School of Agriculture, Food and Ecosystem Sciences - Theses
Permanent URI for this collection
Search Results
1 - 10 of 32
-
ItemThe role of skilled migration in Australian dairy farming and implications for agricultural workforce development( 2020)Employment of a migrant workforce is a key strategy for both the Australian Government and employers to address workforce labour and skill shortages. In the Australian dairy farm sector, structural change has increased the demand for employees with management and technical skills. This led some employers to employ skilled migrants under Temporary Work (Skilled) visas (subclass 457). The 457 visa was introduced by the Australian government in 1996 and abolished in 2017. In March 2018, a new subclass 482 visa was introduced but restricted skilled migrants’ eligibility pathways to obtain Australian permanent residency visas. Focusing on the 457 visa, this thesis examines the research question: "How does the attraction and retention of skilled migrants contribute to development of the dairy workforce?" While skilled migration has been an option for employers in agriculture, the use of the 457 visa in dairy farming in Australia has not been investigated until now. In particular, that involves how the 457 visa has supported a long-term workforce development strategy by sourcing skilled labour from the international labour market. The conceptual framework for this study integrates psychological contract theory, relating to the employment relationship between skilled migrants and farm employers, with theories of workforce development systems, relating to the sectoral and institutional arrangements governing the workforce. The conceptual framework was applied in the design of the research and in the analysis and interpretation of data. A qualitative case study research design was implemented involving semi-structured interviews with 20 case study farm employers and nine of their skilled migrant employees. A focus group was conducted with 10 industry stakeholders, and three government policy makers and three migration agents took part in semi-structured interviews. The qualitative data analysis tools of grounded theory, including coding, categorisation, conceptualisation and constant comparison of data were applied to derive the findings. The primary motivation of case study farmers in seeking skilled migrant employees under visa 457 was the limited availability of skills in the domestic workforce that were aligned to their current and future skill requirements. These skills requirements were significantly broader than qualifications and experience and were found to include attributes associated with organisational commitment and job involvement. Skill requirements were also contingent on the business stage of the farm. The case study farm employers were able to align the skills of the 457 visa employee with their future business goals, irrespective of whether the business life cycle was in a growth, mature or decline stage. Skilled migrant employees under 457 visas choose Australian dairy farm employment to meet their future needs, such as becoming an Australian permanent resident, and to access Australian dairy industry skills and knowledge. Both the employer and skilled migrant played critical roles in determining the quality of the employment relationship, which, in turn, influenced skilled migrant retention. At the pre-employment phase, a shared understanding between the employer and skilled migrant of each other’s future needs from the employment was significant in both the execution of the formal employment contract and in establishing mutual expectations for the employment relationship. A skilled migrant employee’s awareness of an employer’s provision of socio-cultural support was also found to be key in their decision to accept a job offer and in the quality of the subsequent employment relationship. Significantly, perceived strong employer support to the skilled migrant in accessing permanent residency was found to be a key component of mutuality in the psychological contract between the skilled migrant and their farm employer and was associated with both the retention of the skilled migrant and achievement of farm business outcomes. The workforce governance actors of government, community, industry, and employers play different roles in attracting and retaining skilled migrants on dairy farms. The effectiveness of the agricultural workforce development system is constrained when there is a lack of alignment between these actors with respect to supporting pathways for skilled migrants to achieve permanent residency, and recognition of the critical intermediary role of migration agents during the pre-employment phase. Such systemic misalignment impacts on how successfully skilled migrants and their farm employers achieve mutuality with respect to the psychological contract between them. In turn a misalignment of mutuality can undermine achievement of the farm business goals and skilled migrants’ personal aspirations. The findings of this research highlight how the policies and strategies that support agricultural workforce development strongly influence opportunities and constraints at the business enterprise. This study highlights the need for coordination and alignment across all stakeholders within the dairy workforce development to ensure that policies such as Visa 457 deliver benefit.
-
ItemOptimising the progeny from primiparous sows( 2020)The progeny of primiparous sows (gilts) are recognized as a significant burden on the overall production efficiency of Australian pig herds. Gilt progeny (GP) grow slower and have higher rates of morbidity and mortality compared to the progeny of multiparous sows (sow progeny; SP). Previous research suggests that there is an underlying biological basis for differences between GP and SP. Therefore, the aims of this thesis were to clarify the timeframes of when these differences are in effect by investigating gastrointestinal (GI) development in the pre-weaning period and also to develop late gestational and lactational nutritional interventions to improve GP performance. In doing so, this thesis consists of a series of experiments in which three general hypotheses were tested: (1) GP display poorer production performance compared to SP; (2) GP consistently displayed reduced gastrointestinal (GI) tract development compared to SP and (3) GP production performance could be improved by targeting nutritional interventions towards late gestation and/or lactation. Experiment 1 (Chapter 3) involved the quantification of GI functional development at 4 time points; birth (0h), 24 hours after birth (24h), 1-day pre-weaning (PrW) and 1-day post-weaning (PoW) of GI tissues (stomach, jejunum, ileum and colon). Transepithelial resistance (TER) was measured on all organs of the GI tract while the permeability of macromolecules fluorescein isothiocynate (FD4) and tetramethyl rhodamine isothiocynate (T150) labelled dextrans was measured in the mucosa of the jejunum and ileum. Additional GI function measurements were taken such as tight junction proteins and cytokine abundance in the jejunal and ileal tissues. The main findings were that GP showed early signs of lower GI tract function compared to SP at birth, particularly in terms of lower TER in the stomach tissues of the stomach, jejunum and ileum. However, differences between GP and SP were largely observed from PrW to PoW with GP exhibited poor GI barrier function at weaning reflected the reduced epithelial barrier integrity