School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemMycorrhizal associations of Prasophyllum R.Br. (Orchidaceae) and the conservation of its threatened species(University of Melbourne, 2010)
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ItemNo Preview AvailableA review of methods used to undertake risk assessments of urban trees(University of Melbourne, 2010)
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ItemThe effect of in vitro manure nitrogen composition and lignite application on dairy cattle manure ammonia emission( 2022-09)The major objectives of the master study were to estimate the urinary nitrogen (UN) to faecal nitrogen (FN) ratio from sampled dairy cattle, to quantify the effectiveness of lignite application on reducing ammonia (NH3) emission and to establish the relationships between dairy cattle manure NH3 emission, nitrogen (N) isotope fractionation (delta-15N), the N to phosphorus (P) and N to potassium (K) ratios in diverse manure property and environmental conditions. The in vitro manure incubation system was conducted to explore the manure daily changes, daily NH3 emission and the effect of lignite application on reducing NH3 emission. The UN to FN ratios were approximately 1 to 1, calculated via the N balance study. Total 600 g reconstructed manure was put into each incubation system to achieve a manure UN to FN ratio of 1 to 1 for CT and CT+L, and 2 to 1 for 2U1F and 2U1F+L. Further, 250 g lignite powder was added into CT+L and 2U1F+L and mixed with manure. Acid traps were settled to collect emitted NH3 emission. A total of 15 g manure sample and 15 mL of acid sample were collected daily from each incubation system and stored frozen (-20 degrees centigrade). The daily NH3 emission in the non-lignite group decreased with incubation days while it increased with days in the lignite group. The major NH3 emission occurred in the first 7 days in the non-lignite group and in the last 10 days in the lignite group. There was a weak relationship between temperature and daily NH3-N emission (R2 = 0.30, P <= 0.05). The cumulative NH3-N emission of 2 UN to 1 FN ratio (2U1F) treatment was 45.8% higher than control (CT) treatment in non-lignite groups, while it of 2U1F with lignite application (2U1F + L) was 100% higher than CT with lignite application (CT + L). The lignite application reduced the cumulative NH3-N emission by 87.5% compared to CT and CT + L treatments and 82.9% compared to 2U1F and 2U1F + L treatments. The manure delta-15N from the CT and 2U1F treatments increased with incubation days (R2 = 0.85 and 0.91, respectively; P <= 0.001). However, there was no relationship between manure delta-15N from the CT + L, 2U1F + L treatments and incubation day (R2 = 0.07 and 0.08, respectively; P <= 0.001). The manure N to P ratio decreased with incubation days (R2 = 0.81, 0.73, 0.81, and 0.84 in CT, 2U1F, CT + L, and 2U1F + L treatment, respectively; P <= 0.001). There was a weak relationship between manure N to K ratio and incubation days found in CT treatment (R2 = 0.28, P <= 0.001), while manure N to K ratio decreased with incubation days in the other three treatments (R2 = 0.70, 0.79, and 0.90 in 2U1F, CT + L, and 2U1F + L treatment, respectively; P <= 0.001). Overall, the master studies showed that manure delta-15N could not be used as an accurate biomarker to estimate NH3 emission in relatively low NH3 concentrations (R2 = 0.02, P <= 0.001) while the N to P ratio was better to use (R2 = 0.85, P <= 0.001). The manure delta-15N outperformed to be the best biomarker to estimate NH3 emission in relatively high NH3 concentrations (R2 = 0.83, P <= 0.001). The lignite application was an effective method to reduce NH3 emissions. However, further study is required to investigate the maximum absorption ability of lignite for improving the application in livestock industries.
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ItemAmelioration of the effects of heat stress with antioxidant enzymes superoxide dismutase and catalase in broiler chickens( 2022)Heat stress has become a growing concern in the livestock industry. Elevated temperatures, coupled with rising global animal production is severely impacting animal health, welfare and overall production capacity. Heat stress is associated with a myriad of physiological, metabolic and gastrointestinal changes and has been shown to induce oxidative stress, a condition in which harmful free radicals are produced in excess. Oxidative stress is particularly damaging to macromolecules and causes widespread cell and tissue damage. Emerging research suggests supplementation with antioxidants, such as Vitamin C and Vitamin E, can partially ameliorate the damaging effects of heat stress. Despite considerable research on antioxidant supplementation in livestock, there has been little investigation into the therapeutic effects of antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT). Therefore, the aims were to determine the effect of both antioxidants and antioxidant enzymes on growth parameters, meat quality, gastrointestinal health and markers of oxidative stress in heat stressed broiler chickens.
