Zugl.: Boston, Univ., Diss.

Ultra-slow spreading ridges have a full spreading rate of less than 20 mm/yr, and show deviations from the fundamental characteristics identified at faster spreading rates; however, they are poorly studied compared to faster spreading ridges. In this thesis we aim to build on previous studies in order to further characterise the unique processes occurring at the ultra-slow spreading Southwest Indian ridge (SWIR). This is an exploratory study utilising novel and existing bathymetry, gravity, video imagery data to understand tectonic and volcanic processes along the ridge crest from triple junction to triple junction. We conduct a series of studies which focus on the axial valley morphology, large seamount morphology, the distribution of small seamounts and large seamounts on the ridge, and admittance studies. We show that the long wavelength trends in geophysical data, geochemical data, and axial valley morphology are well correlated. These variations reflect along-axis changes in the crustal and mantle structure, governed by the thermal structure of the ridge. Seamounts provide important morphological evidence of the volcanic and tectonic processes beneath the Earth's surface. We use detailed morphological investigations to show that volcanic and erosional processes on six large seamounts are controlled by the local faulting and melt migration mechanisms. We investigate the distribution of seamounts on the ridge using a numerical algorithm, and demonstrate a lower seamount density than faster spreading ridges. We show that the seamount population statistics vary along the ridge due to changes in the degree of partial melting, magma conduit availability, and melt focussing mechanisms; the locations of three proximal hotspots coincide with increases in the estimated magmatic flux. Finally, best fit elastic thicknesses are determined using a 3D windowed admittance technique, which was tested using synthetic data. We construct a combined convection-flexure model to account for misfits between the observed data and existing flexural theoretical models. The average elastic thickness varies between 7 km and 12 km, and we show a strong dependence on spreading rate.

Magister Commercii - MCom / This research analyses the influence of chieftaincy in party political processes in African states. In this regard, the study employs a case study design in investigating how chieftaincy shapes leadership succession dynamics within the South West African People’s Organisation (SWAPO) in Namibia and the Botswana Democratic Party (BDP) in Botswana

Food accessibility was determined for each Mississippi County, based on data obtained from the Retail Survey regarding common fruits and vegetables in available in food stores. Availability data were correlated with four social-economic/demographic variables: race, median household income, SNAP enrollment, and education. There were negative low magnitude correlations between percentages of Africans American and fresh fruit and vegetables availability, and percentages of SNAP benefits recipients and fresh fruit and vegetables availability. Positive low magnitude correlations were found between income and fresh fruit availability, and education and fruit availability. Lastly, moderate positive correlations were found between education and fruit availability and income and availability. This research can be used to help extension agents and farmers’ market managers better understand places that may have a lack of fresh food available. This research will also allow SNAP-Ed professionals a chance to have an idea of where their services are needed.

[Truncated abstract] Kelp beds of South-Western Australia have high alpha (within habitat) diversity, through high species turnover at small spatial scales. The E. radiata canopy has a strong negative influence on the diversity of the understorey through intense interspecific competition for light. Literature suggests that when the competitively dominant species such as E. radiata are physically removed, diversity will increase, as less competitive species become more abundant. Apart from disturbance, evidence suggests that reef topography at the 1-10 m vertical scale also has an influence on the structure of the kelp beds, particularly in reference to relative abundance of canopy algae and species richness of the assemblage. In this thesis, I explore the role of algal assemblage recovery from physical disturbance to maintain high diversity. I also investigate the influence of reef structure (in terms of topography at the 1-10 m vertical scale) on assemblage recovery. This thesis provides a valuable functional explanation for the high diversity observed in South-Western algal assemblages. In addition, it explores the influence of reef topography which has received little attention to date . . . Overall, this thesis argues that the high alpha diversity in algal assemblages of South-Western Australia is due to local scale processes including disturbance and assemblage recovery which generate diversity by the creation of species rich gap states and by phase-shifts during the recovery process, creating a mosaic of different patch types. Assemblage recovery is composed of several processes, including survival of juvenile kelp sporophytes and canopy shading, added to macroalgal diversity through spatial and temporal variation in their outcomes. Reef topography contributed to algal diversity by influencing the processes associated with assemblage recovery through alteration of key physical variables including light levels and water motion.

