School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemExploring the indirect effects of climate change on fire activity in Australian wet Eucalypt forests( 2022)Understanding the impacts of climate change on future fire activity is critical for assessing the risks posed to biodiversity and communities. However, the mechanisms through which climate change may influence fire activity are varied. In temperate forests, climate change is expected to directly increase fire activity through elevated temperatures and more variable rainfall, resulting in weather conditions conducive to large fire events. However, climate change may indirectly influence fire activity through effects on forest structure and composition. While the direct effects of climate change are well studied, indirect mechanisms are poorly understood. These mechanisms are important because changes to vegetation structure and composition have the potential to amplify or dampen the direct effects of climate change on fire activity through their effects on fuels, particularly dead fuel moisture content (FMC). Forest structure and composition moderate microclimate conditions compared to the open, which is an important factor affecting the moisture content of understorey fuels. FMC is a key determinant of fire activity, particularly in wet Eucalypt forests with high biomass loads. However, our understanding of the magnitude of forest structure and composition effects on microclimate and subsequently FMC dynamics, is a critical knowledge gap in our understanding of climate change effects on future fire activity more broadly. In this thesis, I aimed to quantify the potential for indirect effects of climate change to influence fire activity, through their influence on dead FMC in the wet Eucalypt forests of south-eastern (SE) Australia. In these forests, recurrent high-intensity fire has altered vegetation structure and composition, resulting in a range of alternative forest states to the dominant wet Eucalypt system. To quantify the magnitude of these on potential fire activity, seven alternative forest states and two adjacent open weather stations were instrumented with automated fuel moisture sticks and micrometeorological sensors. FMC and microclimate were measured over a 2-year observation period, and lidar data were used to evaluate the role of forest structure in FMC dynamics. I used a process-based fuel moisture stick model to quantify the relative importance of forest structure effects on microclimate to FMC variability. This model was then used in conjunction with new methods to estimate microclimate from open conditions, and a 48-year climate dataset to model FMC at alternative forest states across the range of climate conditions characteristic to the region. I also evaluated the potential contribution of live species to changes in fuel moisture in a conifer forest and related this to the potential impacts of forest conversion to alternative states. Overall, I found significant differences in dead FMC across alternative forest states, with potentially meaningful implications for fire activity. The sensitivity of FMC to forest structure was examined, with longwave radiation and vapor pressure deficit emerging as key drivers of FMC variability related to structural change. These findings informed the modelling process, where results indicated that differences in FMC related to alternative forest state were greater than the direct effects of climate change (modelled at an open reference site), indicating strong positive and negative feedback processes in this system. Overall, my results suggest that the indirect effects of climate change on potential fire activity are meaningful for fire management, exceeding the role of direct effects in the context of FMC. Consequently, the potential for forests to convert to alternative states is a key issue for land and fire managers.
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ItemDynamics of a flammable species in a forest landscape: A case study on forest wiregrass Tetrarrhena juncea R.Br.( 2022)Species abundance often determines the extent of influence of a species to ecosystem function and processes. Typically, the abundance of a species is constrained by environmental factors within its habitat. However, there are instances where native species becomes prolific and the shift in abundance greatly impacts the ecosystem. Such is the case when a flammable species becomes prolific within its range and alters the flammability of the ecosystem. This is a concern with climate change, as conditions might be tipped in favour of such species. Hence, it is crucial to understand the drivers of abundance to understand how native species can be released from environmental constraints of abundance to become prolific within their own range, and to predict the potential effect of changing environmental conditions on their abundance. Thus, the overarching aim of this thesis was to understand how a flammable native species can become prolific within its own range. This is achieved using a case study species – forest wiregrass Tetrarrhena juncea R.Br. (hereafter wiregrass) – an understorey native species that is of high importance to flammability in the eucalypts forests of south-eastern Australia and grows prolifically under certain conditions. The overarching aim of the thesis was addressed using a mix of research methods to identify the key drivers of wiregrass