Digital soil carbon mapping in diseased Agathis australis forests using site-specific and remote sensing data

ABSTRACTSoil‐borne pathogens can influence microbial communities and ecosystem function, making it important to understand their broader ecological impacts. We investigated interactions between Phytophthora agathidicida (the causal agent of kauri tree dieback) and soil microbial communities, while also comparing detection and community‐profiling methods. Soils from 60 kauri trees across three sites in the Waitākere Ranges, New Zealand, were analysed using loop‐mediated isothermal amplification (LAMP) for pathogen detection, and 16S rRNA gene/ITS gene amplicon sequencing alongside shotgun metagenomics for community characterisation. LAMP detected P. agathidicida in 39/60 samples, while shotgun sequencing detected Phytophthora‐associated DNA at low abundance across all samples. Microbial community structure and functional potential showed weak association with pathogen presence, though differential abundance testing identified several genera enriched in pathogen‐detected soils, including taxa previously linked to disease suppression. Amplicon and shotgun profiles indicated broadly comparable patterns at higher taxonomic and functional levels, while differences between approaches emerged primarily at finer taxonomic resolution. Importantly, functional predictions from PICRUSt2 closely matched shotgun‐derived profiles at broader scales, indicating its suitability as a cost‐effective tool for broad‐scale monitoring. These findings suggest limited direct pathogen effects on microbial communities and highlight how integrating molecular approaches provides complementary insights into soil microbiome‐pathogen interactions.

Kauri (Agathis australis) is a culturally and ecologically important conifer native to Aotearoa New Zealand. It is currently threatened by a dieback disease caused by the soil-borne pathogen Phytophthora agathidicida. The relationship between the plant and its endophytes plays a crucial role in plant growth, host resilience, physiology, and defence mechanisms. This research investigates the potential role of endophytes in supporting systems, particularly concerning kauri dieback disease. The study focuses on identifying and characterizing the endophytic fungi and bacteria associated with the roots of cutty grass (Carex geminate) and kauri grass (Astelia trinervia), which are companion plants in kauri forests found at both diseased and healthy sites. These companion plants are closely associated with kauri and serve as promising models due to their abundance. A total of 61 endophytes were isolated from the roots of both plants using different media. The colony and cell morphology of these isolates were examined, and they were identified as putative Fusarium, Penicillium, Trichoderma, and Aspergillus species. The full 16S rRNA gene and internal transcribed spacer (ITS) region analyses confirmed the phylogenetic identities of the endophytes. Some isolates demonstrated antagonistic effects against Phytophthora agathidicida via dual culture assays. Bioactive metabolites from these endophyte isolates will be extracted for further analysis. This study aims to explore whether root endophytes of companion plants could contribute to biocontrol strategies for combating kauri dieback. This research provides novel insight into mitigating plant pathogens in native forests and ecosystems using companion plants hence, preserving forest integrity.

Agathis australis (kauri), the only member of the ancient conifer family Araucariaceae in New Zealand, is colonised by arbuscular mycorrhizal (AM) fungi. The survival of A. australis is threatened by an Oomycota, Phytophthora agathidicida , the causal agent of kauri dieback. Phosphite injections into the trunk are the primary treatment for kauri dieback and have proven effective in reducing disease symptoms. However, the potential impact of phosphite treatment on AM fungal colonisation within A. australis roots and nodules has not been investigated. We conducted a preliminary investigation into whether AM fungi colonise phosphite‐treated trees. Using a combination of microscopy and metabarcoding of AM fungi 18S nuclear ribosomal small subunit genes, we demonstrate that AM fungi colonise the roots and nodules of A. australis trees three to 4 years post‐treatment. Glomeraceae was found to dominate, and AM fungi community composition and colonisation rates were comparable to previously reported values in trees not treated with phosphite. Soil pH, but not date of phosphite treatment or PA infection status, was found to significantly contribute to AM fungal community composition. This work highlights the importance in investigating colonisation events immediately after phosphite treatment of A. australis and a comparison with untreated trees. AM fungi are likely integral for A. australis forests to thrive, thus, ensuring they are protected in the treatment of kauri dieback is essential.