in response to weaning, mainly in the distal portions of the GI tract (ileum and colon). Differences in GI barrier function between the birth cohort and the weaning cohort suggests that the variation between GP and SP is established in the pre-weaning period. This indicates that the pre-weaning period is critical for optimal GI tract function development for GP and their reduced growth performance compared to SP is likely due to a lack of colostrum/milk consumption. As the development in GI barrier function in the piglet is critical for survival and productive efficiency, we investigated the utility of quantifying intestinal fatty acid binding protein (I-FABP) as a biomarker of GI integrity (chapter 4). Fatty acid binding proteins (FABP’s) are ubiquitous intracellular transport proteins integral to fatty acid metabolism. However, organs of the GI tract have a specific intestinal isoform (I-FABP). The use of FABP’s as biomarkers for organ damage have been proposed, but little is known about the utility if I-FABP as a biomarker in the pig. The outcomes of this experiment showed that plasma I-FABP concentrations were substantially lower in piglets than later in life and this led to significant challenges in detection using existing ELISA based methodologies. While it is interesting that I-FABP is expressed in such low concentrations early in life, to properly understand the utility of I-FABP as an intestinal biomarker will require more sensitive technologies such as mass spectroscopy, which will limit its utility as a biomarker. In order to support growth of GP in the pre-weaning period, various nutritional strategies were investigated and implemented during either late gestation and/or lactation. In experiment 3 (chapter 4), the ketogenic substance 1,3-Butanediol (BD) was fed to gilts and sows from day 90 of gestation to farrowing in order to provide and alternative energy source to GP at farrowing. The main result was that birth litter weights were increased in GP from gilts fed the BD diet and this extended to day 21. Furthermore, the proportion of GP born less than 1.1kg were less from those gilts fed the BD diet, increasing their chances of survival to weaning. Previous research suggests that gilts suffer from high levels of oxidative stress during gestation and possibly lactation compared to multiparous sows resulting in reduced GP growth. Experiment 4 (chapter 5) involved supplementing late gestation and lactation diets with a sugar-cane derived polyphenol mixture (Polygain) to improve GP growth during the pre-weaning period. Furthermore, due to the anti-inflammatory properties of Polygain, weaner diets were supplemented with this mixture to reduce post-weaning inflammation. Polygain was unable to increase GP growth in the pre-weaning period nor did it reduce inflammation measured by the circulation pro-inflammatory cytokine interleukin-1 beta (IL-1b). Interestingly, results from this experiment do suggest that GP exhibit reduce immune function compared to SP reflected in their lower plasma IL-1b concentrations overall compared to SP. Lastly, experiment 5 (chapter 7) investigated the effects of feeding gilts and sows a diet supplemented with lucerne chaff or a diet formulated to have the same estimated fibre, amino acid and energy content as lucerne (SIMLUC) to improve GP performance. These diets were able to increase GP average weight and gilt litter weight at day 21 while a similar effect was not observed in SP. The improvement of D21 litter weights in gilts in response to the LUC and SIMLUC diets fed in late gestation is an important finding which demonstrates the importance of targeted feeding strategies towards gilts to maximize GP performance. In conclusion, results from this thesis indicate that GP are consistently born and weaned lighter and growth slower than SP. They display reduced GI tract development, with GP entering weaning with reduced GI integrity. Furthermore, GP display some signs of reduced immunocompetence compared with SP which may impede their ability to cope with the stressors of weaning. Therefore, nutritional interventions are most likely to work when they support higher milk yields in gilts and support growth of GP in the neonatal and pre-weaning period.
-
ItemWarming a cold shoulder: Animal ethics, sentience, and preferences for human interaction in zoo-housed non-avian reptiles( 2020)Animal welfare science has functionally only existed for a little over 50 years. The last three to four decades in particular have seen a relative boom in the rate of expansion, understanding and attention that this discipline has received. Whilst the foundations of animal welfare science mainly focused on identifying and removing negative welfare states in captive animals, modern scientific inquiry is now starting to understand and approach positive welfare states as a crucial part of any sentient being’s experience of life as well. Positive welfare states may include many elements, such as an animal being fit and healthy, experiencing positive moods and affects, and being able to express natural behaviours (or instead, as this thesis will argue, behaviours that are highly motivated and/or highly rewarding). Encouraging, facilitating and maintaining positive animal welfare states in captive zoo animals are a high priority for modern, ethical zoos. However, there is currently a substantial gap in the published literature exploring positive welfare states associated with human (especially visitor) contact in zoo settings. There is limited research that suggests that human-animal interactions in zoos may potentially be rewarding for some animals that are motivated to participate in, and even ‘solicit’, these interactions, from both familiar husbandry providers (zookeepers) and/or unfamiliar zoo visitors. Ethically, zoos operate under a few key theories pertaining to animal welfare, animal rights, and environmental ethics. A few such theories are: Compassionate Conservation, Conservation Welfare, and Duty of Care. These theories take inspiration from multiple philosophical discourses, and many of them co-exist within the zoological and aquaria communities, institutions and (self-regulated) associations. Many individual institutions may favour particular ethical theories over others, and not all zoos are ethically run, nor is their captivity of certain animals justified or adequate. However, many influential voices within zoological associations are creating a robust model for running ‘modern, ethical zoos’. An amalgamation of many theoretical ethical approaches is required to fully articulate why zoos should, and do, continue to exist. The phylogenetic Class Reptilia (reptiles) is now more correctly termed non-avian reptiles, as recent taxonomic amendments have included all extant and extinct animals back to the clade Diapsida, which includes all dinosaurs, and hence all modern birds - Aves. This now makes reptiles a monophyletic group (i.e. with a single common ancestor). Thus, when discussing modern reptiles, such as tortoises, it is proper to distinguish between avian and non-avian reptiles. Currently, none of the non-avian reptile families have been adequately studied in terms of animal behaviour, cognition and animal welfare sciences. These families include: Sub-order Crocodilia – crocodiles, alligators, gharials, & caimans; Order Lepidosauria, which includes both Squamata – lizards and snakes, and Order Rhynchocephalia – Tuatara; and Order Testudines – turtles, tortoises and terrapins. Declarations of sentience (i.e. feelings) made