distribution and abundance. Firstly, a database of the current distribution for wiregrass were analysed using species distribution modelling to identify highly suitable habitat for wiregrass (Chapter 2). Temperature seasonality, precipitation of the driest month, rainfall seasonality, annual mean temperature, the minimum temperature of the coldest month and soil pH were strongly associated with the suitable habitat of wiregrass. The high importance of climatic factors indicates the distribution of wiregrass may be sensitive to climate change. Highly suitable habitats do not necessarily harbor abundant wiregrass because site-specific factors can also control abundance. Hence, Chapter 3 sought to identify the factors most important to wiregrass abundance in the highly suitable habitat of Mountain Ash-dominated forest. Wiregrass cover was assessed in a field survey across a chrono-sequence of 126 sites with contrasting disturbance histories. Canopy cover and net solar radiation were the most important predictors of wiregrass abundance, with wiregrass cover highest in recently disturbed areas with sparse canopy cover, high light levels, and low precipitation. The final component of the thesis used a glasshouse experiment to quantify causal links between resource availability and wiregrass abundance. Wiregrass growth was more sensitive to water availability than light, whereas biomass allocation and leaf morphology were more sensitive to light availability. Collectively, the results showed that, where wiregrass is present (distribution), three key conditions will greatly favour its prolific growth (abundance): (i) non-limiting water resource; (ii) reduced canopy cover and increased light; and (iii) recent disturbance. These key results strongly suggest wiregrass can become prolific when resources are increased, and the vegetation community is substantially disturbed. Under such conditions, increased wiregrass abundance could create a window of increased flammability for the forest ecosystem. Since climate change can alter resource availability and disturbance regime, shifts in wiregrass abundance are likely to occur under future climate scenarios.
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ItemPredicting future fire regimes and the implications for biodiversity in temperate forest ecosystems( 2022)Fire regimes are changing around the world. Fire seasons are lengthening, high severity fires are occurring more often and in unexpected places. Relationships among fire, climate, and vegetation are varied, dynamic, and under-examined in many ecosystems. While some studies have explored links between fire, climate, and vegetation such as species distributions or future fire weather under changing climate, relatively few have considered the dynamic interactions among all three simultaneously. In this thesis, I develop and apply modelling approaches to predict future fire regimes in south-eastern Australia and explore the implications for fire-responsive functional plant types. In the first quantitative chapter of my thesis (Chapter 2), I develop a new fuel model for south-eastern Australia. I use edaphic, climatic, and fire variables to build a predictive fuel model that is independent of vegetation classes and their future distributions. In Chapter 3, I use my fuel model in a landscape fire regime simulator, alongside multiple predictions of future climate, to examine the immaturity risk to an obligate seeder tree species (Eucalyptus delegatensis). My simulations indicate that this species will be under increased immaturity risk under future fire regimes, particularly for those stands located on the periphery of the current distribution, closer to roads or surrounded by a drier landscape at lower elevations. In Chapter 4, I expand the application of the above simulation approach to examine the relative importance of future fuel and future climate to changing fire regimes in six case study areas across temperate south-eastern Australia. My results indicate that the direct influence of climate on fire weather will be the principal driver of changes in future fire regimes (most commonly involving increased extent, decreased intervals, and an earlier start to the fire season). The indirect influence of climate on vegetation and therefore fuel was also important, acting synergistically or antagonistically with weather depending on the area and the fire regime attribute. Finally, in my fifth chapter, I consider future climate and fire impacts on plant persistence by combining the landscape fire regime simulator with spatially explicit population viability analyses. Obligate seeder species were at risk of population extinction or reduction in more simulation scenarios than facultative resprouters. However, my approach highlighted that the resilience of facultative resprouters might also be tested by climate related changes in demographic processes and fire regimes. Overall, my research has provided new methods and scientific insights into the changing nature of fire regimes in temperate south-eastern Australia. Some negative impacts on biodiversity from a changing fire regime, particularly on more vulnerable plant functional types like obligate seeders, appear inevitable. Further understanding of the complex interactions among fire, climate, and vegetation will enable improved integration of risks to people, property, and biodiversity into land and fire management planning.
