To separate the effects of the abiotic and biotic soil components on plant growth, researchers can compare plants grown in sterilised and unsterilised soil (unsterilised soil approach). However, using this approach can be problematic if the abiotic component of the soil is affected by the sterilisation treatment, which is often the case. We aimed to determine how often this approach is used by plant-soil interaction studies and demonstrate how it can impact plant growth. We reviewed the relevant literature to determine how often the unsterilised soil approach is used and whether the studies that use it acknowledge the 'soil sterilisation' caveat. We then conducted a glasshouse experiment to demonstrate the effect that soil sterilisation has on selected soil nutrients and consequently on plant growth. Our literature review revealed that of the studies that used the unsterilised soil approach, only 23% measured and reported soil nitrogen or phosphorus before and after sterilisation, with 50% of these reporting a change in one or both nutrients. We then showed that the growth of our study species, Eucalyptus saligna, was greater when grown in sterilised soils compared to unsterilised soils. Interestingly, there was a strong positive relationship between the change in ammonium nitrogen and E. saligna growth between the sterilised and unsterilised soils. Given our findings, we advocate that studies that use the unsterilised soil approach should measure the abiotic soil properties before and after sterilisation and if differences are found, these studies should use the inoculation approach instead.

Bell miner associated dieback (BMAD) is a prevalent type of eucalypt dieback along the eastern seaboard of Australia that is caused by repeated psyllid outbreaks, which are due to over-abundant bell miner birds excluding insectivorous birds. Despite strong evidence for this causal model, we have a limited understanding of how abiotic soil properties influence the interactions within the model. To address this knowledge gap, we compared the abiotic soil properties of Eucalyptus saligna forest stands affected and not affected by BMAD in New South Wales (NSW). We then tested whether the differences in the abiotic soil properties altered soil mycorrhizal fungal communities, bell miner bird nesting habitat availability via understorey thickening by Lantana camara (growth) and factors that may influence eucalypt-psyllid interactions including E. saligna feed quantity (tree size and leaf growth rate), feed quality (leaf nutrient content) and chemical defences (terpene emissions). We found that BMAD-affected stands had higher soil available phosphorus than stands not affected by BMAD, which was most likely due to topography. This higher soil available phosphorus was associated with greater L. camara growth and E. saligna leaf phosphorus content, suggesting it may be important in bell miner bird nesting habitat availability and the quality of feed available to psyllids. In contrast, the feed quantity and chemical defences of E. saligna were not related to soil available phosphorus. Our findings show that soil available phosphorus may play an important role in BMAD in eucalypt forests. Therefore, we can use remote sensing generated fine-scale soil nutrient maps to identify eucalypt stands that are vulnerable to BMAD and focus preventative management actions in these areas.

Invasive plants often impact the abiotic and biotic conditions of the ecosystems they invade. These impacts can persist after the removal of the invader as legacy effects that may hamper restoration. We assessed whether the invasion of Cumberland Plain Woodland in Australia by African Olive impacts the performance of native species through legacy effects. We also tested whether the addition of soil inocula from uninvaded Cumberland Plain Woodland and rhizosphere soils can mitigate the effects of invaded soils on native plant performance. To do this, we grew four native Cumberland Plain Woodland species (Australian Indigo, Climbing Saltbush, Hickory Wattle, Wedge-leaf Hop-bush) in mesocosms containing either uninvaded Cumberland Plain Woodland soil, African Olive-invaded Cumberland Plain Woodland soil or invaded Cumberland Plain Woodland soil inoculated with uninvaded or native rhizosphere soil. We found invaded soils to not consistently impact the growth of the Cumberland Plain Woodland species studied. In invaded soil, Hickory Wattle produced lower above and belowground biomass, Climbing Saltbush produced lower belowground biomass and Australian Indigo had a lower root to shoot ratio compared to plants grown in Cumberland Plain Woodland soil. The nodulation of Australian Indigo did not differ between soil treatments, while that of Hickory Wattle responded positively to inoculation. Our results suggest that the addition of native soil biota may improve the outcomes of ecological restoration projects on a species-specific basis.

