Science: Theses and Dissertations

Permanent URI for this collection

https://ir.canterbury.ac.nz/handle/10092/841

Browse

Now showing 1 - 20 of 5099

Open Access
The associations between observed mentor support and mentor-mentee relationship quality and mentee mental health outcomes
(2023) Kashkari, Zara
Although youth mentoring has a long history across multiple cultures, the evidence for its effectiveness as an intervention for youth behavioural and socioemotional difficulties has been rather slow to develop and is dominated by research from North America. Various processes in the mentoring relationship have been investigated as instigating change; however, there is currently a significant gap in the existing literature explicating the role of mentor-provided social support. This study begins to fill this gap by pilot-testing a new measure of observed social support. Video recordings of fifty-three youth mentoring dyads who were part of the Youth-Adult Partnership study (Dutton et al., 2020) were re-assessed according to this new measure based on self-determination theory (Deci & Ryan, 2000). Specifically, mentors’ support behaviours during a creative activity with their mentee were coded according to the degree of autonomy, competence, and relational support and inhibition. This data was then analysed with mentee’s self-reported social, academic, and psychological outcomes. Results showed various group differences in observed support and mentee outcomes according to mentor ethnicity, dyads in same versus cross-cultural pairs, and formal versus informal relationships. No significant associations were found between observed mentor support and mentee developmental assets, self-efficacy, and mental health. Significant associations were found between observed mentor support and mentee-reported relationship quality, which was moderated by whether or not dyads were in a cross-cultural relationship. This study broke new ground in the field of youth mentoring by operationalising mentor support through observation. These findings should be considered preliminary due to the cross-sectional nature of the study design and the small sample and are discussed in light of the limited recent research that has explored similar questions of mentor support through self-report data. Several recommendations are made for additional research to further test and validate this new measure of observed mentor support.
Open Access
Understanding bird damage to buds in Aotearoa/New Zealand kiwifruit (Actinidia chinensis) orchards
(2024) Hollinshead, Jordan
Bird damage to kiwifruit buds (Actinidia deliciosa and Actinidia chinensis) is an issue widely reported by orchardists in Aotearoa/New Zealand (hereafter, Aotearoa). However, little is known about which bird species are responsible and the extent of the damage to kiwifruit buds. The purpose of this study was to investigate three main objectives: 1. Identify the bird species that caused damage to kiwifruit buds and the extent and timing of damage to buds by each species. 2. Investigate whether bud damage levels by birds varied with orchard management types, kiwifruit variety, sward management, and the surrounding landscape. 3. Detail the foraging behaviour and relative location use of pest bird species using focal watches to determine whether birds were also feeding on other sources of food in the orchards, and if location use or behaviour is influenced by management factors such as management type, variety, and sward seed availability. Iselected 18 orchards in the Bay of Plenty region and used bird surveys, focal watches, and trail cameras to identify problem bird species and collect data on their behaviour during the 2022 bud break period. Bud damage surveys were also conducted to create bud damage estimates per orchard block. Within the 18 orchards, I surveyed six red kiwifruit blocks (planted with “RubyRed” Red19) and 28 gold kiwifruit blocks (planted with “SunGold” Gold3). Of a total of 34 blocks, five were organically managed (BioGro organic standards) and 29 were conventionally managed. Local management and environmental factors were recorded to understand whether orchard management, such as the presence of shelterbelts, management of swards (grass) between vines, and surrounding landscape affect patterns of bird abundance and bud damage. Twenty-nine bird species were recorded in orchards. However, only five bird species were observed damaging buds (hereafter referred to as ‘pest’ species): house sparrow (Passer domesticus), tauhou (silvereye; Zosterops lateralis), chaffinch (Fringilla coelebs), greenfinch (Chloris chloris), and on one occasion, a European blackbird (Turdus merula). I also captured videos of common brushtail possums (Trichosurus vulpecula) causing damage to buds in two orchards. The trail cameras captured 28 instances of bud damage. This allowed me to identify two peaks in bud-eating activity: around 60-120 minutes post-sunrise (approx. 7-8 am) and 600 minutes post-sunrise (approx. 4 pm). Additionally, I used images and videos of bird foraging behaviour to identify what damage may look like from certain species. Beak morphology influenced the appearance of bud damage, with larger, thicker bird beaks (e.g. sparrows and finches) leading to larger pieces or whole buds being removed. In contrast, the narrow-beaked silvereye tended to cause smaller cuts out of the kiwifruit buds. However, attempting to use visual assessment of damaged buds to attribute damage on buds to a particular bird species is likely to be difficult due to the similarity between species. Bud damage varied widely both across and within orchards. The minimum mean damage per block was 0.16%, and the maximum was 59.1% (mean = 10.2%, median = 5.36%). A variety of factors influenced bird abundance and bud damage. Interestingly, increasing availability of sward seeds was associated with increasing bird abundance but with decreasing bud damage levels, potentially because grass seeds offer an alternative food source for birds. Shelterbelt volume, management type, and the proportion of vegetation in the surrounding landscape also influenced bird abundance and damage. Understanding which management and environmental factors influence bird abundance and damage may benefit bird management in orchards, such as leaving swards unmown to reduce bird damage levels to kiwifruit buds. During the focal watches, four out of five pest birds (excluding blackbirds) were most often observed foraging, and all five were most often observed on the ground. This result is likely to reflect the foraging preferences of the pest species, where grains and seeds make up a large proportion of their diets. Kiwifruit variety, block management type, and sward seed status all influenced species behaviour and relative location use differently. However, I found that within some species (greenfinches, house sparrows), the availability of sward seed may influence the amount of time spent on the ground compared to in the vines. This provides support to the idea raised in Chapter Two, where high availability of sward seed appears to lead to less foraging on the vines and more time spent on the ground. The ability to draw concise conclusions from this was limited by the difficulty of observing birds in the orchard blocks. Limitations of this research include the generalisability to the whole of Aotearoa, the unequal sample size of management types and varieties, and not including other management or environmental factors that influence bird abundance or damage in my statistical models. Problems encountered during the study include the variation in bud break timing, the methods of measuring sward, and obstruction to the observer’s vision during the focal surveys. However, these limitations and problems prompt future research recommendations to further enable a better understanding of bird damage in kiwifruit orchards. Future research should include multi-year studies, more sites around Aotearoa, and a larger sample size of organic and red variety orchards. Altogether, this research provides a better understanding of how bird species interact with kiwifruit orchards in Aotearoa. This information is especially useful for developing and testing potential bird management measures in the future. Manipulating the availability of sward seed in orchard blocks looks like a promising strategy to minimise bird damage to buds. Manipulating food sources and providing decoy foods has been proven to be effective in other crop systems. My results support these studies, by showing that a higher availability of sward seed in orchard blocks was correlated with an increase in bird abundance, but also a decrease in bud damage. Additionally, pest bird behaviours and relative location use differed across sward seed availability. Future studies could experimentally manipulate sward seed availability within orchards to identify a causable link.
