Doctoral (PhD) Theses

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Theses submitted by Lincoln University doctoral students.

Students wishing to submit theses should see the Depositing theses and dissertations guide.

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    Investigating the effects of source-sink relationships on yield components, fruit development and composition of grapevines : A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University
    (Lincoln University, 2023) Mohajer, Minoo
    Viticulture practices (e.g., pruning, leaf removal, cluster thinning etc.), temperature and other climate conditions all have an influence on grapevine (Vitis vinifera L.) phenology, berry maturation and composition. Leaf removal as a common management practice alters the Leaf Area to Fruit Weight (LA: FW) ratio and may influence the timing of key phenological stages, berry maturation, photosynthesis activity, carbohydrate allocation and yield components. The outcome of this practice depends on the time and degree of leaf removal, the position and area of the removed leaves, the cultivar, and the climate. Winegrape growers need to decide where and when canopy management strategies are required. Therefore, understanding the relationship between different times and positions of leaf removal and yield components, carbohydrate allocation and berry composition could be beneficial for grape growers, particularly commercial vineyards and wineries. The outcomes of these practices on final yield, berry and wine composition are also important. Furthermore, research in two different environments, a vineyard and a glasshouse, could help to a better understand the interaction between source restriction and temperature. This study involved Pinot noir vines, both in outdoor vineyard conditions and within a moderated glasshouse environment. During various stages of the growing season, out of a total of twelve leaves on each shoot, six leaves were systematically removed, while the remaining six were retained at different positions along the shoot. The primary goals of this research were 1) to characterise the influence of apical versus basal leaf removal at three key phases of vine development: flowering, fruit set and bunch closure on the time of veraison, berry maturation parameters (total soluble solids, acidity and berry weight), berry components (seed, skin and pulp), berry composition (phenols, tannin and anthocyanins), vegetative growth (leaf, shoot and root), carbohydrate reserves and yield components; 2) to evaluate the real effect of source limitation achieved by apical and basal leaf removal at flowering and bunch closure on vegetative and reproductive parameters (as stated in aim 1), when the effects of environmental factors, especially temperature, are minimised under a controlled and moderated glasshouse environment; and 3) to investigate the effect of apical and basal leaf removal at flowering and bunch closure on leaf area, net photosynthesis, transpiration, stomatal conductance, and chlorophyll content over a period of time (from flowering to harvest). For the first and second aims, two similar experiments were conducted in a vineyard and a glasshouse. The experiment in the vineyard included two leaf removal positions (apical and basal) and three times (flowering, fruit set and bunch closure). A potted vine experiment with two positions of leaf removal (apical versus basal) at flowering and bunch closure was conducted in the glasshouse. The timing of veraison was determined in both experiments, and key components of berry composition including total soluble solids, pH, titratable acidity, malic acid, phenols, tannin, and anthocyanins were assessed from veraison to harvest. The seeds and skins of the berries were separated, and their fresh and dry weights were measured from veraison to harvest. Seed variability was also assessed by weighing each seed. At harvest(s), fruit set percentage, berry weight, bunch weight, yield, and vegetative growth (leaf, shoot, root) were evaluated. To achieve the third aim, a potted vine experiment was carried out in a glasshouse. Leaf removal treatments were applied at flowering and bunch closure as follows: twelve main leaves retained, six basal leaves retained, six apical leaves retained, leaves 2-7 (counting up the shoot) retained. Before treatments, the leaf area removed and retained were measured, and at harvest, the leaf area of all vines was evaluated. Vine net CO2 gas exchange was monitored from treatment to harvest on selected leaves from the top, middle, and bottom positions, depending on the treatment. Concurrently, leaf chlorophyll content and soil moisture were determined. Fruit set% and harvest bunch weight, vegetative growth and berry maturation were evaluated. Fruit set percentages ranged from 45 to 75% in the vineyard experiment and from 80 to 100% in the moderated glasshouse conditions. The observed result may be attributed to stable environmental conditions that can impact the success of fruit set. Another possibility is that potted (young) vines having only one inflorescence each, thus allowing for a more focused distribution of nutrients and carbohydrates to the flower cluster. In all three experiments, basal leaves retained vines delayed 50% veraison, however, the glasshouse experiments contributed to a greater delay than the vineyard trial. Keeping six apical leaves resulted in a shorter delay than keeping basal leaves.. Source limitation slowed the rate of total soluble solids accumulation in all experiments. Following the delay in veraison, keeping six basal leaves at flowering, fruit set and bunch closure resulted in a reduction in total soluble solids concentrations in the vineyard and potted vine trials. Apical leaves retained vines had lower total soluble solids than non-defoliated vines at the start of veraison due to a few days delay in reaching veraison; however, this delay was compensated during ripening, and there was no difference in total soluble solids between apical leaves retained vines and control at harvest in all three experiments. The hypothesised compensatory mechanisms identified for defoliation stress in basal leaves retained vines were increased chlorophyll content, stomatal conductance, transpiration, and maintenance of soil moisture, all of which enabled an increase in net photosynthesis over a period of time. These treatments, however, were unable to increase leaf area since they were the oldest leaves on the plant and had probably reached their