Range-expanding Plant Research Articles

Plant-soil interactions during the native and exotic range expansion of an annual plant.

Range expansions, whether they are biological invasions or climate change-mediated range shifts, may have profound ecological and evolutionary consequences for plant-soil interactions. Range-expanding plants encounter soil biota with which they have a limited coevolutionary history, especially when introduced to a new continent. Past studies have found mixed results on whether plants experience positive or negative soil feedback interactions in their novel range, and these effects often change over time. One important theoretical explanation is that plants locally adapt to the soil pathogens and mutualists in their novel range. We tested this hypothesis in Dittrichia graveolens, an annual plant that is both expanding its European native range, initially coinciding with climate warming, and rapidly invading in California after human introduction. In parallel greenhouse experiments on both continents, we used plant genotypes and soils from five locations at the core and edge of each range to compare plant growth in soil inhabited by D. graveolens and nearby control microsites as a measure of plant-soil feedback. Plant-soil interactions were highly idiosyncratic across each range. On average, plant-soil feedbacks were more positive in the native range than in the exotic range. In line with the strongly heterogeneous pattern of soil responses along our biogeographic gradients, we found no evidence for evolutionary differentiation between plant genotypes from the core to edge of either range. Our results suggest that the evolution of plant-soil interactions during range expansion may be more strongly driven by local evolutionary dynamics varying across the range than by large-scale biogeographic shifts.

Assessing habitat suitability for selected woody range-expanding plant species in African mountains under climate change

Social-ecological systems in mountains are sensitive to the effects of climate change and are being affected at rates faster than other terrestrial habitats. We need to know which species are likely to be “winners” and which are likely to be “losers” in the context of climate change. This study evaluated the current and predicted future habitat suitability of selected range-expanding woody plant species (Acacia dealbata, Leucosidea sericea, Vernonanthura phosphorica) in African mountains under climate change. These species are representative of range-expanding plants, which have the potential to affect ecosystem services. Future average temperature is projected to decline in African mountains whereas global mean temperatures are projected to increase. Climate-change models may not be capturing dynamics in the climate of African mountains, possibly due to a lack of representative climate data used in calibrating these models. Although only climate variables were assessed, potential species distribution results were considered accurate according to model evaluation metrics, and some static factors thought to influence species distribution were strongly coupled to climate. Vernonanthura phosphorica and A. dealbata are likely to spread under climate change. The extent of habitat suitable for L. sericea is predicted to decline under climate change. An improved understanding of climate change in mountain systems through better representation of mountain climates in climate-change models could enhance the accuracy of species distribution models.

Legacy effect of microplastics on plant-soil feedbacks.

Microplastics affect plants and soil biota and the processes they drive. However, the legacy effect of microplastics on plant–soil feedbacks is still unknown. To address this, we used soil conditioned from a previous experiment, where Daucus carota grew with 12 different microplastic types (conditioning phase). Here, we extracted soil inoculum from those 12 soils and grew during 4 weeks a native D. carota and a range-expanding plant species Calamagrostis epigejos in soils amended with this inoculum (feedback phase). At harvest, plant biomass and root morphological traits were measured. Films led to positive feedback on shoot mass (higher mass with inoculum from soil conditioned with microplastics than with inoculum from control soil). Films may decrease soil water content in the conditioning phase, potentially reducing the abundance of harmful soil biota, which, with films also promoting mutualist abundance, microbial activity and carbon mineralization, would positively affect plant growth in the feedback phase. Foams and fragments caused positive feedback on shoot mass likely via positive effects on soil aeration in the conditioning phase, which could have increased mutualistic biota and soil enzymatic activity, promoting plant growth. By contrast, fibers caused negative feedback on root mass as this microplastic may have increased soil water content in the conditioning phase, promoting the abundance of soil pathogens with negative consequences for root mass. Microplastics had a legacy effect on root traits: D. carota had thicker roots probably for promoting mycorrhizal associations, while C. epigejos had reduced root diameter probably for diminishing pathogenic infection. Microplastic legacy on soil can be positive or negative depending on the plant species identity and may affect plant biomass primarily via root traits. This legacy may contribute to the competitive success of range-expanding species via positive effects on root mass (foams) and on shoot mass (PET films). Overall, microplastics depending on their shape and polymer type, affect plant–soil feedbacks.