Open Access
Packaging, processing, and perceptions : what drives consumer food choices?
(2025) Newman, Kirsty
There is growing evidence that ultra-processed foods are detrimental to health and the environment. This study explored factors influencing food purchase decisions among New Zealand consumers, with a focus on ultra-processed foods. A sample of 316 undergraduate psychology students completed the Schwartz Value Questionnaire and analysed 28 food product images to examine the influence of values and product attributes on food choice. Previous research revealed that, on average, participants noted affordability (price) and pleasure to consume (sensory appeal) as the primary factors influencing their food purchase decisions, with less emphasis on processing and environmental friendliness. This reflective self-evaluation was somewhat confirmed through a policy-capturing analysis in which participants had to evaluate products on a range of dimensions and indicate their purchase intentions. Pleasure to consume was by far the strongest predictor of purchase intention, followed by healthiness, affordability and environmental friendliness. Values were investigated as a potential moderating factor, but no significant effect was found between values and packaged food decision-making. Additional analyses indicated that participants struggled to accurately identify ultra-processed foods, products with higher Health Star Ratings were perceived to be healthier, and more processed foods were perceived to be less environmentally friendly. The current study adds a unique perspective on food decision-making by New Zealand consumers by incorporating health and environmental factors, using real food products, and focussing on ultra-processed foods. Understanding the key factors that shape decisions about ultra-processed foods can pave the way for significant improvements in both health and the environment in New Zealand.
Open Access
Factors affecting shorebird nest success and behaviour at the Ashley-Rakahuri Saltwater Creek River estuary
(2024) Gunby, Eleanor
The survival and reproductive success of shorebirds is negatively affected by factors such as habitat loss and degradation, predation, and human disturbance. Disturbance from humans and avian predators can also affect the distribution and behaviour of non-breeding birds. However, the influence of these factors can be site- and species-specific. Therefore, the objective of this thesis was to determine the key factors that were affecting the nest success, distributions, and behaviour of birds at the Ashley-Rakahuri Saltwater Creek River Estuary, New Zealand. Firstly, I monitored the nests of seven shorebird species at the Ashley Estuary from 2022-2024. Nest success varied between species and years, but black-backed gulls (Larus dominicanus) had the highest nest success, while black-fronted terns (Chlidonis albostriatus) were the least successful. Predation and flooding were the two main causes of nest failure. I also evaluated the effect of habitat variables on banded dotterel (Charadrius bicinctus) and black-backed gull nest success. Black-backed gull nest outcomes were not affected by the measured habitat features, but earlier nests may have been more successful. Banded dotterel nests were more successful in the 2022/23 breeding season, mainly due to increased cat (Felis catus) predation in 2023/24. Successful banded dotterel nests were also closer to water on average than unsuccessful nests. Next, I used scan sampling to study the distribution and behaviour of estuarine birds in response to disturbance by humans and by a native avian predator, the Australasian harrier (Circus approximans). In response to human disturbance, pooled birds [all species except passerines and kingfishers (Todiramphus sanctus)] and waterfowl decreased in the disturbed area but began to return within 10 minutes after disturbance. Shorebirds were always more common in the undisturbed area, irrespective of the stage of human disturbance. Following harrier disturbance, pooled birds and waterfowl were less abundant in the western area of the estuary, while shorebird numbers increased overall regardless of the area, likely due to increased flocking behaviour. In addition to their distributions, bird behaviours may also have been affected by human disturbance. For example, the proportion of birds that were sleeping and preening in sectors bordering the disturbed area decreased during disturbance. Finally, I measured the FIDs and landing distances of estuarine birds in response to approaches by a single pedestrian. There were interspecific differences in FIDs, landing distances, and the method of fleeing used. Both FIDs and landing distances were highest for bar-tailed godwits (Limosa lapponica) and lowest for wrybills (Anarhynchus frontalis). Birds with longer FIDs generally also had longer landing distances, and FIDs and landing distances were typically longer in individuals that fled by flying, rather than walking. Based on the FIDs I measured, banded dotterels would require 66 m setback distances to minimise the effects of pedestrian disturbance, while pied stilts (Himantopus leucocephalus) would require 97 m setback distances. The results of this thesis add to existing knowledge around shorebird nest success and the effects of disturbance on New Zealand estuarine birds. My findings may be useful when developing future management outcomes for birds at the Ashley Estuary and similar sites throughout New Zealand, helping to protect our threatened shorebird species.
Open Access
The sexual victimisation disclosure processes model.
(2024) Catton, Ashley Keith Hoani
This thesis explored the dynamics of sexual victimisation disclosure through the development and empirical validation of the Sexual Victimisation Disclosure Processes Model (svDPM). The model posits that disclosure is an ongoing, relational, and complex process, where risks and benefits are constantly weighed, with each disclosure experience shaping further re-disclosure. It unifies the extant literature and identifies key areas for further research. Across three studies, this research examined the barriers and facilitators of disclosure, identifying then elaborating upon the roles of shame and invalidation in either inhibiting or facilitating re-disclosure. Study 1 introduced a gender-inclusive paradigm for identifying victims of sexual violations, investigating both reasons for and against disclosure. Study 2 experimentally examined the effects of invalidating feedback on shame and its subsequent impact on re-disclosure decisions. Study 3B further investigated how perceptions of invalidation, individual traits, and shame management strategies influence re-disclosure intentions. These findings offer insights into how shame, invalidation, and shame-management strategies contribute to the disclosure process. This work provides practical implications for professionals by guiding the establishment of safe environments conducive to voluntary disclosure, through highlighting the importance of minimising perceptions of invalidation and addressing shame in therapeutic settings.
Open Access
Leader humility in driving successful digital transformation.
(2025) Li, Daisy
The purpose of this study is to explore how leader humility contributes to the success of digital transformation (DT). With the rapid advancements in digital technologies, organisations are under increasing pressure to engage in DT to remain competitive. Leader humility has been recognised for its positive impact on DT outcomes; however, empirical studies are yet to be conducted to understand how leader humility contributes to DT success. This qualitative single-case study used semi-structured interviews with 17 participants from a large Aotearoa New Zealand-based higher education institution to answer the following research questions: (a) What contributes to successful DT; (b) What role does leader humility play in achieving success. The interviews captured the perspectives of end users, DT experts, and humble leaders involved in DT, offering a nuanced understanding of the role of leader humility in achieving successful DT from diverse perspectives. Data were analysed using reflexive thematic analysis. The findings suggest that successful DT is a people-centred change process that integrates technology with user capabilities. Leader humility humanises this process by emphasising the role of employees, who are integral to what successful DT entails. This study contributes to the growing body of research on successful DT, leader humility, and organisational change management, providing practical implications for leaders and HR practitioners in developing and supporting humble leaders to navigate the disruptions of DT.
Open Access
Towards psychological foundations of mathematics.
