Spread Of Invaders Research Articles

Globally invasive Potamopyrgus antipodarum (Gray, 1843) – an indicator of the degraded water systems in relation to native aquatic invertebrates

Global changes in climate and human impact favour invasions of aquatic organisms. Along with habitat modification, the abundance of invasive species might increase, leading to their greater impact on ecosystems functioning in disturbed areas. The appearance of species, which are drivers for ecosystem pollution are useful tool for the indication of some environmental changes in the area. We examine the occurrence of P. antipodarum populations, a global invader that established rivers, oxbow lakes, dam reservoirs, sand pits, gravel pits, and subsidence ponds in Poland (Central Europe). The research aims were to determine the extent of invasion in anthropogenically impacted habitats and the relationship between the abundance of aquatic invertebrates and oxygen concentration, pH, N-NO2, N-NO3, chlorides, and ammonia. This investigation helps elucidate the potential of invader to adapt to adverse environmental conditions in aquatic systems in which it was found dominant. The abundance of P. antipodarum showed an unimodal distribution, being higher in disturbed conditions. In snail communities it was a supereudominant or eudominant species in rivers, gravel pits, sand pits and subsidence ponds. Its relative abundance was the highest in gravel pits, in which it constituted more than 50 percent of benthic fauna. We demonstrated that environmental disturbances and pollution increase the vulnerability of water biocoenoses to invasions and the origin of free niches and that P. antipodarum is an indicator of degraded water systems. Results support the management of aquatic systems colonized by invasive species and highlight the need to assess the level of pollution discharged to prevent their dispersion. Management priorities must include the reduction or halt of invader spread because new aquatic environments are and will be created in industrial areas of the world.

Biochemical characterization and mycorrhizal fungal community of plant species in the Brazilian seasonal dry forest.

Invasive alien plant species (IAPS) have the ability to change the biochemical properties and the arbuscular mycorrhizal fungal (AMF) community structure in their rhizosphere. Organic acids, microbial activity, and AMF play a key role in the invader's spread and also has interactions with the soil chemical factors. Our aim here was to assess the rhizosphere's biochemical factors, AMF community composition, and soil chemical properties associated with Cryptostegia madagascariensis (IAPS) and Mimosa tenuiflora (endemic plant species) from the Brazilian Seasonal Dry Forest. The highest values of total glomalin (5.87 mg g-1 soil), root colonization (54.5%), oxalic and malic acids (84.21 and 3.01 μmol g-1 , respectively), microbial biomass C (mg kg-1 ), Na+ (0.080 cmolc kg-1 ), Ca2+ (7.04 cmolc kg-1 ), and soil organic carbon (4.59 g kg-1 ) were found in the rhizosphere of C. madagascariensis. We found dissimilarities on AMF community structure considering the studied plant species: (i) Racocetra coralloidea, Dentiscutata heterogama, Dentiscutata cerradensis, Gigaspora decipiens, and AMF's richness were highly correlated with the rhizosphere of M. tenuiflora; and (ii). The rhizosphere of C. madagascariensis was highly correlated with the abundance of Claroideoglomus etunicatum, Rhizoglomus aggregatum, Funneliformis mosseae, and Funneliformis geosporum. The results of our study highlight the importance of considering C. madagascariensis as potential hosts for AMF species from Glomerales, and a potential plant species that increase the bioavailability of exchangeable Na and Ca at semi-arid conditions.

Estimating potential global sources and secondary spread of freshwater invasions under historical and future climates