by governments and scientific associations (such as the World Organisation for Animal Health (OIE)) often include reptiles under the assumption of “all vertebrate animals”, but specific declarations of sentience in reptiles are often missing, or overlooked, in scientific writing and welfare-related policies and discussions. Indeed, the historical assumption that reptiles are merely sedentary automata without complex cognitive and sentient capacities persist. Available cognition and sentience research, however, indicates that there is a very solid basis for assuming and declaring that non-avian reptiles do indeed display all relevant capacities to be classified as conscious, aware, and sentient beings. This means that they most likely are consciously aware of their own welfare, and hence their lives and well-being matter to them. This thesis was designed to weave a coherent story connecting animal ethics, states of consciousness, awareness and sentience in non-avian reptiles (that are often overlooked), and experimental research that addresses whether some zoo-housed reptiles perceive human interaction as rewarding, and whether they are indeed motivated to seek these interactions. Three experiments were conducted: An Aldabran Giant Tortoise (Aldabrachelys gigantea) preference test (n=2); a Leopard Tortoise (Stigmochelys pardalis) preference test (n=5); and a zoo visitor survey of behavioural and ethical beliefs about zoo-housed non-avian reptiles, and the acceptability of human-animal interactions and owning wildlife as pets (n=231). Both tortoise preference tests found individual differences between subjects, and I concluded that some individual tortoises do indeed prefer human interaction (shell scratching and neck rubs) over other stimuli in the experimental circumstances. Whether the rewarding component for the tortoises was the interaction with the human or simply a pleasurable outcome was not determined. While these results could not be generalised to all populations of tortoises or reptiles in general, the results showed significant individual preferences amongst the sample populations, indicating that being aware of, and sensitive to, individual animals’ ‘wants’, rather than making decisions at a species level, is warranted for zoo-housed non-avian reptiles. The results of PCAs of visitor survey responses (n=231) found five common ethical beliefs (components) in the sample of zoo visitors, labelled: 1) Human interaction and entertainment priority component; 2) Complicated zoo ethics and animal welfare component; 3) “Wilding”, natural living and anti-captivity sentiments component; 4) Ethical duty of care component; and 5) Animal agency and respect component. There were some significant differences between agreement with Component 2 and respondents’ education level. Furthermore, Wilcoxon’s Signed Rank tests on 3 paired questions (that were answered before and after randomly allocated positive or negative human-animal interaction statements) significantly influenced the re-rated scores to the questions in either the positive or negative direction corresponding to the information provided, showing a significant influence of education (informative statements) on zoo visitor attitudes. Finally, drawing from relevant information of the known capacities of non-avian reptiles, and from the results of the two preference tests conducted herein that indicated some preferences for human interactions by tortoises studied, I investigated an ethical model of human-animal interactions in zoos that may benefit the well-being and positive welfare of both animal and human participants, and proposed some recommendations for improvement of such interactions. These recommendations may be relevant to zoological institutions and their governing associations, and the results of the ethical and experimental chapters within this thesis may help inform evidence-based improvements for non-avian reptile welfare within these institutions.
-
ItemQuantifying wildfire impacts on the structure of fire-tolerant eucalypt forests using airborne lidar data( 2020)Most of the native forests in temperate south-eastern Australia are dominated by resprouter fire-tolerant eucalypts, which are often assumed to quickly recover from even the most severe fires. However, very few studies have quantitatively assessed the effects of fires of different severity on eucalypt forest structure, which limits quantitative analyses of broad-scale fire impacts over time. My Thesis examines wildfire impacts on the structure of fire-tolerant eucalypt forests from tree- to landscape-scales. Using field-based assessments and metrics derived from multi-temporal airborne lidar (Light Detection And Ranging) data, I quantify fire severity effects on the structure of tree crowns, canopy, and understory fuel in a single forest type nearly a decade after an extensive wildfire in south-eastern Australia that started on ‘Black Saturday’, 7 February 2009. I then use the lidar metrics as a basis for evaluating the potential of Landsat satellite imagery to accurately represent variation of forest cover across landscapes. My research provides quantitative evidence that wildfire impacts on the structure of fire-tolerant eucalypt forests are influenced by wildfire severity and can persist for several years after fire. At the scale of individual trees, I quantify impacts of four wildfire severities (unburnt, low, moderate, high) on crown structure using estimates of cover, density and vertical distribution derived from 2016 lidar data validated with field measurements of 51 field plots (0.05 ha). This analysis indicated legacy effects of wildfire at moderate- and high-severity sites where tree crowns were comparatively narrow and more evenly distributed down the tree stem. I then extend my analyses to the forest canopy using a comprehensive set of lidar-derived metrics representing the horizontal and vertical structure of three strata in 1084 pre- and post-fire lidar plots across an area of ~30,000 ha. My results confirm persistent effects of high-severity fire at stand- to landscape-scales, including significant decreases in canopy cover and mean canopy height, and changes in the canopy relief ratio and rumple index consistent with a more heterogeneous and fragmented dominant stratum. Persistent effects of high-severity fire were also evident in my subsequent analysis of lidar-derived understory metrics, namely, increases in the cover and horizontal connectivity of the elevated and midstory strata and increased potential for crown fires through increased vertical connectivity. Using Random Forest (RF) models, I demonstrate that both post-fire canopy and understory fuel structures were more clearly associated with fire severity and pre-fire structural metrics than climatic and topographic variables. Variations in lidar-derived estimates of forest cover (understory, canopy, full profile) were only weakly represented by Landsat spectral indices either alone or combined in RF models with environmental variables. My Thesis demonstrates the utility of airborne lidar data in quantitative assessments of fire impacts on native eucalypt forests of complex structure. My analyses indicate legacy effects of severe fires towards more open and fragmented forest structures, which could influence multiple processes, including ecosystem productivity. These effects combined with increased fuel connectivity could lead to feedbacks in these fire-tolerant forests that narrow future windows for full structural recovery between wildfires.