Insect herbivore pests have been identified as a significant threat to the health and survival of urban trees. In the future, these pest-tree interactions in urban areas may be altered by the increased variability in environmental conditions projected under climate change. However, our understanding of how this may occur is limited. In this short communication, we discuss the factors that increase urban forest vulnerability to insect pests and how climate change will alter these factors. We then discuss how we can help to reduce the negative effects of these factors through actions such as diversifying our urban forests, reducing plant stress and increasing our capacity for early detection of insect pests using emerging biosurveillance technologies. In a time with increasing globalisation aiding in the transport of pests between urban areas, it is important that we remain vigilant to the ever-increasing threats that can compromise our urban green assets and the benefits they provide.

To enhance the establishment of container-grown trees, nursery and urban forest practitioners use root pruning to improve plant root structure. However, some methods of root pruning may cause stress to the plant and reduce shoot growth. One potential approach to mitigating tree stress is the application of biostimulants. This study aimed to determine the impact root shaving, a type of root pruning, has on the growth of urban plant species, and whether biostimulant application mitigates this impact. To address these aims, we applied root shaving (not shaved, shaved) and biostimulant (control, humic substance, protein hydrolysate, seaweed extract) treatments to six tree species that are commonly planted in the Sydney metropolitan area, Australia in a factorial design. The study consisted of a glasshouse and field experiment to simulate nursery production and urban field conditions, respectively. We found that the assimilation rate of the plants was not affected by root shaving but four of the species still experienced reductions in shoot growth in the short-term. This reduction was a result of the plants allocating resources to root growth to compensate for the root loss. However, in the long-term, the plants were able to compensate for this reduction in shoot growth. We found that biostimulant application did not mitigate the short-term impacts of root shaving on plant growth. We can conclude that root shaving and biostimulant application do not affect plant establishment in the long-term.

Urban areas often have low soil water availability due to their impervious surfaces reducing rainfall infiltration. These water-limited conditions may be exacerbated by the projected increases in drought events caused by climate change. As a result, plants that grow in urban areas are vulnerable to drought stress. There are a range of practices that can be used to help mitigate drought stress, including the use of biostimulants. This study aimed to determine whether biostimulant application (1) improves plant performance and (2) mitigates the drought stress on urban plant species. To address these aims, we selected six woody and three graminoid plant species that are commonly planted in Australian urban areas and exposed them to different watering (drought-stressed, well-watered) and biostimulant (control, humic acid, protein hydrolysate, seaweed extract) treatments. We then measured their assimilation rate, growth metrics and biomass allocation. We found that drought stress reduced the assimilation rates and shoot growth of the study species. However, this did not translate into a biomass reduction because the drought-stressed plants reallocated resources towards root biomass. We found no evidence to suggest biostimulant application mitigated the impacts of drought stress on plant performance. Further, the only effect biostimulant application had on plant performance irrespective of the watering treatment was that the seaweed biostimulant increased the plant height growth of the woody species. These results show that the biostimulants used in this study will have a limited effect on the performance of plant species commonly planted in Australian urban areas.