AbstractAimWe employed a climate‐matching method to evaluate potential source regions of freshwater invasive species to an introduced region and their potential secondary spread under historical and future climates.LocationGlobal source regions, with primary introductions to the Laurentian Great Lakes and secondary introductions throughout North America.MethodsWe conducted a climate‐match analysis using the CLIMATE algorithm to estimate global source freshwater ecoregions under historical and future climates with an ensemble of global climate models for climate‐change scenario SSP5‐8.5. Given existing research, we use a climate match of ≥71.7% between ecoregions to indicate climatic conditions that will not inhibit the survival of introduced freshwater organisms. Further, we estimate the secondary spread of freshwater invaders to the ecoregions of North America under historical and future climates.ResultsWe identified 54 global freshwater ecoregions with a climate match ≥71.7% to the recipient Laurentian Great Lakes under historical climatic conditions, and 11 additional ecoregions were predicted to exceed the threshold under climate change. Three of the 11 ecoregions were located in South America, a continent where no matches existed under historical climates and eight were located in the southern United States, southern Europe, Japan and New Zealand. Further, we identify 34 North American ecoregions of potential secondary spread of freshwater invasions from the Great Lakes under historical climatic conditions, and five ecoregions were predicted to exceed the threshold under climate change.Main ConclusionWe provide a climate‐match method that can be employed to assess the sources and spread of freshwater invasions under historical and future climate scenarios. Our climate‐match method predicted increases in climate match between the recipient region and several potential source regions, and changes in areas of potential spread under climate change. The identified ecoregions are candidates for detailed biosecurity risk assessments and related management actions.

Cas12a2 elicits abortive infection through RNA-triggered destruction of dsDNA

Bacterial abortive-infection systems limit the spread of foreign invaders by shutting down or killing infected cells before the invaders can replicate1,2. Several RNA-targeting CRISPR–Cas systems (that is, types III and VI) cause abortive-infection phenotypes by activating indiscriminate nucleases3–5. However, a CRISPR-mediated abortive mechanism that leverages indiscriminate DNase activity of an RNA-guided single-effector nuclease has yet to be observed. Here we report that RNA targeting by the type V single-effector nuclease Cas12a2 drives abortive infection through non-specific cleavage of double-stranded DNA (dsDNA). After recognizing an RNA target with an activating protospacer-flanking sequence, Cas12a2 efficiently degrades single-stranded RNA (ssRNA), single-stranded DNA (ssDNA) and dsDNA. Within cells, the activation of Cas12a2 induces an SOS DNA-damage response and impairs growth, preventing the dissemination of the invader. Finally, we harnessed the collateral activity of Cas12a2 for direct RNA detection, demonstrating that Cas12a2 can be repurposed as an RNA-guided RNA-targeting tool. These findings expand the known defensive abilities of CRISPR–Cas systems and create additional opportunities for CRISPR technologies.

Tracking a killer shrimp: Dikerogammarus villosus invasion dynamics across Europe

AbstractAimInvasive alien species are a growing problem worldwide due to their ecological, economic and human health impacts. The “killer shrimp” Dikerogammarus villosus is a notorious invasive alien amphipod from the Ponto‐Caspian region that has invaded many fresh and brackish waters across Europe. Understandings of large‐scale population dynamics of highly impactful invaders such as D. villosus are lacking, inhibiting predictions of impact and efficient timing of management strategies. Hence, our aim was to assess trends and dynamics of D. villosus as well as its impacts in freshwater rivers and streams.LocationEurope.MethodsWe analysed 96 European time series between 1994 and 2019 and identified trends in the relative abundance (i.e. dominance %) of D. villosus in invaded time series, as well as a set of site‐specific characteristics to identify drivers and determinants of population changes and invasion dynamics using meta‐regression modelling. We also looked at the spread over space and time to estimate the invasion speed (km/year) of D. villosus in Europe. We investigated the impact of D. villosus abundance on recipient community metrics (i.e. abundance, taxa richness, temporal turnover, Shannon diversity and Pielou evenness) using generalized linear models.ResultsPopulation trends varied across the time series. Nevertheless, community dominance of D. villosus increased over time across all time series. The frequency of occurrences (used as a proxy for invader spread) was well described by a Pareto distribution, whereby we estimated a lag phase (i.e. the time between introduction and spatial expansion) of approximately 28 years, followed by a gradual increase before new occurrences declined rapidly in the long term. D. villosus population change was associated with decreased taxa richness, community turnover and Shannon diversity.Main ConclusionOur results show that D. villosus is well‐established in European waters and its abundance significantly alters ecological communities. However, the multidecadal lag phase prior to observed spatial expansion suggests that initial introductions by D. villosus are cryptic, thus signalling the need for more effective early detection methods.

