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    Diversity of entomopathogenic fungi (EPF) in soil across adjacent forest and pasture habitats and their interactions with arthropod hosts : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Manawatu, New Zealand
    (Massey University, 2025-10-29) Guerrero, Michelle
    Entomopathogenic fungi (EPF) are natural pathogens of insects that play a critical role in regulating arthropod populations and maintaining ecological balance. These fungi are commonly found in the soil, where they interact with invertebrates and with other microorganisms, making soil an essential reservoir for collecting EPF isolates. Understanding the distribution and prevalence of EPF across different habitats is crucial for their effective utilization in the biological control of agricultural pests. In this thesis, the diversity of entomopathogenic fungi (EPF) in adjacent forest and pasture habitats of the North Island, New Zealand, was comprehensively investigated. This study utilized an integrative approach, combining traditional techniques such as insect baiting and semi-selective plating with advanced molecular methods, including metagenomics and metabarcoding, to explore EPF communities across these contrasting habitats. In Chapter 1, I introduced the current understanding of EPF and identified key research gaps, setting the foundation for the study. Chapter 2 focused on the incidence of EPF across forest, forest-pasture boundary, and pasture habitats and the association with soil invertebrates. The results showed the highest EPF prevalence in forest soils, followed by boundary zones and finally pastures, demonstrating the influence of habitat conditions on EPF diversity. In Chapter 3, I characterized EPF isolates, primarily Beauveria spp. and Metarhizium spp., and found that forest and boundary soils caused up to 80% mortality in Tenebrio molitor larvae within seven days, indicating their insecticidal potential. Chapter 4 expanded the analysis by applying metagenomic and metabarcoding approaches, revealing additional fungal taxa, such as Cordyceps, Lecanicillium and Ophiocordyceps, which traditional methods could not detect. Chapter 5 assessed the efficacy of EPF isolates against agricultural pests, with pasture-derived isolates achieving higher pathogenicity and potential as cost-effective biocontrol agents. Finally, in Chapter 6, I synthesized these findings, emphasizing the ecological importance of soil habitats as reservoirs for EPF diversity and the adaptability of local isolates to specific environments. I recommended future research to expand studies into transitional zones, conduct field trials, and investigate the evolutionary mechanisms underpinning EPF adaptation and pathogenicity.
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    Sound of the underground : revealing the unheard and unseen world of soil beings through sonic and generative design : a thesis presented in partial fulfilment of the requirements for the degree of Master of Design at Massey University, Wellington, New Zealand
    (Massey University, 2024) Bell, Zoe
    Sound of the Underground is an immersive installation revealing the unheard and unseen world of soil life. One teaspoon of soil contains more microorganisms than humans on earth (Sprunger 2), a vulnerability that is exacerbated by their inaudibility and invisibility to human life. Their lives elude our sensory capacity within the modern world, and therefore our current processes and relationships with soil are to treat it like ‘dirt’: a dead, dark and quiet place in which capitalist exploitation and extraction damage topsoil health. The result of this impacts the health of the planet and its human and non human inhabitants. Investigating the role of sound in the human experience and as vibrational communications belowground, the research reveals how two worlds are becoming closer. As anthropogenic (human) noise traverses the biophillic sound of soil webs, these worlds are more reliant on each other than we may believe. As a project emerging from Aotearoa New Zealand, a Te Ao Māori worldview acknowledges the sensitivities and complexities of our soils, as well as the indivisible link between oneone ora and tāngata ora. The research is guided by the He Awa Whiria or Braided River framework. This mixed-method approach allows the research to move between a Māori worldview of our relationships with soil and western-centric ecoacoustic research. Methods of acoustic investigation are employed to reveal the unheard. Ecoacoustics record the sound of soil organisms and pick up frequencies beyond the human hearing range. These recently developed research methods are unearthing the need to understand how we can better care for enhanced soil futures. The unseen is explored by participating in wairākau or composting, then examining samples under the microscope. I harness generative design methods to create audio-reactive evolving systems that draw from ideas of mauri and the nature of soil life. Sound of the Underground was supported by Wellington-based artist and filmmaker, Mumu Moore, who incorporates sounds of Taonga Pūoro (traditional Māori instruments). The installation explores the conversations expanding both the human and soil realms, immersing you in ancient vibrations that will lead you deeper into relationship with our soils.
