The biogeography and ecology of P. balfouriana, a subalpine conifer endemic to California, were studied. Direct gradient-analysis, classification, and ordination were combined to identify the primary factors controlling the tree community in the southern Sierra Nevada. Competition, disturbance, and temperature were inferred as the most important factors regulating the tree community. Pinus balfouriana responded strongly to variation in soil drainage, distrubance, and temperature. Wildfire was the most important chronic disturbance agent in southwestern Inyo National Forest. Stochastic models of wildfire probability in space and time were developed. Evidence of thunderstorm genesis zones in the vicinity of Overlook Mountain and Ball Mountain in the Golden Trout Wilderness was found. A gradient in wildfire ignition probability was identified. Wildfire ignition is most likely at 2700 m elevation on submesic sites. Wildfire return interval is long enough to permit the coexistence of P. balfouriana and P. murrayana; and, short enough that it has important fitness consequences for P. balfouriana. Wildfire disturbance may limit the geographic range of the species in the southern Sierra Nevada. There was a close negative correlation between the abundance of P. balfouriana near the lower-forest-border and the wildfire disturbance gradient. However, the northern range boundary is probably not determined solely by wildfire disturbance. The canopies of mature P. balfouriana were found to be highly elliptic (when viewed from above) with the major axis of the ellipse oriented exactly north-to-south. This trait permits maximum photosynthesis in the early morning and late afternoon. It simultaneously minimizes evaporative demands during midday. Elliptic canopies minimize solar interception during winter and maximize it during summer. This is important for carbon-balance since the photosynthetic apparatus is only active for a brief period during mid-summer. The lower-forest-border was accurately predicted with a carbon-balance model strongly suggesting carbon-balance limitations. The dispersal potential of P. balfouriana, in the absence of vertebrate seed dispersers, was studied. Anemochory under modern climatic conditions would permit closure of the disjunction in P. balfouriana within a single (120,000 year) glacial cycle.

Foxtail pine (Pinus balfouriana) is a subalpine conifer endemic to California, notably separated into two disjunct subspecies. Previous studies have described the northern subspecies,Pinus balfouriana subsp. balfouriana,as having an uncommonly high level of genetic differentiation and no discernible spatial patterns in phenotypic variation. This study seeks to characterize the spatial genetic structure and patterns of selection of the northern subspecies (Pinus balfouriana subsp. balfouriana) using genome-wide data and to identify the influence of ecology and environment on the unique genetic patterns. I show that genetic differentiation among populations is much less than previously estimated (FST= 0.000644) and there is weak isolation-by-distance structure, but ongoing gene flow is unlikely. Within populations, stand density and competitor effects contribute to inbreeding. I also show that previously measured traits are predominantly determined by genetics. Analyzing by sliding window in the genome, I show that connectivity patterns vary widely throughout the genome and identify several areas that are important to the genetic architecture of the phenotypic traits and plasticity (GxE). Overall, there is high connectivity, genetic similarity, and genetically based trait variation among and within populations of the northern subspecies of foxtail pine due to historical processes, despite biotic interactions driving inbreeding. Persistent genetic isolation, however, may make adaptation to future climate a challenge for the subspecies.

No description available.

Millets are C4 annual grasses that are mainly used for food and feed. This thesis describes two studies that evaluated drought tolerance of pearl millet cultivars (Pennisetum glaucum [L.] R. Br) grown for grain. A third study is also included in the thesis that evaluated foxtail millet (Setaria italica [L] Beauv) and pearl millet grown as cover crops and forage during a pasture renovation. The main focus of the thesis involved evaluation of Senegalese pearl millet cultivars for drought tolerance. Drought is one of the most important threats to pearl millet production in Senegal as it limits yield in most parts of the country. Although water stress on pearl millet is common during the growing season, a little is known about how terminal drought affects yield in Senegalese pearl millet cultivars. To address this issue, two field experiments were conducted in 2014 and 2015. The first field study evaluated 20 pearl millet cultivars under water stress and categorized based on their yield response. Whereas the second year field trial used four cultivars from the first field trial in a more detailed study to give recommendations for farmers in Senegal. The experiments were complete randomized block designs. Pearl millet cultivars were grown under irrigation until flowering then the stress treatment was applied by stopping the irrigation in half of the plots. Eleven cultivars showed a statistical indifference to water stress and considered the most drought tolerant. Four cultivars were selected from the 11 for the second year experiment. Of these, cultivar 4 (ICMV IS 89305) and 10 (SOSAT c 88) exhibited higher tolerance to terminal water stress based on evaluation of yield components and drought stress indices. These cultivars could be a good target for further breeding and selection in Senegal. Although the cultivars were more drought tolerant, both had relatively low total biomass. When used in a larger scale, these cultivars could potentially benefit farmers in Senegal and enhance food security. The second part of this thesis addressed use of a forage type millets – specifically foxtail and pearl millet. In the US, these millets are primarily serve as a summer cover crops that can be used for forage. The objective of this experiment was to compare yield and forage quality of foxtail and pearl millet cover crops and their effect on subsequent pasture establishment. A field experiment was conducted in Virginia in 2014 to address this objective. Pearl millet and foxtail millet were randomly planted in 12 plots each and harvested in late summer. Plots were then converted to tall fescue (Schedonorus phoenix (Scop.) Holub) pasture. Foxtail millet had a significantly higher soil cover than pearl millet but the two species did not differ in terms of total biomass, forage quality, or their effect on tall fescue pasture establishment. / Master of Science

The goal of this project was to determine the genetic architecture of water-use efficiency (WUE) for foxtail pine, which included genomic loci, and effect sizes of this trait. Foxtail pine is a subalpine endemic conifer that inhabits two distinct regional populations separated by 500 km in the mountains of California. In order to achieve this goal, a robust linkage map containing thousands of genetic markers was created using four megagametophyte arrays ranging in size from approximately 70 to 95 megagametophytes. Quantitative trait loci (QTL) discovered for WUE were mapped along the linkage map using linear mixed models and five half-sibling families grown in a common garden. Effect sizes of these QTL were tested for differences between the two regional populations of foxtail pine.