[Truncated abstract. Please see the pdf format for the complete text. Also, formulae and special characters can only be approximated here. Please see the pdf version for an accurate reproduction.] This thesis examines the water use, ecophysiology and hydraulic architecture of Eucalyptus marginata (jarrah) growing on bauxite mine rehabilitation sites in the jarrah forest of south-western Australia. The principal objective was to characterise the key environment and plant-based influences on tree water use, and to better understand the dynamics of water use over a range of spatial and temporal scales in this drought-prone ecosystem. A novel sap flow measurement system (based on the use of the heat pulse method) was developed so that a large number of trees could be monitored concurrently in the field. A validation experiment using potted jarrah saplings showed that rates of sap flow (transpiration) obtained using this system agreed with those obtained gravimetrically. Notably, diurnal patterns of transpiration were measured accurately and with precision using the newly developed heat ratio method. Field studies showed that water stress and water use by jarrah saplings on rehabilitation sites were strongly seasonal: being greatest in summer when it was warm and dry, and least in winter when it was cool and wet. At different times, water use was influenced by soil water availability, vapour pressure deficit (VPD) and plant hydraulic conductance. In some areas, there was evidence of a rapid decline in transpiration in response to dry soil conditions. At the end of summer, most saplings on rehabilitation sites were not water stressed, whereas water status in the forest was poor for small saplings but improved with increasing size. It has been recognised that mature jarrah trees avoid drought by having deep root systems, however, it appears that saplings on rehabilitation sites may have not yet developed functional deep roots, and as such, they may be heavily reliant on moisture stored in surface soil horizons. Simple predictive models of tree water use revealed that stand water use was 74 % of annual rainfall at a high density (leaf area index, LAI = 3.1), high rainfall (1200 mm yr-1) site, and 12 % of rainfall at a low density (LAI = 0.4), low rainfall (600 mm yr-1) site, and that water use increased with stand growth. A controlled field experiment confirmed that: (1) sapling transpiration was restricted as root-zone water availability declined, irrespective of VPD; (2) transpiration was correlated with VPD when water was abundant; and (3) transpiration was limited by soil-to-leaf hydraulic conductance when water was abundant and VPD was high (> 2 kPa). Specifically, transpiration was regulated by stomatal conductance. Large stomatal apertures could sustain high transpiration rates, but stomata were sensitive to hydraulic perturbations caused by soil water deficits and/or high evaporative demand. No other physiological mechanisms conferred immediate resistance to drought. Empirical observations were agreeably linked with a current theory suggesting that stomata regulate transpiration and plant water potential in order to prevent hydraulic dysfunction following a reduction in soil-to-leaf hydraulic conductance. Moreover, it was clear that plant hydraulic capacity determined the pattern and extent of stomatal regulation. Differences in hydraulic capacity across a gradient in water availability were a reflection of differences in root-to-leaf hydraulic conductance, and were possibly related to differences in xylem structure. Saplings on rehabilitation sites had greater hydraulic conductance (by 50 %) and greater leaf-specific rates of transpiration at the high rainfall site (1.5 kg m-2 day1) than at the low rainfall site (0.8 kg m-2 day1) under near optimal conditions. Also, rehabilitation-grown saplings had significantly greater leaf area, leaf area to sapwood area ratios and hydraulic conductance (by 30-50 %) compared to forest-grown saplings, a strong indication that soils in rehabilitation sites contained more water than soils in the forest. Results suggested that: (1) the hydraulic structure and function of saplings growing under the same climatic conditions was determined by soil water availability; (2) drought reduced stomatal conductance and transpiration by reducing whole-tree hydraulic conductance; and (3) saplings growing on open rehabilitation sites utilised more abundant water, light and nutrients than saplings growing in the forest understorey. These findings support a paradigm that trees evolve hydraulic equipment and physiological characteristics suited to the most efficient use of water from a particular spatial and temporal niche in the soil environment.

