Impact of Phytophthora agathidicida infection on canopy and forest floor plant nutrient concentrations and fluxes in a kauri‐dominated forest

Schwendenmann, Luitgard; Michalzik, Beate

doi:10.1002/ece3.7326

Cited by 3 publications

(3 citation statements)

References 92 publications

(105 reference statements)

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“…They also revealed that 71% of kauri dieback zones were within 50 m of a walking track, suggesting that kauri dieback is predominantly spread by humans. Unfortunately, climate change may also abet P. agathidicida, with the possibility of increasing pathogenicity and spread (Schwendenmann & Michalzik, 2021), as has occurred or is expected to occur with other Phytophthora species (Gustafson et al, 2022;Jamieson et al, 2012;Scott et al, 2013;Shaw & Osborne, 2011;Thompson et al, 2014;Woods et al, 2016).…”

Section: Current Spreadmentioning

confidence: 99%

Exploring Phytophthora agathidicida Oospore Viability and Germination

Fairhurst¹

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Kauri trees are a species native to the northern parts of Aotearoa/New Zealand. They are a crucial part of the ecosystem and are taonga (sacred/treasured) to the indigenous people. However, kauri are threatened by kauri dieback disease caused by the oomycete Phytophthora agathidicida. P. agathidicida has a complex lifecycle involving several important spore types. Arguably the oospore is the most important as these spores are essential for the long-range transmission of disease. In the field, oospores can survive extreme physical and chemical stresses and are capable of persisting dormant in the soil for years before germinating and continuing the disease cycle. However, these spores are difficult to produce and study in the laboratory, with few techniques available for P. agathidicida. The overall goal of my thesis was to explore the chemical signals that trigger or suppress oospore germination. The ability to modulate oospore germination has potential applications in controlling and mitigating disease outbreaks. The first specific aim of this research was to develop a protocol for producing and isolating viable P. agathidicida oospores in vitro. Incubation time, media type and the addition of β-sitosterol were explored as variables to optimise oospore growth. The optimal growth conditions were clarified 10% (w/v) carrot broth with 30 mg/mL β-sitosterol, grown for >3 weeks at 22 °C, in the dark. The optimised protocol produced approximately 5-fold more oospores than existing methods. I quantified the viability of laboratory-produced oospores using two different techniques: (i) germination in the presence of kauri extract and (ii) a colourimetric viability assay that utilises methylthiazolyldiphenyl tetrazolium bromide (MTT) to distinguish between viable and non-viable oospores. Overall, a method for producing and isolating oospores in vitro was successfully developed, with yields, viability and germination rates comparable to those reported in the literature for other Phytophthora species. During the development of the oospore production protocol, it became clear that an improved assay for quantifying oospore viability was needed: the MTT-based viability assays are based on subjective assessment of colour and therefore are low-throughput and potentially unreliable. Therefore, the second specific aim of this research was to develop a high-throughput fluorescence-based method for quantifying oospore viability. I selected and tested five different fluorescent dyes (fluorescein diacetate, FUN-1, SYTO 9, propidium iodide, and TOTO-3 iodide) for their effectiveness at staining viable and/or non-viable oospores. First, I developed a viability staining assay using fluorescein diacetate and TOTO 3 iodide that effectively differentiated viable, non-viable, and damaged oospores. I then developed a workflow to automate the detection of oospore viability using Ilastik, R, and CellProfiler. This pipeline increased the throughput of the assay and removed user bias. The third specific aim of this research was to develop a germination assay and apply it to find modulators of oospore germination. Due to the asynchronous germination of oospores, the germination assay was scored qualitatively. A 96-well plate-based assay utilising kauri root extract was developed and used to screen a compound library containing 379 compounds. This yielded 11 compounds that either activated or inhibited the germination of oospores. Four of these chemicals (decanoic acid, D-glucosamine, hydroxylamine, and alloxan) were validated as inhibitors of oospore germination in subsequent germination assays. These four chemicals were also tested using the fluorescence-based viability assay, killing between 25–94% of oospores. A further two chemicals (L phenylalanine and myo-inositol) were validated as activators of oospore germination. This screening assay has not only led to the discovery of several compounds that could be explored for use as control agents but has also shown that this method is a valuable method for discovering chemicals that are lethal to oospores. The final aim of this research was to transform P. agathidicida protoplasts and utilise RNA interference to understand the molecular triggers that cause oospores to germinate. I optimised a protoplasting protocol for use with P. agathidicida and succeeded in producing large numbers of protoplasts. However, I could not generate a stable transformant of P. agathidicida. Overall, this research has provided new tools for the study of oospores, as well as insights into the chemicals that modulate oospore germination. These results will hopefully facilitate further studies on this key part of the Phytophthora disease cycle and ultimately support the development of tools to manage kauri dieback disease.