More than three quarters of terrestrial habitats have been transformed by human activities (Ellis et al., 2021). As a result, reversing land degradation is one of humanity's chief imperatives, with the United Nations declaring 2021–2030 the Decade of Ecosystem Restoration. Restoring degraded lands requires rebuilding and protecting ecological communities that support biodiversity and ecosystem functions. These efforts normally focus on macroscopic native organisms (usually plants) that through time have co-evolved and developed interaction networks with other species across a diverse range of niches. The rich interdependencies in such ecological interaction networks (EINs) enhance the integrity of ecosystems and improve resilience to stressors (e.g., Barnes et al., 2020). However, the restoration of these networks is often ineffective, with unpredictable outcomes, in part because restoration usually focuses on a few plant species or specific animal habitats, and therefore wider interaction networks are generally not considered. Some researchers have also suggested that networks (e.g., plant–pollinator) develop as "passengers" of restored plant communities (e.g., Menz et al., 2011), while others have argued that the restoration of key taxa has the potential to re-establish functional networks (Pocock et al., 2012). Restoration would thus benefit from approaches that facilitate the reassembly of EINs early in the process, e.g., through targeted rewiring of key biotic interactions. One promising approach is the direct manipulation of soil microbes to enhance restoration success (Koziol et al., 2022). Working with soil microbial communities to restore vegetation is not a new idea (Coban et al., 2022), but identifying and using specific soil microorganisms to shortcut the development of key plant–microbial interactions to enhance the colonization and persistence of diverse native plant communities is. Soil microbes play a crucial role in the functioning of all ecosystems, e.g., influencing plant performance by maximizing nutrient uptake and alleviating the impacts of stressors (Trivedi et al., 2020). Microbes are heterogeneously distributed in soils, largely because of variations in abiotic properties such as pH and organic carbon (Fierer, 2017). Therefore, when ecosystems experience degradation that alters abiotic soil properties, their soil microbial communities (and associated functions) are also altered. It has therefore been suggested that restoring and maintaining healthy soil microbial communities would benefit ecological restoration (here referring to the re-establishment of native plant communities; Coban et al., 2022). However, a recent global meta-analysis has clearly shown that manipulations of soil microbial communities during ecological restoration have had varied success (Gerrits et al., 2023), suggesting that the wholesale manipulation of soil microbial communities is difficult, if not impossible, partly due to the altered abiotic soil properties of degraded lands. A more feasible option than the wholesale manipulation of soil microbial communities to reassemble critical plant–microbial interactions during ecological restoration may be the manipulation of specific microbes. It can be argued that symbiotic mutualists (e.g., mycorrhiza, rhizobia) are the key microbes to target for the restoration of critical interactions. The benefit of manipulating such mutualists to improve plant performance has been well demonstrated in agricultural systems and, to some extent, in natural environments (e.g., Farrell et al., 2020). For example, large-scale revegetation trials in Australia showed that inoculation with generalist rhizobia enhances the establishment of Acacia seedlings in some, but not all, habitats (Thrall et al., 2005). Similarly, Koziol and Bever (2017) found that the benefits of inoculation with arbuscular mycorrhizal fungi (AMF) for grassland restoration in North America were dependent on the type of AMF used. These two examples illustrate that the outcomes of interventions to reassemble key plant–mutualist interactions during restoration are varied and context-dependent. Using the restoration of land previously invaded by alien species as an example, we provide ideas on how to identify the most-promising soil microbial mutualists to predictably re-establish key native species interactions during restoration. We studied the impacts of African olive (Olea europaea subsp. cuspidata) invasion in the Critically Endangered Cumberland Plain Woodland (CPW) in southwestern Sydney, Australia. We grew seedlings of the native legume Acacia implexa (hickory wattle) in soils collected from sites that had been cleared of African olive and restored 25 years ago (restored soil), sites where dense African olive is still present (invaded soil), and reference sites where African olive has never invaded (uninvaded soil). Hickory wattle forms mutualisms with rhizobia. These bacteria stimulate the formation of specialized structures, called nodules, in the roots of legumes where they fix atmospheric nitrogen in exchange for plant-derived sugars. Levels of nodulation and nitrogen fixation, however, depend on the availability of compatible and effective rhizobia. For example, hickory wattle nodulates exclusively with Bradyrhizobium strains. We isolated DNA from the nodules of hickory wattle seedlings grown in the three soil types and used DNA barcoding to identify Bradyrhizobium strains that are characteristic of each soil type (i.e., indicator taxa; see Le Roux et al., 2018 for similar methodologies). We found the relative abundance of indicator Bradyrhizobium taxa of invaded and uninvaded soils to be negatively and positively correlated, respectively, with nodulation across all soil types, while the relative abundance of non-indicator taxa did not correlate with nodulation (Figure 1). The example above clearly illustrates the impact of invasion on the availability of mutualists for native plants. In instances such as these, it is critical that we incorporate our knowledge of EINs (Moreno-Mateos et al., 2020) to determine the most effective mutualists at the community level to enhance restoration success; however, there are currently no guidelines on how to ascertain which will be most effective. Identifying