-
ItemRoot and collar rot pathogens associated with yield decline of processing tomatoes in Victoria, Australia( 2020)The processing tomato industry in Victoria, Australia, has experienced a yield decline over the last decade, resulting in losses estimated at 10% per annum. The decline was attributed to the necrosis of lateral and feeder rootlets and the collar region resulting in plant stunting and a reduction in fruit production. Therefore, the hypothesis underlying this study was that the decline is caused by the cumulative effects of damage by a complex of soil-borne root and collar rot pathogens. Surveys of processing tomato crops were undertaken over three consecutive growing seasons between 2016 and 2019 to investigate the pathogens, symptoms and diseases associated with yield decline. Soil-borne fungal and oomycete pathogens were the focus but bacterial pathogens, viruses, nematodes and phytoplasmas were also noted. Systematic isolation from diseased roots and the collar region of plants putatively infected by fungal and oomycete pathogens was undertaken. Identification of isolates was based on cultural morphology, ITS sequencing and in some cases commercial qPCR testing. Fusarium oxysporum and Pythium spp. were the most abundant putative pathogens associated with plants exhibiting poor growth. Other putative pathogenic fungi and oomycetes which were less commonly encountered included Alternaria spp., Colletotrichum coccodes, Fusarium solani, Phytophthora nictotianae, Phytophthora cajani, Plectosphaerella spp., Rhizoctonia solani, Sclerotinia minor and S. sclerotiorum. A novel Fusarium collar and root rot disease of processing tomatoes was discovered during the surveys. The disease was characterised by chocolate-brown streaking in the internal collar and tap root tissue, as well as lateral root rot of stunted tomato plants. Morphological characterisation and multi-loci phylogenetics (ITS, ef1a and Pgx4), were used to identify the causal pathogen as Fusarium oxysporum. The disease was initially thought to resemble Fusarium Crown and Root Rot (FCRR) caused by Fusarium oxysporum f. sp. radicis-lycopersici (Forl), a disease which has not been reported in Australia. However, subsequent pathogenicity and physiological assessments of isolates suggested the disease was caused by a novel Fusarium pathogen. Consequently, this disease was named chocolate streak disease (CSD) to differentiate it from FCRR. Pythium was the second most abundant organism isolated during the surveys. As Pythium is a large genus consisting of species beneficial, neutral and detrimental to plant growth, further investigation was required to understand the impact of Pythium spp. on processing tomato growth and yield. Eleven species of Pythium were identified based on cultural characteristics and phylogenetic analysis using ITS, Cox-1 and Cox-2 gene sequences. None of these Pythium species had been reported previously from processing or table tomatoes in Australia. In addition, this is the first report of P. carolinianum, P. heterothallicum, P. recalcitrans and a new Pythium sp. from field-grown tomato crops globally. Pythium dissotocum was the most abundant and widespread species. Pythium ultimum, P. aphanidermatum and P. irregulare were the most aggressive towards both seedlings and mature plants, causing pre- and post-germination damping-off, severe root rot and stunting. Collectively, the evidence provided by this study supports the hypothesis that a complex of root and collar rot pathogens, particularly F. oxypsporum and Pythium spp., are contributing to the 10% yield loss in Victorian processing tomatoes.
-
ItemQuantifying fire-severity patterns using optical remote sensing data in temperate eucalypt forests of south-eastern Australia( 2020)Wildfires have significant biophysical and ecological impacts on ecosystems worldwide from local to regional and national scales. The magnitude of such impacts is related to wildfire severity. Recent increases in wildfire occurrence have been associated with climate change, however whether there has also been a change in fire severity remains underexamined in many biomes. Better understanding of fire-severity patterns is required for effective wildfire management, particularly in the fire-prone landscapes of temperate south-eastern Australia, which support a diversity of forests varying in species composition, structure, and post-fire regeneration strategies. Thus, the overarching aims of my Thesis were to accurately quantify wildfire severity at landscape scales and to examine spatial and temporal variation in wildfire severity across a range of forest types in Victoria, south-eastern Australia. To meet the overarching aims, my Thesis involves: (1) identification of optimal optical spectral indices for mapping fire severity across the dominant and most fire-prone forest types in Victoria; (2) a comparison of the accuracy of two different fire-severity mapping approaches, namely single spectral indexing thresholding and machine learning; (3) using the acquired knowledge, the development of fire-severity maps for large (>1000 ha) wildfires occurring in Victoria between 1987 and 2017, and a retrospective analysis of changes in spatial patterns of high-severity fires over that period; and (4) an analysis of the relative importance of four groups of environmental variables (namely fire weather, fuel, topography and climate) as predictors of high-severity fire extent and landscape configuration. My evaluation of remote sensing based spectral indices indicated that the best-performing indices of fire severity varied with forest type and forest functional group, but that there is scope to group forests by structure and fire-regeneration strategy to simplify fire-severity classification in heterogeneous forest landscapes. Results from my comparative analysis confirmed that machine learning outperformed the spectral index thresholding approach for mapping fire severity in most cases, increasing overall accuracy by 11% on a forest-group basis, and 16% on an individual wildfire basis. My results also confirmed that the accuracy achieved with a reduced set of predictor variables that included the previously identified optimal indices of fire severity was not improved by adding more variables. Greater overall accuracies (by 12% on average) were achieved when in-situ data (rather than data from other fires) were used to train the machine-learning algorithm. As such, my study demonstrates the utility of machine-learning algorithms for streamlining a robust fire-severity mapping approach across heterogeneous forested landscapes. Analysis of spatial patterns highlighted that high-severity wildfires in temperate Australian forests have increased in extent and aggregation in recent decades. The total and proportional high-severity burned area increased through time from 1987 to 2017. While the number of high-severity patches per year remained unchanged in that period, the variability in high-severity patch size increased, and high-severity patches became more aggregated and more irregular in shape. Finally, key findings from my models on the relative importance of environmental drivers (climate, fire weather, fuel, and topography) were that fuel type and fire weather were the most important predictors of the extent and configuration of high-severity fires in Australian temperate forests. My Thesis presents one of the most comprehensive analyses of fire-severity patterns from remote sensing data in Australia. My research results support the reliable estimation of wildfire severity from optical images using machine-learning algorithms once optimal spectral indices are identified and when in-situ training data are available for individual fires. Importantly, the quantified shifts in fire regimes across Victoria’s forested landscapes may have critical consequences for ecosystem dynamics, as fire-adapted temperate forests are more likely to be burned at high severities relative to historical ranges, a trend that seems set to continue under projections of a hotter, drier climate in south-eastern Australia. It is therefore critical that forest scientists and land managers continue to acknowledge and quantify changing wildfire-severity patterns so that they are better informed to address the ecological consequences.