Colonization Dynamics of Potential Stowaways Inhabiting Marinas: Lessons from Caprellid Crustaceans

Despite the fact that stowaway transport is an increasingly common invasion pathway, its key ecological aspects, such as colonization dynamics of potential invaders on human transport vectors, are poorly understood. Considering that marinas may function as stepping-stone habitats for the spread of marine invaders, they provide a unique opportunity for understanding the first steps in the stowaway pathway. One of the dominant groups inhabiting marinas are caprellid crustaceans. These small invertebrates have demonstrated a high potential for introduction and establishment far beyond their distribution range. Here, we analyzed the colonization dynamics of caprellid species inhabiting marinas of Cádiz Bay (Spain) on plastic collectors and discussed their implications on invasion success. We found that collectors largely mirrored the resident caprellid community assemblages after just one month of deployment, showing that caprellid species inhabiting marina structures have a high capacity to colonize new artificial substrates. Moreover, the two non-indigenous species found, Caprella scaura and Paracaprella pusilla, successfully established dense and well-structured populations in the collectors (including all sex/age groups considered). We suggest a potential interplay between colonization ability and stowaway organisms’ invasion success. Furthermore, collectors used are supported as a useful tool in the early detection of non-indigenous species and their monitoring in relation to resident species.

Evaluating invasion risk and population dynamics of the brown marmorated stink bug across the contiguous United States.

Invasive species threaten the productivity and stability of natural and managed ecosystems. Predicting the spread of invaders, which can aid in early mitigation efforts, is a major challenge, especially in the face of climate change. While ecological niche models are effective tools to assess habitat suitability for invaders, such models have rarely been created for invasive pest species with rapidly expanding ranges. Here, we leveraged a national monitoring effort from 543 sites over 3 years to assess factors mediating the occurrence and abundance of brown marmorated stink bug (BMSB, Halyomorpha halys), an invasive insect pest that has readily established throughout much of the United States. We used maximum entropy models to estimate the suitable habitat of BMSB under several climate scenarios, and generalized boosted models to assess environmental factors that regulated BMSB abundance. Our models captured BMSB distribution and abundance with high accuracy, and predicted a 70% increase in suitable habitat under future climate scenarios. However, environmental factors that mediated the geographical distribution of BMSB were different from those driving abundance. While BMSB occurrence was most affected by winter precipitation and proximity to populated areas, BMSB abundance was influenced most strongly by evapotranspiration and solar photoperiod. Our results suggest that linking models of establishment (occurrence) and population dynamics (abundance) offers a more effective way to forecast the spread and impact of BMSB and other invasive species than simply occurrence-based models, allowing for targeted mitigation efforts. Implications of distribution shifts under climate change are discussed. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Extracellular RNA as a potential activator of Neutrophil Extracellular Traps by Candida albicans biofilm

Neutrophils represent the first line of innate host defense. The ability to inhibit the development of infections is associated with the involvement of several fighting strategies. The still poorly understood mechanism is netosis, involving the release of Extracellular Neutrophil Traps (NETs). NETs are complexes of chromosomal DNA and granule content. Such a web-like structure inhibits the spread of invaders. Netosis plays a significant role in combating Candida albicans infections. It has been shown that several factors, composing C. albicans cell surface mediate NETs production. However, the development of difficult to eradicate fungal infection is associated with the formation of the biofilm structure, which partially protects the pathogen cells from contact with the host’s immune system. One of the reasons for the creation of a such protective environment is the production of the extracellular matrix (ECM). The major components of the C. albicans ECM layer are lipids, proteins, carbohydrates but also extracellular nucleic acids, among which we observed a significant RNA content. Considering that the ECM consisting of RNA molecules is one of the first lines of contact between biofilms and neutrophils, our current studies aimed to assess the potential role of extracellular RNA in the triggering of the netosis process by human neutrophils in vitro. We showed that RNA purified from C. albicans biofilm structure and the whole cells have the capability to induction of ROS-dependent netosis pathway. Additionally, cell migration analysis indicate that RNA molecules may also be an effective chemotactic agent. This work was supported by NCN (2019/33/B/NZ6/02284).

