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Pathogenicity and virulence-associated factors of Pseudomonas syringae pv. syringae and [P. amygdali pv. morsprunorum] strains from New Zealand sweet cherry (Prunus avium) orchards
No full textPreviously genetically characterised strains of Pseudomonas syringae. pv. syringae (Pss), [P. amygdali pv. morsprunorum] (Pam, syn. P. s. pv. morsprunorum race 1) and Pseudomonas spp. from New Zealand were characterised for their pathogenicity and ag-gressiveness in plant tissue and associated virulence factors. Lesions on detached, Pss-inoculated immature fruit increased rapidly in size and, at 10 days post inoculation (dpi), had larger areas under the disease progress curve (AUDPC) than Pam-inoculated fruit (48.9 and 22.0, respectively). Detached leaves infiltrated with Pss-developed symptoms within 1 dpi and from 2 dpi for Pam. Necrosis from most Pss strains extended into the leaf veins by 7 dpi, while Pam strains' necrosis was confined to the inoculation site. On detached 1-year-old cherry shoots, Pseudomonas spp. strains exhibited the smallest mean lesion size (2.1–2.4 mm), whereas larger mean lesion sizes were observed with Pss strains (5.7–13.7 mm) and Pam strains (3.9–14.0 mm). A functional T3SS was inferred for Pss and Pam strains based on the hypersensitivity reactions observed on tobacco leaves and symptoms elicited on cherry tissue. Syringomycin production was prevalent (88%) among Pss strains. In contrast, only 1.4% of Pam strains produced coronatine. Most Pss strains (97.0%) were able to catalyse ice formation. The coexistence of strains with varying degrees of virulence and non-pathogenic strains suggests a complex ecological balance, where multiple factors, including genetic variation, virulence traits and environmental conditions, shape the population dynamics and disease outcomes
The impact of soil, year and genotypic vigour on the release of allelopathic metabolites by wheat
No full textRecurrent selection for increased shoot vigour produced germplasm with enhanced leaf width and leaf area. Genotypes produced in the third cycle of the recurrent selection were top-crossed with two Australian commercial wheat cultivars (Yitpi and Wyalkatchem) generating high vigour lines. Here, in replicated controlled environment experiments and over two years in the field, the effect of the breeding with early shoot vigour on root development, and the presence of secondary allelopathic metabolites and microbially transformed phytotoxic molecules as part of below-ground competitiveness, were examined. The vigour lines were assessed for early root growth and interaction with annual ryegrass, both physical and chemical, in hydroponics and field soil. Breeding lines were compared to Australian commercial cultivars, genotypes of the third cycle of the recurrent selection, the heritage cultivar Federation and triticale. Below-ground, compared to commercial cultivars, the increased vigour lines demonstrated increased competitive ability. In all the experiments, vigorous lines possessed longer total root length and root hair length. In the controlled environment, numerous secondary metabolites, some previously identified to have allelopathic effects on weeds, were detected in the roots and the rhizosphere. In the two-year field study results showed significant differences of secondary phytotoxic metabolite levels between the drier than long-term average 2019 and wetter than average 2020. Contrary to previous results, this work showed increased levels of metabolites and microbial-transformed molecules in the wetter season. However, the genetic variation for early vigour didn’t result in significant differences in the presence of allelopathic molecules
Research at the interface between Indigenous knowledge and soil science; weaving knowledges to understand horticultural land use in Aotearoa New Zealand
No full textAddressing the complex challenges of soil and food security at international and local scales requires moving beyond the boundaries of individual disciplines and knowledge systems. The value of transdisciplinary research approaches is increasingly recognised, including those that value and incorporate Indigenous knowledge systems and holders. Using a case study at Pōhatu, Aotearoa New Zealand, this paper demonstrates the value of a transdisciplinary approach to explore past Māori food landscapes and contribute to contemporary Māori soil health and food sovereignty aspirations. Engaging at the interface between soil science and Indigenous knowledge (mātauraka Māori) in an Aotearoa New Zealand context, we provide an example and guide for weaving knowledges in a transdisciplinary context. Here, mātauraka Māori, including waiata (songs) and ingoa wāhi (place names), provided the map of where to look and why, and soil analysis yielded insight into past cultivation, soil modification and fertilisation practices. Both knowledges were needed to interpret the findings and support Māori to re-establish traditional horticultural practices. Furthermore, the paper extends the current literature on the numerous conceptual frameworks developed to support and guide transdisciplinary research by providing an example of how to do this type of research in an on-the-ground application
Weaving knowledges to understand historical horticultural land use at Pōhatu
No full textAs Western models of food production are being increasingly relied upon for global food security, urban populations are losing sight of where food comes from, and what is required to produce sufficient, high-quality food. Given the central role of soil in food production, there is a growing need to understand the (dis)connections between soil, food and people. Existing research suggests that individual disciplines alone are unsuitable for addressing these challenges, and that inter- and transdisciplinary research approaches are required. In an Aotearoa New Zealand context, one approach is looking to opportunities that weave together the knowledge streams of soil science and mātauranga Māori (Māori knowledge).