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    Impact of phosphate fertiliser derived fluorine on soil microbiology and white clover (Trifolium repens L) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy (PhD) in Environmental Sciences at Massey University, Palmerston North, New Zealand
    (Massey University, 2019) Thangavelautham, Geretharan
    Fluorine (F) is a significant contaminant in most phosphate fertilisers and fertiliser-derived F is accumulating in New Zealand agricultural soils as a consequent of phosphate fertiliser application. There is potential for soil fluoride (F⁻) to detrimentally affect soil biological functions such as nitrogen fixation by Rhizobium leguminosarum, and to alter soil properties. Fluorine accumulation in soil may require changes to future land use and management practices. The aim of this thesis is to investigate whether phosphate fertiliser-derived soil F has a detrimental effect on soil microorganisms. A novel analytical method for soil F analysis was developed to measure the total soil F concentration based on extraction with dilute NaOH. The relative error between a novel 4 mol L⁻¹ NaOH extraction and the conventional fusion method was < 2 for organic-matter and volcanic parent material derived soils but was > 2 for recent and pallic soils. Precision of the 4 mol L⁻¹ NaOH extraction method, measured through repeat analysis of three further soils (n = 270), was calculated as < 9% Relative Standard Deviation (RSD). To define a standard method to quantify the bioavailable F concentration in soil, samples were extracted with water, 1 mol L⁻¹ HCl, 0.01 mol L⁻¹ CaCl2, 0.01 mol L⁻¹ KCl, and 1 mol L⁻¹ NH4Cl. Compared to water, 0.01 mol L⁻¹ CaCl2 had high relative recovery (of bioavailable F) in soils which have elevated Fe and Al content. Therefore, 0.01 mol L⁻¹ CaCl2 is recommended to measure the bioavailable F concentration of New Zealand pastoral soils. There is no data available which describes the toxic effect of bioavailable F on R. leguminosarum in New Zealand soils. A laboratory incubation experiment and MicroResp 96-well format respiration-inhibition assay were conducted to investigate the effect of F on R. leguminosarum and white clover. Rhizobium leguminosarum growth was not significantly suppressed by F⁻ concentrations less than 100 mg L⁻¹. The normal rod-shaped bacterium cell of R. leguminosarum was morphologically altered when exposed to F⁻ concentrations above 100 mg L⁻¹. The IC10 values determined for F⁻ toxicity to R. leguminosarum were higher than 100 mg F⁻ L⁻¹. Pottle-based experiments showed that white clover growth was not significantly supressed at a F⁻ concentration < 70 mg L⁻¹, while healthy nodules were formed up to a F⁻ concentration of 100 mg L⁻¹. Light and TEM micrographs of nodules revealed that the Rhizobium-white clover interaction was not influenced by F⁻ concentrations up to 100 mg L⁻¹. To assess the potential effects of lime and compost amendment on the bioavailability of F, laboratory F⁻ adsorption/desorption experiments were conducted. Results revealed that at pH < 6, F⁻ adsorption significantly (p < 0.05) increased as a function of compost application. At soil pH > 6, F⁻ adsorption was not significantly (p > 0.05) influenced by compost. Lime application increased the soil pH and maximum F⁻ adsorption was recorded at soil pH between 5.5 – 6.8. These results showed that soil pH significantly influences (p < 0.05) F⁻ desorption and this should be considered in the management of pastoral soil with elevated F. A pot trial was conducted to quantify the effect of added F (equivalent to 0 - 50 years of F accumulation via the continuous application of phosphate fertiliser) on soil properties, soil microbial activity, white clover growth, and R. leguminosarum in an Allophanic soil. F addition (0 – 385 mg kg⁻¹) significantly (p < 0.05) increased soil pH and Dissolved Organic Carbon (DOC) from 5.18 to 5.53 and from 270.5 to 331.3 mg kg⁻¹, respectively. The CaCl2-extractable F concentration increased from 4.95 to 12.67 units as a function of added F. Microbial biomass carbon and soil enzyme activities, and white clover growth and interaction with R. leguminosarum, were not influenced by added F⁻ up to the highest concentration used in this study. White clover variety Merlyn and Tribute shoot F concentration was increased from 4.9 to 19.9 mg kg⁻¹ DM and 5.12 to 16.68 mg kg⁻¹ DM, respectively, however these concentrations are not expected to represent a risk to grazing livestock. This study highlights that the 4 mol L⁻¹ NaOH extraction method is a simple and accurate technique to measure the total F concentration for soils which have high Fe, Al and organic matter content. Water extractable and 0.01 mol L⁻¹ CaCl2-extractable F concentration are recommended to measure the bioavailable concentration of F in New Zealand soils. Current New Zealand bioavailable F concentrations are orders of magnitude lower than the F⁻ concentration assessed to be toxic to R. leguminosarum and white clover, and this suggests there is no imminent risk of soil F to R. leguminosarum. Compost is not recommended as an amendment for soils which have a pH above 6.0 to minimize the bioavailable soil F⁻ concentration. Lime application is suitable in such soils to minimize the bioavailable soil F⁻ concentration through altering soil pH. The major fraction of added F is immobilised by Allophanic soil and this effectively reduces the available F concentration to plants and soil microorganisms. Future work is recommended to investigate the uptake mechanism of bioavailable F into white clover shoots and roots. However, there is no evidence to suggest that F concentrations in New Zealand soil are a risk to New Zealand’s pasture-based farming systems.