene is produced, it is sensed in Arabidopsis thaliana by a family of 5 receptors. I show that ETR2 in Arabidopsis is responsible for modulation of the microtubule cytoskeleton assembly as loss-of –function mutations to this gene cause randomized microtubule assembly in trichomes and increase sensitivity to microtubule depolymerising drugs in root hairs. In studies of plant:pathogen interactions, ethylene is a central signaling agent required for plant resistance. While it has been shown that etr1 mutants show increased susceptibility to fungal pathogens, exogenous ethylene has also been shown to speed the progress of pathogenesis. Using Fumonisin B1 (FB1) to induce cell death I show that etr1-1 has accelerated cell death while ein4-1 has a reduced rate of necrosis. Further to this, mutations to the other three ethylene receptors do not have any effect on the rate of cell death. My interest in cell development led to the characterization of an activation tagged Populus tremula x P. alba line with increased trichome initiation. The gene responsible for these phenotypes was identified as PtMYB186, which also affected growth rate, transpiration rate, photosynthetic capacity, and resistance to the Tussock moth larvae. Together these studies provide a new framework for our understanding of how the ethylene signal is modulated in plants and the controls behind cellular development. This knowledge will help reconcile studies which show that ethylene has different effects on plant development and provide new avenues of research into trichome development. / Thesis (Ph.D, Biology) -- Queen's University, 2009-01-13 10:08:03.605

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The First Nation community of Poplar River in Northern Manitoba is using a UNESCO World Heritage Site nomination to assist with meeting local needs. Going beyond the expected, non-renewable resource development, Asatiwisipe First Nation is taking control over its own developmental plans, and forging an ecologically sustainable vision of community-controlled economic and political development. This initiative is an escape from the ‘progress trap’ where Indigenous resource stewardship practices will guide sustainable community economic development. This thesis explores the application of intangible cultural heritage as a lens for looking at the culture/nature discussion, food sovereignty, Indigenous resource management as well as Aboriginal and treaty rights. Based on longitudinal research over the past eight years, this dissertation is a collection of interviews and narratives from community members, personal experiences and policy research. Despite systemic Eurocentrism and many challenges, permanent protection of the Poplar River Community Conserved Area through the World Heritage Site nomination is perhaps the best solution for the community as it is an initiative that has been instigated by the First Nation itself.

Afforestation and stand development can significantly affect soil respiration and net ecosystem productivity (NEP). I studied 1) the effects of afforestation on NEP by comparing cropland previously planted to barley (on a barley-barley-alfalfa-alfalfa-alfalfa rotation) and that converted to a hybrid poplar (Populus deltoides Populus petrowskyana var. Walker) plantation and 2) the NEP along a chronosequence of stands aged 5-, 8-, 14-, and 16-year old in 2009 in central Alberta, Canada. Soil respiration and NEP decreased in the first two to three years after afforestation, while both generally increased with stand development. The ecosys model was used to simulate carbon dynamics in the plantations over a 20-year rotation under contrasting soil conditions. Soil conditions of the 14-year-old plantation accumulated the greatest amount of ecosystem carbon over the whole rotation. The research indicated that plantations could be a net carbon source in the first few years after afforestation and then became a net carbon sink, helping to mitigate net CO2 emissions for the remainder of the rotation. / Soil Science