(2025) Grice, Matt
In the algebraic world, addition and multiplication are special. In the geometric world, lines, circles, right angles, parallel lines, etc. are special. Attempts to lay foundations for arithmetic (such as Peano’s axioms or the ZFC axioms) are evidence that addition and multiplication are special. Likewise, the fact that Euclid’s axioms for plane geometry include lines, circles, right angles, parallel lines, etc. are evidence that these objects are special. While these foundations are successful at doing what is required of them - facilitating the proving of theorems about addition, multiplication, lines, circles, etc. - they do not address the question of why these objects are special; indeed, these foundations rest on the presupposition of this fact. This thesis attempts to answer this question. When we say that addition, multiplication, and the fundamental geometric objects are special, we mean primarily psychologically so, but also mathematically. In order to explain the special status (psychologically speaking) of addition and multiplication, we use four foundational mathematical concepts - monotonicity, convexity, continuity, and isomorphism - to uniquely identify natural, rational, and real addition, and (positive) real multiplication. To explain the special status (psychologically speaking) of lines, circles, right angles, and parallel lines, we use three foundational mathematical concepts - distance, symmetry, and betwixity (betweenness) - and reconstruct Euclidean plane geometry from these concepts. We then show that each of these concepts is - prior to being a formal mathematical concept - a fundamental and intuitive psychological concept; a preverbal principle of perceptual organization that is biologically based and shapes how humans and non-humans alike perceive the world. Essentially, we are laying down psychological foundations for arithmetic and geometry. In the course of laying down these foundations, we ask questions about familiar mathematical objects that mathematicians do not usually ask; our goals are somewhat distinct from those of the mathematician. Consequently, in our efforts to answer such questions we sometimes find a new mathematical perspective from which to view these familiar objects; in this way, we also help to (partially) explain why these familiar objects are mathematically special, and not merely psychologically so. In particular, we lean heavily on the order-theoretic structure of the natural numbers; we also view natural addition through topological, metric-theoretic, and lattice-theoretic lenses.
Open Access
The sedimentology, stratigraphy and geochemistry of the Waipara Greensand.
(2024) Spinks, Ted
The Waipara Greensand is a middle to late Paleocene glauconitic muddy sandstone, which contains the earliest fossil examples of penguins (Aves: Sphenisciformes) and other Paleocene marine birds in the world. Three main outcrops of the Waipara Greensand in the mid-Waipara River, Broomfield, Canterbury are known for their abundance of vertebrate fossils, Site 1, Site 2 and Site 3. Sampling has been undertaken at Site 3 by Morgans et al (2005), and the geochemistry was studied by Hollis et al. (2012) and Hollis et al. (2014), with a particular focus on organic geochemical proxies. However, the focus of these studies was on the top of the formation in what is known as the Waipawa organofacies, with less detail in the lower part of the formation. Additionally, the most productive site for vertebrate fossils is at Site 2, which has not been sampled or measured, leaving early marine bird fossils without context stratigraphically, and therefore without understanding of palaeoenvironments during the time of deposition. Here, a detailed description of the sediments from Site 2 and Site 3 are presented. Using proxies from pXRF and biomarker data (including Glycerol Dialkyl Glycerol Tetraethers (GDGT’s), hopanes, n-alkanes, Total Organic Carbon (TOC) and bulk organic carbon δ13C), as well as field sedimentary descriptions and petrography, changes in palaeoenvironment through the mid-late Paleocene in the mid-Waipara Section at Site 2 are described. With the data collected from petrography and pXRF analysis, it is interpreted that elemental concentrations are primarily controlled by low sediment accumulation resulting in optimal conditions for glauconite diagenesis. Nutrient like elements showed a relationship to increased TOC values and productivity in the Waipawa organofacies. Increasing TOC values through stratigraphy correlate to higher BIT values and more positive δ13C values, indicate increased erosion of 13C terrestrial carbon into the marine basin during the deposition of the Waipawa organofacies. TEX86 sea surface temperature trends show warming during the deposition of the lower Waipara Greensand, followed by a trend of cooling, and then warming again in the Waipawa organofacies. Low sediment accumulation and moderate organic content resulted in seafloor diagenetic environments that are destructive to calcareous components such as invertebrate fossils but are constructive for the formation of glauconite, dolomite, and pyrite at the seawater/sediment sub-oxic transition zone. These diagenetic conditions are also conducive for the phosphatisation of vertebrate fossils resulting in their preservation. Cooler climate, and thus calmer weather patterns, during the mid Paleocene likely contributed to the accumulation of 13C enriched organic carbon in the terrestrial setting. Increased erosion of terrestrial organic matter is correlated with an increase in SSTs in the Waipawa organofacies, suggesting increase storm intensity may be a mechanism for the deposition of the Waipawa organofacies. Nutrients adsorbed onto this terrestrial organic matter may have increased productivity, which could influence evolution of marine vertebrates in the late Paleocene.
Open Access
Summer abundance of Frazil ice along the Victoria Land Coast, Antarctica, based on satellite imagery,
(2024) Boyland, Daniel
The growth of frazil ice marks the initial stage of sea ice formation. It often develops at the ocean surface when katabatic winds drive ice away from the coast and leave the ocean exposed to the freezing atmosphere. Brine is rejected as the sea water freezes, leading to the production of high salinity shelf water. This dense water sinks beneath the surrounding seawater and can flow under ice shelves. This triggers ice shelf basal melting near the grounding line deep within the ice shelf cavity. Freshwater is released, which mixes with the high salinity shelf water and rises up along the ice shelf base, leading to the formation of supercooled ice shelf water. As this water emerges out of the ice shelf cavity, pressure is relieved, leading to a positive feedback loop where the freezing point is raised even further. This results in the ice shelf water becoming in situ supercooled, which is alleviated by the growth of frazil ice crystals. The outflow of ice shelf water and subsequent production of frazil ice crystals is a significant contributor to Antarctica's coastal sea ice mass balance. In combination with latent heat polynyas, ice shelf water-induced sea ice production contributes to around 10% of the total Antarctic sea ice budget from an area that makes up only 1% of Antarctica’s maximum sea ice extent. Antarctic sea ice extent has experienced an unprecedented decline in recent years, following a positive trend that was at odds with climate models. Changes in both the input of ice shelf water and offshore wind patterns may contribute to these sea ice trends. Despite their significance, ice shelf/ocean/sea ice interactions are poorly understood, owing to the logistical difficulties of taking in situ measurements. This thesis used satellite remote sensing of the Victoria Land coast in the Western Ross Sea to detect summer frazil ice abundance, which is a potential indicator for the emergence of ice shelf water. This involved classifying sea ice types from Landsat 8, MODIS, and Sentinel-1 data, with a random forest machine learning algorithm in Google Earth Engine. These classified images were then used to generate heat maps of sea ice abundance, alongside sea surface temperature maps that were created from thermal imagery. Sentinel-1 radar image data was unable to detect frazil ice sufficiently, as the HH backscattering of frazil ice matched that of wind-roughened sea surfaces, while its HV backscattering was below the Noise Equivalent Sigma Zero. Landfast sea ice could not be adequately distinguished from pack ice, as their backscattering values largely overlapped. Sea ice types were more successfully classified with the optical sensors, although the lower spatial resolution of MODIS led to significant spectral mixing. Frazil ice appeared most abundant in the Terra Nova Bay polynya area, next to the Nansen Ice shelf and Drygalski Ice Tongue, where consolidated sea ice was scarce due to strong offshore katabatic winds, while the North Victoria Land coast had little frazil ice but abundant consolidated sea ice. This seems to indicate that frazil ice forms more readily when other sea ice types are absent and is also more easily detected by satellites under these conditions. Frazil ice was also detected in McMurdo Sound, but in lower abundance than in Terra Nova Bay. There is a significant amount of ice shelf water here, which may have contributed to frazil ice formation. Spectral mixing could explain why frazil ice appears less abundant in McMurdo Sound where there is a large amount of landfast sea ice and pack ice, even in summer.