This research applies a transdisciplinary research approach that weaves together mātauraka Māori and soil science to explore the (dis)connections between soil, food, and people through a study of past food landscapes at Pōhatu (Flea Bay) on Te Pātaka o Rākaihautū (Banks Peninsula). This case study employs the He Awa Whiria, Braided Rivers, framework to weave mātauraka Māori and soil science when addressing the questions of Mana Whenua (the Māori community with customary authority over this land), regarding their past horticultural land use in the bay. Analysis of soil horizons modified with rounded beach gravels and organic matter additions identified phytoliths with a morphotype consistent with kūmara leaves with corresponding trace element elevations, indicating potential sources of nutrients. Our research findings can be used by Mana Whenua in their efforts to re-establish these horticultural practices, thus helping to reconnect soil, food, and people. Furthermore, our transdisciplinary approach provides guidelines for others seeking to move beyond the traditional boundaries of soil science to address challenges related to soil and food security, both in Aotearoa New Zealand and internationall
Development of a gastrointestinal parasite infection model to study chronic stress in livestock and impact on meat quality
No full textLivestock stressors are known to have an impact on both animal welfare and meat quality. As a model of acute stress, we have previously demonstrated the impact of pre-slaughter simulated mustering on several important meat quality markers in lamb, including high pH [1, 2]. To examine a chronic stressor in livestock, we have adapted a model of a sub-clinical infection with gastrointestinal nematode(GIN) parasite infection in sheep. Six month old ram lambs were challenged with a mixed infection of Trichostrongylus colubriformis and Teladorsagia circumcincta (Treatment group, n=6), which are common gastrointestinal parasites frequently encountered in pasture, and compared with those without parasites (Control, n=6) (AEC2023-71). The goal is to understand how parasite infection can impact on inflammatory response as a proxy for animal welfare, along with determining if parasite infection has an impact on meat quality markers. We will also use an emerging metabolomics method, rapid evaporative ionisation mass spectrometry, to provide complementary analytical information on changes to organ and meat metabolite and lipid composition. This data will contribute towards defining and designing further investigations on chronic stressors in livestock. In future, characterised biomarkers of stressors could be used for enhancing animal welfare and confirm the relationship between minimising pre-slaughter stressors and improving the consistency of meat quality
What if? Scenario simulations with the Wairau Plain groundwater model
No full textPresentation at NZHS 202
A landscape-based approach to optimise carbon sequestration in temperate freshwater wetlands, New Zealand: A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University
No full textFreshwater wetlands, often overlooked in mainstream carbon policy, function as credible carbon sinks. Referred to as ‘teal carbon zones,’ these ecosystems exceed many terrestrial systems in their capacity to store carbon, owing to high primary productivity and waterlogged, anaerobic soil conditions that slow organic matter decomposition. Yet despite this potential, freshwater wetlands remain marginal in global carbon accounting frameworks, and their design for carbon storage and outcomes is a growing area of interest in landscape architecture. This doctoral research responds to this opportunity by investigating how plant community composition, soil type, and plant–soil interactions influence carbon storage in two temperate inland freshwater wetlands, Travis and Sparks Wetlands, in Ōtautahi Christchurch, New Zealand.
The aim is to develop a landscape-informed design framework that places carbon sequestration at the centre of freshwater wetland design and management. A mixed-methods approach is adopted, including case study and survey research methods, field-based vegetation and soil assessments, standard laboratory analyses, and established carbon accounting protocols. Above-ground carbon is estimated using biomass regression equations and volume-derived methods. Soil carbon stocks are estimated through the life belt and the soil type methods to 90 cm depth. Maps assess the spatial variability of soil parameters within wetland areas. A novel ‘carbon-profile’ method is developed to integrate vegetation and soil carbon data at the plant assemblage level, enabling finer-grained insights into the spatial distribution of carbon within freshwater wetland systems.