suitable mutualists for use in restoration is further complicated by the fact that establishing ecological interactions requires the introduction of species with compatible traits, phenologies, and high encounter probability (Moreno-Mateos et al., 2020). We suggest that paying attention to the structural properties of EINs among plant and soil microbial mutualists can help ecologists identify the most-promising microbial mutualists for effective use in restoration. All species interactions fall somewhere along a continuum of specialization with, at one end, specialist species interacting with only one or a few taxa, while at the other end, generalists can successfully interact with a wide range of taxa. Mutualistic EINs are typically nested, e.g., with specialist plant species interacting with generalist mutualists, while generalist plants interact with both generalist and specialist mutualists (e.g., Figure 2D). The mutualists interacting with generalist host plants are also often mutually substitutable in terms of the benefits they provide to their hosts, i.e., being functionally redundant. Conversely, the mutualists of specialist plants may not be substitutable. For example, network analyses between rhizobia and invasive and native legumes in South Africa showed that native legumes with highly specialized rhizobium interactions were unable to persist in invaded habitats, while generalist native legumes could, but only in association with novel rhizobia (Le Roux et al., 2016). The introduction, retention, or removal of specialists may thus strongly influence the functioning of EINs (Warwick et al., 2022). Introducing super-generalist mutualists that are compatible with both specialist and generalist plant species, identified via network analyses in reference sites (e.g., rhizobium species 1 in Figure 2D), will provide symbiotic benefits to the highest number of native plant species to increase plant functional diversity in degraded soils. For the hickory wattle example, we suggest that indicator Bradyrhizobium strains of uninvaded (i.e., reference) soil will be of high restoration value if network analysis identifies them as also having strong links with generalist native legume species. Like super-generalist mutualists, the introduction of super-generalist host plants may be useful targets for ecological restoration, with possible knock-on benefits to other trophic networks (Pocock et al., 2012). These host plants could be introduced without mutualists, as they are likely to encounter compatible partners in degraded soils or, alternatively, they can be used to "trap" mutualists for inoculum development in reference sites. In networks with high connectivity and low modularity, super-generalist host species could also facilitate indirect interactions, such as mutualist spillover (Warwick et al., 2022). Despite its promise, rewiring specific connections in EINs may have consequences for other networks. For instance, introducing certain plant species combinations to promote pollination may cause changes in parasitism or herbivory (e.g., Windsor et al., 2021). We suggest that future research explore the effectiveness of generalist endosymbionts that are also effective mutualists of specialist plants for use as inoculants in restoration (also see Pocock et al., 2012). While plant endosymbiotic mutualists are promising targets for assisting ecological restoration, they only make up a small fraction of all the microbes that plants interact with, and plant-associated microbiomes are a vast untapped reservoir of plant-beneficial microbes. The assembly of these microbiomes is not a random process and is controlled by interactions among host plants, the abiotic environment, and microbial taxa. Firstly, we can consider that the microbial community of the bulk soil acts effectively as the regional pool, with both abiotic (e.g., soil nutrients) and biotic (e.g., plants) conditions creating a filter resulting in local microbial community composition. The trajectory of microbial community assembly is then influenced by a range of factors including local abiotic conditions, dispersal ability, priority effects, disturbance, propagule pressure, niche differentiation, and competition (Trivedi et al., 2020). Given this complexity, is it likely that we can design strategies to manipulate plant-associated microbiomes that will enhance restoration success? Network analyses again provide important insights by identifying microbes that frequently co-occur and play critical regulatory roles in microbiome assembly and functioning (so-called keystone taxa). For example, using a combination of network analysis and top-down experimental manipulation of soil microbial communities, Romdhane et al. (2022) showed that patterns of co-occurrence inferred from network analysis broadly matched the ecological interactions between microbial taxa under experimental conditions. Further, keystone microbial taxa influence the physiology, anatomy, behavior, and reproduction of higher organisms (Trivedi et al., 2020). For instance, interconnected phyllosphere keystone taxa are a strong predictor of health in Arabidopsis thaliana (Agler et al., 2016). A key challenge will be to enable the reassembly of plant-associated microbial networks around keystone taxa to enhance restoration outcomes in the long term, with agricultural research suggesting that we are still a long way from predictably assembling microbial communities (French et al., 2021). Our inability to isolate and cultivate most microorganisms also poses a significant challenge to implementing this strategy. These challenges represent important priorities of future research efforts. J.L.R.: conceptualization (lead); writing original draft (lead); formal analysis (supporting); review and editing (equal); visualization (equal). M.L.: review and editing (equal). D.G.: review and editing (supporting); formal analysis (supporting); visualization (equal). A.M.: review and editing (equal); visualization (equal). The authors thank the Editor-in-Chief, Pamela Diggle, for the invitation to write this "On the Nature of Things" essay and for comments on an earlier draft of the manuscript. We also thank Peter Thrall and an anonymous reviewer for the valuable comments they provided on our paper.