Open Access
Cognitive-style diversity and decision-making in leadership teams: exploring the roles of conflict, cohesion, and psychological safety
(2024) Meuli, Melinda
The role of cognitive diversity in team decision-making continues to interest practitioners and scholars due to the importance of effective decision-making for organisational success. The aim of this study is to deepen the understanding of how cognitive-style diversity affects decision quality and satisfaction in leadership teams. To achieve this, the potential mechanisms that transmit the effects and the climate factors that facilitate these relationships are investigated. Drawing from past literature, it was hypothesised that diversity in the rational and intuitive cognitive styles would be related to lower cohesion and higher conflict within leadership teams, thereby negatively affecting decision quality and team satisfaction. Additionally, it was expected that psychological safety would buffer the negative effects of cognitive-style diversity on team conflict, as well as the negative effect of conflict on team effectiveness, while higher levels of perspective taking within teams would mitigate the negative impact of cognitive-style diversity on team cohesion. Twenty-eight leadership teams from Aotearoa New Zealand, Australia, and the United Kingdom participated in this cross- sectional study via online surveys. Unexpectedly, the results revealed a positive association between cognitive-style diversity and team satisfaction mediated by cohesion. Cognitive-style diversity was not associated with team effectiveness through conflict, also counter to expectations. These findings were contrary to predictions made in line with the similarity- attraction paradigm that cognitive diversity would disrupt team processes due to interpersonal tension. As hypothesised, moderation analyses indicated that in conditions of higher psychological safety, team conflict was associated with higher decision quality, whereas in conditions of lower psychological safety, conflict had a negative relationship with decision quality. However, neither psychological safety nor perspective taking moderated the indirect relationships between cognitive-style diversity and team effectiveness. This research contributes to team diversity literature by highlighting cognitive styles as a valuable form of cognitive diversity for enhancing leadership team satisfaction. Furthermore, the results highlight psychological safety as an integral factor in whether conflict contributes to effective team decision-making.
Open Access
Time off : an analysis of recreation at Scott Base.
(2024) Wichers, Hubertha
This thesis analyses the significance of and factors influencing recreational activities that occur at Scott Base, New Zealand’s Antarctic research station in the Ross Sea region. Recreation has played a crucial role in Antarctica throughout history. Early 20th-century explorers such as Scott and Shackleton recognised the importance of recreation and entertainment on Antarctic expeditions. It provided much-needed distraction and relief from living in close quarters, harsh climatic conditions, and isolation from the rest of the world. Recreation eased tensions, enhanced camaraderie and team cohesion, and promoted a positive culture whereby different ranks and roles enjoyed activities together (Ferrar, 2017; Scott, 1905). The importance of recreation in remote work environments remains equally significant today. It benefits an individual’s mental, physical and social health (McArdle, 2013; Scully et al., 1998; Street et al., 2007; Vella et al., 2023), and fosters positive relationships and cohesion across different roles (Iverson, R & Maguire, C., 2000; Perring et al., 2014) and visitor groups at research facilities such as New Zealand’s Scott Base in Antarctica. This thesis aims to answer the following research question: What recreational activities take place at Scott Base and why? To fully address this question, three subsidiary topics are explored, 1) the range of recreational opportunities in Antarctica, 2) the recreational activities undertaken at Scott Base, and 3) the factors that influence recreation at Scott Base. The most frequently undertaken recreational activities at Scott Base include walking, indoor individual sports, gym activities, socialising at the bar, familiarisation trips (tours to points of interest in the area), reading, snow and ice sports, and indoor games and movies. The primary reason for recreational engagement was social motivation, which sometimes manifested as a desire for solitude within Scott Base's busy environment. The main constraint to recreational engagement was limited time, exacerbated by the long working week. A lack of induction, training, or guidance, as well as the prohibition of specific activities, ranked as the second and third constraints, respectively. A conceptual model for recreational supply and demand in remote work environments was developed, incorporating the factors and constraints that impact recreational engagement. This model contextualises recreational demand and supply, visitor needs and expectations, organisational supply resources, and recreational supply and demand constraints within organisational, strategic, and natural environments. Unlike general recreational models, it accounts for the unique characteristics of a population that is largely selected by an organisation which also facilitates almost all recreational activities. This model raises awareness of how different components interact, enabling improved management to enhance employee health and wellbeing. National Antarctic Programmes are encouraged to commission further research into their recreational programmes to assess how well their provisions meet the needs and expectations of visitors. Researchers are invited to critique and further develop this conceptual model, refining it for the health and wellbeing of workers and organisations operating in remote environments.
Open Access
Uniformity is a myth : insights from Aotearoa New Zealand Pleurotus on intraspecific variation in fungal genotypes and phenotypes.