The results reveal that wetland plant communities and soil types have a strong influence on how carbon is stored, both above and below ground. Notably, Travis Wetland stored significantly more soil carbon (51,266 Mg C to 90 cm depth) than Sparks Wetland (3,358 Mg C), due in part to its mix of peat and mineral soils. Plant communities with higher proportions of woody species, particularly those in forest and woodland types, consistently stored more above-ground carbon. Conversely, herbaceous communities, while lower in above-ground biomass, were associated with greater soil carbon concentrations. This inverse relationship highlights the importance of understanding carbon partitioning across biomass and soil pools within wetland plant communities. Plant functional traits, such as root depth, root morphology, litter quality, plant height, size, stem and wood densities, growth rate further shape carbon inputs to both soil and biomass layers. Greater species and structural diversity help distribute carbon more evenly across canopy, understory, and root layers. Canopy structure modulates the microclimate, influencing soil temperature, moisture, and organic matter dynamics. Furthermore, vertical soil carbon density distribution across eight soil types indicate that soil texture, bulk density, and saturation levels play critical roles in stabilising carbon at depth, while pH and salinity influence microbial activity and organic matter preservation. From these findings, a carbon-responsive landscape-framework is proposed. It outlines key considerations for plant species selection, species assemblage design, and soil condition management, with emphasis on aligning vegetation types with underlying soil characteristics. By embedding carbon sequestration into the early stages of freshwater wetland design, this research proposes actionable strategies to elevate freshwater wetlands as climate mitigation infrastructures in urban environments
Investigating the impact of morphology on spatial patterns of groundwater exchange in the Wairau River
No full textBraided rivers are common to many regions of New Zealand. Often, they are major drivers of groundwater recharge in the coastal regions. Understanding of the processes of water exchange between rivers and regional aquifers is mandatory for sustainable management of these aquifers. Recent research has proposed the concept of a braidplain aquifer (BPA), a shallow reservoir within the active braidplain channel of the rivers, in hyporheic and parafluvial exchange with the river and simultaneously with the regional aquifer (Wilson et al. 2024). the shallow nature of the braidplan aquifer suggests that morphological changes of braided rivers, that are frequently caused by flood events, highly impact these systems and their interaction with regional aquifers. this work aims to investigate and visualize the morphological effects on river - groundwater exchange in a section of the Wairau River by a detailed physics-based modelling of the coupled system
Land use change disrupts the network complexity and stability of soil microbial carbon cycling genes across an agricultural mosaic landscape
No full textTo understand the effects of agricultural land use change and management on soil carbon (C) cycling, it is crucial to examine how these changes can influence microbial soil C cycling. Network analysis can offer insights into the structure, complexity, and stability of the soil microbiome in response to environmental disturbances, including land use change. Using SparCC-based co-occurrence networks, we studied how land use change impacts the connectivity, complexity, and stability of microbial C-cycling gene networks across an agricultural mosaic landscape in Canterbury, New Zealand. The most densely connected networks were found in land uses that were under the most intensive agricultural management, or under naturally regenerating vegetation. The microbial C-cycling gene networks from both land uses presented high network connectivity, low modularity, and a low proportion of negative gene interactions. In contrast, microbial C-cycling genes from native forests, which had the most stable and undisturbed plant cover, had the lowest network connectivity, highest modularity, and a greater proportion of negative gene interactions. Although the differences in total soil C content between land uses were small, the large effects of land use on the network structure of microbial C-cycling genes may have important implications for long-term microbial soil C cycling. Furthermore, this research highlights the value of using microbial network analysis to study the metabolic gene interactions shaping the functional structure of soil microbial communities in a manner not typically captured by more traditional forms of microbial diversity analysi
Emerging climatic pressures: Connecting CO₂ and river ecosystems in a warming world
No full textThis presentation introduces the Emerging Climatic Pressures (ECP) MBIE Research Programme, a five-year study of the ecological and biogeochemical effects of rising CO₂ pressures on the Waikato River and freshwater environments more generally.
In terms of the carbon cycle, river corridors can be thought of as the largest nexus, or interface between the continents, oceans, and atmosphere. The ECP programme examines whether CO₂ exchanges occurring across this interface are defining emerging trends in water quality, that deviate from those expected based on total nutrient loads.
Our programme therefore asks fundamental questions about the relationship between CO₂ exchange and water quality (i.e. pH, dissolved nutrients, carbonate saturation); and how future atmospheric CO₂ levels could influence ecosystem phenology (e.g. phytoplankton succession) and the habitability of freshwater for molluscs (e.g., kākahi). These scientific questions are relevant to water quality attributes that matter to communities (e.g. safety for contact recreation), industry (e.g., drinking water source contamination), and Māori (e.g., mahinga kai)