This research investigates how the soundscape of Native forests reflects forest health and how it may signal early signs of Kauri Mate ( Phytophthora agathidicida ; dieback) infection. Grounded in mātauranga Māori (Māori [the Indigenous peoples of New Zealand] knowledge) from Te Rarawa (a tribe in the northern North Island, New Zealand), the study combines Indigenous knowledge with modern technology to develop a sonic-based method for ecological restoration. Recorded soundscapes from healthy kauri (a coniferous tree, northern New Zealand; Agathis australis ) are layered with taonga puoro (traditional Māori instruments), karakia (chants), and parāoa (sperm whale) calls, blended with the 528 Hz healing frequency to create immersive environments aligned with the forest’s mauri (life force). This methodology acknowledges the interconnectedness of all living entities and aims to restore ecosystems through vibration and sound. Findings recommend community-led, culturally grounded soundscape interventions to support forest health, while strengthening spiritual and emotional connections between people, place, and environment.

Context Agathis australis (kauri) is endemic to New Zealand (NZ) and classified as Endangered by the International Union for the Conservation of Nature. Although still the main priority, in situ conservation alone is no longer sufficient to safeguard species from extinction, especially when they are threatened by climate change and pathogens. Ex situ conservation provides opportunities to maintain plants as seeds, tissue culture or living collections in botanic gardens or germplasm repositories. Aims The current study aimed to quantify the production of viable seed in ex situ collections of A. australis growing at the Ōtari Native Botanic Garden and optimise seed banking methods. Methods Cones were collected from six specimens over 5 years and the production of viable seeds quantified. Seed germination protocols were established, the impact of desiccation assessed and the role of storage temperature (5°C, −18°C and −196°C) on seed viability evaluated. Lastly, the fatty acid profiles of fresh and stored seed were determined. Key results Viable seed production varied significantly between individual trees and years. Seeds were not desiccation sensitive but to maintain viability, it was essential to store seeds at −18°C or −196°C. Seeds had high amounts of long-chain fatty acids which increased following storage. Conclusion Ex situ collections of A. australis are a valuable tool for the development of conservation methods such as seed collection, germination and seed banking. Implications This study provides essential information to maximise the contribution of ex situ living collections for research into phenology, seed physiology and germplasm storage, which can guide integrated conservation and restoration actions for Agathis species.

Developmental timing in the female reproductive cycle of Araucaria araucana: seasonality and evolutionary perspectives.

Abstract In 2014, a fire at the Glasgow School of Art’s Mackintosh Building revealed the use of New Zealand kauri (Agathis australis D. Don Lindley) masquerading as oak pillars. A description of this timber as ‘cheap ballast’ in a 2015 Guardian article prompted investigation into the awareness, export, and use of kauri in the United Kingdom (UK). Awareness of kauri in the UK developed during the 1800s, as botanical knowledge of New Zealand flora increased and through discussion of kauri forests, trees, and timber in a range of academic and general publications. The earliest kauri exports were spars for the Royal Navy and between 1850 and 1894, approximately 79 shipments of kauri were dispatched to the UK, with over half occurring in the 1880s and 1890s. At that time, an economic recession and oversupply in NZ pushed the timber companies to seek a share of the ‘home’ (UK) market. The promotion of kauri in the UK (and Europe) included the display of timber and finished products at international exhibitions. Kauri was sold throughout the UK and was used for a wide variety of purposes, including furniture, joinery, fixtures, and fittings. Sent as intentional cargo, it was more than ‘cheap ballast’, and its presence in the UK demonstrates the colonial timber trade and ties between New Zealand and Britain in the 1800s and early 1900s.