Temporal dynamics of range expander and congeneric native plant responses during and after extreme drought events.

Climate change is causing range shifts of many species to higher latitudes and altitudes and increasing their exposure to extreme weather events. It has been shown that range-shifting plant species may perform differently in new soil than related natives; however, little is known about how extreme weather events affect range-expanding plants compared to related natives. In this study we used outdoor mesocosms to study how range-expanding plant species responded to extreme drought in live soil from a habitat in a new range with and without live soil from a habitat in the original range (Hungary). During summer drought, the shoot biomass of the range-expanding plant community declined. In spite of this, in the mixed community, range expanders produced more shoot biomass than congeneric natives. In mesocosms with a history of range expanders in the previous year, native plants produced less biomass. Plant legacy or soil origin effects did not change the response of natives or range expanders to summer drought. During rewetting, range expanders had less biomass than congeneric natives but higher drought resilience (survival) in soils from the new range where in the previous year native plant species had grown. The biomass patterns of the mixed plant communities were dominated by Centaurea spp.; however, not all plant species within the groups of natives and of range expanders showed the general pattern. Drought reduced the litter decomposition, microbial biomass, and abundances of bacterivorous, fungivorous, and carnivorous nematodes. Their abundances recovered during rewetting. There was less microbial and fungal biomass, and there were fewer fungivorous nematodes in soils from the original range where range expanders had grown in the previous year. We concluded that in mixed plant communities of range expanders and congeneric natives, range expanders performed better, under both ambient and drought conditions, than congeneric natives. However, when considering the responses of individual species, we observed variations among pairs of congenerics, so that under the present mixed-community conditions there was no uniformity in responses to drought of range expanders versus congeneric natives. Range-expanding plant species reduced soil fungal biomass and the numbers of soil fungivorous nematodes, suggesting that the effects of range-expanding plant species can trickle up in the soil food web.

Disentangling nematode and arbuscular mycorrhizal fungal community effect on the growth of range-expanding Centaurea stoebe in original and new range soil

AimsNumerous organisms show range expansions in response to current climate change. Differences in expansion rates, such as between plants and soil biota, may lead to altered interactions in the new compared to the original range. While plant-soil interactions influence plant performance and stress tolerance, the roles of specific soil organisms driving these responses remain unknown.MethodsWe manipulated the abundances of nematodes and arbuscular mycorrhizal fungi (AMF), collected from original and new range soils, and examined their effects on the biomass of range-expanding Centaurea stoebe and native Centaurea jacea. In the first approach, nematode and AMF communities were extracted from field soils, and inoculated to sterilized soil. In the second approach, the abundance of soil organisms in soil inocula was reduced by wet sieving; at first, plants were grown to condition the soil, and then plant-soil feedback was determined under ambient and drought conditions.ResultsThe origin of soil communities did not influence the biomass production of range-expanding or native plant species, neither by addition nor by (partial) removal. However, after conditioning and under drought, range expanding C. stoebe produced more biomass with soil communities from the original range while C. jacea, native to both ranges, produced more biomass with new range soil communities.ConclusionsWe show that nematode and AMF communities from original and new range have similar effect on the growth of range expanding C. stoebe. Our results highlight that the effect of soil communities on plant growth increases after soil conditioning and under drought stress.

Plant population and soil origin effects on rhizosphere nematode community composition of a range-expanding plant species and a native congener

Climate change causes species range expansions to higher latitudes and altitudes. It is expected that, due to differences in dispersal abilities between plants and soil biota, range-expanding plant species will become associated with a partly new belowground community in their expanded range. Theory on biological invasions predicts that outside their native range, range-expanding plant species may be released from specialist natural enemies, leading to the evolution of enhanced defence against generalist enemies. Here we tested the hypothesis that expanded range populations of the range-expanding plant species Centaurea stoebe accumulate fewer root-feeding nematodes than populations from the original range. Moreover, we examined whether Centaurea stoebe accumulates fewer root-feeding nematodes in expanded range soil than in original range soil. We grew plants from three expanded range and three original range populations of C. stoebe in soil from the original and from the new range. We compared nematode communities of C. stoebe with those of C. jacea, a congeneric species native to both ranges. Our results show that expanded range populations of C. stoebe did not accumulate fewer root-feeding nematodes than populations from the original range, but that C. stoebe, unlike C. jacea, accumulated fewest root-feeding nematodes in expanded range soil. Moreover, when we examined other nematode feeding groups, we found intra-specific plant population effects on all these groups. We conclude that range-expanding plant populations from the expanded range were not better defended against root-feeding nematodes than populations from the original range, but that C. stoebe might experience partial belowground enemy release.