(2024) Hera, David
The aim of my thesis is to contribute to our understanding of intraspecific variation in fungi through the study of five Pleurotus species in Aotearoa New Zealand, exploring phenotypic and genotypic variation by applying methodology spanning systematics, ecology, biology, genomics, conservation, and food science. Intraspecific variation drives evolution, breeding, and food production practices, with implications for conservation, pathogenicity, biotechnology, and agriculture. Although well-studied in animals and plants, few mycological studies have focused directly on intraspecific variation, despite its growing recognition in the field. Edible oyster mushrooms (Pleurotus) are ideal model organisms because they experience natural selection in the wild and artificial selection in cultivation. As a foundation to assess phenotypic and genotypic variation in Pleurotus species of Aotearoa, I first conducted a phylogenetic study to clarify the species boundaries within the genus (Chapter 2). I constructed a multi-gene phylogeny using ITS, LSU, RPB1, RPB2 and Tef markers. I discovered a cryptic indigenous subspecies within P. pulmonarius and resolved taxonomic ambiguities around P. djamor in Aotearoa. Confusion over species boundaries has previously led to the importation of this species, which has a potential for invasion and hybridisation with indigenous species. These refined species boundaries have significant implications for conservation and biosecurity. Building on the refined species boundaries, I assessed how vegetative and reproductive growth traits vary between and within species. This study included three clonal replicates of 104 strains of five Pleurotus species grown in controlled conditions (Chapter 3). I discovered that intraspecific trait variation matched or exceeded interspecific variation, and found remarkably high levels of variation between clonal replicates of strains. Cultivated strains displayed less intraspecific variation than wild strains, suggesting the impact of cultivation history on phenotypic variation. My findings stress the necessity of true biological replication in mycology and challenge conventional definitions of individuality. To understand genotypic variation within a wild-collected fungus, I conducted population genomic analyses and the first Pleurotus pangenome analysis using 29 P. purpureo-olivaceus strains from across the South Island (Chapter 4). I found a highly conserved core genome and overall genetic homogeneity, which was contrasted by diverse mating type loci and a large accessory genome. Instead of multiple populations isolated by distance or topographical barriers, my findings support a single panmictic South Island P. purpureo-olivaceus population with unrestricted gene flow. Variation in fungi occurs at many levels and affects conservation, biodiversity, food production, and biotechnology. Both fundamental research and practical applications of fungi can benefit from considering the range of phenotypes and genotypes rather than species means and reference strains. My work contributes to a holistic understanding of fungal species and individuality, advancing fungal biology and informing cultivation practices and strategies for biodiversity conservation in the face of global environmental change. The diversity of Pleurotus phenotypes supports the identification of productive strains for indigenous oyster mushroom cultivation to enhance agricultural resilience, although further research and collaboration with indigenous communities – iwi Māori – are essential to ensure appropriate benefit sharing.
Open Access
Plant pathogen spillover : assessing the impact of exotic plant species on New Zealand’s native ecosystems.
(2024) Tan, Megan
New Zealand has experienced numerous introductions of exotic plant species since human arrival. Exotic plant invasions can alter native ecosystems by introducing pathogens that facilitate spillover to native species. This thesis investigates factors that could impact the likelihood of pathogen spillover from exotic plant species onto native species. The research comprises two components: an observational field study and a controlled experimental analysis. The field study focused on the abundance of foliar fungal hyphae in five native plant species within areas dominated by exotic plants. Using a new, cost-effective method for fungal quantification, it was found that species effects had a stronger influence on fungal abundance than exotic plant proximity. Endophyte diversity and generalist fungal species occurrence also showed no significant correlation with exotic plant abundance. The results highlight host-specific traits as important factors in endophyte dynamics. The experimental component examined the effect of exotic soil sources on the growth and disease prevalence of three native plant species. Findings suggested weak phylogenetic signals in pathogen dynamics, with low disease prevalence and mixed outcomes for biomass accumulation. This research demonstrates that while exotic plants contribute to environmental complexity, their role in driving fungal spillover to native species is nuanced and dependent on host traits and ecological context. This work advances methodologies for fungal measurement and contributes to understanding pathogen-host interactions, informing conservation strategies for New Zealand’s ecosystems.
Open Access
Understanding selective bacterial nutrient uptake through structural and functional analysis.
(2024) Newton-Vesty, Michael Charles
This thesis presents two stories related to metabolite uptake by bacteria. The first focuses on sialic acid uptake, while the second focuses on organosulfonate uptake. Sialic acids comprise a large family of structurally related α-keto acid sugars, commonly found occupying the terminal position of mammalian glycoconjugates that cover mucosal cell surfaces. The uptake and metabolism of sialic acids by pathogenic bacteria is linked to infection and disease in humans; hence, inhibition strategies targeting sialic acid metabolism present a novel avenue for antimicrobial development. Here I focus on the mechanisms of sialic acid uptake by bacteria. Escherichia coli uses two closely related major facilitator superfamily transporters to import distinct forms of sialic acid, with the ability to transport more than one form thought to confer a competitive advantage. Here I investigate, for the first time in vitro, how EcNanX facilitates the import of 2,7-anhydro-N-acetylneuraminate (2,7-an-Neu5Ac), an anhydro form of sialic acid. An EcNanX green fluorescent protein fusion construct was used to monitor expression and assess detergent stability, however, this construct was unstable and unsuitable for characterisation. The final EcNanX construct, which included a C-terminal octa-histidine tag, readily formed dimers and was screened for structural determination using single-particle cryo-electron microscopy. A small dataset yielded promising 2D classes and a low-resolution reconstruction validating the dimerisation properties of EcNanX. A structural model of EcNanX was generated and used to dock the 2,7-an-Neu5Ac substrate, allowing residues specific to 2,7-an-Neu5Ac transport, as opposed to the most common sialic acid N-acetylneuraminate (Neu5Ac), to be identified. Through mutagenesis of the substrate-binding site, EcNanX was successfully engineered to import Neu5Ac via an in vivo bacterial growth assay. These findings lay the groundwork for further structural and biophysical characterisation of EcNanX and enhance our understanding of alternative pathways for sialic acid metabolism, which may be leveraged for the development of novel antimicrobials in future. Sulfate-reducing bacteria, such as Desulfovibrio species, are implicated in human disease due to hydrogen sulfide production and have bioremediation potential for industrial applications. One key oxidised sulfur source is the organosulfonate isethionate, which is imported by the sulfate-reducing bacterium Oleidesulfovibrio alaskensis using a tripartite ATP-independent periplasmic (TRAP) transporter (OaIsePQM). This system relies on the substrate-binding protein (OaIseP) to scavenge isethionate and deliver it to the membrane transporter component (OaIseQM) for import into the cell. OaIseP was studied to define the mechanism of isethionate binding, the first step in the TRAP transport cycle. The binding affinity of isethionate to OaIseP was determined by isothermal titration calorimetry and is comparable to other TRAP substrate-binding proteins. X-ray crystal structures of OaIseP in the ligand-free and isethionate-bound forms were obtained and showed that in the presence of isethionate, OaIseP adopts a closed conformation whereby two domains of the protein fold over the substrate. This conformation of OaIseP is stabilised by both interdomain contacts and contacts to isethionate. Serendipitously, two crystal forms with sulfonate-containing buffers (HEPES and MES) bound in the isethionate-binding site were discovered. However, these do not evoke domain closure, presumably because of the larger ligand size. Together, the data helps unravel the molecular details of how a TRAP substrate-binding protein binds a sulfonate-containing substrate, rather than a typical carboxylate-containing substrate. The structure of isethionate-bound OaIseQM in complex with a megabody was determined to 2.98 Å (extending to 2.2 Å in some regions) via single-particle cryo-electron microscopy. As sialic acid TRAP transporters are the only members of the family that have been structurally characterised, the structure of OaIseQM contained novel features including a unique orientation of the fusion helix that links the Q- and M-subunits through the membrane, and only two Na+-binding sites (instead of three in other homologues). The OaIseQM structure allowed the isethionate-specific substrate-binding site to be defined, as well as three bound lipids to be resolved, consistent with those found in the sialic acid TRAP transporters. OaIseQM was shown to be functional using a proteoliposome transport assay, while models of the complete OaIsePQM complex were generated to shed light on the conformational changes undergone during the full TRAP transport cycle. The OaIsePQM models highlight a potential allosteric ‘scoop loop’ from the M-subunit to prompt isethionate release by OaIseP. This work expands the knowledge of TRAP transport, providing insight into the mechanisms underpinning transport which may inform future antibiotic development.
