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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]

Summary: Plant associated mutualists can mediate invasion success by affecting the ecological niche of nonnative plant species. Anthropogenic disturbance is also key in facilitating invasion success through changes in biotic and abiotic conditions, but the combined effect of these two factors in natural environments is understudied.To better understand this interaction, we investigated how disturbance and its interaction with mycorrhizas could impact range dynamics of nonnative plant species in the mountains of Norway. Therefore, we studied the root colonisation and community composition of arbuscular mycorrhizal (AM) fungi in disturbed vs undisturbed plots along mountain roads.We found that roadside disturbance strongly increases fungal diversity and richness while also promoting AM fungal root colonisation in an otherwise ecto‐mycorrhiza and ericoid‐mycorrhiza dominated environment. Surprisingly, AM fungi associating with nonnative plant species were present across the whole elevation gradient, even above the highest elevational limit of nonnative plants, indicating that mycorrhizal fungi are not currently limiting the upward movement of nonnative plants.We conclude that roadside disturbance has a positive effect on AM fungal colonisation and richness, possibly supporting the spread of nonnative plants, but that there is no absolute limitation of belowground mutualists, even at high elevation. See also the Commentary on this article by Bueno et al., 230: 883–885. [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]

Although the problem of plant invasions is expected to increase with climate change, there is as yet little experimental evidence, in particular, for the effects of extreme weather events. We established communities of European meadow species, which were subjected to warming and extreme event (drought and deluge) treatments in a factorial design at an experimental garden in Zurich, Switzerland. Phylogenetically matched pairs of native and alien species ( Bromus erectus, B. inermis, Trifolium pratense, T. hybridum, Lactuca serriola, and Conyza canadensis) were introduced into the communities to test if invader performance is favored by warming and extreme events, and if alien invaders perform better than native colonizers. With a warming of on average 0.3 °C, a higher cover of native plant communities was observed, while drought decreased cover in the short-term and lowered biomass. Germination, survival, and growth of the introduced species were lower under elevated temperature. Survival of all pairs and growth of Trifolium was greater in drought pots, while deluge had no effect. While the alien species showed a faster rate of increase in the number of leaves, mortality of alien species was greater than of native species. Overall, the performance of the focal species varied much more among taxonomic groups than native/alien provenances. The results suggest that with climate change, different types of extreme events will differ in the severity of their effects on native plant communities. Meanwhile, the effects of climate change on plant invasions are more likely to operate indirectly through the impacts on native vegetation. [ABSTRACT FROM AUTHOR]

Background: In temperate mountains, most non-native plant species reach their distributional limit somewhere along the elevational gradient. However, it is unclear if growth limitations can explain upper range limits and whether phenotypic plasticity or genetic changes allow species to occupy a broad elevational gradient. Aims: We investigated how non-native plant individuals from different elevations responded to growing season temperatures, which represented conditions at the core and margin of the elevational distributions of the species. Methods: We recorded the occurrence of nine non-native species in the Swiss Alps and subsequently conducted a climate chamber experiment to assess growth rates of plants from different elevations under different temperature treatments. Results: The elevational limit observed in the field was not related to the species' temperature response in the climate chamber experiment. Almost all species showed a similar level of reduction in growth rates under lower temperatures independent of the upper elevational limit of the species' distribution. For two species we found indications for genetic differentiation among plants from different elevations. Conclusions: We conclude that factors other than growing season temperatures, such as extreme events or winter mortality, might shape the elevational limit of non-native species, and that ecological filtering might select for genotypes that are phenotypically plastic. [ABSTRACT FROM PUBLISHER]

Aim To assess the population genetic consequences of the colonization of two species with contrasting mating systems, Solidago canadensis and Lactuca serriola, along altitudinal gradients in both their native and introduced ranges. Location Allegheny Mountains, West Virginia and Wallowa Mountains, Oregon, USA; Valais, southern Switzerland. Methods Leaf material was collected from populations along altitudinal gradients and genotyped at seven microsatellite loci for each species. Differences in variability between native and introduced areas and in relation to altitude were analysed using linear models. Differences in the genetic, geographical and altitudinal structure of populations between areas were analysed by AMOVA, cluster analysis and Mantel tests. Results Genetic variation within and across populations of S. canadensis was significantly reduced, while populations of L. serriola were significantly more variable, in the introduced area. Genetic diversity decreased significantly with altitude for S. canadensis but not L. serriola. Genetic structure of S. canadensis was similar in both areas, and populations were isolated by geographical but not altitudinal distance. By contrast, population structure of L. serriola was much weaker in the introduced area, and populations were not isolated by distance in either area. Main conclusions Solidago canadensis has experienced a strong genetic bottleneck on introduction to the Valais, but this has not prevented it from colonizing a wide altitudinal range. Variation in neutral markers is therefore not necessarily a good measure for judging the ecological behaviour of a species. By contrast, the greater variability of L. serriola in the introduced area, where it also occurs over a greater altitudinal range, can be explained by increased outcrossing among admixed populations. This suggests that the ecological amplitude of alien species might be enhanced after population admixture in the new range, especially for species with highly structured native populations. However, even genetically depauperate introduced populations can be expected to colonize the same environmental range that they occupy in the native area. [ABSTRACT FROM AUTHOR]

Due to altered ecological and evolutionary contexts, we might expect the responses of alien plants to environmental gradients, as revealed through patterns of trait variation, to differ from those of the same species in their native range. In particular, the spread of alien plant species along such gradients might be limited by their ability to establish clinal patterns of trait variation. We investigated trends in growth and reproductive traits in natural populations of eight invasive Asteraceae forbs along altitudinal gradients in their native and introduced ranges (Valais, Switzerland, and Wallowa Mountains, Oregon, USA). Plants showed similar responses to altitude in both ranges, being generally smaller and having fewer inflorescences but larger seeds at higher altitudes. However, these trends were modified by region-specific effects that were independent of species status (native or introduced), suggesting that any differential performance of alien species in the introduced range cannot be interpreted without a fully reciprocal approach to test the basis of these differences. Furthermore, we found differences in patterns of resource allocation to capitula among species in the native and the introduced areas. These suggest that the mechanisms underlying trait variation, for example, increasing seed size with altitude, might differ between ranges. The rapid establishment of clinal patterns of trait variation in the new range indicates that the need to respond to altitudinal gradients, possibly by local adaptation, has not limited the ability of these species to invade mountain regions. Studies are now needed to test the underlying mechanisms of altitudinal dines in traits of alien species. [ABSTRACT FROM AUTHOR]

A topic of great current interest is the capacity of populations to adapt genetically to rapidly changing climates, for example by evolving the timing of life-history events, but this is challenging to address experimentally. I use a plant invasion as a model system to tackle this question by combining molecular markers, a common garden experiment and climatic niche modelling. This approach reveals that non-native Lactuca serriola originates primarily from Europe, a climatic subset of its native range, with low rates of admixture from Asia. It has rapidly refilled its climatic niche in the new range, associated with the evolution of flowering phenology to produce clines along climate gradients that mirror those across the native range. Consequently, some non-native plants have evolved development times and grow under climates more extreme than those found in Europe, but not among populations from the native range as a whole. This suggests that many plant populations can adapt rapidly to changed climatic conditions that are already within the climatic niche space occupied by the species elsewhere in its range, but that evolution to conditions outside of this range is more difficult. These findings can also help to explain the prevalence of niche conservatism among non-native species. [ABSTRACT FROM AUTHOR]