ABSTRACTPhytophthora agathidicida, a plant pathogenic oomycete, causes fatal dieback disease in New Zealand kauri trees (Agathis australis). Currently, few treatments exist to prevent or cure this infection. Previous research has demonstrated the potent in vitro inhibition of multiple lifecycle stages of P. agathidicida by the oomycide oxathiapiprolin. In this study, we have evaluated the efficacy of oxathiapiprolin in planta as either a protective or curative treatment. Kauri seedlings (1–2 years old) were treated with 10 or 50 mg of oxathiapiprolin, in the form of Zorvec Enicade, per seedling as a soil drench either before (7 days) or after (15 days) inoculation with P. agathidicida NZFS 3770 to test for protective and curative activities, respectively. Results showed that oxathiapiprolin treatments successfully protected the kauri seedlings from disease, with the higher dose (50 mg) demonstrating greater efficacy. However, the treatments did not cure kauri seedlings already infected with P. agathidicida, likely because the infection was already well‐established by the time of treatment. This study demonstrates that, while oxathiapiprolin shows protective effects against P. agathidicida infection in kauri seedlings, its lack of curative properties significantly limits its potential as a practical tool for managing kauri dieback disease.

The southern conifer Agathis australis (D.Don) Lindl. is a large and long-lived species endemic to Aotearoa New Zealand. It is threatened due to past logging activities, pathogen attack and potentially climate change, with increasing severity and frequency of drought and heatwaves across its distribution. Like many large tree species, little is known about the carbon dynamics of this ecologically and culturally significant species. We explored seasonal variations in non-structural carbohydrates (NSCs) and growth in trees ranging from 20 to 175 cm diameter at breast height (DBH). NSCs were seasonally stable with no measurable pattern across seasons. However, we found growth rates standardised to basal area and sapwood area (growth efficiency) declined with tree age and stem NSC concentrations (including total NSCs, sugars and starch) all increased as trees aged. Total NSC concentrations were 0.3%–0.6% dry mass for small trees and 0.8%–1.8% dry mass for larger trees, with strong relationships between DBH and total NSC, sugar and starch in stems but not roots. Cumulative growth efficiency across the two-year study period declined as tree size increased. Furthermore, there was an inverse relationship between growth efficiency across the two-year study period and NSC concentrations of stems. This relationship was driven by differences in carbon dynamics in trees of different sizes, with trees progressing to a more conservative carbon strategy as they aged. Simultaneously declining growth efficiency and increasing NSC concentrations as trees age could be evidence for active NSC accumulation to buffer against carbon starvation in larger trees. Our study provides new insights into changing carbon dynamics as trees age and may be evidence for active carbon accumulation in older trees. This may provide the key for understanding the role of carbon processes in tree longevity.

ABSTRACT A new species of Blattidae cockroach is described from northern Aotearoa New Zealand. Celatoblatta kauri sp. nov. can be distinguished from similar conspecific species by its distinctive facial markings. The recorded distribution of Celatoblatta kauri sp. nov. matches that of the historic distribution of kauri forest (Agathis australis) in northern New Zealand. Zoobank LSID: urn:lsid:zoobank.org:pub:93794424-1A7B-4CCA-A7A1-A303BCE8EACA.

ABSTRACTDisease caused by plant pathogens can shape plant community structure and composition, especially if the host species plays important ecological roles. The New Zealand kauri, Agathis australis, is a foundation species that modifies its soil environment and, by doing so, it acts as an ecological filter selecting for a distinctive suite of plant species that co‐occur preferentially with it. Kauri is threatened by kauri dieback disease caused by Phytophthora agathidicida. Despite kauri's ecological importance in structuring plant communities, little is known about the consequences of kauri dieback on the plant species ecologically associated with kauri—kauri associates. This study examined (1) the environmental drivers of diseased kauri occurrences, (2) the correlations between the occurrences of kauri associates and environmental factors and (3) which kauri associates frequently co‐occurred with diseased kauri as a result of shared environmental responses. A joint species distribution model with nine environmental factors was used to analyse the occurrences of diseased kauri and 16 kauri‐associated plant species located within a 10‐m radius of 761 kauri trees in lowland kauri‐podocarp‐broadleaved forests of Waitākere Ranges, Auckland, New Zealand. Our results showed that diseased kauri occurred more frequently in sites at lower elevation, with shallower organic soil layers and a history of logging or timber processing disturbance. Additionally, successional strategies influenced the relationship between kauri associate occurrences and environmental factors, with kauri associates characteristic of early succession frequently co‐occurring with diseased kauri due to environmental factors. This suggests that kauri dieback could either cause the retrogression of succession in kauri forests or that kauri in younger stands were more likely to be diseased. Both of these possibilities indicate that kauri dieback would likely change the successional trajectory of kauri forests. Future studies should integrate longitudinal demographic data with disease progression to investigate the mechanistic effects of disease on kauri community dynamics.