-
ItemImplications of plant cell structure and dietary lipids on digestion of polyphenols from black carrots( 2020)Polyphenols are widely studied due to their antioxidant activities with the capacity of preventing the generation of free radicals and reactive oxygen species and are therefore associated with reduced risks of chronic diseases caused by excessive oxidative stress. Matrix factors, including plant structure and interactions between polyphenols and macromolecules from diets play crucial roles in the bioaccessibility, digestion and absorption of polyphenols. While it is known that structural changes of polyphenols occur during digestion, the influence of the dietary matrix is not well understood. This project presents a stepwise approach, using black carrot as a model plant and both in vivo and in vitro digestive models, to understand digestion of phenol-rich plant foods and its effect on gut microbiome composition as well as long-term plasma antioxidant capacity under influence of plant cell structure, polyphenol-lipid interactions and polyphenol structural biotransformation. The results provided a comprehensive view of the digestion of phenol-rich plant in context of a whole diet and implied the significance of matrix factors in polyphenols bioavailability and colonic microbiome response to phenol-rich plant digestion. There has been a lack of standardised measurement of polyphenol activity and structure that can be generally applied to various fruits and vegetables. Here, improved methods of detection of potential antioxidant activity of food substances were modified and standaridsed, using high-throughput 96-well plate assays, and individual polyphenols were separated and quantified using HPLC-PDA and LC-ESI-QTOF/MS. Sixteen plant foods were tested. Factor analysis (FA) and Pearson’s correlation tests showed high correlations among 2,2’-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), 1,1-Diphenyl-2-picryl-hydrazyl (DPPH), ferric reducing antioxidant potential (FRAP) and phenolic acids, implying the comparable capabilities of scavenging the DPPH/ABTS free radicals and reducing ferric ions from the antioxidant compounds in the samples. Developing these assays in high-throughput mode allows various fruits and vegetables of different origins to be analysed. Black carrots, together with other anthocyanin-rich fruits and vegetables, showed high antioxidant activities among the tested plant foods. Bioaccessibility of plant phytochemicals to digestive processes is dependent on the integrity of the plant cell but the fate of phenolic compounds is not well described. An in vitro simulated digestive system was used to detect the bioaccessible antioxidant activities and individual polyphenols of black carrots at gastric, small intestinal and colonic digestive stages via the standardised antioxidant assays and LC-ESI-QTOF/MS. Possible degradation pathways of phenolic compounds were proposed. The majority of polyphenols in black carrots were decomposed through anthocyanin and phenolic acid deglycosylation, and phenyl acids and/or benzoic acids pathways during small intestinal and colonic digestions. Using an in vitro system provided standardised interpretation of the biochemical pathways in digesting plant phytochemicals during digestion. The bioavailability of polyphenols is further affected by plant cell structure and dietary compounds. The effect of plant cell structure (raw carrot dices and cooked puree) and dietary lipids (sunflower oil, beef tallow and coconut oil) on polyphenol bioaccessibility and these effects were next studied by investigating the long-term consumption of phenol-rich plants on plasma total antioxidant capacity (TAC) and atherogenic index (AI) with a whole animal (in vivo) pig model. Processing black carrot to smaller particles and inclusion of dietary lipids, especially coconut oil (rich in medium-chain fatty acids (MCFAs)), significantly increased polyphenols bioaccessibility due to attenuated cell wall trapping and increased structural stability of polyphenols enhanced by phenol-micellised lipids interactions. However, the overall bioaccessibility of polyphenols, especially anthocyanins, were low after small intestinal digestion with only around 5% of cooked puree and around 2% of raw diced carrots bioaccessible due to the low stability of anthocyanins at pH 7. The in vivo pig study verified the low bioavailability of polyphenols in black carrots with diets supplemented with black carrots not showing statistically significant increases in plasma TAC in a porcine model after the 4-week length of the study, although it showed the trend with significantly higher plasma TAC in low-fat diet-carrot puree group compared to that of the groups with high-fat diet control and high-fat diet-carrot dices. However, excessive long-term administration of the high-fat diet induced significantly higher plasma AI. These results indicated that although dietary lipids enhance polyphenols bioaccessibility during digestion, consumption of plant material could not counterbalance the negative impacts from long-term excessive intake of lipids. The effect of dietary supplementation of the plant material on the composition of the gut microbiome and production of short-chain fatty acids (SCFAs) were studied both in vitro and in vivo through 16S rRNA sequencing and GC-FID. Presence of dietary black carrots modulated gut microbiome with increased relative abundances in health beneficial bacteria (including the Prevotella, Prevotellaceae NK3B31 group, and Lactobacillus) were observed after 20 h simulated colonic fermentation in the in vitro model. When lipids were included in the dietary matrix, the effect of black carrot was attenuated with more similar microbiome compositions shown between carrot-lipid matrix and the corresponding lipid control groups. In the pig study, however, limited microbial compositional changes were found in pigs with a high- or low-fat diets when combined with pureed or diced carrot. Influence from other polysaccharides in background diets, genetic backgrounds and colonic milieu of the hosts could have contributed to the gut microbiome resilience to the added polyphenols and dietary fibre. Coconut oil (rich in MCFAs) showed much more significant impacts on gut microbiome modulation in vitro compared to sunflower oil and beef tallow (rich in long-chain polyunsaturated fatty acids (PUFAs) and saturated fatty acids (SFAs) respectively) with an increase relative abundance in colonic pathogenic Escherichia. Higher levels of SCFAs were produced by digesta supplemented with raw diced carrots during in both in vitro and in vivo studies. Limited effects on total SCFAs produced were shown when digesta was supplemented with both sunflower oil and beef tallow, but addition of sunflower oil promoted beneficial butyrate production. Coconut oil showed antibacterial activity with significantly reduced SCFAs production. These results contribute to our knowledge of digestion of phenol-rich plants under the influence from complex dietary mixes and the effect on the vast fermentative diversity of the gut microbiome, which could possibly more accurately simulated and reflected the human colonic status responses to the interventions of daily consumed fruits and vegetables. Overall, this project indicated that the impact of polyphenols in the digestive tract should be considered in the context of plant cellular structure and interactions with dietary macromolecules. Destructed cell walls enhanced the absorption of polyphenols but also reduced the fermentation possible from dietary fibre in the large intestine. Bioavailability of polyphenols from anthocyanin-rich plant foods is low due to structural instability of anthocyanins during digestion. Dietary lipids enhance polyphenols bioaccessibility during digestion, but addition of plant material could not counterbalance the negative impacts from long-term excessive intake of lipids when considering a whole animal model. Coupling phenol-rich plant foods with diets containing low amounts (around 5%) of fat could be a good approach to increase the bioavailability of polyphenols.