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ItemFinding the hidden smoke: Exploring the use of digital technologies for assessing grapevine smoke contamination and taint in grapes and wine( 2021)Grapevine smoke contamination and the subsequent development of smoke taint in wine has resulted in significant financial losses for winemakers throughout the world. Unfortunately, the incidence of grapevine smoke exposure is expected to rise as the number and intensity of wildfires increase due to the effects of climate change. Wines produced from smoke affected grapes are characterised by unpleasant smoky aromas, rendering them unpalatable and therefore unprofitable. Traditionally, chromatographic techniques such as gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC) have been used for assessing the levels of smoke-derived volatile phenols and their glycoconjugates in grapes and wine. However, these methods are time consuming, expensive and require destructive sample preparation as well as the use of trained personnel. Furthermore, sensory evaluation of wine samples using human panels may be subject to bias due to individual variability of the participants, as well as being expensive and time consuming as large groups of participants must be recruited and trained. In addition to this, a number of methods have been identified for ameliorating smoke taint in wine such as the use of activated carbon and reverse osmosis. While effective at reducing levels of volatile phenols for smoke taint amelioration, they are unable to act on glycoconjugates, and therefore a gradual resurgence of smoky aromas may arise as these glycoconjugates are hydrolysed back into their free active forms over time. This research therefore investigated alternative methods for assessing the degree of grapevine smoke exposure and the level of smoke taint in wine using digital technologies coupled with machine learning (ML) modelling based on artificial neural networks (ANN), and whether the use of a cleaving enzyme prior to the addition of activated carbon could be effective at ameliorating smoke taint in wine. Near-infrared (NIR) spectroscopy was used to obtain a chemical fingerprint of grape berries, leaves, must and wine. These readings were then used as inputs to develop ANN models that showed high accuracy in the classification of berries and leaves according to the level of smoke exposure and degree of taint (97% – 98%), as well as predicting the levels of smoke-derived volatile phenols and their glycoconjugates in grapes, must and wine (R = 0.98 – 0.99). Additionally, models predicting consumer responses towards smoke tainted wines using NIR berry and wine spectral readings were created which displayed high accuracy in their predictive abilities (R = 0.97 – 0.98). The results demonstrated that NIR spectroscopy coupled with ML modelling can provide accurate, rapid and non-destructive tools for assessing grapevine smoke contamination and smoke taint in wine, in addition to predicting the sensory responses of consumers towards smoke tainted wines. Furthermore, the models developed can be used together to form an integrated smoke taint detection system that growers and winemakers can use in-field or in the winery to assess grapes and wine. A low-cost electronic nose (E-nose) was used to assess the aroma potential of smoke-tainted wines. Readings from the e-nose were used as inputs to develop ML models that showed high accuracy in predicting the levels of eight volatile aromatic compounds in wine (R = 0.99), the degree of smoke aroma intensity (R = 0.97). These two models may be used together with previously developed models that predict the levels of smoke-derived volatile phenols and their glycoconjugates and 12 wine descriptors to provide winemakers with a greater picture of the degree of smoke taint and the aroma profiles of smoke-tainted wines. In addition to this, the use of a cleaving enzyme (ZIMAROM, Enologica Vason) prior to treatment with activated carbon was found to be effective in ameliorating smoke taint and may help delay the resurgence of smoky aromas by hydrolysing glycoconjugates into their free volatile phenol forms which can then be removed by the addition of activated carbon. An ANN model displaying high accuracy (98%) was also developed using the readings from the e-nose to classify wine samples according to the type of smoke-taint amelioration treatment applied to assess their effectiveness. The model may offer winemakers a cost-effective, non-destructive, rapid, and accurate tool to assess the effectiveness of smoke taint amelioration treatment by activated carbon with/without the addition of a cleaving enzyme.
