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Canada thistle is a pervasive perennial weed, causing challenges to agricultural and natural ecosystems globally. Although research has focused on the phenology, genetics, and control of Canada thistle, little is known about the rhizosphere microbiome and the role plant–microbe interactions play in invasion success. This study investigated the rhizosphere microbiome of Canada thistle across diverse climates, soils, and crops in the U.S. northern Great Plains. Soil and rhizosphere samples were collected and bacterial 16S and fungal ITS2 sequencing were performed to characterize the core microbiome and identify potential factors contributing to invasion success. Amplicon sequencing revealed a stable core microbiome that was detected in the Canada thistle rhizosphere across all locations. The core microbiome was dominated by the bacterial phyla Actinobacteriota and Proteobacteria and fungal phyla Ascomycota and Basidiomycota. Differential abundance analysis showed rhizosphere fungal communities were enriched in pathogen-containing genera with a 1.7-fold greater abundance of Fusaria and a 2.6-fold greater abundance of Gibberella compared to bulk soil. Predictive functional profiling showed rhizosphere communities were enriched (p < 0.05, FDR corrected) in plant pathogen fungal guilds which represented 19% of the fungal community. The rhizosphere microbiome was similar in composition across environments, highlighting the stable association between Canada thistle and specific microbial taxa. This study characterized the core microbiome of Canada thistle, and the findings highlight plant–microbe interactions shaping invasive behavior. These findings are important for understanding the ecological impacts of plant invasion and soil-microbe ecological processes. [ABSTRACT FROM AUTHOR]

We assessed the impact of road disturbances on the dominant mycorrhizal types in ecosystems at the global level and how this mechanism can potentially lead to lasting plant community changes. We used a database of coordinated plant community surveys following mountain roads from 894 plots in 11 mountain regions across the globe in combination with an existing database of mycorrhizal–plant associations in order to approximate the relative abundance of mycorrhizal types in natural and disturbed environments. Our findings show that roadside disturbance promotes the cover of plants associated with arbuscular mycorrhizal (AM) fungi. This effect is especially strong in colder mountain environments and in mountain regions where plant communities are dominated by ectomycorrhizal (EcM) or ericoid‐mycorrhizal (ErM) associations. Furthermore, non‐native plant species, which we confirmed to be mostly AM plants, are more successful in environments dominated by AM associations. These biogeographical patterns suggest that changes in mycorrhizal types could be a crucial factor in the worldwide impact of anthropogenic disturbances on mountain ecosystems. Indeed, roadsides foster AM‐dominated systems, where AM‐fungi might aid AM‐associated plant species while potentially reducing the biotic resistance against invasive non‐native species, often also associated with AM networks. Restoration efforts in mountain ecosystems will have to contend with changes in the fundamental make‐up of EcM‐ and ErM plant communities induced by roadside disturbance. [ABSTRACT FROM AUTHOR]

Abstract: Question: How does type of disturbance alter plant community composition when an invasive species with high intrinsic population growth rate is present? The sagebrush steppe is a cold semi‐arid steppe dominated by the native shrub Artemisia tridentata Nutt., native bunchgrasses, and has been invaded by the non‐native winter annual Bromus tectorum L. Location: Sagebrush steppe, Montana, USA. Methods: We assessed the effect of fire and soil disturbance, due to bulldozing to create a firebreak, on the resilience of plant communities and their resistance to invasion by B. tectorum. Plant species richness and species composition were monitored for 3 years at two sites post‐fire and firebreak construction. Results: Burned plant communities were resilient and had similar native grass cover and native species richness compared with the unburned sites after 3 years. Soil disturbance from firebreak construction resulted in species composition that was distinct and had lower native grass cover. Type of disturbance also affected the community's resistance to B. tectorum. Bromus tectorum cover was similar in burned and unburned areas, but increased up to three times and remained high where soil disturbance occurred, suggesting a shift to an alternative state. Conclusion: In this northern portion of the sagebrush steppe, communities with native plant cover were resilient to fire but not soil disturbance, which facilitated B. tectorum increase and a transition to an alternative state. In areas of high native plant cover, management tactics should avoid soil disturbance. [ABSTRACT FROM AUTHOR]

Monitoring the elevation limits of non-native species is a potentially sensitive means of detecting effects of environmental change on invasion dynamics and species ranges. The aim of this study was to investigate temporal changes in the distribution of non-native plant species along elevation gradients in the Swiss Alps by repeating, in 2009, a regional survey from 2003 of 230 sites ranging in elevation from 200 to 2400 m a.s.l. We also studied the fine-scale spatiotemporal population structure of two of the non-native species – Erigeron annuus and Solidago canadensis – along an elevation gradient in a heterogeneous landscape. Most non-native species in the Swiss Alps rapidly decline in probability of occurrence as elevation increases. We found little change in the elevation ranges limits of species in time, suggesting that most species are not rapidly expanding at their high elevation range limits. For most species, populations were more dynamic (colonizations and extinctions) at the upper range limit where occurrence rapidly declined. Population turnover was negatively correlated with probability of occurrence at the regional and local scale. At low elevations, where probability of occurrence was higher, the number of individuals in a population was also greater. At the local and regional scales, E. annuus and S. canadensis had similar range limits. At the local scale, propagule production of both E. annuus and S. canadensis was greater in the core of their distributions at lower elevations, and distance to nearest neighbor increased as occurrence decreased. Our data demonstrate that range limits of non-native species at high elevation are associated with high population turnover, which results in a transition zone characterized by source-sink dynamics. Populations within this zone exhibit reduced probability of occurrence, and smaller patches. This result has important implications for the monitoring of spreading species along environmental gradients. To understand these limits and predict range expansion, multi-year monitoring and demography data that includes information on colonization and extinction events will be needed. [ABSTRACT FROM AUTHOR]

Mountain ecosystems have been less adversely affected by invasions of nonnative plants than most other ecosystems, partially because most invasive plants in the lowlands are limited by climate and cannot grow under harsher high-elevation conditions. However, with ongoing climate change, invasive species may rapidly move upwards and threaten mid-, and then high-elevation mountain ecosystems. We evaluated this threat by modeling the current and future habitat suitability for 48 invasive plant species in Switzerland and New South Wales, Australia. Both regions had contrasting climate interactions with elevation, resulting in possible different responses of species distributions to climate change. Using a species distribution modeling approach that combines data from two spatial scales, we built high-resolution species distribution models (=250 m) that account for the global climatic niche of species and also finer variables depicting local climate and disturbances. We found that different environmental drivers limit the elevation range of invasive species in each of the two regions, leading to region-specific species responses to climate change. The optimal suitability for plant invaders is predicted to markedly shift from the lowland to the montane or subalpine zone in Switzerland, whereas the upward shift is far less pronounced in New South Wales where montane and subalpine elevations are already suitable. The results suggest that species most likely to invade high elevations in Switzerland will be cold-tolerant, whereas species with an affinity to moist soils are most likely to invade higher elevations in Australia. Other plant traits were only marginally associated with elevation limits. These results demonstrate that a more systematic consideration of future distributions of invasive species is required in conservation plans of not yet invaded mountainous ecosystems. [ABSTRACT FROM AUTHOR]