While it is now well established that many Europeans were delighted with the landscapes they encountered in colonial Australia, the pioneer narrative that portrays colonists as threatened and alienated by a harsh environment and constantly engaged in battles with the land is still powerful in both scholarly and popular writing. This thesis challenges this dominant narrative and demonstrates that in a remarkably short period of time some colonists developed strong connections with, and even affection for, their 'new' place in Western Australia. Using archival materials for twenty-one colonists who settled in five regions across southern Western Australia from the 1830s to the early 1900s, here this complex process of belonging is unravelled and several key questions are posed: what lenses did the colonists utilise to view the land? How did they use and manage the land? How were issues of class, domesticity and gender roles negotiated in their 'new' environment? What connections did they make with the land? And ultimately, to what extent did they feel a sense of belonging in the Colony? I argue that although utilitarian approaches to the land are evident, this was not the only way colonists viewed the land; for example, they often used the picturesque to express delight and charm. Gender roles and ideas of class were modified as men, as well as women, worked in the home and planted flower gardens, and both men and women carried out tasks that in their households in England and Ireland, would have been done by servants. Thus, the demarcation of activities that were traditionally for men, women and servants became less distinct and amplified their connection to place. Boundaries between the colonists' domestic space and the wider environments also became more permeable as women ventured beyond their houses and gardens to explore and journey through the landscapes. The selected colonists had romantic ideas of nature and wilderness, that in the British middle and upper-middle class were associated with being removed from the land, but in colonial Western Australia many of them were intimately engaged with it. Through their interactions with the land and connections they made with their social networks, most of these colonists developed an attachment for their 'new' place and called it home; they belonged there.

Puccinellia (puccinellia ciliata) and tall wheatgrass (Thinopyrum ponticum) often show ecological zonation in saline landscapes, with puccinellia occurring in less elevated more saline/waterlogged locations, and tall wheatgrass occurring in more elevated less saline/waterlogged locations. The aims of this study were to: (a) characterize the observed ecological zonation at a field site, (b) quantify the effects of variables likely to explain growth differences of the two plants in glasshouse experiments, and (c) identify and compare anatomical and physiological mechanisms that explain these zonation patterns. At an experiment in the field near Kojonup (0522824E, 6244579N), puccinellia was found to colonise the lower more severely salinised and waterlogged zones of the landscape, with tall wheatgrass occupying the higher less affected zones. These differences in zonation were clearly associated with variance in soil salinity and water-table depth. Glasshouse experiments in soil revealed that low pH values, low calcium concentrations and variation in salinity alone did not explain the ecological zonation observed in the field. However, there was a substantial difference in the responses of the two plant species to waterlogging in combination with salinity. Puccinellia grew better under saline waterlogged conditions than tall wheatgrass, which was associated with better regulation of Na+ and K+ under saline/waterlogged conditions than in tall wheatgrass. Under non-saline conditions, waterlogging (hypoxia) decreased shoot weights in puccinellia by 15% and in tall wheatgrass by 20%. Similar growth results were obtained in nutrient solution culture, where waterlogging was simulated by lowering the oxygen in solutions through bubbling with N2 gas. Under saline hypoxic conditions, puccinellia, compared to tall wheatgrass, showed increased growth and maintenance of selectivity of K+ over Na+ across adventitious roots. Solution experiments revealed adaptive traits responsible for conveying better growth and ion maintenance present in puccinellia, but not tall wheatgrass, such as inducement of a barrier to radial oxygen loss in the basal regions of adventitious roots (not previously reported in the literature for puccinellia), formation of root aerenchyma and packing of cortical cells and suberin deposition in hypodermal and endodermal root cell layers. These results should assist in targeting pasture species, and predicting their growth response, in saline and waterlogged landscapes. Further work on examining the genetic material of puccinellia is warranted in order to identify genes that could be transferred into crop plants to convey salt and waterlogging tolerance.