Soil predator loss alters aboveground stoichiometry in a native but not in a related range-expanding plant when exposed to periodic heat waves

Increasing frequency and magnitude of climatic extremes, such as heat waves are expected to enhance abiotic stresses on ecological communities. It has been proposed that ecological communities in disturbed habitats may be most sensitive to climatic extremes, as disturbance may reduce density and diversity of higher trophic level organisms like predators. However, there is little experimental evidence that climatic extremes indeed have stronger impact on functioning of such trophically downgraded ecosystems. Here, we experimentally examine how removal of predators from soil communities affects plant performance under periodic heat waves. We used a native plant species, and a congeneric native that is currently expanding its range because of climate change. We used soil nematode communities as the model system, as these are most abundant soil animals and their communities are trophically diverse. Predatory nematodes were manually removed from intact soil nematode communities (mainly the adults as some juveniles are impossible to manually remove) to create a trophically downgraded soil. Intact nematode communities and communities with reduced predatory nematodes were added separately to soils that were planted with either the native Centaurea jacea or the range-expanding congener Centaurea stoebe. Half the experimental units were exposed periodically to experimental heat waves of 10 °C above the control temperature. Our results show that the C: N and C: N: P ratio of plant shoots in predator-reduced soils became lower when exposed to periodic heat waves, however, only in the native plant C. jacea. The decrease in C: N ratio corresponded with increase of an herbivorous nematode in trophically intact soils of C. jacea independent of warming, whereas this relationships disappeared in warmed and predator-reduced soils. Our results accordingly highlight that periodic heat waves may affect stoichiometry of certain plant species by altering trophic interactions in predator-reduced soils.

Community-level interactions between plants and soil biota during range expansion.

Plant species that expand their range in response to current climate change will encounter soil communities that may hinder, allow or even facilitate plant performance. It has been shown repeatedly for plant species originating from other continents that these plants are less hampered by soil communities from the new than from the original range. However, information about the interactions between intra‐continental range expanders and soil communities is sparse, especially at community level.Here we used a plant–soil feedback experiment approach to examine if the interactions between range expanders and soil communities change during range expansion. We grew communities of range‐expanding and native plant species with soil communities originating from the original and new range of range expanders. In these conditioned soils, we determined the composition of fungi and bacteria by high‐throughput amplicon sequencing of the ITS region and the 16S rRNA gene respectively. Nematode community composition was determined by microscopy‐based morphological identification. Then we tested how these soil communities influence the growth of subsequent communities of range expanders and natives.We found that after the conditioning phase soil bacterial, fungal and nematode communities differed by origin and by conditioning plant communities. Despite differences in bacterial, fungal and nematode communities between original and new range, soil origin did not influence the biomass production of plant communities. Both native and range expanding plant communities produced most above‐ground biomass in soils that were conditioned by plant communities distantly related to them. Synthesis. Communities of range‐expanding plant species shape specific soil communities in both original and new range soil. Plant–soil interactions of range expanders in communities can be similar to the ones of their closely related native plant species.

Plant-Soil Feedbacks and Facilitation Influence the Demography of Herbaceous Alpine Species in Response to Woody Plant Range Expansion