Open Access
Scenarios for disaster risk management at caldera volcanoes
(2024) Calderon, Rodrigo
Caldera volcanoes are recognized for being extended volcanic systems capable of producing very large, destructive, although relatively infrequent, explosive eruptions (VEI 6 or over). While large explosive eruptions are often a key concern for disaster risk management planning, caldera unrest is one of the most frequent events from calderas. Usually, it includes the activation of hydrothermal systems, the release of gases, triggering earthquakes, and ground deformation as a manifestation of changes in magma dynamics. Caldera unrest is highly challenging for risk management, given the high uncertainty in whether its occurrence may lead to an eruption and the comparatively less understood potential impacts on society. Planning disaster risk management strategies and operations in calderas requires addressing those uncertainties from caldera unrest and the wide range of potential eruptions through the coordination of multiple agencies at national, regional, and local levels. The need for multi-agency coordination adds another challenge to disaster risk management due to various agencies’ perspectives, interests, and requirements. The construction of “scenarios” has proven useful for emergency planning in variable and uncertain conditions, which might be useful for caldera risk management. Scenarios may work as “boundary objects” that intersect and produce information from science and practitioners’ expertise, addressing a common resource in support of agencies and in collaboration with others. The collaborative approach of producing scenarios allows scientific credibility and relevance for management practitioners in the resulting information. In this sense, how scenarios are produced is almost as important as the specific resulting scenarios, given that they require several discussions and building trust among participants. This research aims to compile and generate caldera eruption scenarios to support disaster risk management strategies for caldera volcanic activity. The research is split across three objectives: 1) identify the main challenges in caldera risk management (through a disaster risk assessment lens), 2) develop a scenario framework addressing those gaps and challenges, and 3) conceptualize the scenario development process and the embedded volcanic risk information. This thesis provides an introductory chapter providing details of this research's aims and objectives, and the three core thesis chapters address them. Those chapters include a literature review (chapter 2), co-development of a modular scenario framework (chapter 3), and the research engagement process to produce scenarios (chapter 4). The later chapters review relevant literature focused on calderas with particular attention on caldera unrest to define a conceptual framework for disaster risk management planning based on the production of scenarios. Calderas from Taupō Volcanic Zone Te Ahi Tupua (TVZ) in Aotearoa New Zealand, are then used as a case study, in which a collaborative process is initiated by the Caldera Advisory Group (CAG), which is a joint committee that includes agencies with the statutory responsibility for risk management for calderas at national, regional, and local levels, volcano scientists, and iwi-Māori (indigenous people of Aotearoa New Zealand) representatives. This research engagement process involved presentations, discussion meetings, workshops, and personal communication about specific information required to inform the development of management strategies at calderas. The need for producing hazard characterization capable of illustrating caldera unrest is defined in earlier stages of the engagement process. However, it is also stated that there is a need to represent impact and risk information rather than only hazards, which challenges the current knowledge about the potential consequences of caldera unrest. As a result of this process, a modular scenario framework is co-produced to include multiple pathways of potential activity over TVZ based on caldera unrest and eruption records. The scenario framework includes three stages of volcanic activity increasing in complexities for disaster risk management, including caldera unrest (module 1), transition unrest (module 2), and eruption (module 3), in which sequences could be arranged in different pathways, creating several short or long scenario sequences depending on users’ requirements. The modules include information about volcanic activity, the represented hazard and the amount of people and infrastructure exposed to those hazards. The thesis also describes the conceptual evolution of a modular scenario framework and its application in real case studies including a formal risk assessment for Transpower NZ, the Aotearoa New Zealand electrical grid operator, and supporting the risk communication response triggered by the TVC caldera unrest during 2022 and 2023. The thesis provides the lessons and recommendations for future co-production of scenarios and required advances in caldera volcanic risk modelling, especially for caldera unrest processes, such as ground shaking and deformation. A final summary chapter succinctly describes this research's components and conclusions.
Open Access
Pulsed laser deposition of Co₂MnGa and Co₂MnGe Heusler thin films.
(2024) Emeny, Chrissy
The investigation of material candidates with well-defined spin polarisation at room temperature is of significant interest to the developing research in the field of Spintronics. The class of materials, known as Heusler alloys, have gained attention due to their predicted half-metallic behaviour that results in an electronic band structure where electrons can be up to 100% spin polarised. Preserving the half-metallicity of the Heusler crystal lattice requires the atomic lattice sites to be arranged as an L2₁ crystal structure. The thin film investigations of these materials have been conducted primarily using the deposition techniques of low-temperature sputtering and molecular beam epitaxy (MBE). The deposition conditions of these methods commonly required the use of post-growth annealing above 500 K to improve the crystallinity of the thin films in order to achieve both a high degree of long-range crystal order, and the desired arrangement of the atomic lattice sites. This thesis investigates the growth of as-deposited single-crystal Heusler films using the method of pulsed laser deposition (PLD). This technique is ideal for exploring hetero-epitaxial deposition of complex materials, like the ternary Heusler alloys, by utilising the vaporisation of stoichiometric targets. The deposition conditions that result in single-crystal thin films can be efficiently investigated by altering the growth parameters of the laser fluence, the laser repetition rate, the substrate material, and the substrate temperature. Thin films of the Heusler alloys, Co₂MnGa and Co₂MnGe, were created using PLD to investigate the growth parameters required to produce single-crystal films that are atomically arranged as the L2₁ crystal structure, with a high degree of long-range crystal order. The films were measured using the diffraction methods of in-situ RHEED and XRD to examine the properties of the crystal lattices. SEM imaging was used to aid the identification of the films’ growth modes and quantify the particulate densities on the surface of the films. The magnetic and magnetotransport properties of magnetisation hysteresis, Hall resistivity, and magnetoresistance were investigated by conducting measurements with a SQUID and PPMS in fields up to 5 T, with applied temperatures of 3 – 300 K. Single-crystal Co₂MnGa thin films were successfully deposited using PLD on the substrates of MgO(100) and GaAs(100) heated to temperatures of 450 - 700°C. The Co₂MnGa thin films that exhibited structural and magnetic properties in agreement with bulk Co₂MnGa were produced using the optimised substrate temperature of 450°C. The minimum atomic disorder of the Co₂MnGa film series was identified from XRD measurements of the (100) crystal planes as the B2 phase. The L2₁ phase was confirmed for Co₂MnGa deposited at 700°C on MgO(100) from XRD measurements of the superlattice crystal planes.