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ItemRegime resistance and accommodation in sustainable energy transitions( 2020)To help accelerate the decarbonisation of electricity generation and meaningfully mitigate climate change, a more nuanced understanding of the power and influence of incumbent electricity firms in government policymaking is required. Building on sustainability transitions literature, concepts from neo-Gramscian political economy and insights from strategic management, this study investigated the ways in which incumbent electricity generators, network operators, retailers, and their industry organisations sought to influence residential solar power policy. The single case study is focused on Victoria, Australia, using data obtained from multiple sources, including: legislation; policy submissions, reports and documents; organisational documents and materials; media releases and articles; and transcripts of in-depth, semi-structured interviews with key informants from electricity utilities and their industry peak bodies. The study examined federal and state government policy instruments that supported the installation of residential solar power before it explored attempts by incumbent electricity firms and their industry organisations to influence the development of Victorian feed-in tariffs, the State Government’s primary policy instrument. The research found that incumbent actors contributed to the (re)production of a socio-technical regime by drawing on material, institutional and discursive forms of power to execute strategies of resistance and accommodation. Incumbent actors resisted feed-in tariffs by discussing them in negative terms, building alliances with opposed civil society organisations, lobbying policymakers and reminding them of their mutually dependent relationship. However, incumbent actors accommodated feed-in tariffs by working with government to implement its policy initiatives. Incumbent firms accommodated renewables more generally by operating renewable energy business units and joining renewable energy industry organisations, although the later served to moderate support for feed-in tariffs. The study also found that a number of external and internal factors shaped the strategic approach of incumbent electricity firms and limited the extent of their resistance. High public support for residential solar power and strong government determination to implement feed-in tariffs were key external factors that discouraged greater resistance from incumbent firms. Key internal factors included the assessment of feed-in tariffs as low risk to the ongoing profitability of incumbent firms, and higher policy priorities, the achievement of which necessitated good relations with government and the sacrifice of lower policy priorities. These findings suggest that a neo-Gramscian approach to understanding politics and power in sustainable energy transitions offers useful insights for policymakers, incumbent and renewable energy firms, and civil society organisations who seek to accelerate the decarbonisation of electricity generation.
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ItemEffect of elevated carbon dioxide and high temperature on major micronutrients in strawberry( 2019)In this study, four different folate derivatives (tetrahydrofolic acid – THFA, 10-formylfolic acid – 10FFA, 5-formyltetrahydrofolic acid – 5FTHFA, 5-methytetrahydrofolic acid (5MTHFA)) were identified in fresh and freeze-dried strawberry samples. The individual and interaction effects of increased [CO2] and temperature on total folates content were significant (P≤0.05), and the responses were cultivar dependant. Total folate content in strawberries varied from 52.6 ± 5.1 µg to 364.8 ± 16.0 µg/100 g FW in cultivar ‘Albion’ and from 48.6 ± 7.0 µg to 237.4 ± 23.8 µg/100 g FW in cultivar ‘San Andreas’. Although, increased temperature positively affected the total folates content under lower [CO2] levels, the effects turned negative at the highest [CO2] concentration (950 pm). Higher temperature reduced the content of total folates in strawberries by 26% and 13% in cultivar ‘Albion’ and ‘San Andreas’, respectively. Impacts of elevated [CO2], higher temperature and their interactions on total vitamin C content in strawberries were statistically significant (P≤0.05) and the responses were cultivar dependent. Vitamin C contents in cultivar ‘Albion’ and ‘SA’ fresh strawberries were in a range of 59 ± 7 mg to 133 ± 15 mg/100 g FW and 56 ± 9 mg to 132 ± 9 mg/100 g FW, respectively. Increased growth temperature to 30 °C at 650 ppm [CO2] enhanced the amounts of vitamin C significantly (P≤0.05) to a maximum by 123% and 132% in cultivars ‘Albion’ and ‘San Andreas’, respectively. However, that effect wasn’t detected when the CO2 concentration was increased further to 950 ppm, and vitamin C concentrations drastically decreased by 36% and 31% in Albion’ and ‘San Andreas’, respectively. In general, folates and vitamin C contents were significantly (P≤0.05) higher in FD strawberry than fresh fruits. The next step of the study was to study the accessibility of increased polyphenols, vitamin C and folates in the fruits of fresh and frozen strawberries using simulated in vitro gastrointestinal digestion and colonic fermentation. Elevated [CO2] (ambient to 950 ppm) and higher temperature (ambient to 30 °C) enhanced the accessibility of polyphenols, folate and vitamin C in strawberries. Bioaccessibility of Pel-3-Glu increased from 67% to 88% in fresh strawberries when exposed to elevated growth. The exact amounts of individual polyphenols in accessible fraction were significantly (P≤0.05) higher in fresh fruits of strawberries grown under elevated growth conditions. For example, the highest amounts