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ItemUsing field experiments to test associations between plant traits and fire regimes( 2021)Conservation of biodiversity in fire-prone landscapes requires a thorough understanding of how plants are impacted by fire regimes. Altered fire regimes, due to changes in climate and land use, will likely impact many plant species in arid and semi-arid ecosystems. The study of functional traits – including fire-related traits that help plants to persist in areas subject to recurrent fire - provides a way to understand how plants respond to contemporary and future fire regimes. In my first chapter I studied the influence of a large-scale fire and climate gradient on variation of functional traits of a serotinous tree species, Callitris verrucosa. I measure intraspecific variation in fire-related traits including level of serotiny, bark thickness and tree size on C. verrucosa populations along a 340 km north-south gradient in semi-arid southeastern Australia. Level of serotiny was strongly associated with fire frequency: tree-level of serotiny increased at stands estimated to experience higher fire frequency, while the variation in level of serotiny at standsincreased with lower fire frequency. After accounting for tree size, relative bark thickness was also strongly associated with fire frequency and average annual rainfall. Thicker bark is allocated to smaller stems in areas that experience more frequent fire. In my second chapter, I used a field experiment to explore topkill of resprouting eucalypts after a planned burn in a semi-arid mallee woodland. I measured fire-related traits of eucalypt trees and stems including bark thickness, basal diameter, and canopy height, as well as elements of fuels including litter depth, ground cover, and vertical strata. The probability of topkill declined with taller stems (>3 m): taller mallee eucalypts appear to ‘escape’ low intensity fire. Fuels were also important, with topkill higher in areas with increased cover of hummock grass. Overall, my research demonstrates clear relationships between plant functional traits -including serotiny, 3 height and bark thickness - and fire regimes. This knowledge can be used to inform manipulations of fuels, habitat structure and plants through planned burning, to achieve a wide range of social and environmental objectives. Moreover, the demonstrated variation in C. verrucosa fire-related traits could be used to guide restoration efforts. For example, seeds sourced from southern locations, where populations have higher levels of serotiny, may promote resilience under a scenario of more frequent fire. While the extent to which fire regimes will change is uncertain, field experiments help us learn about contemporary processes and forecast future changes.
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ItemThe role of tubulins in secondary cell wall deposition in woody tree species( 2020)Woody trees are an essential source of timber, pulp, paper and biofuel, and advances in biotechnology provide opportunities for the improvement of traits of interest for specific end uses. Cellulose microfibrils, the basic structural component of plant cell walls, are responsible to a large degree for wood mechanical and physiological properties. The angle between the direction of the helical windings of cellulose microfibrils in plant secondary cell walls, or microfibril angle (MFA), plays critical roles in a tree’s development and has become a subject of major interest in forest biotechnology, particularly in detailed studies of the secondary cell wall of xylary (wood) cells. While our knowledge of how exactly the cellulose synthase complex (CSC) acts in response to environmental and genetic cues remains sketchy, guidance of cellulose deposition has been repeatedly accredited to microtubules, a cytoskeleton component formed of protein dimers of alfa- and beta-tubulin. Nevertheless, few studies explore the cytoskeleton roles in secondary cell wall deposition in woody tree species. Reaction wood (RW) develops in response to gravitational stimulus through a series of changes at the cellular and molecular levels. Tubulin genes have been previously reported to be upregulated during RW formation and differences in their expression might lead to differences in microtubule assembly. This differential microtubule organisation might be related to changes on cell wall morphology, including MFA. In this study, cortical microtubule array organisation was therefore assessed in samples from trees forming RW and stems growing upright (normal wood). To further investigate if perturbation of microtubule organisation would impact wood formation, microtubule-interacting drugs were applied to wood tissue depositing SCW in vivo and in vitro. Together, results indicate that tubulins play an essential role in cellulose deposition in the secondary cell wall of woody tree species to ensure appropriate microfibril orientation.