Where are they now? Tracking the Mediterranean lionfish invasion via local dive centers

Invasive species are globally on the rise due to human-induced environmental change and are often a source of harm to their new ecosystems. Tracking the spread of invaders is crucial to better manage invasive species, and citizen science is often used to collect sighting data. However, this can be unreliable due to the general public's limited expertise for accurate identification and a lack of clear absence data. Here, we introduce a refined method of citizen science by tracking the spread of the invasive lionfish (Pterois miles) in the Mediterranean Sea using dive centers' expertise on local marine wildlife. We contacted 1131 dive centers on the Mediterranean coast via email and received 216 responses reporting whether or not lionfish were present in their area and, if present, the year they were first sighted. Currently, lionfish sightings are observed in the eastern half of the Mediterranean, though the front is continuing to move west with the furthest sighting as far as Corfu, Greece (19.939423°E, 39.428017°N). In 2020, lionfish also expanded their invasive range north on the Turkish Aegean coast to Karaburun (26.520657°E, 38.637033°N), showing that the invasion is ongoing. We found that the invasive range is now exceeding previous invasion models, highlighting the need for additional research on lionfish biology to inform management efforts. Continuous monitoring of invasive fronts based on dive center reports and a better understanding of what makes lionfish so invasive is crucial to creating effective management strategies and mitigating their negative impact on native ecosystems.

Multi-site experiments demonstrate that control of invasive corals (Tubastraea spp.) by manual removal is effective

Sun corals Tubastraea spp. from the Indo-Pacific have invaded hard grounds in the Caribbean, Gulf of Mexico, Brazil and Canary Islands where they cause significant ecological and economic damage to native systems, industry and society. In Brazil the National Plan for the Prevention, Control and Monitoring of the Sun Coral requires that sun corals are reduced to acceptable levels in nature and eradicated from vectors. Here we tested the efficiency of manual removal as a management tool at three sites along 260 km of Brazil's coastline with different oceanographic conditions (Ilha Grande, Rio de Janeiro and Cabo Frio). Four treatments were applied to shorelines undergoing management: (a) community removal (the whole benthic community scraped and stripped to bare rock), (b) sun coral single removal (c) sun coral repeated removal at 2 mo revisit) and (d) control areas naturally devoid of Tubastraea spp. Benthic communities were sampled over time using cover estimated from underwater photographs and larvae quantified in plankton trawls during management. The act of manual removal had no significant effect on sun coral larval abundance. The repeated removal method reduced cover at all sites to zero but a single removal was sufficient at sites with low densities of sun coral. The treatment effects varied systematically between sites, depending on local propagule pressure and invasion history. Manual removal is efficient and readily available and should be implemented in synergy with other methods to slow the spread of invaders, promote ecosystem recovery and allow time for the development of additional tools.

Inter‐ and intraspecific selection in alien plants: How population growth, functional traits and climate responses change with residence time

AbstractAimWhen alien species are introduced to new ranges, climate or trait mismatches may initially constrain their population growth. However, inter‐ and intraspecific selection in the new environment should cause population growth rates to increase with residence time. Using a species‐for‐time approach, we test whether with increasing residence time (a) negative effects of climatic mismatches between the species’ new and native range on population growth weaken, and (b) functional traits converge towards values that maximize population growth in the new range.LocationGermany.Time period12,000 years BP to present.Major taxa studiedForty‐six plant species of the Asteraceae family.MethodsWe set up a common‐garden mesocosm‐experiment using annual plant species with a wide range of residence times (7–12,000 years) and followed their population dynamics over 2 years. We calculated climatic distance between the common garden and the species’ native range. We also measured key functional traits of each species to analyse trait–demography relationships and test trait convergence with increasing residence time.ResultsWe found no support for the hypothesis that negative effects of climatic mismatches on population growth weaken with residence time. However, seed mass had a clear negative effect on population growth. As expected under such strong directional selection between or within species, increasing residence time led seed mass to converge to low values that increase population growth. Accordingly, population growth tended to increase with residence time.Main conclusionsWe identify trait but not climatic mismatches as important constraints on population growth of invaders. Understanding how inter‐ and intraspecific selection shapes functional traits of alien species should improve the predictability of future invasions and help understanding of limits to the population growth and spread of invaders already present. In a broader context, this study contributes to the conceptual integration of invasion biology with community, functional and population ecology.