of Pel-3-Glu (19.89±0.4 mg/100 g FW), Pel-3-Rut (2.55±0.5 mg/100 g FW), p-coumaric (0.23±0.02 mg/100 g FW), ferulic (1.33±0.05 mg / 100 g FW), quercetin (1.97±0.2 mg/100 g FW) and p- coumaroyl (0.65±0.05 mg/100 g FW) were detected in fed state simulated gastrointestinal digesta of fresh strawberry grown under elevated growth conditions. Fresh strawberries grown under ambient growth contained 93.09±6.2 µg/100g folates and 18.55±0.5 mg/100g vitamin C as bioaccessible fractions under fed state while, elevated growth enhanced soluble folates and vitamin C up to 188.63±7.5 µg/100g and 30.48±0.3 mg/100g, respectively. Fresh strawberries contained higher amounts of accessible micronutrients than frozen strawberries, while increased bile contents in intestinal fluid (fed state) facilitated the release of bioactive compounds to gastrointestinal fluid. The insoluble fraction of strawberry digests after gastrointestinal digestion was then subjected to in vitro colonic fermentation using human faecal cultures and basal media. The soluble fraction of fermented strawberry digests was extracted to analyse polyphenols, folates and vitamin C. Higher contents of folate (7.90±0.05 µg/100 g FW), vitamin C (33.6±1.0 ng/100 g FW), Pel-3-Glu (2.00±0.14 mg/100 g FW), and p-coumaric (39±5 µg/100 g FW) were observed in soluble fraction of fermented precipitate after simulated gastrointestinal digestion at fasted state in frozen strawberries. These bioactive compounds and their metabolites would play an important role in the human colon by maintaining a healthy environment via scavenging the free radicals. According to the current study, the amount of bioaccessible bioactive compounds in strawberry could vary quantitatively and qualitatively based on growth and storage conditions as well as the status of digestion (fed or fasted state). Increased carbon dioxide and temperature in the growth environment enhanced the bioaccessibility of polyphenols, folates and vitamin C in strawberries. It can be concluded that strawberry fruits grown under elevated [CO2] and temperature may not be visually attractive comparing to normal strawberries. However, considering their nutritional value, those fruits can be promoted as freeze-dried strawberry in value added foods such as dairy products. Additionally, these research outcomes would help the commercial growers to focus on the nutritional aspects of fruits and vegetables grown under such elevated and extreme environmental conditions in the future. However, as a very little information is available concerning the interactive effects of elevated [CO2] and high temperature on fruits and vegetables in the field, more researches are needed to confirm the results from glasshouse studies.
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ItemBiochemical and physiological mechanisms of legume nitrogen fixation under higher atmospheric CO2 concentrations( 2019)Atmospheric CO2 concentration ([CO2]) is expected to rise from a current level of ~400 to 550 µmol mol-1 by 2050. It is well established that elevated [CO2] enhances plant growth and yield. However, the stimulation of plant growth at elevated [CO2] requires additional nitrogen (N) and prolonged exposure to elevated [CO2] potentially risks N limitation. Legumes can overcome such limitations by fixing aerial N. Previous studies under Free Air CO2 Enrichment (FACE) have shown that elevated [CO2] can stimulate N2 fixation, but it is unknown to what extent this applies to dryland Mediterranean environments or what impact environmental interactions have. Legumes grown in dryland environments frequently experience terminal drought accompanied by high temperature during reproductive phases. It has been suggested that elevated [CO2] delays the effect of drought by conserving soil water, maintaining N2 fixation mechanisms for longer under drought. This thesis addresses this gap by investigating the growth and N economy of three legumes (lentil, field pea and faba bean) in a FACE facility in a semi-arid environment where seasonal and experimentally controlled drought was imposed. In addition to N2 fixation itself, the supply and translocation of N compounds to the maturing grain is another point of interest, because it is crucial in maintaining grain N concentration. This thesis investigated N2 fixation, remobilization and grain quality of dryland legumes under predicted future e[CO2] atmosphere conditions, including interactions with drought, heat waves, and genotypes. Free Air CO2 Enrichment technology was used to simulate future growing conditions in the field with target [CO2] as expected by the middle of this century. Elevated [CO2] stimulated N2 fixation through increased nodule number, nodule biomass, and nodule activity to a greater extent under unstressed conditions. Soil water savings under elevated [CO2] were only temporary, so that drought reduced nodule activity due to lower C/sucrose supply and therefore decreased N2 fixation. Consequently, elevated [CO2] was found to stimulate N2 fixation of all three species of legumes, but this effect was smaller under drought or heat stress. The decrease of N2 fixation under drought caused depletion of grain N concentration under elevated [CO2]. In contrast, when soil water was sufficient, N2 fixation continued throughout the grain filling period, and grain N concentration was maintained under elevated [CO2]. Traits that allow N2 fixation for longer throughout the growing season, e. g. by exploiting potential water savings mechanisms under elevated [CO2], may confer benefits under future climatic conditions. Findings of this study are now available to underpin new strategies for improvement of the N2 fixation potential of legumes as atmospheric [CO2] continues to increase in the future.
