School of Agriculture, Food and Ecosystem Sciences - Theses
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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.