Plant species migrations, or range shifts, in response to changing climate are one of many interacting factors influencing plant population and community dynamics in an era of global change. Range shifts may cause novel assemblages of competing species because species may respond to changing climate at different rates. Range-expanding species may directly influence resident species through resource competition or indirectly by modifying the local environment both aboveground and belowground. Further, range-expanding plant species can create novel plant-soil feedbacks (PSFs) by altering soil microbial community structure and function and the interactions of resident plant species with microbial symbionts. These changes can have important implications for resident plant population dynamics and their ability to coexist with novel competitors. Here we test the impacts of competitive interactions and plant-soil feedbacks (PSFs) of a range-expanding sagebrush species (Artemisia. rothrockii) on the demography and population growth rates of two resident alpine plant species (Koeleria macrantha and Eriogonum ovalifolium). We use an experimental, multi-year field approach combined with integral projection modeling to determine how PSFs and competition influence species coexistence in both the historic and range expansion zone of A. rothrockii. We find that sagebrush has an overall net negative effect on herbaceous plant demography, primarily due to negative PSFs for plants growing in sagebrush-conditioned soil. However, these negative soil effects are partially buffered via facilitation effects for herbs growing under or nearby sagebrush canopies. In general, population growth rates were more sensitive to survival than other demographic rates, furthermore this sensitivity to survival was higher for herbaceous species in sagebrush soils. Identifying the major drivers of plant population dynamics and species interactions remains an important and unresolved question in ecology. PSFs are a central mechanism influencing plant species interactions, yet the majority of PSF research has made little direct connection between plant population dynamics and PSFs in situ. We believe that utilizing a field-based approach, focusing on multiple components of plant demography, is an important next step in understanding the role of PSFs and species interactions in a rapidly changing world.

Rhizosphere and litter feedbacks to range-expanding plant species and related natives.

Plant–soil feedback (PSF) results from the net legacy effect that plants leave in the composition of soil communities and abiotic soil properties. PSF is induced by the rhizosphere and by litter inputs into the soil, however, we have little understanding of their individual contributions. Here, we examine feedback effects from the rhizosphere of living plants, decomposing litter and their combination.We used four pairs of climate warming‐induced range‐expanding plant species and congeneric natives, and examined PSF effects on plant biomass production, as well as on decomposition in their new range.We tested the hypothesis that the plant rhizosphere provides less negative feedback to range‐expanders than to the congeneric natives, and that feedback mediated by litter decomposition does not provide such a difference because decomposers might be less specialized than pathogens. To determine PSF, we used soil from the congener species within each pair as an ‘away’ soil to indicate whether range‐expanders may have lost their specialized soil biota upon arrival in the novel range.Our results show that although range‐expanding plant species and their congeneric natives developed neutral PSF in both rhizosphere‐ and litter‐conditioned soils, two of the four range‐expanders produced more biomass than natives in soils conditioned by litter, that is, soils with high nutrient content. Shoot litter from two out of four range‐expanding species decomposed more than that of natives, but decomposition was unaffected by soil conditioning. Synthesis. We compared PSF effects of range‐expanders and congeneric natives mediated via both the rhizosphere and litter using the congeneric species as a control. Under those conditions, PSF effects were neutral and not affected by plant origin. Therefore, we conclude that studies not comparing within plant genera may overestimate the impact of plant origin on PSF. Still, even under those conditions range‐expanders appeared to benefit more from high soil nutrient availability than natives, thus providing a possible advantage over congeneric natives.

Range-expansion effects on the belowground plant microbiome.

Plant range expansion is occurring at a rapid pace, largely in response to human-induced climate warming. While the movement of plants along latitudinal and altitudinal gradients is well documented, effects on the belowground microbial communities remains largely unknown. Further, in range expansion not all plant species are equal: in a new range the relatedness between range-expanding plant species and native flora can influence plant-microbe interactions. Here we used a latitudinal gradient across Europe to examine bacterial and fungal communities in the rhizosphere and surrounding soils of range-expanding plant species. We selected range expanders with and without congeneric natives in the new range, and as a control, the congeneric natives, totaling 382 plant individuals collected across Europe. In general, a plant’s status as range expander was a weak predictor of bacterial and fungal community composition. However, microbial communities of range-expanding plant species became more similar to each other farther from their original range. Range expanders unrelated to the native community also experienced a decrease in the ratio of plant pathogens to symbionts, giving weak support to the enemy release hypothesis. Even at a continental scale the effects of plant range expansion on the belowground microbiome are detectable, though changes to specific taxa remain difficult to decipher.

Belowground Consequences of Intracontinental Range-Expanding Plants and Related Natives in Novel Environments.