Phosphite (HPO32–) is an effective chemical treatment used to manage Phytophthora diseases in natural and horticultural environments. In New Zealand it is applied as a trunk injection to protect the threatened endemic foundation tree, Agathis australis (kauri), from the invasive pathogen P. agathidicida. It is applied as a foliar spray in natural ecosystems in Australia to protect against a range of Phytophthora-associated diseases and retain plant biodiversity and abundance. Foliar spray application could be a useful method for broad area treatment and to protect isolated and difficult-to-reach stands of kauri, or in plant production settings. In this study, we assessed the efficacy of phosphite when applied as a foliar spray to inhibit P. agathidicida colonisation, the phytotoxicity response and whether the phosphite was translocated to the roots using two glasshouse experiments with 2- and 6-year-old kauri plants. The foliar phosphite treatment effectively reduced colonisation by P. agathidicida in the 2-year-old plants and elevated concentrations of phosphite in the roots of the 6-year-old plants were detected. Phytotoxicity increased with increasing phosphite concentration in both trials. The addition of the surfactant Du-Wett® reduced phytotoxicity for older leaves in the 6-year-old plants. In both assays, phytotoxicity symptoms were most severe on young leaves but had no effect on the production of fresh growth following treatment, suggesting that any ill effects were short-lived. This study indicates that phosphite foliar sprays may be an effective tool to manage kauri dieback under the appropriate circumstances.

ABSTRACTAimsUnderstanding the impacts of forest tree pathogens on understorey sapling populations is critical for understanding their population‐level effects and the likely successional trajectories of infected communities. We assessed the impacts of Phytophthora agathidicida, a soil‐borne pathogen, on the sapling population dynamics of the disease‐susceptible, locally dominant canopy tree, the conifer kauri (Agathis australis, Araucariaceae). We also examined the indirect effects of P. agathidicida on likely resistant allospecifics that span a range of shade‐tolerances as saplings, to predict future successional trajectories.LocationWaitākere Ranges, west of Auckland, Aotearoa‐New Zealand.MethodsWe analysed data from four kauri‐dominated permanent plots in Aotearoa‐New Zealand warm temperate rain forests. Two plots were early‐successional and two were late‐successional, one in each pair had overstorey kauri showing intense visual P. agathidicida symptoms, and the other overstorey kauri showing few symptoms. We examined the association between kauri trees and saplings using point pattern analysis and the relationship between the level of crowding around saplings and their growth and survival rates. We compared the growth and survival rates of kauri and allospecifics, categorised by shade tolerance, among the plots.ResultsKauri forms sapling banks under conspecific trees that were less dense in late‐successional forests and in those where the overstorey kauri showed symptoms of P. agathidicida infection. Despite having lower densities, kauri sapling growth rates were higher in symptomatic plots. The growth rates of light‐demanding allospecifics were also higher in these plots, with minor differences in mortality and growth rates for more shade‐tolerant allospecifics. P. agathidicida may promote sapling growth and survival of kauri and some allospecifics in infected plots.ConclusionsSapling vital rates and population sizes differed between asymptomatic and symptomatic plots, particularly in early‐successional settings, where P. agathidicida may reset succession in early‐successional communities back to those dominated by species that first colonised after disturbance.