-
ItemThe effects of rooting volume, greywater irrigation and reduced sunlight on climbing plants for indirect green façades in urban environments( 2020)Dense urban areas with limited ground space are often deprived of vegetation. By growing climbing plants on buildings as indirect green facades, vegetation can be implemented in a way that uses limited space and seamlessly integrates man-made structures with nature. Benefits of indirect green facades include air purification, noise reduction, micro-climate regulation, provision of natural habitats and improvement of the physical and psychological well-being of urban residents. However, in order to provide effective ecosystem services, indirect green facades need to develop great vegetation coverage to cover buildings, which can be challenging due to small rooting volumes, lack of potable water availability for irrigation and variable light conditions, imposed by site constraints and weight loading of containers on elevated structures. Therefore, it is important to research how indirect green facades can be successfully developed for cities in the presence of unfavorable growing conditions to ensure their sustainability. In this thesis, I have investigated how woody climbing plants respond to different growing conditions by evaluating their morphological and physiological traits. The three objectives of this thesis are: 1. To evaluate the effect of rooting volume on climbing plant growth, coverage and thermal tolerance in the first growing season (Ch 2); 2. To investigate whether greywater is a viable irrigation resource for indirect green facades in cities by assessing changes in substrate chemical properties and the growth response of six climbing plant species (Ch 3); 3. To explore how shade affects leaf traits and thermal tolerance of climbing plant species assisting green facade design and plant selection (Ch 4). In chapter two, to examine the impacts of rooting volume on climbing plant species during the first growing season for their establishments, three rooting volumes (21, 42 and 63 L) were utilised to grow two climbing plant species; the slower-growing Akebia quinata and the faster-growing Pandorea pandorana, on east- and west-facing aspects. It was hypothesised that the reduced rooting volume will adversely affect growth, wall coverage and thermal tolerance of climbing plant species. The smallest rooting volume (21 L) significantly reduced plant biomass growth, specific leaf area and percentage wall coverage for both species over the measured six-month period. Surprisingly, neither climbing plant species significantly increased in growth and vegetation coverage when provided with the largest rooting volume (63 L) as compared with medium rooting volume (42 L). The shoot:root ratio and thermal tolerance of climbing plant species however remained unchanged across three different rooting volumes. A significant decline in the ratio of variable to maximum fluorescence (Fv/Fm) was observed for all climbing plants on the west-facing aspect due to heat stress, irrespective of rooting volume treatment. The outcomes of chapter two suggests that, for a wall area of 2.8 m2 with stainless-steel mesh (1.45 m (W) by 1.95 m (H)), 42 L rooting volume is adequate to support plant growth and coverage of indirect green facades for the first growing season. Practically, for every cubic metre of rooting volume, A. quinata and P. pandorana could approximately achieve 10.2 m2 and 21.3 m2 of wall coverage at the end of the first growing season. In chapter three, an 18-week glasshouse experiment was conducted to evaluate the effects of greywater irrigation on substrate chemical properties (pH and electrical conductivity) and the growth of six climbing plant species. I hypothesised that domestic greywater would change substrate properties by increasing pH and electrical conductivity, and thereby adversely affect the growth and health of climbing plant species. Synthetic greywater formulated to conform with domestic greywater was used in this study. Three irrigation treatments were applied to container-grown climbing plants: (1) potable water irrigation, (2) greywater irrigation, and (3) greywater irrigation with a potable water ‘flushing’ once every three weeks. After 18 weeks, the results showed that substrate pH did not differ among treatments; however, increased substrate electrical conductivity was evident in containers receiving the greywater with potable water flushing treatment. Both greywater treatments had no significantly detrimental effects on plant biomass, leaf area, gas exchange rates, or water use when compared with potable water irrigation. The outcomes indicated that domestic greywater can be safely used to irrigate climbing plants for indirect green facades, reducing the need for the use of potable water and supporting more sustainable design of indirect green facades in urban environments. In chapter four, a 15-week field experiment was designed to assess how seven climbing plant species respond to changing light conditions from full-sun to shade, with respect to the adjustment in leaf morphology, physiology, and photochemistry for mature plants. The hypotheses were (1) a change from sun to shade will increase specific leaf area (SLA), leaf expansion rate, and chlorophyll content of climbing plants; whilst decreasing leaf photosynthetic rate (A1500), stomatal conductance (gs), light compensation point (LCP) and thermal tolerance (T50), and (2) deciduous climbing plant species will be more plastic (greater changes in morphology and physiology) in response to shade than evergreen species. Significant increases in SLA, and unchanged gs, LCPs and T50 were observed in all seven climbing species after being provided shady conditions. In contrast, the variation in species response to reduced light intensity levels was evident in leaf expansion rates, A1500 and Chl a+b. Leaf expansion rate and A1500 remained unchanged for most of the climbing plant species by the shade treatment. However, significant increases in leaf expansion rate were observed in evergreen Gelsemium sempervirens and Jasminum azoricum. In addition, significant decreases in A1500 were recorded in deciduous Ampelopsis brevipedunculata and Vitis ‘Ganzin Glory’ as well as evergreen Pandorea pandorana under the shade treatment. On the other hand, leaf Chl a+b was significantly increased in most of the climbing plant species by the shade treatment, except for deciduous V. ‘Ganzin Glory’ and evergreen G. sempervirens. Irrespective of light intensity levels, deciduous climbing plant species displayed significantly greater SLA, leaf expansion rates, A1500, gs, and Chl a+b, whilst lower LCP than evergreen species in this study. On the contrary, deciduous climbing plant species were not more plastic than evergreen species in the overall response to the reduced light intensity levels. However, a greater reduction in A1500 in response to shade was observed in deciduous climbing species as compared with evergreen species. The findings of chapter four demonstrated that these seven climbing plant species can maintain growth