maximum size. On the other hand, the compensatory mechanisms observed for the vines that retained apical leaves involved keeping a high rate of photosynthesis, transpiration and stomatal conductance as high as non-defoliated vine, while also increasing leaf size from the time of treatment application until harvest. As these leaves were young and immature they were still able to increase leaf size from the time of treatment application until harvest. In the vineyard trial, the compensatory strategy of basal leaves retained vines was insufficient, resulting in reduced yield components. Although basal leaves retained vines had no detrimental effect on yield components in the glasshouse experiments, the analysis of vegetative growth and carbohydrate reveals that all basal leaves retained treatments had reduced shoot diameter, shoot weight, and root weight/carbohydrate in all three experiments. This means that in basal leaves, transferring energy to sink organs by increasing photosynthesis (resulting in a delay in veraison) was possibly inadequate and came at the expense of perennial organs. In the vineyard experiment, keeping apical leaves at flowering reduced fruit set percentage and vine capacity (an estimate of the above ground dry weight of the vine), while the other times (fruit set and bunch closure) in all three experiments had no effect on yield components, carbohydrate reserves and vegetative growth when compared to control vines. Skin total phenols and tannin increased when six apical leaves were retained at flowering in the vineyard experiment, whereas the same treatment in the glasshouse had no effect on phenols or tannin, suggesting that the increase in phenols and tannin in the vineyard is most likely due to changes in the microclimate after removing the basal leaves, and defoliation has no significant effect on tannin and phenols in a control environment. Basal leaves retained treatments had reduced skin anthocyanins in both vineyard and glasshouse studies, which was not only because of the delay in veraison since basal leaves retained vines had lower anthocyanins concentration than non-defoliated vines at the same total soluble solids. While reduced carbohydrate availability is a primary factor affecting anthocyanin production in defoliated grapevines, there are other factors such as hormonal balance and light environment, and environmental factors that can also play a role in determining the final anthocyanin concentration in grape skins.
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    The making of a globally-recognised wine region: A case study of Ningxia, China : A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University
    (Lincoln University, 2023) Zhai, Beifang
    Recent theorising about place-making – a key element of regional development and a core theoretical construct in the field of human geography – emphasises the need for researchers to adopt a relational perspective and a naturalistic methodology to understand how, through action and interactions, people create new economic spaces. Building on this literature, this study examines the implication of the commodification of place based on the global countryside and rural culture economy in the context of a wine region in China. The study interprets how local, regional and national actors and agencies in China are working in concert to create a globally-recognised wine region. The study’s location is Ningxia – a rural area with established vineyards and boutique winery clusters. The place-making process involves the local implementation of central government policies and initiatives designed to raise the region’s international profile as a place of high quality wine production and associated wine tourism opportunities for visitors. Throughout the process of commodifying place, this wine region is marked by evidence of global connectivity and flows but, at the same time, this study reveals that these global forces intersect with, and are modified by, local contingencies and specificities including political, economic, physical, cultural and technological elements. The political influences are mainly framed around the regional government and the government authority, the Administration of Development of Grape Industry of Ningxia (ADGIN), as well as regional policies and regulations from the central Chinese government. Economic influences are primarily recognised through financial transactions and capital investment, and marketing activities. The physical characteristics of the location are fundamental to any wine industry and, in this context, have been largely explained in terms of the physical elements of terroir, a French term, further reflecting the influence of the global in the local. Local cultural influences are manifest in the interpretation of the concept of terroir through a traditional Chinese culture and philosophy lens, so that the physical elements of terroir are influenced by local cultural elements. The technological forces discussed mainly relate to the adoption, at a local level, of technological knowledge and equipment in grape growing and wine production. Thus, global forces are interwoven with the local development of the wine industry, through industrial (capital investment), technical and cultural attributes, and new social relationships associated with wine originating beyond the regional level influence the development of a collective regional body. This study contributes to the conceptualisation of a relational sense of place in a particular Chinese wine region and the examination of the process of making a wine region by discussing the construction of a wine region from the perspective of key supply-side stakeholders; by understanding the role of Chinese political and cultural values in making a wine region; and by addressing the interaction of local and global forces in the locality. This study also contributes to the creation or interpretation of local terroir from local-global nexus by investigating a wine region with its specific features in the Chinese context. Finally, his study contributes to providing a reflection of the fact that the global-local nexus means that the emergence of a wine region is not uniform and that global factors and local/regional factors are manifest in different ways. These global-relational perspectives provide insights into how the Ningxia wine region can be perceived as a “newly differentiated global countryside”, being transformed by the interaction of global forces with extant local elements.