Safeguarding Iconic Tree Species, Dependent Ecosystems, and Regional Economies: A New Zealand Perspective on Controlling Kauri Dieback

Several papers have been published in the last two decades about the peculiar cortices that commonly are present in Cretaceous amber pieces from diverse terrestrial western Tethyan localities. These cortices are constituted by networks of filamentous structures, and have been identified as mycelia composed of hyphae of resinicolous fungi according to a multidisciplinary research of Albian Spanish samples using diverse techniques. Main evidence indicating its fungal nature was the taphonomic scenario inferred and the detection of preserved chitin polysaccharides in the filamentous structures, using specific chitin markers visualized under confocal laser microscopy. Herein is present a similar fungal colonization pattern forming thin cortices observed in extant kauri pine resin (Agathis australis: Araucariaceae) from New Zealand. It has been compared with the typical pattern previously observed in the Spanish Cretaceous amber cortices. The similar fungal cortices in Agathis resins are considered as taphonomic and ecological analogues, but no phylogenetic relationship is suggested. The palaeoecological implications, with regard to Spanish Cretaceous forest environmental conditions that this extant correlate suggests, are discussed; also a new unusual growth of resinicolous fungus with the same microscopic hyphae features in Cretaceous amber are presented. Conclusions can be extended to Cretaceous amber cortices from other Laurasian localities.

Global climate variability is projected to result in more frequent and severe droughts, which can have adverse effects on New Zealand’s endemic tree species such as the iconic kauri (Agathis australis). Several studies have investigated the physiological response of kauri to medium- and long-term water stress; however, no research has used hyperspectral technology for the early detection and characterization of water stress in this species. In this study, physiological (stomatal conductance (gs), assimilation rate (A), equivalent water thickness (EWT)) and leaf-level hyperspectral measurements were recorded over a ten-week period on 100 potted kauri seedlings subjected to control (well-watered) and drought treatments. In addition, plant functional traits (PTs) were retrieved from spectral reflectance data via inversion of the PROSPECT-D radiative transfer model. These data were used to (i) identify key PTs and narrow-band hyperspectral indices (NBHIs) associated with the expression of water stress and (ii) develop classification models based on single-date and multitemporal datasets for the early detection of water stress. A significant decline in soil water content and physiological responses (gs and A) occurred among the trees in the drought treatment in weeks 2 and 4, respectively. Although no significant treatment differences (p > 0.05) were observed in EWT across the whole duration of the experiment, lower mean values in the drought treatment were apparent from week 4 onwards. In contrast, several spectral bands and NBHIs exhibited significant differences the week after water was withheld. The number and category of significant NBHIs varied up to week 4, after which a substantial increase in the number of significant indices was observed until week 10. However, despite this increase, the single-date models did not show good model performance (F1 score > 0.70) until weeks 9 and 10. In contrast, when multitemporal datasets were used, the classification performance ranged from good to outstanding from weeks 2 to 10. This improvement was largely due to the enhanced temporal and feature representation in the multitemporal models. Among the input NBHIs, water indices emerged as the most important predictors, followed by photochemical indices. Furthermore, a comparison of inverted and measured EWT showed good correspondence (mean absolute percentage error (MAPE) = 8.49%, root mean squared error (RMSE) = 0.0026 g/cm2), highlighting the potential use of radiative transfer modelling for high-throughput drought monitoring. Future research is recommended to scale these measurements to the canopy level, which could prove valuable in detecting and characterizing drought stress at a larger scale.

Ngā mihi ki a koe and to all of the viewers and readers of Kairaranga, it’s such a pleasure to have the chance to kōrero with you all today. Ko wai au? I te taha o tōku matua, no Indonesia ahau. I te taha o tōku māmā, no Airani, Kōtirana, me Ingarangi ahau. On my dad’s side, I’m from Indonesia, from Central Java, and from my mum’s side, Irish, Scottish, and English ancestry. I grew up in the beautiful west of Tāmaki Makaurau, amongst the kererū and kauri trees there, and that’s a place that has really shaped me. I did my schooling in Tāmaki Makaurau, out west in Auckland and then went to university in Tāmaki Makaurau and then offshore in the Netherlands. My career has basically been dedicated to children’s rights, human rights and social justice. Throughout the various roles that I’ve had, a focus on children and their rights has always been there, and over the past 10 years or so I’ve really deepened that even more. I went and did my Masters and then my PhD in international children’s rights law, but practice and working to advance the rights of tamariki, of mokopuna has always been something that has been my guiding force, whether that’s been overseas internationally working for organisations like Unicef advocating in places like the European Union and the Council of Europe, or back home here in Aotearoa New Zealand. I really have a strong belief in the potentiality of all of our mokopuna, all our children and young people. To see them fully flourish, their full range of holistic rights really need to be upheld and realised in their everyday lives. I guess it’s all of those different threads that have led me through into this role as Chief Children’s Commissioner, which is such a privilege, but also a very, very big responsibility. I’m grateful to work with an amazing team and board alongside me, and the focus is really now on ensuring that we’re advocating as strongly as possible for the rights of mokopuna here in Aotearoa New Zealand.