and health by adjusting leaf morphology and physiology when experienced changing light conditions from full-sun to shade. The findings suggested that the seven climbing plant species can maintain or increase vegetation wall coverage and provide ecosystem service benefits in cities with variable light conditions. Overall, this thesis has indicated that climbing plants can grow successfully with relatively small substrate volume (42 L). It was also shown that a lower limit exists for the rooting volume required to support the early growth and vegetation wall coverage of indirect green facade climbing plants. This thesis also raises the possibility that domestic greywater can replace potable water irrigation of building indirect green facades in urban environments, as there was no deleterious effect on either substrate properties or climbing plant growth. Furthermore, the seven climbing species evaluated in this thesis all could adapt to the changing light conditions from full-sun to shade by adjusting leaf traits to maintain growth (leaf expansion). Despite the limitation noted in rooting volume, woody climbing plant species were quite resilient and adaptable to the different growing conditions evaluated in this thesis. This would likely enable them to maintain their function and performance and thereby continue to deliver ecosystem services under fast-changing urban environments. The findings of this thesis have significant implications for the understanding of how woody climbing plants respond to potentially unfavorable growing conditions, providing insights into plant selection for indirect green facades in urban environments. This thesis further supports the possibility to implement indirect green facades as an integrated approach of sustainable urban greening and water management on high-rise buildings. Further research should be undertaken however with a longer experimental period (beyond six months), the inclusion of more climbing plant species and field studies (i.e., existing indirect green facades on buildings). The research should also be conducted with the inclusion of different types of substrates with the application of on-site greywater and various light intensity levels (e.g., lower or higher).
-
ItemMicrowave and biochar soil treatment alleviates arsenic phytotoxicity in wheat and rice( 2020)Abstract Arsenic (As) is a toxic metalloid, which is carcinogenic i.e. cancerous to humans. Besides the drinking water, accumulation of As in food grains through plant uptake, when cultivated in As contaminated soils, is a potential route of human dietary As exposure. This has inspired research into alleviating grain As accumulation, despite there being already existing strategies with major disadvantages such as low efficiency, high costs, and usage being restricted to smaller-scale operations. Therefore, pre-sowing microwave (MW) soil heating and sawdust biochar were used to investigate if they can reduce As concentration in wheat and rice. Microwave is a form of electromagnetic radiation, which can produce heat in the soil by inducing the rotation of the dipoles of polar molecules (e.g. water). Microwave heating depends on the dielectric properties of the soil. Therefore, a study was conducted to determine the dielectric properties of different types of soils with different moisture content. The results showed that the soil moisture was the major contributor to the dielectric behavior of soil since dielectric properties increase as soil moisture increases. Soil types also had an influence as the dielectric properties of sandy soil were much lower than the other soils such as clay and loam soil. To investigate the effect of MW and biochar on wheat and rice grain As concentration, both the wheat and rice soils were spiked with five As concentrations (As-0, As-20, As-40, As-60, and As-80 mg kg-1 soil). In addition to MW, biochar was used to reduce rice grain As accumulation since biochar has been gaining attention for its heavy metal immobilization capacity. After As application, three levels of biochar (BC-0, BC-10, and BC-20 t ha-1 soil) were added only in the rice-growing soil. Then, soils were treated for 0, 3, and 6 minutes (MW-0, MW-3, and MW-6) in an MW chamber to achieve the soil temperature of around room temperature, 60 oC, and 90 oC respectively. The crops were grown in a completely randomized design with four replications in a glasshouse during 2017 (wheat) and 2018 (rice). The results demonstrated that, in both the wheat and rice, MW soil treatments, especially the MW-6, alleviated As phytotoxicity and facilitated less grain total As concentration compared with the MW-0 treatment across all the soil As concentrations. Also, MW treatment significantly reduced the concentration of arsenite [As(III)], the most toxic form of As. Decreased grain As concentration in rice was recorded at BC-10 in lower levels of soil As concentrations (As-20 and As-40) while, a negative impact was observed at BC-20 across all the soil As concentration, compared with BC-0 treatment. Furthermore, rice grain As(III) concentration increased significantly in BC-20 treatment. Thus, MW-6 treatment could be used for the alleviation of grain As concentration in wheat and rice grain, whereas more study is needed for the best biochar application rate. However, understanding the residual effect of MW and biochar is crucial for the sustainability of the treatment. Therefore, the same varieties of wheat and rice were grown in the following year, using the same pots, without the addition of further MW or biochar treatment. The results revealed that, 360 days after MW soil treatments there was still the potential to alleviate grain As concentration in both wheat and rice. A similar result was observed for biochar treatment in the residual year with a positive effect at BC-10 and a negative effect at BC-20 treatment. Furthermore, it is unclear whether MW soil treatment is just a heating effect or if there is some other effect of the electromagnetic wave involved. Therefore, a glasshouse pot study was designed to investigate the effect of MW and conventional electric oven (EO) soil heating on As phytotoxicity alleviation in rice. The soil was spiked with three levels of soil As concentration (As-0, As-40, and As-80 mg kg-1) prior to applying MW and EO heat treatments, to achieve the soil temperature of around 80 - 90 oC. The results showed that, there was no statistically significant difference between MW and EO treatments regarding As phytotoxicity alleviation. However, the positive effect was more in MW treatment than the EO treatment. Significantly less total energy required in the MW to treat the soil than the EO. Besides the As phytotoxicity alleviation, the effect of MW soil heating on soil microorganisms, particularly bacteria, was a topmost concern and investigation was needed to ascertain that MW soil heating does not affect it drastically. Therefore, an experiment was designed to investigate the effect of MW heating (80 - 90 oC) on the soil bacterial community in As contaminated (As-0, As-40, and As-80 mg kg-1 soil) soils. The 16S