Impervious surfaces that characterise urban areas can make them harsh, water-limited places for plants to grow. To help alleviate plant stress under these challenging drought conditions, a range of soil additives can be utilised. Although well-studied individually, our understanding of the interaction between different soil additives in alleviating drought stress in urban areas is rudimentary. The aim of this study was to (1) assess the growth of urban horticultural plant species under drought stress and (2) determine whether drought stress in these species is alleviated by the use of soil additives, both individually and in combination. We grew six plant species (three trees, three graminoids) commonly planted in Australian urban areas under two watering regimes (drought-stressed, well-watered) and four soil additive treatments (no additive, microbial additive only, biochar only, microbial additive and biochar), and assessed their performance. We found that drought stress significantly reduced the growth of the six study species. Surprisingly, this decrease in growth was not reduced with the use of soil additives, despite biochar increasing soil water content and mycorrhizal colonisation when used in combination with the microbial additive. However, the addition of biochar significantly delayed the visual onset of drought stress across all species. Our results show that soil additives can be used as a cost-effective management strategy to increase plant resilience to drought stress in urban areas.

Background and aims Invasive plants often alter soil abiotic and biotic conditions which can benefit their own growth while harming native species. The impacts on native species may persist as legacy effects after the invasive species has been controlled and removed. This study focused on the Critically Endangered Cumberland Plain Woodland (CPW) vegetation in Australia, where we examined the soil impacts, and their associated legacy effects, associated with the invasion of African olive ( Olea europaea subsp. cuspidata ). Methods Seedlings of O. europaea subsp. cuspidata and two native legume species, Acacia implexa and Indigofera australis , were grown in different sterilised and unsterilised soils: uninvaded CPW soil, restored CPW soil where O. europaea subsp. cuspidata was removed approximately 20 years ago, and soil from sites still under O. europaea subsp. cuspidata invasion. We characterised nitrogen-fixing rhizobia in the root nodules of seedlings of the two legumes using next-generation sequencing (NGS) barcoding. Results Olea europaea subsp. cuspidata did not appear to condition the soil to favour its own growth and grew best in uninvaded CPW soil. The performance of both native legume species, however, was negatively impacted when grown in sterilised and unsterilised invaded soils, relative to their growth in CPW and restored soils. The soils from invaded sites affected the associations between both legume species and their rhizobium mutualists. Nodulation was higher in CPW and restored soils than in invaded soils, indicating that the availability of rhizobia was negatively impacted by O. europaea subsp. cuspidata . This was confirmed by a negative link between nodulation and the abundance of rhizobia that were characteristic of invaded soils. Conclusion Our findings demonstrate that O. europaea subsp. cuspidata invasion affects the availability of microbial mutualists for native legumes in the CPW. The soil conditions created by O. europaea subsp. cuspidata do not benefit its own performance and these impacts do not persist as legacy effects 20 years after the removal of the invader.