Integrating across knowledge systems to drive action on chronic biological invasions

Designing and implementing long-term management strategies for chronic biological invasions is amongst the most vexing ecological research problems. Two key challenges to resolving this problem are: (a) integrating science-based and values-based (e.g. spiritual, cultural, economic and ethical) knowledge sources and (b) developing durable knowledge generation and curation platforms to co-ordinate long-term research efforts. We begin by identifying knowledge sources (stakeholder values, forecasts of invader spread and impacts, management technologies and operational logistics) to guide the high-level actions (governance framework design, selection of ethical management technologies, definition of long-term objectives, design of management strategies and operational plans implementing strategies) required for management of chronic invasions. We use exotic conifer invasions in New Zealand as an example. Next, we propose a transdisciplinary knowledge ecology framework where each knowledge source is represented by a separate knowledge generation and curation platform (i.e. knowledge ecosystem) and linked through high-level actions. We detail the structure and function of a single knowledge ecosystem (forecasting spread and impacts), and document two case studies to illustrate how knowledge ecosystems might (a) increase participation of individual researchers within long-term research efforts, and (b) facilitate inclusion of non-researchers in developing a common knowledge base. Finally, we propose a set of guidelines for combining science-based and values-based reasoning in decision-making via localised governance structures. We suggest that viewing knowledge ecologies as an integrated collection of distinct knowledge ecosystems offers a promising approach for identifying, generating, curating and integrating the knowledge sources needed to improve management of chronic biological invasions.

Evolution of an inferior competitor increases resistance to biological invasion.

Biodiversity is imperilled by the spatial homogenization of life on Earth. As new species invade ecological communities, there is urgent need to understand when native species might resist or succumb to interactions with new species. In the California Floristic Province, a global biodiversity hotspot, we show that populations of a native grass (Vulpia microstachys) have evolved to resist the competitive impacts of a dominant European invader (Bromus hordeaceus). Contrary to classic theory, which predicts that competing species co-evolve to differentiate their niches, our evidence is instead most consistent with the native species having evolved to better compete for those resources used by the invader, curtailing the invader's spread. Evolution to resist an invader was achieved despite populations interacting within a diverse background community (22 species 0.5 m-2 on average), refuting the oft-cited hypothesis that high diversity precludes the evolution of pairwise species interactions. Lastly, unlike studies that have explored the demographic consequences of evolution under competition, ours does so with naturally evolved populations. Our study highlights evolution as an underappreciated coexistence mechanism, acting to buffer species from extinction in the face of biological invasion.

Gridlock and beltways: the genetic context of urban invasions.

The rapid expansion of urban land across the globe presents new and numerous opportunities for invasive species to spread and flourish. Ecologists historically rejected urban ecosystems as important environments for ecology and evolution research but are beginning to recognize the importance of these systems in shaping the biology of invasion. Urbanization can aid the introduction, establishment, and spread of invaders, and these processes have substantial consequences on native species and ecosystems. Therefore, it is valuable to understand how urban areas influence populations at all stages in the invasion process. Population genetic tools are essential to explore the driving forces of invasive species dispersal, connectivity, and adaptation within cities. In this review, we synthesize current research about the influence of urban landscapes on invasion genetics dynamics. We conclude that urban areas are not only points of entry for many invasive species, they also facilitate population establishment, are pools for genetic diversity, and provide corridors for further spread both within and out of cities. We recommend the continued use of genetic studies to inform invasive species management and to understand the underlying ecological and evolutionary processes governing successful invasion.