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    Development of an integrated strategy to manage Sclerotinia sclerotiorum : A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University
    (Lincoln University, 2023) Dassanayaka, Madhavi Prasadani
    Sclerotinia sclerotiorum is a ubiquitous, necrotic fungus with a broad host range and as a plant pathogen infects a wide range of plants in New Zealand, including many economically important crops. Managing S. sclerotiorum by a single management practice is challenging due to the naturally high pathogenicity and the production of survival structures (sclerotia) in the soil. Hence, the aim of this study was to investigate the potential of combined applications of biofumigation, Perlka® and the biocontrol agent, Coniothyrium minitans, for controlling S. sclerotiorum. In the in vitro experiments done to test the effect of medium and cold preconditioning on carpogenic germination of sclerotia and development of apothecia, it was observed that carpogenic germination of sclerotia and the total number of apothecia per Petri plate was greater in water agar compared to potting mix and sand. Comparatively, the differentiation of apothecia was greater in potting mix and faster in sand. The isolates which originated from the Auckland region (LUPP2650, LUPP2651 and LUPP2662) showed greater carpogenic germination and development of apothecia compared to those originating from Canterbury (LUPP469, LUPP480, LUPP483, LUPP462) under the in vitro conditions used in this study. A few isolates (LUPP479, LUPP480, LUPP2660) showed a positive response for cold preconditioning (at 4°C) in terms of germination of sclerotia (%) and/or time to develop the first apothecium. The in vitro assessment showed that Brassica juncea ‘Caliente 199’ has greater potential to inhibit the mycelial growth of 10 isolates of S. sclerotium (60%) compared to the other tested biofumigant crops, Eruca sativa ‘Nemat’ (rocket) (29%), Brassica juncea ‘Unknown’ (brown mustard) (10%) and Sinapis alba ‘SKU 4295’ (white mustard) (7%). Plant tissue of ‘Caliente 199’ harvested at 50% or 100% flowering and adjusted to 80% (w/w) moisture resulted in greater mycelial inhibition compared with the vegetative tissue. High quantities of plant tissue of ‘Caliente 199’ of 5 g and 10 g resulted in greater mycelial inhibition than lower quantities. The EC50 of the S. sclerotium isolates LUPP475 and LUPP2650 was 3.76 g and 3.23 g, respectively. Using whole plant tissue (shoots + roots) and only shoot tissue resulted in a similar inhibition of the mycelial growth in all four isolates tested. The S. sclerotiorum isolate LUPP475 showed more tolerance to biofumigation with ‘Caliente 199’ compared to LUPP2650 in terms of mycelial inhibition. Using the plant tissue of ‘Caliente 199’ at 50% or 100% flowering and adjusting to 80% (w/w) moisture at the higher quantities (10 g) resulted in the maximum inhibition of mycelial germination of sclerotia of four S. sclerotiorum isolates. Whole plant tissues showed better inhibition of mycelial germination of sclerotia than only shoots. S. sclerotiorum isolates LUPP475 and LUPP2650 indicated a fungistatic effect on mycelial germination of sclerotia by ‘Caliente 199’ but isolates LUPP458 and LUPP463 germinated rapidly even after exposure to 10 g of whole plant tissues. Using ‘Caliente 199’ equivalent to the field rates of 75 t/ha and 100 t/ha inhibited the carpogenic germination of sclerotia by ~46% compared to the control but failed to reduce the sclerotial viability. In the box bioassays, using Perlka® alone, equivalent to the field rate of 400 kg/ha, resulted in complete inhibition of carpogenic germination although sclerotial viability was not reduced. Applying C. minitans resulted in complete inhibition of carpogenic germination and significant sclerotial mortality (95.0%). Applying C. minitans in combined application with Perlka® also resulted in 100% suppression of carpogenic germination and greater sclerotial mortality (97.5%). A synergistic effect of the combined application on carpogenic germination of S. sclerotiorum sclerotia was not observed, and sclerotial mortality was indicated to be predominantly due to the antagonistic effect of C. minitans. Under glasshouse conditions, applying C. minitans in the combined treatment with biofumigation resulted in significant suppression of apothecial development and Sclerotinia disease of lettuce. Applying Perlka® also provided a significant reduction of apothecial development and effective control of Sclerotinia disease of lettuce. Biofumigation