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Section: Current Spreadmentioning

confidence: 99%

Exploring Phytophthora agathidicida Oospore Viability and Germination

Fairhurst¹

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“…The few kauri that do remain are mostly located in northern forests of the North Island and are threatened by the 'kauri killer' pathogen Phytophthora agathadicida (PA), which causes the so far incurable disease known as kauri dieback (Bradshaw et al, 2020;Hood, 2021;Lambert et al, 2018;Schwendenmann & Michalzik, 2021). The first reported case of PA on mainland Aotearoa occurred in 2006 (Beever et al, 2009), although it is estimated that the pathogen has been present in NZ soils prior to its discovery.…”

Section: Introductionmentioning

confidence: 99%

“…Although the exact repercussions of kauri loss on NZ ecosystems won't be known unless kauri extinction occurs, the rich diversity of species flourishing in kauri forests, indicates that the effects of kauri loss will be devastating to NZ flora and fauna (Schwendenmann & Michalzik, 2021).…”

Section: Introductionmentioning

confidence: 99%

Kauri Dieback Prevention: Relational Values of Knowledge Producers

Ehler¹

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Researchers and knowledge producers play a key role in kauri dieback knowledge production. Whilst their scientific discoveries are well documented in literature, their personal experiences and stories of working on kauri dieback are not. Yet these experiences and stories give key insights into the factors that shape kauri dieback knowledge production, and provide an understanding of how the current kauri dieback research landscape is operating. This research thesis therefore aims to understand kauri dieback researchers through the lens of relational values, a subset of environmental values. Relational values emerge from the relationships between people and the natural environment and are useful for unpacking the relationship between researchers and kauri trees. Using semi-structured interview data from six kauri dieback knowledge producers this research finds that relational values shape and motivate kauri dieback research. Relational values are therefore inherent in science practices, yet there are forces within the current research landscape that stymie the ability for these values to manifest. This research finds that funding structures, fragmentation in the research space and the urgency of kauri dieback against Aotearoa’s postcolonial backdrop push-back on researcher’s ability to realise their values. In turn this results in researchers feeling burnt-out and frustrated. This research therefore argues the importance of relational values in future considerations of the kauri dieback research landscape to alleviate current tensions and challenges that researchers face in the space.

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The threat of a major tree pathogen to forest soil mesofauna food webs and ecosystem functioning

Struijk,

Stavert,

Le Grice

et al. 2024

Front. Ecol. Evol.

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Tree pathogens threaten the survival of many forest foundation tree species worldwide. However, there is limited knowledge of how dieback of foundation tree species may threaten other components of forest ecosystems, such as soil biodiversity and associated ecosystem functions. Kauri (Agathis australis), threatened by the root-borne pathogen Phytophthora agathidicida, are culturally and ecologically significant tree species that exert great influence on soil properties. We aimed to characterise soil mesofauna community structure and energy fluxes in kauri forests and assess the potential threat that tree pathogens such as P. agathidicida pose to belowground ecosystems. We sampled soil mesofauna communities and identified specimens to functional feeding groups at 24 pairs of kauri and adjacent broadleaf trees in sites across the Waitākere Ranges Regional Park, Aotearoa – New Zealand. We attributed kauri canopy health scores, measured tree diameter, slope, forest floor depth, and soil carbon dioxide efflux. We also analysed soil samples for P. agathidicida presence, total carbon, and total nitrogen. We constructed soil mesofauna food webs associated with kauri and broadleaf trees, and assessed the uniqueness of food webs associated with kauri and the impacts of P. agathidicida on density, biomass, mean body mass, and energy fluxes of mesofauna taxonomic and trophic groups. We found omnivores with larger body mass at kauri where P. agathidicida was detected (i.e., P. agathidicida-positive soils). Compared to broadleaf trees, mesofauna density and biomass were lower in soils under kauri, and body masses of Symphyla and omnivores were smaller in soils under kauri. Differences in mesofauna community response variables between tree types were mainly modulated by the soil C:N ratio, which had positive effects under broadleaf and neutral to negative effects under kauri. Energy fluxes to detritivores and fungivores were greater under larger trees, regardless of tree type or P. agathidicida detection status. Our findings suggest that kauri support soil mesofauna food webs that are distinctly different from those found under broadleaf trees in the same habitat. A decreased presence of this foundation species may be linked to future impacts on soil mesofauna in this forest ecosystem with increasingly advanced stages of kauri dieback.

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Impact of Phytophthora agathidicida infection on canopy and forest floor plant nutrient concentrations and fluxes in a kauri‐dominated forest

Abstract: Natural disturbances can substantially alter a range of ecosystem processes and related functions, and consequently ecosystem services

Cited by 3 publications

References 92 publications

Exploring Phytophthora agathidicida Oospore Viability and Germination

Exploring Phytophthora agathidicida Oospore Viability and Germination

Kauri Dieback Prevention: Relational Values of Knowledge Producers

The threat of a major tree pathogen to forest soil mesofauna food webs and ecosystem functioning

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