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ItemFunctional aspects of root and leaf development in dryland crop water use under elevated CO2( 2018)Atmospheric CO2 concentration ([CO2]) is rising due to anthropogenic activities and is expected to reach ~550 μmol mol-1 by 2050 and exceed ~700 μmol mol-1 by the end of this century. As the main substrate of photosynthesis, this rising [CO2] has direct implications for plant metabolism, such as stimulating net photosynthetic CO2 assimilation rate (Anet) in C3 crops and leading to greater biomass production and yield through the so-called ‘CO2 fertilisation effect’. In addition, elevated [CO2] (e[CO2]) lowers stomatal conductance (gs), and thus may reduce transpiration rate. Increased assimilation and lower transpiration result in higher leaf-level water use efficiency, which lead to the assumption that crop water use will be lower under e[CO2]. On the other hand, e[CO2] increases leaf area, which tends to increase transpiration and therefore canopy water use. Therefore, the net response of crop water use to e[CO2] is dependent on the balance between e[CO2]-induced reduction of gs and e[CO2]-induced stimulation of transpiring leaf area. These responses under e[CO2] are further complicated by other environmental variables and growing conditions. The response of crop water use to e[CO2] will be of particular interest for dryland agriculture, where water is nearly always the most limiting factor for crop production. This project investigated the functional aspects of root and leaf development on water use of dryland wheat (Triticum aestivum L.) and canola (Brassica napus L.) under a future e[CO2] using experiments with different water and nitrogen regimes, soil types and cultivars. Free Air CO2 Enrichment (FACE) technology was used to simulate future growing conditions in the field with a target atmospheric [CO2] expected by the middle of this century. This was supplemented by glasshouse studies to investigate crop physiological response to e[CO2] under more controlled conditions. Increased leaf-level water use efficiency under e[CO2] stimulated biomass and yield per unit water used, but this commonly resulted in little change in seasonal water use in this dryland, terminal drought environment. However, the dynamics of crop water use during the growing season varied depending on [CO2], whereby early in the season greater stimulation of leaf growth counteracted the increased leaf-level water use efficiency and resulted in greater water use under e[CO2] relative to a[CO2]. Under field conditions, the accumulated water use at the end of the season was then similar both under a[CO2] and e[CO2], pointing to the overriding effect of the seasonal conditions. Under water-limited conditions, e[CO2]-induced stimulation of root growth especially in the deeper soil layers maintained plant physiological processes by improving access to deeper soil water. This greater assimilation rate later in the season ensured better assimilate supply to the developing grains, which resulted in better yield benefits from the ‘CO2 fertilisation effect’. In addition, this thesis shows that interactions between growing conditions (experimental water and N regimes) and expression of genotypic traits (cultivars contrasting in vigour, transpiration efficiency and N use efficiency) play a decisive role in determining potential biomass and yield benefits from rising [CO2]. Observed genotypic variability in response to e[CO2] suggests a potential breeding opportunity to maximise the benefit from ‘CO2 fertilisation effect’.
