School of Agriculture, Food and Ecosystem Sciences - Theses
Permanent URI for this collection
Search Results
1 - 3 of 3
-
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.
-
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.
-
ItemMethane and carbon dioxide exchange in the tropical savannas of northern Australia: the role of termites( 2011)Termites are one of the most uncertain components of global CH4 budget mainly because of the lack of long-term field based studies from different biogeographical regions. This thesis investigated the exchange of CH4 and CO2 between termites and atmosphere, and between soil and atmosphere in the tropical savannas of northern Australia. Diurnal variations in CH4 fluxes were measured from mounds of Microcerotermes nervosus, Microcerotermes serratus and Tumulitermes pastinator every four hours over a 24 hour period. There was large diurnal variation in mound CH4 fluxes caused by diurnal temperature patterns. Mound CH4 fluxes measured between 10:00 and 12:00 hours best represented the mean daily flux. Seasonal measurements of mound CH4 fluxes were up to 25-fold greater in the wet season than the dry season and always greater in the wet season for all investigated species. Detailed studies in M. nervosus revealed that these differences were not associated with changes in environmental pattern but seasonal changes in termite mound population size. The magnitude of diurnal and seasonal variations in mound CH4 fluxes measured in this study suggest that estimates of global CH4 emissions from termites that do not account for such variations will contain larger errors and uncertainty. The contribution of mound-building, hypogeal and wood-nesting termites to the CH4 balance was estimated for a savanna woodland at Howard Springs near Darwin. Methane fluxes were measured from termite mounds and from the soil - from which CH4 fluxes from hypogeal termites were estimated. Methane fluxes from wood-nesting termites were estimated based on known species abundance. Termites were an annual CH4 source of +0.24 kg CH4-C ha-1 y-1 and soils a CH4 sink of -1.14 kg CH4-C ha-1 y-1. Thus, termites offset 21% of CH4 consumed by soil methanotrophs, but overall the savanna ecosystem was a sink for CH4 of -0.90 kg CH4-C ha-1 y-1. Two indirect methods were tested to predict CH4 and CO2 fluxes from termite mounds. The first predicted mound CH4 fluxes from ‘easier-to-measure’ mound CO2 fluxes. The second predicted CH4 and CO2 fluxes from termite mounds based on the relationship between internal mound concentrations and external mound flux. For both indirect methods the prediction errors were small when calculated separately for each species, whereas, a generic relationship or predictions between species resulted in large errors, probably associated with different mound structures for different species. This study shows that CO2 emissions from termite mounds are up to two orders of magnitude greater than CH4 emissions, when expressed in CO2-equivalents. There was large variation in both CH4 and CO2 fluxes from termite mounds and soil among different sites which suggests caution when scaling up fluxes from the plot or site scale to a regional or greater scale. This study filled important knowledge gaps in the ecosystem ecology of termites and Australian savannas. This study establishes North Australian savannas as one of the few biogeographical regions where the contribution of termites to ecosystem CH4 exchange has been investigated. The study highlights the difficulties associated with predicting CH4 flux from termites on a biome scale, which are caused by the high temporal and species-specific variability in flux. Future studies will have to consider these issues in order to reduce the uncertainty of the role of termites in the global CH4 budget.