To enhance urban greening outcomes, nursery and urban forest practitioners can use biostimulants to improve plant performance. However, to date, little is known about their actual effectiveness in enhancing urban greening outcomes. This study aimed to gain insight into the use of biostimulants in urban forestry in Australia. To do this, the authors distributed a questionnaire to urban forestry practitioners within Australia that asked how and why they use biostimulants, as well as their attitude towards them. The majority of respondents (82%) reported that they use biostimulants, with the most cited reason for their use (75%) being to improve establishment after transplanting. Seaweed extract biostimulants were the most frequently used biostimulant type (35%), with foliar spray being the most popular application method (29%). Overall, most of the respondents were at least somewhat satisfied with their experience in using biostimulants (73%), with the vast majority believing that they improved plant quality/performance (96%). This questionnaire has not only demonstrated how common biostimulant use is in urban forestry in Australia but also how positively its use is regarded by practitioners.

In 2010, the fungal plant pathogen that causes Myrtle rust, Austropuccinia psidii , which is native to South America, was first detected in Australia and has since had significant impacts on several Australian Myrtaceae species. Despite this, our understanding of the role secondary metabolites play in plant susceptibility to A. psidii is limited. This study aimed to determine: (1) whether secondary metabolite (phenolics, terpenes) production is induced after A. psidii inoculation and if so, (2) how their production relates to A. psidii susceptibility. To test these aims, we selected seven Myrtaceae species that have a wide range of within-species variability in their susceptibility to A. psidii . We found that five of the study species significantly increased either their phenolic or sesquiterpene production post-inoculation suggesting their pre-inoculation secondary metabolite levels were not sufficient to combat A. psidii infection. The two species ( Angophora costata and Corymbia citriodora ) that did not increase their secondary metabolite production post-inoculation tended to have the greatest pre-inoculation production levels amongst the species. Interestingly, across all species, monoterpenes were the only secondary metabolite found to reduce plant susceptibility to A. psidii . This study contributes to our limited understanding of the role that secondary metabolites play in plant susceptibility to A. psidii . In light of these findings, future research should aim to identify biomarkers (e.g. individual chemical compounds) that confer resistance to A. psidii , so that individuals with these biomarkers can be utilised in commercial and conservation projects.

It is projected that the frequency and intensity of extreme drought and heatwave events will increase under climate change. Urban forests may be particularly vulnerable to these extreme climatic events given that the impervious surfaces that characterise urban environments reduce precipitation infiltration and absorb and re-radiate heat. Therefore, we must enhance the tolerance of urban forests to water and heat stress to ensure their continual survival in the face of ongoing climate change. Although rarely considered, this may be achieved by sourcing plants from provenances adapted to these stressors. This study aimed to determine whether the provenance of urban plant species influences their tolerance to water and heat stress. To address this aim, we grew two common Australian urban tree species, Acacia implexa and Eucalyptus tereticornis , from different climatic (i.e. rainfall, temperature) provenances under well-watered and water-stressed conditions before subjecting them to a heatwave. We then assessed the stress tolerance of the provenances using anti-oxidant activity (% radical scavenging/mg), the maximum potential quantum efficiency of photosystem II (F v /F m ) and biomass accumulation (g). We found that the water-stressed plants had significantly less biomass accumulation than their well-watered counterparts due to extensive leaf shedding. Surprisingly, the heatwave did not exacerbate the stress imposed on the plants by water stress. Further, the stress indicators suggested that the water-stressed plants rapidly recovered when watered post-heatwave. We found water stress tolerance differences between provenances for A. implexa but not E. tereticornis . However, these differences did not reflect variation in climate between the provenances but rather biomass accumulation differences. Our results suggest that stress tolerance differences between provenances are species-specific and influenced by biomass accumulation, which may be affected by multiple climatic and environmental factors. Therefore, we can conclude that it may be difficult to identify stress-tolerant provenances to plant in urban environments.