Tomorrow Never Dies: biodegradation and subsequent viability of invasive macrophytes following exposure to aquatic disinfectants

Aquatic invasive alien species (IAS) negatively impact freshwater ecosystems worldwide. As suppression and eradication of established invader populations are often complex, costly and resource-intensive, the prevention of further invader spread is considered a key aspect of proactive management measures. Although broad-spectrum aquatic disinfectants have been suggested as a suitable decontamination mechanism to enhance invader spread-prevention strategies, inconsistencies concerning their effectiveness are reported within the literature. Here, we examine the use of two aquatic disinfectants, which were developed to kill damaging microbes, to induce substantial degradation of the apical fragmentary propagules of five invasive macrophytes: Crassula helmsii (Kirk) Cockayne; Egeria densa Planchon; Elodea canadensis Michx; Hydrocotyle ranunculoides Linnaeus; Lagarosiphon major (Ridley) Moss. Apical fragments were exposed to 0% (0 g L-1), 2% (20 g L-1) or 4% (40 g L-1) solutions of Virkon® Aquatic and Virasure® Aquatic, for submergence treatments of five, fifteen, thirty or sixty minutes. After 28 days, degradation of treated fragments was significantly greater than that of control groups, particularly for 4% solutions and longer exposure times. Despite this, sustained viability in relation to shoot and/or root regrowth was exhibited by almost all plant species. However, new shoot growth rates were significantly reduced following exposure to all treatments. At matched concentrations, there was no significant difference between the two disinfectants. Overall, it appears that the examined aquatic disinfectants will not curtail the spread of these invasive macrophytes. Yet, longer submergence times, multiple applications and synergistic effects of different biosecurity treatments may enhance preventative measures against further spread and this requires investigation.

Mass appearance of the Ponto-Caspian invaderPontogammarus robustoidesin the River Tisza catchment: bypass in the southern invasion corridor?

The river Danube is the backbone of the ‘southern invasion corridor’, one of the most important passages for the spread of Ponto-Caspian invaders in Europe. However, not all of these species used the passive or active upstream movement in the main channel to reach the upper sections and tributaries, some found detours. Mass occurrences of the Ponto-Caspian peracarid,Pontogammarus robustoides(Sars, 1894) were recorded at 17 sites along the entire Hungarian section of the River Maros, for the first time in the River Tisza catchment and also in Hungary. Those populations are found ca. 707 km upstream from the closest known and confirmed locality in the lower Danube section. We confirmed their identity by DNA barcoding and showed that all individuals fit in with the lower Danube population, thus identifying the source of this introduction. The most likely vector allowing the jump dispersal of the species is fish stocking in the Romanian section of the River Maros, which − combined with downstream drift to the Serbian Danube section and the relatively busy ship traffic between Belgrade and Vienna − might provide the opportunity to bypass the dispersal barrier represented by the unregulated Middle Danube and open the way towards Western Europe.

Populations of a widespread invader and co-occurring native species vary in phenotypic plasticity.

Phenotypic plasticity can promote plant invasions and enhance impacts on native species, but little is known about variation in plasticity among invader populations compared with native species. Variation in plasticity among invader populations could inform more precise predictions of invader spread and impacts across heterogeneous resource environments. We used a common garden experiment with sun and shade treatments to test for variation in plasticity among 12 populations of an invasive grass (Imperata cylindrica), and to determine whether the invader exhibited greater plasticity than six native species that co-occur in the Southeast USA. Principal component analysis revealed that invader populations from different native ranges consistently varied from each other and native species in traits linked to more favorable phenotypes under resource limitation. Overall, the invader exhibited greater plasticity than native species did, as demonstrated by higher plasticity index values for traits such as plant height, leaf mass ratio, and root:shoot ratio. Variation in phenotypic plasticity among invader populations suggests the potential for evolution of plasticity, and greater plasticity of invader populations than native species may underlie invader dominance. Differences in plasticity among populations appears to play an important role in predictions of the spread and potentially the impacts of invasive species.