Leaf surface microbial communities play an important role in forest ecosystems and are known to be affected by environmental and host conditions, including diseases impacting the host. Phytophthora agathidicida is a soil-borne pathogen that causes severe disease (kauri dieback) in one of New Zealand’s endemic trees, Agathis australis (kauri). This research characterised the microbial communities of the A. australis phyllosphere (i.e. leaf surface) using modern molecular techniques and explored the effects of P. agathidicida on those communities. Fresh leaves were collected from trees where P. agathidicida was and was not detected in the soil and characterisation of the leaf surface microbial community was carried out via high-throughput amplicon sequencing of the internal transcribed spacer (ITS) and 16S ribosomal RNA regions. Nutrients in leaf leachates were also measured to identify other possible drivers of microbial diversity. The dominant phyllosphere microbial phylum was Proteobacteria followed by Acidobacteria. The phyllosphere microbial richness of A. agathis associated with P. agathidicida-infected soils was found to be generally lower than where the pathogen was not detected for both prokaryote (bacterial) and fungal phyla. Leaf leachate pH as well as boron and silicon had significant associations with bacterial and fungal community structure. These findings contribute to the development of a comprehensive understanding of A. australis leaf surface microbial communities and the effects of the soil pathogen P. agathidicida on those communities.

Phytophthora are causing declines in forest tree species worldwide and the chemical control treatment, phosphite, is the only treatment consistently shown to provide some protection to natural ecosystems from Phytophthora diseases. Phosphite inhibits Phytophthora growth and sporulation whilst boosting defence responses in the plant host. It is unclear, however, the extent of the impact of phosphite on Phytophthora species assemblages and inoculum abundances in soil around trees following treatment within natural ecosystems. In New Zealand, kauri (Agathis australis), an endemic and threatened foundation species, suffers from a dieback disease primarily caused by Phytophthora agathidicida. Phosphite is applied by trunk injection to kauri and has been shown to improve resin ‘bleed’ symptoms from basal trunk lesions and to promote recovery of thinned canopies. Phytophthora community and inoculum abundance were investigated in response to phosphite treatments at two field sites (Huia and Waitoki) in infected kauri stands in Auckland, New Zealand. At Huia, soil sampling and tree health surveying were conducted in November 2023 on trees treated with phosphite in 2012 as part of an earlier study. At Waitoki, the response to phosphite treatment was monitored 6 and 18 months following treatment. Phytophthora species were detected using soil baiting and metabarcoding of Environmental DNA (eDNA) from soil and quantified with qPCR of root and soil DNA. Three species were detected with soil baiting (P. agathidicida, P. cinnamomi, and P. multivora) and two additional species with metabarcoding (P. pseudocryptogea, and an unknown clade 7 species similar to P. europaea). Phytophthora cinnamomi was the most abundant species, followed by P. agathidicida. Both species were more likely to occur together than by chance alone and were associated with declining tree health. The P. europaea-like species was in approximately 50 % of the samples and was less likely to occur in roots with poorer health, or in association with P. agathidicida. The abundance of P. agathidicida inoculum was lower in the soil around the phosphite-treated trees than around the untreated control trees 1.5 years after treatment at Waitoki. Phosphite halted the lateral expansion of basal resin bleeds, and resin viscosity was reduced. Not only did phosphite treatments improve kauri dieback symptoms, but the phosphite treatments potentially had a direct impact on the epidemiology of the disease by reducing inoculum load around treated trees, with direct implications for disease management as an effective way to protect uninfected areas and minimise the spread of inoculum from infested zones.