Plants have evolved a vast array of secondary metabolites that help defend them against natural enemy attack. The production of these secondary metabolites is influenced by environmental factors, such as temperature, rainfall (soil water availability) and atmospheric [CO2], which may be altered under climate change. This study aimed to test how two of these environmental factors, namely soil water availability and [CO2], will affect secondary metabolite and biomass production in Eucalypts. To investigate this, we measured secondary metabolite and biomass production of three Eucalypt species (Eucalyptus grandis, E. moluccana, E. saligna) grown under ambient and elevated [CO2] (400 and 600 ppm, respectively) and water-stressed and well-watered conditions, in a fully factorial glasshouse experiment. The secondary metabolites measured were foliar phenolic concentration as well as terpene and green leaf volatile emissions. We found that water stress did not alter secondary metabolite production. Unsurprisingly, the water-stressed plants maximised their water uptake potential by reducing shoot biomass but maintaining root biomass. The detrimental effects of water stress on shoot biomass production were not reduced under elevated [CO2] compared to ambient [CO2], despite all species experiencing significant reductions in stomatal conductance. Further, [CO2] as a single factor did not have a significant effect on species' net carbon gain, with an increase in green leaf volatile emissions under elevated [CO2] being mitigated by a reduction in shoot biomass production. These results suggest that reductions in carbon gains due to water stress will affect the growth of Eucalypts rather than their chemical defence capabilities.

While saltmarsh communities are endangered in many parts of the world due to anthropogenic impact, the risk of invasion by exotic plants is considered to be low because of their saline conditions. However, in urban areas, saltmarshes receive high nutrient freshwater input through stormwater discharge. We tested if invasion of saltmarsh by exotic plant species was facilitated by increased nutrients and reduced salinity associated with urban stormwater input. In a manipulative glasshouse experiment, we grew saltmarsh communities under four treatments: high salinity-low nutrients (control), high salinity-high nutrients, low salinity-low nutrients and low salinity-high nutrients. We then invaded the saltmarsh communities with four common invasive exotic plants. Their survival rates were monitored weekly for seven weeks before final harvesting. All exotic species showed significantly higher survival in the 'low salinity' treatment compared to the 'high salinity' treatment. There was variability among species, with three of four having low survival rates (0-3%) under 'high salinity' conditions, while survival of Protasparagus aethiopicus was reduced to only 53-59%. Our findings suggest that under natural conditions of saltmarshes, the establishment of exotic plant seedlings is restricted. Additional freshwater increased the survival of invading exotic species significantly, whereas adding nutrients increased biomass production but not necessarily survival of exotics. However, the results can be highly species dependant as shown by the unexpected salinity tolerance of P. aethiopicus. Reduction in salinity of saltmarsh due to stormwater input facilitates invasion by exotic plant species that would otherwise be unable to tolerate the highly saline environment.

Extreme heatwaves and drought have been shown to significantly affect urban tree survival, with potentially substantial economic costs for urban managers and local governments. During the 2019–2020 austral summer, the western Sydney Local Government Area (LGA) of Penrith experienced unprecedented high temperatures with less than 60 % of average rainfall compared with the proceeding five summers. This culminated in the highest temperature ever recorded in greater Sydney, of 48.9 °C. It is increasingly important that trees for urban applications are selected to be able to withstand such conditions. In early 2020, we conducted a visual assessment of canopy damage on street trees found in the Penrith LGA following the 2019–2020 summer heatwaves. We assessed the health of over 5500 trees and classified them as undamaged, lightly damaged, heavily damaged or defoliated. We found that more than 10 % of all the trees assessed displayed some level of canopy damage, with exotic deciduous species showing the greatest proportion of canopy damage. A logistic regression revealed that for exotic deciduous species, the probability of having sustained no canopy damage was 79 % lower than that for native evergreen species. Using these data, the economic costs to replace damaged trees was calculated using two scenarios that incorporated costs of tree planting and maintenance: low cost (replacing all heavily damaged and defoliated trees with juvenile trees) and high cost (replacing all heavily damaged and defoliated trees with advanced trees), with costs ranging from $500,000 to $800,000 (AUD). We also calculated the cost of replacing all individuals of the most damaged species with more climate-resilient species in order to secure the urban forest and found that the cost would be over AUD$1,000,000. This research highlights the importance of careful planning to ensure urban forest resilience and economic sustainability in the face of climate change.