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ItemThe economic impact of climate change on perennial crops: the coconut industry in Sri Lanka and the value of adaptation strategies( 2016)Coconut is an important food crop in the Sri Lankan economy which utilises nearly 20 percent of its arable lands. This industry is shifting from an export orientation to a domestic industry; mainly due to the population-driven domestic demand and stagnating coconut production. Nearly 65 per cent of annual production is consumed domestically as fresh coconut, while the remaining 35 per cent is utilised by the processing sector for products including coconut oil, desiccated coconut and copra. Coconut production fluctuates with climate. This yield fluctuation has considerable impact on industry stakeholders due to inelastic supply of and demand for fresh coconuts. Government interventions are ad hoc and numerous. Further, the effectiveness of these strategies is questioned in the absence of a consistent analytical framework. This study developed an economic framework; an equilibrium displacement model for the Sri Lankan coconut industry which analyses the impact of different policy interventions. The model was tested for seven hypothetical scenarios of external shocks. The model was subsequently used to analyse the likely impact of climate change in this study. An analytic hierarchy process was used to estimate the biophysical impact of coconut yield under future climatic scenarios. Climate, soil and topography were the main considerations of the model. The outcomes of this model as yield changes were used as a supply shift in the economic model. The total change in economic benefits and distribution of these benefits were estimated to find out the magnitude of the economic shock and impact on different stakeholders. The findings show that the coconut industry in Sri Lanka will face a loss equivalent to 4,795 Rs.Million which is nearly 5 percent of the total value of the industry at equilibrium. The mostly affected stakeholders are wholesalers and domestic coconut consumers. Then the impact of different adaptation options and cost effectiveness were considered to address the impact of climate change. Among these yield increasing adaptation practices, irrigation during dry periods was promising the highest productivity levels. However, the investments were not cost effective for large scale irrigation systems and availability of a water source was a major concern. Fertilizer application and moisture conservation were also identified as cost effective practices that would offset the yield loss and provide extra gain. Development of a heat tolerant cultivar would be a long term sustainable solution with the observed and expected increase in maximum temperature. However, this may take several years and still worthy to invest on. The findings are useful in assessing potential future impacts and directing the industry policies.
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ItemAntioxidant defence systems and symptom expression of wheat infected with Barley yellow dwarf virus and grown under elevated CO2( 2016)Barley yellow dwarf virus (BYDV) is regarded as the most significant viral pathogen of wheat worldwide. Symptoms produced during viral infection may have an interactive effect with environmental conditions expected under future anthropogenic climate change, including the rising atmospheric CO2 concentration. In particular, antioxidant defence systems – including the key non-enzymatic antioxidants ascorbate and glutathione – play an important role in regulating potentially harmful reactive oxygen species (ROS) produced during plant-virus interactions. However, the role of ascorbate and glutathione during systemic virus infection and growth under elevated CO2 (eCO2) is not well understood. This thesis investigated BYDV infection of three Australian wheat cultivars: the BYDV-susceptible spring wheat ‘Yitpi’, the susceptible winter wheat ‘Revenue’ and the resistant winter wheat ‘Manning’. In addition, the system was investigated under eCO2 to determine any interactions with infection on symptom expression and antioxidant defence capacity. Studies were performed within controlled environment chambers and the field at the Australian Grains Free Air CO2 Enrichment (AGFACE) facility located in the semi-arid grain-growing region of Horsham, Victoria, Australia. The response of plants to virus infection and eCO2 was assessed by measurement of the total concentration and redox state of ascorbate and glutathione. In addition, symptom expression was measured including growth, photosynthesis, stomatal conductance, leaf chlorophyll and nitrogen, and disease incidence and severity. BYDV infection was associated with an imbalance in antioxidative metabolism, which is an indicator of oxidative stress. Greater ROS turnover is the likely cause of the observed decrease in total ascorbate and glutathione and increase in the oxidised fraction of ascorbate after infection. In particular, a decrease in total ascorbate was the most consistent response to infection by all cultivars grown in both chambers and the field. The present research demonstrates that the observed imbalance in non-enzymatic antioxidant metabolism can be used as a marker for oxidative stress during systemic BYDV infection of wheat. The antioxidant response of both the BYDV-susceptible and resistant winter wheat cultivars was similar. Oxidative stress was not influenced by the putatively different virus concentration between these cultivars, but simply by virus infection alone. Infection was also associated with decreased biomass and height in both these cultivars and in both chamber and field studies, which indicates a sensitivity of the resistant cultivar to infection regardless of a putatively lower virus concentration. Despite few interactive effects between virus and eCO2 treatments on symptom expression, eCO2 altered the expression of yellowing disease symptoms in virus-infected plants, although not consistently between cultivars and environmental growing conditions. In addition, although there were significant changes to antioxidants in plants grown under eCO2, results were not consistent between studies. Research into this topic increases our understanding of how plants respond to virus infection and oxidative stress, and how plant-virus interactions may change under future eCO2. With the findings presented in this thesis, I have furthered the knowledge of this area by elucidating the response of ascorbate and glutathione during systemic wheat-BYDV interactions, and reinforced the potential use of these metabolites as markers of oxidative stress.