Open Access
The neural noise-cancellation mechanism in tinnitus: explored in surgically induced unilateral deafness in adult humans
(2024) Park, MinChul
Tinnitus is a hearing disorder characterised by sounds heard without a physical source. The classical explanation for this experience involves hearing loss-triggered excessive neural noise within the central auditory pathway. Since not everyone with hearing loss experiences tinnitus, there must be additional features to the explanation with the neural noise-cancellation mechanism hypothesising those with tinnitus exhibit not only excessive neural noise, but also a reduced ability to “cancel out” this noise. The surgically induced unilateral deafness (UD) group seem to offer a rare opportunity to explore the noise-cancellation mechanism of tinnitus in a relatively well-controlled way, due to a homogeneous pattern of complete hearing loss in the surgery ear with only a portion experiencing tinnitus. The current thesis is a collection of four electroencephalography (EEG) studies designed with this overarching aim. Studies 1 and 2 compared the cortical auditory evoked potential (CAEP) and the auditory brainstem response (ABR) between UD individuals with associated tinnitus (UD+T; n = 13) and without (UD-T; n = 8), and binaurally hearing control group (n = 13). Stimuli were delivered in quiet and in noise respectively in each study. The noise-cancellation process is thought to work on cortical structures, hence group differences should manifest at the cortical level only. Study 1 showed precisely this pattern. The UD ABR wave III/V ratio was higher than the control group while only the UD+T group showed higher CAEP N1 amplitudes, consistent with their perception of tinnitus. The ABRs show an additive effect (sensitive to both stimulus and noise levels) and the CAEPs show a non-additive effect (sensitive to noise only) with mechanisms behind these phenomena also implicated in the tinnitus-related neural noise-cancellation. In study 2, both UD groups showed ABR additivity, but CAEP non-additivity was only seen in the UD+T group. The collective results of studies 1 and 2 point towards inadequate neural noise-cancellation system in the UD+T group. The thalamic reticular nucleus (TRN) is the hypothesised structure involved in neural noise-cancellation and its non-invasive biomarker involves sleep spindles (a sleep EEG hallmark). The exploratory study 3 examined the hypothesis that if UD+T individuals show inadequate neural noise-cancellation, this would be reflected in sleep spindles. However, no group differences in a range of sleep spindle parameters were observed, suggesting similar TRN activity regardless of the presence of tinnitus. However, a dual trend towards increased sleep spindle amplitude and decreased density in the UD+T group was observed, which might warrant further exploration. Lastly, study 4 used resting-state EEG to compare the brain rhythms of study groups. The UD group showed higher temporal region gamma power, which is associated with deafferentation induced maladaptive neuroplasticity in the auditory cortex, along with stronger phase amplitude coupling in the ventral anterior cingulate cortex relative to the control group. Amongst future plans, it will be interesting to note whether these trends are relevant in clinical and applied research determining the causal mechanisms of tinnitus.
Open Access
Occupational noise induced hearing loss : conservation policies and barriers.
(2025) Makaruse, Nyasha
Background. Occupational noise-induced hearing loss (ONIHL) is a major cause of preventable morbidity and one of the most prevalent work-related health hazards globally. Occupational hearing conservation programs (HCPs) rely on a hierarchy of control measures for prevention, early detection, and diagnosis of ONIHL. Typically, the goal of HCPs is not complete prevention of ONIHL so much as minimising risk of ONIHL to some acceptable level. Despite HCPs, ONIHL remains a leading cause of morbidity implying potential ineffectiveness. Our main aims were to: (i) Assess evidence on commonly used noise-exposure limits, associated NIHL risk levels among workers, and predicted excess risk at these levels. (ii) Develop an understanding of the incidence, compensation costs, and trends of ONIHL in New Zealand and other high-income countries. (iii) Investigate practices, perceived barriers, facilitators, and challenges with existing HCPs in high-income countries, using New Zealand as a case study. (iv) Examine the accuracy and precision of noise monitoring and surveillance methods. (v) Investigate the susceptibility of different audiometric test frequencies in early ONIHL stages and evaluate commonly used early flag/shift criteria. Methods The thesis used a variety of methodological approaches and types of data to address the aims, including secondary data via systematic reviews, and primary data via analysis of ONIHL compensation databases, and garnering expert input via the Delphi technique and cross-sectional surveys. More specifically: i) Three systematic reviews addressed five research questions on accuracy and precision of different noise-exposure assessment methods, susceptibility of audiometric test frequencies to early ONIHL changes, sensitivity of early detection metrics, ONIHL levels at various noise exposures, and differences between observed and predicted excess risk. ii) A retrospective analysis of ONIHL compensation data from five high-income countries (Australia, Germany, New Zealand, Hong Kong, and Canada) examined incidence rates, trends, and costs over a decade. iii) A cross-sectional online survey with quantitative and qualitative questions was conducted with stakeholders (employees, employers, occupational health specialists) to assess practices, barriers, strengths, and challenges of existing HCPs. A validated questionnaire covering key HCP components was adapted, piloted, and administered in English via Qualtrics from July 2023 to April 2024. Results The first systematic review assessing occupational noise exposure and the associated excess risk at different noise limits found that, as expected, higher noise levels were linked to an increased risk of ONIHL. Commonly used prediction models estimated an excess risk of 8% to 22% for exposure to 85 dBLAeq, 8hr, 8hr over 40 years. Variability in estimates was attributed to differences in ONIHL definitions and inconsistencies in hearing conservation practices. Across the five high-income countries where complete data was available, 131,433 newly compensated ONIHL cases were identified, with males comprising 96.3% of cases. The construction and manufacturing sectors were primary contributors to ONIHL. Across all study countries, ONIHL ranked among the top three work-related conditions, with incidence rates ranging from 5 to 148 per 100,000 employed workers. Rehabilitation compensation costs exceeded USD 800 million during the study period, with Germany accounting for the highest expenses. Overall, nearly USD 2 billion was spent on ONIHL compensation during this period, including pension costs associated with ONIHL cases in Germany. The analysis of compensation data showed that in New Zealand, male workers comprised over 90% of new ONIHL cases, with more than 50% occurring among workers aged 65 years and older. The mining, manufacturing, agriculture, forestry, and fishing sectors had the highest ONIHL incidence rates. Submitted and accepted compensation claims rose until 2016, followed by a decline. Despite fewer new cases post-2016, the economic burden persisted, marked by increasing annual costs. The survey involved 58 participants, including 40 occupational health specialists, 9 employees in noisy environments, and 9 employers/supervisors. Results indicated a lack of understanding among employees regarding ONIHL and proper Hearing Protection Devices (HPD) use, signalling ineffective training. Baseline hearing tests were often delayed, and noise measurements were deemed costly. Current HPDs are uncomfortable, leading to frequent removal. Despite this, occupational health specialists reported a gradual increase in awareness, with audiometry and ONIHL education becoming common during annual health checks. Notably, 67% of employers/supervisors overlook noise ratings when purchasing equipment. Financial barriers to implementing HCPs, particularly in lower-income countries, were also considered. A systematic review