Intraspecific and interspecific variation in the xylem functional traits of Callitris species growing along an aridity gradient

More severe and prolonged drought events as a result of climate change, have the potential to cause broad scale forest and woodland dieback worldwide. The Australian continent is primarily comprised of arid biomes. However, rapid climate change-induced desertification threatens these surprisingly diverse ecosystems. Callitris is Australia’s most successful conifer genus, yet they remain they remain vulnerable to drought-induced decline. Given Callitris are the primary structural component of vegetation in many Arid-Australian ecosystems, their persistence is the most important factor preventing the collapse of these ecosystems. Resistance to drought-induced xylem cavitation has emerged as a key physiological trait determining the survival of tree species under water-limited conditions. Under the influence of aridity, Callitris have evolved the world’s most cavitation resistant xylem, yet little is known about the xylem anatomy liable to convey this. The main objective of this thesis was to identify the anatomical xylem traits and attributes associated with cavitation resistance in Callitris. The main body of work in this thesis involved analysis of microscopic anatomical traits through the use and development of several microscopy techniques. An inter-specific study produced a complementary dataset of xylem anatomical traits for branches of 15 Callitris and closely related species, building on the physiological dataset by Larter et al. (2017). An intraspecific study among five C. glaucophylla populations required the physiological and anatomical traits measurements. An intraspecific increase in cavitation resistance with aridity was found among the five populations in both the primary branches and roots. To understand whole plant hydraulic function, variability in xylem anatomical traits in the tertiary branches, secondary branches and trunks, of C. glaucophylla, in relation to the primary branches and roots was also explored. A greenhouse experiment tested the plasticity of anatomical traits in C. glaucophylla seedlings grown under contrasting water treatments. Mainly, among seedlings grown under well-watered conditions, height growth and more hydraulically efficient roots are prioritised, while more mechanically reinforced tracheids and safer but less efficient pit traits are favoured among seedling grown under water deficit

Electron-band theory inspired design of magnesium-precious metal bulk metallic glasses with high thermal stability and extended ductility

Magnesium-based bulk metallic glasses (BMGs) exhibit high specific strengths and excellent glass-forming ability compared to other metallic systems, making them suitable candidates for next-generation materials. However, current Mg-based BMGs tend to exhibit low thermal stability and are prone to structural relaxation and brittle failure. This study presents a range of new magnesium–precious metal-based BMGs from the ternary Mg–Ag–Ca, Mg–Ag–Yb, Mg–Pd–Ca and Mg–Pd–Yb alloy systems with Mg content greater than 67 at.%. These alloys were designed for high ductility by utilising atomic bond-band theory and a topological efficient atomic packing model. BMGs from the Mg–Pd–Ca alloy system exhibit high glass-forming ability with critical casting sizes of up to 3 mm in diameter, the highest glass transition temperatures (>200 °C) of any reported Mg-based BMG to date, and sustained compressive ductility. Alloys from the Mg–Pd–Yb family exhibit critical casting sizes of up to 4 mm in diameter, and the highest compressive plastic (1.59%) and total (3.78%) strain to failure of any so far reported Mg-based glass. The methods and theoretical approaches presented here demonstrate a significant step forward in the ongoing development of this extraordinary class of materials.ISSN:2045-232

Visualization of xylem embolism by X-ray microtomography: a direct test against hydraulic measurements

X-ray microtomography (microCT) is becoming a valuable noninvasive tool for advancing our understanding of plant-water relations. Laboratory-based microCT systems are becoming more affordable and provide better access than synchrotron facilities. However, some systems come at the cost of comparably lower signal quality and spatial resolution than synchrotron facilities. In this study, we evaluated laboratory-based X-ray microCT imaging as a tool to nondestructively analyse hydraulic vulnerability to drought-induced embolism in a woody plant species. We analysed the vulnerability to drought-induced embolism of benchtop-dehydrated Eucalyptus camaldulensis plants using microCT and hydraulic flow measurements on the same sample material, allowing us to directly compare the two methods. Additionally, we developed a quantitative procedure to improve microCT image analysis at limited resolution and accurately measure vessel lumens. Hydraulic measurements matched closely with microCT imaging of the current-year growth ring, with similar hydraulic conductivity and loss of conductivity due to xylem embolism. Optimized thresholding of vessel lumens during image analysis, based on a physiologically meaningful parameter (theoretical conductivity), allowed us to overcome common potential constraints of some lab-based systems. Our results indicate that estimates of vulnerability to embolism provided by microCT visualization agree well with those obtained from hydraulic measurements on the same sample material

Visualization of xylem embolism by X-ray microtomography : a direct test against hydraulic measurements

X-ray microtomography (microCT) is becoming a valuable noninvasive tool for advancing our understanding of plant–water relations. Laboratory-based microCT systems are becoming more affordable and provide better access than synchrotron facilities. However, some systems come at the cost of comparably lower signal quality and spatial resolution than synchrotron facilities. In this study, we evaluated laboratory-based X-ray microCT imaging as a tool to nondestructively analyse hydraulic vulnerability to drought-induced embolism in a woody plant species. We analysed the vulnerability to drought-induced embolism of benchtop-dehydrated Eucalyptus camaldulensis plants using microCT and hydraulic flow measurements on the same sample material, allowing us to directly compare the two methods. Additionally, we developed a quantitative procedure to improve microCT image analysis at limited resolution and accurately measure vessel lumens. Hydraulic measurements matched closely with microCT imaging of the current-year growth ring, with similar hydraulic conductivity and loss of conductivity due to xylem embolism. Optimized thresholding of vessel lumens during image analysis, based on a physiologically meaningful parameter (theoretical conductivity), allowed us to overcome common potential constraints of some lab-based systems. Our results indicate that estimates of vulnerability to embolism provided by microCT visualization agree well with those obtained from hydraulic measurements on the same sample material

Visualization of xylem embolism by X‐ray microtomography: a direct test against hydraulic measurements

X-ray microtomography (microCT) is becoming a valuable noninvasive tool for advancing our understanding of plant–water relations. Laboratory-based microCT systems are becoming more affordable and provide better access than synchrotron facilities. However, some systems come at the cost of comparably lower signal quality and spatial resolution than synchrotron facilities. In this study, we evaluated laboratory-based X-ray microCT imaging as a tool to nondestructively analyse hydraulic vulnerability to drought-induced embolism in a woody plant species. We analysed the vulnerability to drought-induced embolism of benchtop-dehydrated Eucalyptus camaldulensis plants using microCT and hydraulic flow measurements on the same sample material, allowing us to directly compare the two methods. Additionally, we developed a quantitative procedure to improve microCT image analysis at limited resolution and accurately measure vessel lumens. Hydraulic measurements matched closely with microCT imaging of the current-year growth ring, with similar hydraulic conductivity and loss of conductivity due to xylem embolism. Optimized thresholding of vessel lumens during image analysis, based on a physiologically meaningful parameter (theoretical conductivity), allowed us to overcome common potential constraints of some lab-based systems. Our results indicate that estimates of vulnerability to embolism provided by microCT visualization agree well with those obtained from hydraulic measurements on the same sample material