Introduced exotic plant species that originate from other continents are known to alter soil microbial community composition and nutrient cycling. Plant species that expand range to higher latitudes and altitudes as a consequence of current climate warming might as well affect the composition and functioning of native soil communities in their new range. However, the functional consequences of plant origin have been poorly studied in the case of plant range shifts. Here, we determined rhizosphere bacterial communities of four intracontinental range-expanding plant species in comparison with their four congeneric natives grown in soils collected from underneath those plant species in the field and in soils that are novel to them. We show that, when controlling for both species relatedness and soil characteristics, range-expanding plant species in higher latitude ecosystems will influence soil bacterial community composition and nutrient cycling in a manner similar to congeneric related native species. Our results highlight the importance to include phylogenetically controlled comparisons to disentangle the effect of origin from the effect of contrasting plant traits in the context of exotic plant species.

LAESI mass spectrometry imaging as a tool to differentiate the root metabolome of native and range-expanding plant species

Main conclusionLAESI-MSI, an innovative high-throughput technique holds a unique potential for untargeted detection, profiling and spatial localization of metabolites from intact plant samples without need for extraction or extensive sample preparation.Our understanding of chemical diversity in biological samples has greatly improved through recent advances in mass spectrometry (MS). MS-based-imaging (MSI) techniques have further enhanced this by providing spatial information on the distribution of metabolites and their relative abundance. This study aims to employ laser-ablation electrospray ionization (LAESI) MSI as a tool to profile and compare the root metabolome of two pairs of native and range-expanding plant species. It has been proposed that successful range-expanding plant species, like introduced exotic invaders, have a novel, or a more diverse secondary chemistry. Although some tests have been made using aboveground plant materials, tests using root materials are rare. We tested the hypothesis that range-expanding plants possess more diverse root chemistries than native plant species. To examine the root chemistry of the selected plant species, LAESI-MSI was performed in positive ion mode and data were acquired in a mass range of m/z 50–1200 with a spatial resolution of 100 µm. The acquired data were analyzed using in-house scripts, and differences in the spatial profiles were studied for discriminatory mass features. The results revealed clear differences in the metabolite profiles amongst and within both pairs of congeneric plant species, in the form of distinct metabolic fingerprints. The use of ambient conditions and the fact that no sample preparation was required, established LAESI-MSI as an ideal technique for untargeted metabolomics and for direct correlation of the acquired data to the underlying metabolomic complexity present in intact plant samples.

Influence of seed size on performance of non-native annual plant species in a novel community at two planting densities

Climate warming enables plant species to migrate to higher latitudes and altitudes. Within Europe, the Mediterranean harbours many species that might expand their ranges towards Western Europe. Small seed size may facilitate dispersal, however, it may impair establishment of the range-expanding plant species in the novel vegetation. In a greenhouse experiment, we examined effects of average seed size of Mediterranean plant species on their establishment in a mixed community of Western European plant species. Applying two levels of densities of the natives and a herbivory treatment, we tested how seed size is linked to response in plant growth and fitness in novel vegetation. While all non-native plant species showed a negative response to increased planting density, species with small seeds showed a less negative response. This effect persisted under herbivory. Our data suggest that small-seeded non-native plant species may tolerate competitive pressure from novel plant communities better than large-seeded species, so that small seed size may confer a higher probability of establishment of non-native species in novel communities.

Belowground Plant-Herbivore Interactions Vary among Climate-Driven Range-Expanding Plant Species with Different Degrees of Novel Chemistry.

An increasing number of studies report plant range expansions to higher latitudes and altitudes in response to global warming. However, consequences for interactions with other species in the novel ranges are poorly understood. Here, we examine how range-expanding plant species interact with root-feeding nematodes from the new range. Root-feeding nematodes are ubiquitous belowground herbivores that may impact the structure and composition of natural vegetation. Because of their ecological novelty, we hypothesized that range-expanding plant species will be less suitable hosts for root-feeding nematodes than native congeneric plant species. In greenhouse and lab trials we compared nematode preference and performance of two root-feeding nematode species between range-expanding plant species and their congeneric natives. In order to understand differences in nematode preferences, we compared root volatile profiles of all range-expanders and congeneric natives. Nematode preferences and performances differed substantially among the pairs of range-expanders and natives. The range-expander that had the most unique volatile profile compared to its related native was unattractive and a poor host for nematodes. Other range-expanding plant species that differed less in root chemistry from native congeners, also differed less in nematode attraction and performance. We conclude that the three climate-driven range-expanding plant species studied varied considerably in their chemical novelty compared to their congeneric natives, and therefore affected native root-feeding nematodes in species-specific ways. Our data suggest that through variation in chemical novelty, range-expanding plant species may vary in their impacts on belowground herbivores in the new range.