comparing various noise measurement methods various methods found that a hybrid approach (combining task-based, subjective rating, and trade mean measurements) performed with negligible bias, high precision, and accuracy comparable to gold-standard personal dosimetry. Given the variation in HCP assessment strategies, namely in relation to audiometric monitoring, systematic review-2 explored the relative importance of each audiometric test frequency. The results suggested that those frequencies above 8 kHz, particularly 12-16 kHz, were most susceptible to early ONIHL, while conventional frequencies of 3-6 kHz were also susceptible. Therefore, depending on which frequencies are used in early flag metrics, audiometric monitoring processes might have low sensitivity and specificity, but modifications can improve performance. Another feature of HCPs that can vary are the criterion noise exposure levels that trigger action. Conclusions The thesis provides valuable insights into high-risk groups for ONIHL. The findings emphasise the need for sector-specific preventive measures. The findings also emphasise the need for intensified ONIHL prevention efforts, particularly within the manufacturing and construction industries across high-income countries. The thesis highlights the disproportionate representation of males among the new ONIHL cases, whether due to their concentration in noisy settings or inherent susceptibility to noise-induced hearing changes. The economic burden is evident, as nearly USD two billion was allocated for compensation of ONIHL costs. The significant burden of ONIHL as a leading occupational issue, and the present work also offers fresh insights for areas to target towards intensified prevention and intervention efforts for accelerated reduction in new ONIHL cases. Improving awareness and training programs, as well as expanding the variety of HPDs, are crucial for enhancing compliance and HPD utilisation. Consistent and timely audiometric monitoring, along with comprehensive noise assessments, aligns with evidence-based practices. Addressing these gaps can tailor HCPs to effectively prevent ONIHL, promoting better health outcomes for workers in noisy work environments. A variety of relatively lower-cost noise exposure assessment methods had relatively high accuracy and precision levels comparable to personal dosimetry. These findings are particularly relevant for low-income countries where occupational noise measurements should be obtained with minimal work disruptions and costs. There is a need to refine ONIHL monitoring metrics and study extended high frequencies for early detection. In addition, improved noise exposure guidelines are required, based on long-term multinational data to generate more precise risk estimates.
Open Access
Artificial leaf surfaces as surrogates to study microbial phyllosphere colonization
(2023) Bernach, Michał
The phyllosphere comprises all above ground surfaces of plants. Leaves are dominating this habitat. Leaf surfaces feature diverse microenvironments for microbial colonizers, among which bacteria are the most prominent. The spatial and temporal variability of leaves heavily impacts its colonizers, modulating plant-microbe and microbe-microbe interactions. To study individual factors shaping this environment, it is considered advantageous to deconstruct plant leaf surfaces into their individual aspects with surrogate surfaces proposed to aid in this. The aim of this thesis was thus to develop biomimetic leaf replicas of Arabidopsis thaliana incorporating properties such as leaf topography or hydrophobicity, while allowing for survival of microbial colonizers on the surface in the absence of a living plant host. As a first step to create a biomimetic leaf surface, relevant properties of a selection of polymers - agarose, polydimethylsiloxane (PDMS) and gelatin were characterized. The chosen parameters aimed towards replicating key features of the leaf surface - topography, hydrophobicity, establishing a timeframe for potential experimentation and assessment of materials influence on bacterial colonizers. Based on this analysis, PDMS was determined to be the most suitable material for the fabrication of biomimetic leaf replicas for use in phyllosphere microbiology. Next, PDMS-based membranes were optimized to enable the diffusion of water and nutrients to the surface in order to sustain microbial life. The decrease of material thickness and addition of filler polymers to produce hybrid PDMS membranes (Carbopol, Pemulen, cellulose or polyvinylpyrrolidone) increased water permeability of PDMS, mostly without affecting the ability of PDMS to mimic leaf surface topography and its hydrophobicity. Furthermore, (hybrid-)PDMS membranes were found to be permeable to fructose. This demonstrates the possibility of delivering nutrients to biomimetic leaf surfaces in comparable degrees as to live leaf surfaces. Fructose delivered through the membranes also affected divisions of bacteria on the surface of flat PDMS and their distribution over time. Finally, all the characteristics investigated and developed were combined to fabricate PDMS leaf replica membranes. These biomimetic surfaces constitute the first reported example of surrogates which allow for survival of bacteria on topographically heterogenous and hydrophobic substrates mimicking plant leaves. Additionally, 3D models of leaf topography were developed to enable fabrication of PDMS leaf replica membranes with identical surface features. Such leaf replicas would enable higher comparability and transferability of experimental work. In conclusion, the biomimetic surfaces developed as part of this thesis represent an important platform technology for the phyllosphere microbiology toolbox.
Open Access
Accelerating the transition from pasture to native forest
(2024) Gerard, Maia
There is a growing interest in improving the rate of reforestation for climate change mitigation and preventing biodiversity decline. In New Zealand, a number of reforestation projects are being initiated on ex-farmland hill country. Te Whenua Ora/High Bare Peak (HBP) is a 540 ha ex-farmland area in Banks Peninsula, Canterbury that is now managed for conservation. Approximately 35% of HBP is covered in native forest, with sheep remaining on half the property to manage the grass sward. This presented an opportunity to test how to accelerate reforestation by determining barriers to natural regeneration. First, I used a multifactorial experiment to test the effects of grass competition, herbivory, seed limitation and aspect on the survival of native woody seedlings. North-facing aspects, sheep grazing, and seed limitation all reduced seedling establishment. Grass competition likely occurred, but the grass treatments in spring were not enough to improve seedling survival. Natural regeneration of native trees will be slow in exposed pastures but should be best on southern aspects near seed sources. Second, animal grazing often inhibits the regeneration of woody species under existing forest canopies. The stocking rate of sheep has been lowered at HBP. I placed cut māhoe (Melicytus ramiflorus) branches, potted karamu (Coprosma robusta) seedlings and trail cameras to determine whether palatable species continue to be inhibited due to sheep grazing. Of thirteen sites selected in kānuka forest, ten incurred damage to experimental plants within 30 days. Continuation of sheep grazing in the forest fragments will slow the rate of succession and favour species less palatable to sheep. Third, lack of birds for plant-bird mutualisms, especially seed dispersal, could slow the rate of regeneration. I conducted surveys of bird abundance at HBP and Hinewai Reserve, a well restored 1250 ha native forest in eastern Banks Peninsula. Five-minute bird counts found abundances of bird species that carry out pollinating and seed-dispersing roles were very similar at HBP and Hinewai. This suggests that birds are dispersing sufficient seeds to the surviving forests at HBP and dispersal will not be a barrier to natural regeneration. Manipulation of sheep grazing in pastures with minimal forest should be trialled to improve seedling establishment of less palatable species in pasture, then sheep could be removed once woody pioneers have established. Active restoration (planting) into pasture may need to be considered for areas where natural regeneration is slow to accelerate forest regeneration.