alone failed to provide substantial control of either apothecial development or Sclerotinia disease of lettuce. The biological control of S. sclerotiorum using C. minitans can be recommended as a vital component in an integrated pest management (IPM) programme. Also, Perlka® provided effective control of S. sclerotiorum and proved to be a compatible component in an IPM approach. It is recommended to allow at least 6-8 weeks between C. minitans treatment and planting biofumigant plants because of the greater sensitivity of C. minitans to the volatile bioactive compounds and to allow the antagonist to colonise the sclerotia. Leaving 7-14 days between the Perlka® pretreatment and sowing biofumigant seeds (Brassica spp.) is also recommended to avoid the possible phototoxic effect of Perlka®. The results of this study will aid in the development of an IPM strategy to achieve sustainable control of S. sclerotiorum. Field experiments testing the selected treatments or treatment combinations are needed utilizing different crops and seasons within New Zealand.
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    Three essays on CEO expertise power and bank strategic decisions : A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University
    (Lincoln University, 2023) Ali, Maisam
    A CEO's expertise power is a combination of a CEO’s educational background, career path and experience, which influences the critical components of the bank task environment, e.g., bank diversification, bank lending and other financial services, thus, needing a close attention to investigate the CEO’s expertise power and bank key decisions. This thesis comprises three essays on a chief executive officer’s (CEO’s) expertise power and bank strategic decisions using US commercial banks data from 1990-2020. The first essay examines the effect of a CEO’s expertise power on bank diversification. The results show that a CEO's expertise power is positively associated with bank diversification. Market competition and board composition (size and independence) positively moderate this relationship. The results also show that CEO delta and vega are the underlying mechanisms through which expertise power leads to higher diversification. I address endogeneity concerns using the two-stage least squares, Heckman estimation and the Differences-in-Differences approaches and check robustness in several ways. The second essay examines the effect of a CEO’s expertise power on bank lending growth. The result reveals that a CEO's expertise power is positively associated with bank loan growth. Further, the result shows that GDP growth, board size and gender diversity positively and financial crises negatively affect this relationship. In channel analyses, I find that bank opacity (information asymmetry) and CEO delta (CEO pay-performance sensitivity) are the underlying mechanisms through which the CEO’s expertise power is associated with loan growth. I address endogeneity concerns using the fixed effects, generalized method of moments (GMM) and Heckman's two-stage approaches. The third and final essay examines the effect of CEO expertise power on bank tax avoidance. The result shows that a CEO's expertise power is positively associated with bank tax avoidance. The result also finds that diversification and gender diversity negatively and board size and financial crises positively affect this relationship. In channel analyses, the result reveals that CEO delta and vega are the underlying mechanisms through which the CEO’s expertise power is associated with bank tax avoidance. I address endogeneity concerns using the fixed effects, generalized method of moments (GMM), Differences-in-Differences (DID) and Heckman's two-stage approaches. This study enhances the scope of upper echelon theory by examining the implications of CEO characteristics (expertise power) for bank diversification, loan growth and tax avoidance decisions. This study provides a new explanation for bank diversification, loan growth and tax avoidance that will be useful for policymakers in developing bank strategy for CEO appointment that affects bank decisions. This study has several managerial and practical implications. The findings show that expert CEOs are highly skilled managers who can efficiently manage bank risk and other challenges, such as financial crises, reduce bank information asymmetry that improves bank lending, improve bank risk management and performance that generate more cash flows. Thus, CEO expertise contributes to bank stability by making value enhancing decisions.