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ItemEconomic analysis of ameliorating subsoil constraints using subsoil manure in a cropping system( 2019)To date, no studies have accounted for the effects of the yield and/or price risks that will occur over a run of years on the profitability of investing in ameliorating subsoil constraints within a cropping system. While addressing subsoil constraints is likely to increase grain yield, the key economic question for a grower is whether the income from extra grain produced covers the extra costs of ameliorating the subsoil. The focus of this thesis was the likely profit and risk of investing in ameliorating subsoil constraints. Investment costs and annual activity gross margins for a set rotation were used to estimate the economic performance of subsoil amelioration. The marginal change to the gross margin as a result of subsoil amelioration was assessed using partial discounted cashflow budgets. Risk analysis was used to assess the effect of price and yield variability on the mean and variance of outcomes from an investment in ameliorating subsoil constraints in cropping. This study shows an investment in subsoil amelioration was more profitable on average than an alternative investment earning 6% (real). The size of the expected extra yield benefits and longevity of these benefits are the most important factors for a grower to consider when assessing the likely merit (return and risk) of investing in subsoil amelioration in their own situations.
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ItemTree pit stormwater control measures as a tool to improve street tree growth and mitigate the urban stream syndrome( 2018)Cities globally are embracing stormwater control measures (SCMs) to mitigate the environmental damage to urban waterways caused by impervious runoff. Concurrently, efforts are underway to increase urban forest canopy to reduce urban heat and green neighbourhoods. Tree pits are a promising SCM with potential to address both of these issues in dense urban areas. As tree pits may have a small footprint, they allow for implementation without competing for highly-valued space, and may promote tree growth, thus enhancing the benefits provided by the tree. This thesis investigates how effective tree pits may be at reducing runoff and promoting tree growth and which design characteristics drive their performance. A streetscape experiment was conducted, comparing four tree pit designs to a standard street tree planting. Tree growth and runoff retention were measured over an 18-month period and the relationship between the tree pit water regime and tree growth investigated. Tree pits substantially increased tree growth, with median growth in tree pits with an underdrain approximately double that of the standard street tree planting. For tree pits where the tree received stormwater directly at the tree root ball but did not have an underdrain, tree growth was strongly correlated with the soil exfiltration rate. Low exfiltration rates (<20 mm hr-1) resulted in poor growth or death of the tree, whereas pits with higher exfiltration rates showed equal or increased growth compared with the standard street tree planting. A tree pit water balance model was developed and calibrated using the streetscape experiment data to identify tree pit characteristics influencing runoff retention. Sensitivity analysis of the water balance model identified pit exfiltration rate and impervious catchment area as the key drivers of runoff retention. The model was then applied to possible implementation scenarios to explore circumstances where tree pits may achieve meaningful reductions in runoff. For the streetscape experiment scenario, large catchment areas and overall low exfiltration rates resulted in poor runoff retention performance (runoff volume reductions of only 5%). However, if the tree pit area to catchment area ratio was significantly increased (from 0.1% to 4.4%) through increasing tree pit density and tree pit area, and decreasing the catchment areas for each pit, the model suggests that it may be possible to achieve runoff volume reductions of 90% and reduce the frequency of runoff to 15 days per year, returning runoff flows to near pre-development conditions. In practice, achieving significant runoff reductions with tree pits will be most practicable when tree pits are implemented alongside a suite of complimentary SCMs such as rainwater tanks and permeable paving. Such an approach allows tree pits to treat the runoff fromthe public road and footpath surfaces only, requiring smaller tree pits that may integrate into the streetscape without competing for space. This study is the first fully replicated field experiment testing alternative designs for street tree pits. The findings of this thesis highlight that tree pits may increase tree growth and achieve meaningful reductions in runoff and improves understanding of the factors that should be considered in their design.