Interspecific differences in nematode control between range-expanding plant species and their congeneric natives

Climate change enables range expansions of plants, animals and microbes to higher altitudes and latitudes. Plants may benefit from range expansion when they escape from natural enemies. However, range expansion becomes a disadvantage when plants become disconnected from organisms that control enemies in the new range. Here, we examined nematode control in the root zone of range-expanding plant species and congeneric natives. In a greenhouse, we determined bottom-up (by the plants) and top-down (by natural enemies of the nematodes) control of two root-feeding nematode species (Helicotylenchus pseudorobustus and Meloidogyne hapla) in the rhizospheres of two range-expanding plant species, Centaurea stoebe and Geranium pyrenaicum, and two congeneric natives, Centaurea jacea and Geranium molle. Pots with plants growing in sterilized soil were inoculated with either a microbial soil community from the newly colonized natural habitat, a mixture of native microbial nematode antagonists, or a combination of these two communities. We tested the hypotheses that bottom-up control of root-feeding nematodes would be strongest in the root zone of range expanders and that top-down control would be strongest in the root zone of native plant species. We observed profound intra- and interspecific differences in bottom-up and top-down control among all four plant species. Bottom-up control by the range-expanding plant species was either strong or weak. Top-down control by microbes was strongest in native Centaurea. The addition of a mixture of both microbial communities reduced control of M. hapla in the root zones of the native plant species, and enhanced its control in the root zones of range-expanding plant species. We conclude that there was species-specific bottom-up and top-down control of root-feeding nematodes among the four plant species tested. Range-expanding plant species influenced their microbial rhizosphere community differently compared to native plant species, but top-down control in the root zone of natives was not systematically superior to that of range-shifting plant species.

The epigenetic footprint of poleward range-expanding plants in apomictic dandelions.

Epigenetic modifications, such as DNA methylation variation, can generate heritable phenotypic variation independent of the underlying genetic code. However, epigenetic variation in natural plant populations is poorly documented and little understood. Here, we test whether northward range expansion of obligate apomicts of the common dandelion (Taraxacum officinale) is associated with DNA methylation variation. We characterized and compared patterns of genetic and DNA methylation variation in greenhouse-reared offspring of T.officinale that were collected along a latitudinal transect of northward range expansion in Europe. Genetic AFLP and epigenetic MS-AFLP markers revealed high levels of local diversity and modest but significant heritable differentiation between sampling locations and between the southern, central and northern regions of the transect. Patterns of genetic and epigenetic variation were significantly correlated, reflecting the genetic control over epigenetic variation and/or the accumulation of lineage-specific spontaneous epimutations, which may be selectively neutral. In addition, we identified a small component of DNA methylation differentiation along the transect that is independent of genetic variation. This epigenetic differentiation might reflect environment-specific induction or, in case the DNA methylation variation affects relevant traits and fitness, selection of heritable DNA methylation variants. Such generated epigenetic variants might contribute to the adaptive capacity of individual asexual lineages under changing environments. Our results highlight the potential of heritable DNA methylation variation to contribute to population differentiation along ecological gradients. Further studies are needed using higher resolution methods to understand the functional significance of such natural occurring epigenetic differentiation.

Top-down control of root-feeding nematodes in range-expanding and congeneric native plant species

Climate warming may result in range expansion of species towards previously colder environments, and it has been demonstrated that in the new range successfully range-expanding plant species can be less attacked by aboveground and belowground enemies than congeneric natives. Plant enemies may be controlled naturally by complex bottom-up and top-down interactions with their hosts, however, little is known about how these interactions may operate in the new range. Here, we examine how root-feeding nematodes are controlled in the root zone of successfully range-expanding plant species in comparison with congeneric plant species native to the new range. As range-expanding plant species can have less negative soil feedback than congeneric natives, we tested the hypothesis that top-down control of root-feeding nematodes may be strongest on range-expanding plant species. To test this, we grew four pairs of range-expanding plant species and their native congeners in field soil, to which we added soil microbes, nematodes, or microarthropods from the new habitat. Addition of soil microorganisms and microarthropods reduced the numbers of root-feeding nematodes, being strongest when microorganisms were added. Opposite to our expectation, nematode control was not more effective in the root zone of range-expanding than native plant species. We conclude that top-down control of root-feeding nematodes is highly plant species-specific and that top-down control of these nematodes in the root zone of range-expanding plant species can be as effective as in the root zone of congeneric natives.