[Truncated abstract] Eleven sites, each with the trio of land uses: Eucalyptus globulus plantation, pasture and natural vegetation, representing from the Mediterranean climate, high rainfall region (<550 mm annually) of south-western Australia were investigated to assess medium-term changes in the P-supplying capacity of soils in eucalypt plantations growing on agricultural land. The natural vegetation soils were a benchmark for comparing soil P change since land clearing and development for agriculture. The experimental framework provided an ideal basis for studying changes in P forms since land clearing and fertilization for agriculture and the ensuing conversion to plantations (on an average 9 years ago). Conventional soil P indices measure plant available P that is more relevant to short duration annual crops and pastures. To predict medium-term P availability, P forms were determined using Hedley et al.’s (1982) fractionation scheme and fractions were grouped using the Guo and Youst (1998) criteria into readily, moderately and sparingly available P. The P species were also determined by 31P NMR spectroscopy of 0.5M NaOH-0.1M EDTA extracts. Hedley et al.’s (1982) inorganic P extracted by anion exchange resin and by NaHCO3 are widely considered to be approximations to the actual plant available P. The availability to plants of other P fractions is less certain and this is examined in an experiment to compare the plant availability of various P fractions in soils from fertilized and unfertilized land uses following exhaustive cropping in the glasshouse. The soil texture for the sites studied included coarse sand, loamy sand, clayey sand, and sandy loam. Surface soils (0-10 cm) have pH(CaCl2) in the acidic range (mean 4.4) and there is no significant difference due to differences in land use (P<0.05). The soils are of low EC (1:5 H2O) - 6 mS m-1. There is an almost 5-fold variation in organic C among sites (from 1.4% to 8%) but organic C values did not show any significant effect (P<0.05) of changes in land use. To evaluate the degree of similarity of soils within each triplet set at a site principal component analysis was carried out on those soil chemical⁄mineralogical characteristics that were least likely to be affected by changes in land use practices. This analysis showed good matching of the triplet of sub-sites on the whole, especially for the duo of pasture and plantation land uses. This degree of matching of the trio of land uses was considered while interpreting the effects of land use on the forms and behaviour of soil P, and variations due to various extents of mismatch were mostly addressed using statistical techniques including regression analysis to interpret sub-site difference

[Truncated abstract] Native Australian soils contain very low amounts of phosphorus. The soils of southwestern Australia are ancient and highly weathered. Consequently, the availability of phosphorus in these soils is too low for cropping purposes, so the application of P is necessary to maintain productivity. When P is applied to soil, typically as soluble superphosphate, it tends to be transformed to increasingly less soluble forms over time. Sparingly soluble forms of soil P are relatively inaccessible to Triticum aestivum; however, many grain legumes have a higher P-acquisition efficiency, allowing them to access pools of soil P that T. aestivum cannot. The P-acquisition efficiency of some grain legumes has been attributed in part to their ability to release large quantities of carboxylates, coupled with the development of cluster roots for species such as Lupinus albus. There are a number of unexplained observations in terms of the P-acquisition efficiency of grain legume species and the way that those species respond to P fertilisation. This PhD project aimed to study carboxylate release from a range of crop species, and investigate its role in variation among species for acquisition of phosphorus from sparingly soluble forms (chapter 1). ... L. albus (chapter 5). There was considerable variation in P acquisition among accessions. The variation cannot be attributed to differences in carboxylate release, cluster-root development or whole root system rhizosphere extract pH as measured in this study. We hypothesise that the variation might be attributed to differences in the ratio of release of protons and other cations localised around cluster roots. In conclusion studies of carboxylate exudation and sparingly soluble forms should use more than a single form if the aim is to draw generalised conclusions on P-uptake efficiency from sparingly soluble forms. Comparative studies of a range of species are a useful tool for enhancing our understanding of root physiology. While the benefit of carboxylates for providing access to poorly soluble P has been demonstrated, questions remain as to potential other roles for carboxylates, particularly in species that do not form cluster roots. Variation in P uptake among accessions of L. albus is present, and more work on proton release and ion balance of root clusters is necessary to understand intraspecific variation.