rRNA bacterial gene copy numbers decreased significantly after MW soil heating but recovered back to its previous number 42 days post treatment. The bacterial diversity also decreased significantly in MW treated soils but did not recover even after 56 days from MW heating. However, there was no noticeable effects of soil As concentration on bacterial community were observed. Furthermore, relative abundance of some beneficial bacteria such as Bacillus and Symbiobacterium were significantly higher in the MW treated soils. Thus, MW soil heating at 80 - 90 oC can potentially be applied for As phytotoxicity alleviation without significantly destroying the ecologically important taxa. Overall, pre-sowing MW soil heating could be applied as a novel technique to alleviate As phytotoxicity in wheat and rice with lower As accumulation in the grain. Thus, application of the MW technology in the As contaminated area like Bangladesh could add another feather in the crown of the As remediation techniques and help to reduce the human health risk through As contaminated food grain. However, further research needed before adopting the MW soil heating technique where different aspects should be explored such as response of MW technology in the field condition, scaling up the MW equipment for field application, cost of MW application in the field at farmers level, long-term effect of MW treatment on soil nutrient dynamics, soil organic matter and soil biota and sustainability of the MW technology in field condition. Also, sawdust biochar could be used in combination with MW soil heating for As phytotoxicity alleviation; however, more study needed to set the appropriate rate of biochar application.
-
ItemDivergence in forest structure and evapotranspiration over a chronosequence between Eucalyptus regnans and Acacia dealbata( 2020)Abstract Climate-induced changes in fire regimes in south east Australia have the potential to alter ecosystem and ecohydrological resilience in native Eucalyptus forests. A drier, hotter climate is triggering short-return, high-intensity, mega-fire events across Australia. In Victoria, over 189,000 ha of fire-sensitive, Eucalyptus regnans and Eucalyptus delegatensis forests have been burned two or more times within the past 18-years. Under these multiple burn conditions, fire-sensitive forests are highly vulnerable to ecological tipping points. Naturally occurring E. regnans is a dominant species in the higher rainfall regions of south east Australia. However, short interval fires (15-20 years) hinder the regeneration potential of this serotinous, obligate-seeder species, which then allows fast-growing, co-occurring understorey species such as Acacia dealbata to replace E. regnans as the dominant forest type. Replacing long-lived E. regnans forests (250-300 years) with short-lived A. dealbata (80-90 years) may have significant ecohydrological implications in water supply catchments. A bottom-up, plot-based approach was used to measure Et in typical E. regnans and A. dealbata forests of various ages to develop empirical models of the hydrological response of forested water catchments to vegetation change. Field-based measurements of the various components of Et were taken from 10, 35 and 75/80-years old stands of each forest type. A forest inventory survey was carried out to quantify structural trajectories, including stand mean dbh, stand basal area and stand sapwood area in the two forest types. Transpiration was measured at the field using the heat ratio method together with micrometeorological conditions in the two forests. Throughfall, stem flow and evaporation from the forest floor were measured across the age sequence of each forest type. Throughout this research, eco-hydrologic processes along the chronosequence are modelled and then compared between the life cycles of E. regnans and A. dealbata forests. Regeneration response to fire and ecohydrological properties of both forest types were similar during the initial stage of stand development up to age 10. However, stand structure, including mean stem diameter, basal area, stocking density and sapwood area, begins to diverge significantly between the two forest types after age 20. In both forest types, sapwood area reduces with stand age after age 20, but at a faster rate in A.dealbata. Once the forest structure starts to diverge, overstorey transpiration, overstorey Et and total Et of the two forest types also begin to diverge, driven primarily by divergence in sapwood area. In addition, mean sap velocity averaged for the 20, 35- and 75-80-years age classes was about 34% higher in E. regnans, although the difference was only statistically significant at age 20. This suggests that differences in sap velocity between the two forests also partly explained the divergence in overstorey Et between the two forest types. VPD is the strongest predictor of sap velocity in both forest types under non-water limited conditions. Daily sap velocity model for E. regnans could be further modified by accounting for forest age. The results provide a strong indication that after age 20, overstorey transpiration in Acacia-dominated forests is substantially lower than in the E. regnans forests they replace. Therefore, overstorey transpiration was the primary driver of differences in total Et between the two forest types, followed by differences in canopy interception. Soil evaporation contributed only 3% to the differences in Et between the two forest types. Differences in Et partitioning between the two forest types imply a link between forest structure and the forest water budget. In senescing A. dealbata, understorey transpiration contribution of 29.8% to system Et was similar to that of overstorey transpiration (31.2%), indicating the understorey and overstorey contribute equally to total Et at the final stage of Acacia forests. This suggests that, after the Acacia life cycle finishes, the Et regime will transit into a new state that will be dominated by shrubby understorey species. The findings of this research suggest that climate-driven high-frequency wildfires alter the composition and structure of E. regnans forest as a result of a change in the dominant overstorey species from E. regnans to A. dealbata. This species shift alters forest hydrological parameters, especially mean sap velocity and sapwood area, leading to changes in eco-hydrologic processes in the forest. These results highlight that species shift due to climate change can have important ecohydrological implications, resulting in evapotranspiration regime shift. Further, the present research suggests that climate-related species change from E. regnans to A. dealbata will alter the hydrologic response of water supply catchments. This type of eco-hydrologic response may be played out in many ecosystems in the future. By considering all studied changes in forest structure, evapotranspiration and water yield, this climate-induced species replacement is an ecologically significant vegetation change in the native E. regnans forests, reflecting extensive hydrological implications for the water supply catchments.