School of Agriculture, Food and Ecosystem Sciences - Theses

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    The effect of in vitro manure nitrogen composition and lignite application on dairy cattle manure ammonia emission
    SONG, YUMENG ( 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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    Amelioration of the effects of heat stress with antioxidant enzymes superoxide dismutase and catalase in broiler chickens
    Artaiz, Olivia ( 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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    Using field experiments to test associations between plant traits and fire regimes
    Kreger, Isaac Daniel ( 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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    The role of tubulins in secondary cell wall deposition in woody tree species
    Machado Tobias, Larissa ( 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.