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    Impacts of no tillage on nitrate leaching and associated mechanisms in arable cropping systems : A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University
    (Lincoln University, 2023) Li, Jinbo
    Nitrate (NO3-) leaching from agriculture is a growing environmental concern, and various strategies have been proposed to mitigate these losses. While many strategies aim to lower soil NO3- concentrations, they may not always be effective because NO3- leaching is also influenced by frequency and intensity of drainage events, which are affected by hydrological processes. No tillage (NT) has been proposed as an effective management practice to reduce NO3- leaching by influencing drainage. However, limited research has been conducted to identify how, and under what conditions, NO3- leaching can be reduced by regulating drainage with NT management practices. The aims of this study were to determine: (1) the relative importance of hydrological (i.e., drainage) and biochemical risk factors (i.e., NO3- concentration) and associated mechanisms in determining NO3- leaching losses at the global scale, (2) how and under what conditions NO3- leaching reduction can be achieved through regulating drainage with NT practices, and (3) the potential mechanisms explaining the effect of NT on drainage and NO3- leaching. It was hypothesized that (1) hydrological factors had a greater impact on global NO3- leaching variability than biochemical factors, (2) NO3- leaching was more sensitive to drainage in areas with higher nitrogen application rates and lower risks of fast flow, and that reducing NO3- leaching losses could be achieved by regulating drainage under these conditions, (3) the impact of NT on drainage and NO3- leaching was associated with tillage type (inversion vs. non-inversion tillage), soil properties, climate factors, and management practices; and (4) the greater drainage and leaching of NO3- associated with NT would be primarily attributed to higher soil water content rather than preferential flow. These hypotheses were tested through a combination of two meta-analyses of globally published data and field experimentation in New Zealand. The principal aim of the first meta-analysis was to assess the extent to which drainage contributed to NO3- leaching and the degree of sensitivity of NO3- leaching to drainage, aiming to identify the specific conditions under which regulating drainage could be more effective in reducing NO3- leaching. The second meta-analysis aimed to identify the specific conditions under which a reduction in NO3- leaching from NT practices may be feasible. The results of the first meta-analysis indicated that NO3- leaching variability was more closely linked to drainage than NO3- concentration, and that NO3- leaching was more sensitive to drainage in scenarios where fast flow drainage was less probable, such as NT and non-inversion tillage, and high N fertilizer rates were used. The results of the second meta-analysis revealed that NO3- leaching under NT was typically 7% higher than under inversion tillage but was comparable to non-inversion tillage. Greater NO3- leaching under NT was primarily attributed to drainage, and long-term NT cropping systems on high-SOC (soil organic carbon) soils were found to offer the most significant potential for mitigating NO3- leaching. Finally, field experiments were conducted in Canterbury to investigate the impact of NT on soil hydraulic properties and preferential solute transport, with the aim of elucidating the mechanism behind the increased risk of NO3- leaching under NT relative to inversion tillage using New Zealand as a case study. The findings indicated that NT resulted in greater average soil water content than inversion tillage, but there was no evidence to suggest that NT increased the risk of preferential flow. This suggests that greater drainage and NO3- leaching under NT relative to inversion tillage may be due to increased soil water content rather than preferential flow. Collectively, this study emphasizes the important role of drainage management in reducing global NO3- leaching risks, particularly in situations where fast flow drainage is less common (e.g., conservation tillage) and high N fertilizer rates are utilized. This study also highlights that adopting NT on average had greater NO3- leaching losses than inversion tillage and the greater NO3- leaching loss under NT is mainly through changes to soil hydrological properties that modulate intensity and frequency of drainage events. However, these effects are production system specific due to non-linear interactions between environmental and management conditions. NT increases the risks of NO3- leaching on low SOC soils and where NT adoption is short-term. In contrast, NO3- leaching is reduced by NT where it is practiced in the longer-term and on soils with high SOC content.