Allocation of invasive plant management expenditures for conservation: Lessons from Florida, USA

AbstractAlthough the ecological impacts of biological invasions are well studied, comprehensive analyses of spending on invasive species management are lacking. Such analyses could inform both effective resource allocation and management planning. We evaluated long‐term invasive plant management expenditures and their potential geographic, economic, and ecological drivers for freshwater and terrestrial conservation areas in Florida, USA. Average expenditures for managing invaders were approximately US$45M annually, with over 90% of funding provided by the state. Our model showed that expenditures were best predicted by the prevalence of waterways and abundance of invaders, indicating that funding was allocated towards asset protection in highly invaded aquatic and terrestrial habitats. Higher spending was directly correlated with reduced area invaded for the costliest invader (Hydrilla verticillata, ~$10M/year), demonstrating management efficacy and constructive use of resources. Our study highlights that significant funding is required to manage plant invaders in Florida and that greater funding would likely limit the extent of invasions. Additional analyses of management cost‐effectiveness for Florida and other regions would benefit from consistent collection and reporting of high‐resolution management data. Given the exponential rate of spread of many invaders, additional and sustained management funding is needed for early detection and rapid, effective control of invasive species.

Invasive plant species identity affects soil microbial communities in a mesocosm experiment

Plant invasions can considerably modify soil microbial communities and processes. The direction and magnitude of these changes depend on invasive plant species. This problem has been studied in the field using a space-for-time substitution approach, but rarely in experimental conditions. Therefore, the aim of this study was to compare the effects on soil microbial properties in a mesocosm experiment of four invasive plant species in Europe, namely, Impatiens glandulifera, Reynoutria japonica, Rudbeckia laciniata and Solidago gigantea, and two expansive species native to Europe but invasive in North America, namely Artemisia vulgaris, Phalaris arundinacea, as well as a mixture of these two species grown in pots in two loamy sand soils differing in elemental concentrations and pH. After two years, microbial activity was measured using soil respiration, urease and arylsulfatase activity; total, bacterial and fungal biomass was measured using substrate-induced respiration (SIR) and/or phospholipid fatty acid analysis (PLFA); and community structure was measured using PLFA. Soil microbial parameters were significantly affected by plant species, soil type and their interaction. Contrary to expectations, R. japonica did not exhibit a strong negative effect on soil microorganisms. Microbial activity and/or biomass in soils under R. japonica, A. vulgaris, R. laciniata and/or species mixture were relatively high, though it depended to some extent on microbial parameters and soil type. In contrast, most microbial parameters had rather low values in bare (unplanted) soil and soils under P. arundinacea and S. gigantea. The largest differences between species were observed in the case of fungal biomass and fungi:bacteria ratio in both soils. Fungal biomass under A. vulgaris and R. japonica was a few times higher than in soils under S. gigantea, P. arundinacea and/or I. glandulifera. Our experiment proved that invasive plant species can modify soil microbial properties considerably during a period as short as two growing seasons. Alterations in the soil environment can potentially be considered as niche construction and support the growth and spread of invaders.

Full steam ahead: direct steam exposure to inhibit spread of invasive aquatic macrophytes

Biosecurity protocols designed to prevent invader spread have become integral to invasive species management strategies. However, application of many proposed spread-prevention practices is inhibited due to low practicality, high expense, undesirable non-target effects and a lack of known efficacy. Here, we examine the use of direct steam exposure to induce substantial fragment (i.e. propagule stage) degradation of seven invasive macrophytes: Ceratophyllum demersum, Crassula helmsii, Egeria densa, Elodea canadensis, Elodea nuttallii, Lagarosiphon major and Potamogeton crispus. Each species was independently exposed to steam treatments in loose clumps of three fragments, steamed at a distance of 2–3 cm from the source, for varied exposure times: 10 s, 30 s, 1 min, 2 min, and 5 min. Furthermore, we develop and apply a novel degradation scale describing visual tissue biodegradation stages and/or resumption of growth for fragmentary propagules. Steam treatments were observed to be highly efficacious, with total degradation being induced by 10 s of direct steam exposure. This was apparent for all species following a seven day recovery period, except C. demersum, which took until 21 days. Conversely, control specimens displayed excellent survival and/or viability (i.e. resumption of growth). Therefore, we argue that this innovative, yet simple technique can be used to improve biosecurity practices to inhibit the spread of invasive macrophytes.