Soil microbial community structure of range‐expanding plant species differs from co‐occurring natives

1. Due to global warming and other changes in the environment, many native and exotic plant species show range expansion from lower to higher latitudes. In the new range, the (in)ability of range-expanding plants to establish associations with local soil microbes can have important consequences for plant abundance; however, very little information exists on rhizosphere communities of range-expanding plant species. Here, we examine the rhizosphere microbial community composition of range-expanding plant species in comparison with phylogenetically related species that are native in the invaded range. 2. We tested the hypothesis that range-expanding plants species would promote fewer shifts in rhizosphere communities than congeneric natives would. In order to test this, soil was collected from the invaded habitat and six range-expanding and nine congeneric natives were planted individually in pots to condition soil microbial communities. 3. After harvesting, individuals of the same species were planted in conditioned own and control soils to test the legacy effects of soil conditioning on biomass production. The control soils were mixtures of soils conditioned by all other plant species, except congenerics. After 10 weeks of plant growth, we determined the rhizosphere community composition of bacteria, fungi, arbuscular mycorrhizal fungi (AMF) and Fusarium spp. 4. All groups of microbes were analysed qualitatively using denaturating gradient gel electrophoresis (DGGE). Ergosterol was determined as a quantitative measure of nonarbuscular mycorrhizal fungal biomass, and real-time PCR was applied to detect amounts of Fusarium spp. 5. Range-expanding plants had less fungal hyphal biomass and lower amounts of Fusarium spp. in the rhizosphere than congenerics. Bacterial community composition was influenced by a combination of soil conditioning and plant origin, whereas fungal communities, AMF and Fusarium spp. were less pronounced in their responses to the experimental treatments. 6. Synthesis. We conclude that the lack of legacy effects in range-expanding plant species compared with natives may be due to differences in bacterial rhizosphere community composition, or to different quantities of potential pathogenic fungi. If the range-expanding plant species were benefiting more from AMF, effects will not have been due to differences in community composition, but we cannot exclude other options, such as different effectiveness of AMF or other soil biota in the rhizosphere of range-expanding vs. native plant species. The greater accumulation of bacterial and fungal pathogens in the rhizosphere of natives in relation to range expanders might explain the successful establishment of range-expanding plants.

Contrasting patterns of herbivore and predator pressure on invasive and native plants

Invasive non-native plant species often harbor fewer herbivorous insects than related native plant species. However, little is known about how herbivorous insects on non-native plants are exposed to carnivorous insects, and even less is known on plants that have recently expanded their ranges within continents due to climate warming. In this study we examine the herbivore load (herbivore biomass per plant biomass), predator load (predator biomass per plant biomass) and predator pressure (predator biomass per herbivore biomass) on an inter-continental non-native and an intra-continental range-expanding plant species and two congeneric native species. All four plant species co-occur in riparian habitat in north-western Europe. Insects were collected in early, mid and late summer from three populations of all four species. Before counting and weighing the insects were classified to trophic guild as carnivores (predators), herbivores, and transients. Herbivores were further subdivided into leaf-miners, sap-feeders, chewers and gallers. Total herbivore loads were smaller on inter-continental non-native and intra-continental range-expanding plants than on the congeneric natives. However, the differences depended on time within growing season, as well as on the feeding guild of the herbivore. Although the predator load on non-native plants was not larger than on natives, both non-native plant species had greater predator pressure on the herbivores than the natives. We conclude that both these non-native plant species have better bottom-up as well as top-down control of herbivores, but that effects depend on time within growing season and (for the herbivore load) on herbivore feeding guild. Therefore, when evaluating insects on non-native plants, variation within season and differences among feeding guilds need to be taken into account.