We introduce the AusTraits database - a compilation of values of plant traits for taxa in the Australian flora (hereafter AusTraits). AusTraits synthesises data on 448 traits across 28,640 taxa from field campaigns, published literature, taxonomic monographs, and individual taxon descriptions. Traits vary in scope from physiological measures of performance (e.g. photosynthetic gas exchange, water-use efficiency) to morphological attributes (e.g. leaf area, seed mass, plant height) which link to aspects of ecological variation. AusTraits contains curated and harmonised individual- and species-level measurements coupled to, where available, contextual information on site properties and experimental conditions. This article provides information on version 3.0.2 of AusTraits which contains data for 997,808 trait-by-taxon combinations. We envision AusTraits as an ongoing collaborative initiative for easily archiving and sharing trait data, which also provides a template for other national or regional initiatives globally to fill persistent gaps in trait knowledge.

We introduce the AusTraits database - a compilation of measurements of plant traits for taxa in the Australian flora (hereafter AusTraits). AusTraits synthesises data on 375 traits across 29230 taxa from field campaigns, published literature, taxonomic monographs, and individual taxa descriptions. Traits vary in scope from physiological measures of performance (e.g. photosynthetic gas exchange, water-use efficiency) to morphological parameters (e.g. leaf area, seed mass, plant height) which link to aspects of ecological variation. AusTraits contains curated and harmonised individual-, species- and genus-level observations coupled to, where available, contextual information on site properties. This data descriptor provides information on version 2.1.0 of AusTraits which contains data for 937243 trait-by-taxa combinations. We envision AusTraits as an ongoing collaborative initiative for easily archiving and sharing trait data to increase our collective understanding of the Australian flora. ### Competing Interest Statement The authors have declared no competing interest.

Le Roux et al. suggest that documented increases in local plant richness in response to climate change should consider the nature of 'new' species. They find that species responsible for increases in richness in areas that have experienced significant disturbance and climate change are often invasive and/or weedy species.

In 2010, the parasitic fungus Austropuccinia psidii (myrtle rust) was detected in Australia. Austropuccinia psidii infects immature growth of myrtaceous species. Many of Australia's myrtaceous species occur within fire-prone vegetation communities and have the capacity to resprout after fire. Therefore, it is likely that new post-fire growth may be vulnerable to A. psidii infection, causing subsequent flow-on effects to species' persistence and community dynamics. The aim of this study was to test the impacts of A. psidii on native Australian Myrtaceae species after fire. We grew eight native susceptible species in a glasshouse experiment before burning them and inoculating the resprouting new growth of half the plants with A. psidii. We assessed the effect of A. psidii on the architecture, growth and biomass allocation of our study species. Although general patterns were observed across species, results were found to be species-specific. Austropuccinia psidii significantly reduced the height of two of the eight species (Callistemon citrinus and Eucalyptus moluccana), but none of the species had increased branching. As expected, specific leaf area was lower (9%) in inoculated plants - although only significant for C. citrinus and E. dalrympleana - and leaf biomass was greater (15%), but significant for Angophora costata only. Finally, biomass allocation did not significantly differ between infection treatments. We can conclude that the effect of A. psidii infection on fire-damaged plants has significant impacts on plants at the species level, which may have flow-on effects at the community level, especially after repeated infections. Furthermore, these impacts may be exacerbated in the future under climate change, as the predicted increase in frequency and intensity of fires across Australia will result in more frequent new growth availability, providing more opportunities for A. psidii infection.