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ItemThe influence of urbanization on stream temperature regimes( 2017)Streams draining urban catchments are relatively warmer than non-urban streams. Catchment urbanization and subsequent stormwater drainage systems are likely a primary cause of this warming of urban streams, however, the extent of these causes and their relative contribution to the degradation of thermal regimes still remain unclear. Addressing this knowledge gap is important to provide guidelines for thermal regime restoration measures. Stream temperature data were collected continuously at a 15 minute time step from temperature loggers deployed across 82 sites around the city of Melbourne (population ~5 million people), in south-eastern Australia, over a 3 year period. After screening for periods with zero flow and removing logger errors, 53 sites with >80% of good quality data over a >30 month period were selected to calculate a set of temperature metrics that indicate the spatial patterns of thermal regimes (mean, mean daily maximum, mean daily minimum, mean diel change, maximum weekly average temperature, mean summer, mean winter, summer maxima and number of days exceeding threshold levels of 24, and 29C per year). To indicate temporal dynamics, the maximum amplitude of temperature surges during storm events was calculated (a surge was defined as >1 C temperature change recorded over 30 minute intervals). All temperature metrics were then linearly regressed with catchment and climatic variables to identify the main drivers of surges in temperature. The thermal regime of the study streams was also examined with reference to the thermal tolerances of native fish occurring in the region. The majority of streams in the study were unlikely to exceed tolerable temperature limits for most Australian native fish species. Spatial variation in temperature (~88%) were most plausibly predicted by models that included attenuated impervious cover (a measure of urban drainage systems), attenuated forest cover (a measure of riparian deforestation), mean annual discharge volume and mean annual air temperature. Stream temperature surges were observed most commonly after rain events and depending on the antecedent weather, the amplitude of surges was either positive or negative. Positive surges (i.e. increases in temperature) were most commonly observed in autumn, with fewer positive surges in summer than in winter. Negative surges (i.e. decreases in temperature) were most common in spring and summer, and least common in winter and autumn. The variations in the amplitude of negative surges (~74%) were explained by the attenuated imperious cover; however, the drivers of spatial variations in positive surges remained unclear. Surges are small and less common and thus, the potential degradation of stream ecosystem cannot be expected from temperature surges. Therefore, temperature surges were appeared not to be an important aspect of urban stormwater impacts on stream ecosystems in Melbourne water region. The temperature models suggest that increasing the extent of drainage systems and riparian deforestation in future climate change would have a potential to limit thermal habitats suitable for temperature-sensitive fish species. Moreover, riparian reforestation was shown not to be able to overcome the influence of drainage systems.
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ItemFormulating curcumin in a biodegradable polymeric composite material: a step towards wound healing applications( 2017)The natural process of wound healing typically consists of four distinct but overlapping phases which include, hemostasis (platelet aggregation and blood clot formation), inflammation (migration of blood cells), proliferation (angiogenesis or blood vessel formation), and remodelling (reorganisation of collagen and scar tissue formation). However, in diabetic patients, this elaborate well-programmed process becomes disrupted, and there is an urgent need for compounds and formulations that can improve wound healing in these cases. A variety of natural components, including curcumin, have been identified as wound-healing agents. Curcumin, is a yellow hydrophobic natural polyphenolic pigment derived from the rhizomes of the herb Carcuma longa, which has been identified as the active principal of turmeric. The inability to efficiently deliver curcumin in a soluble form presents a chief challenge for its clinical use. Here we characterised, and optimised different biodegradable and biocompatible formulations of curcumin encapsulated particles, in order to enhance the efficiency of curcumin wound healing effect. The size of the optimised curcumin particles ranged from 1286 to 1485 nm, with an encapsulation efficiency of 75%. The zeta potential exhibited values in the range of (-7.2) to (-7.96) with the PDI of 0.4. Physical characterisation using TEM imaging ensured the successful fabrication and encapsulation of curcumin in the polymeric matrix, which had been fabricated in rod shape. Release profile occurred in a biphasic manner including an initial burst, followed by a sustained release trend for curcumin particles. In vitro cytotoxicity assays along with microscopic imaging confirmed safety of the applied concentration of curcumin particles below 25 µg/ml. Moreover, the results of cellular uptake study validated the internalisation of curcumin particles. Overall this thesis, elucidated the developed biocompatible and biodegradable formulations for curcumin encapsulation do have the potential to be employed as a drug delivery vehicle for curcumin. Further validation of the potential of this preparation to enhance wound healing is still needed.