The germination and emergence of a seedling, or seedling recruitment remains an essential process in the establishment of a plant. This establishment can be limited by the availability of microsites within the soil profile, or the availability of seed within a given area. Three field experiments were initiated in Saskatchewan, Canada to examine the relative effect of seed and microsite limitations on weed seedling recruitment. The first experiment examined the effect of landscape position as well as nitrogen (N) rate and tillage system (zero tillage vs. conventional tillage) on weed seedling recruitment from an indigenous weed population. Survey results indicated habitat differentiation of the weed population with wild oat and cleavers preferentially recruiting in the lower landscape positions, Russian thistle and Kochia in the upper landscape positions, while green foxtail recruited in high levels on all landscape positions. This suggested that different weed species have different microsite requirements for weed seedling recruitment across contrasting landscape positions. The second field experiment examined the effect of landscape position and moisture availability on weed seedling recruitment from an artificial hand-seeded weed seedbank. This experiment indicated that seed limitation remained a very important factor, but even when irrigated, total seedling recruitment did not reach maximum recruitment, indicating water was not the only limiting resource for weed seedling recruitment. Microsite limitations were greatest on the upper slope position for all species with green foxtail having the greatest overall recruitment of the species across all landscapes and moisture regimes. The third experiment examined the effect of tillage system and density on weed seedling recruitment of wild oat, green foxtail, and wild mustard. Again, weed seedling recruitment remained a function of both microsite and seed limitations as absolute recruitment values increased for each density examined in this experiment. The agronomic significance of microsite limitation was negligible as high weed population numbers occurred for the highest weed seeding densities. Overall, microsite limitations remained negligible in these experiments for arable agriculture with the main influence on weed seedling recruitment most often being seed limitation in the natural seedbank.

The goal of the project was to enhance the period of weed growth prior to seeding in order to reduce weed emergence and weed competition after the crop has been planted. Weed growth was stimulated using either light tillage or by applying nitrogen fertilizer early in the spring. Light disturbance significantly increased pre-seed weed emergence while early applied nitrogen did not appear to have an effect. Post seeding weed emergence levels and weed biomass were similar among the light tillage and early nitrogen treatments. Therefore the goal of decreasing weed competition after seeding was not attained. Future research should focus on long-term strategies to reduce weed populations in field rather than seasonal strategies. / October 2006

The germination and emergence of a seedling, or seedling recruitment remains an essential process in the establishment of a plant. This establishment can be limited by the availability of microsites within the soil profile, or the availability of seed within a given area. Three field experiments were initiated in Saskatchewan, Canada to examine the relative effect of seed and microsite limitations on weed seedling recruitment. The first experiment examined the effect of landscape position as well as nitrogen (N) rate and tillage system (zero tillage vs. conventional tillage) on weed seedling recruitment from an indigenous weed population. Survey results indicated habitat differentiation of the weed population with wild oat and cleavers preferentially recruiting in the lower landscape positions, Russian thistle and Kochia in the upper landscape positions, while green foxtail recruited in high levels on all landscape positions. This suggested that different weed species have different microsite requirements for weed seedling recruitment across contrasting landscape positions. The second field experiment examined the effect of landscape position and moisture availability on weed seedling recruitment from an artificial hand-seeded weed seedbank. This experiment indicated that seed limitation remained a very important factor, but even when irrigated, total seedling recruitment did not reach maximum recruitment, indicating water was not the only limiting resource for weed seedling recruitment. Microsite limitations were greatest on the upper slope position for all species with green foxtail having the greatest overall recruitment of the species across all landscapes and moisture regimes. The third experiment examined the effect of tillage system and density on weed seedling recruitment of wild oat, green foxtail, and wild mustard. Again, weed seedling recruitment remained a function of both microsite and seed limitations as absolute recruitment values increased for each density examined in this experiment. The agronomic significance of microsite limitation was negligible as high weed population numbers occurred for the highest weed seeding densities. Overall, microsite limitations remained negligible in these experiments for arable agriculture with the main influence on weed seedling recruitment most often being seed limitation in the natural seedbank.

The goal of the project was to enhance the period of weed growth prior to seeding in order to reduce weed emergence and weed competition after the crop has been planted. Weed growth was stimulated using either light tillage or by applying nitrogen fertilizer early in the spring. Light disturbance significantly increased pre-seed weed emergence while early applied nitrogen did not appear to have an effect. Post seeding weed emergence levels and weed biomass were similar among the light tillage and early nitrogen treatments. Therefore the goal of decreasing weed competition after seeding was not attained. Future research should focus on long-term strategies to reduce weed populations in field rather than seasonal strategies.

The goal of the project was to enhance the period of weed growth prior to seeding in order to reduce weed emergence and weed competition after the crop has been planted. Weed growth was stimulated using either light tillage or by applying nitrogen fertilizer early in the spring. Light disturbance significantly increased pre-seed weed emergence while early applied nitrogen did not appear to have an effect. Post seeding weed emergence levels and weed biomass were similar among the light tillage and early nitrogen treatments. Therefore the goal of decreasing weed competition after seeding was not attained. Future research should focus on long-term strategies to reduce weed populations in field rather than seasonal strategies.