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The enemy release hypothesis (ERH) attributes the success of some exotic plant species to reduced top‐down effects of natural enemies in the non‐native range relative to the native range. Many studies have tested this idea, but very few have considered the simultaneous effects of multiple kinds of enemies on more than one invasive species in both the native and non‐native ranges. Here, we examined the effects of two important groups of natural enemies–insect herbivores and soil biota–on the performance of Tanacetum vulgare (native to Europe but invasive in the USA) and Solidago canadensis (native to the USA but invasive in Europe) in their native and non‐native ranges, and in the presence and absence of competition.In the field, we replicated full‐factorial experiments that crossed insecticide, T. vulgare–S. canadensis competition, and biogeographic range (Europe vs. USA) treatments. In greenhouses, we replicated full‐factorial experiments that crossed soil sterilization, plant–soil feedback, and biogeographic range treatments. We evaluated the effects of experimental treatments on T. vulgare and S. canadensis biomass.The effects of natural enemies were idiosyncratic. In the non‐native range and relative to populations in the native range, T. vulgare escaped the negative effects of insect herbivores but not soil biota, depending upon the presence of S. canadensis; and S. canadensis escaped the negative effects of soil biota but not insect herbivores, regardless of competition. Thus, biogeographic escape from natural enemies depended upon the enemies, the invader, and competition. Synthesis: By explicitly testing the ERH in terms of more than one kind of enemy, more than one invader, and more than one continent, this study enhances our nuanced perspective of how natural enemies can influence the performance of invasive species in their native and non‐native ranges., We examined a leading hypothesis of plant invasion, the enemy release hypothesis, in terms of multiple invasive species, multiple natural enemies, and multiple continents. We found that escape from natural enemies depends on the enemies, the invader, and competition.

Developing invasive plant management strategies is an important task in modern ecology, conservation biology and land management. Solidago gigantea is considered a problematic invader in Europe and Asia, where it forms dominant stands that can decrease species diversity. There is, therefore, an urgent need for effective management to reduce S. gigantea infestations and their negative impacts. We examined the efficacy of multiple approaches to S. gigantea management in Hungary. In our study, we evaluated the effect of several long‐term management techniques such as grazing, mowing and periodic flooding on the invader's density as well as native community diversity. In addition, we investigated the short‐ and long‐term effects of mowing combined with other treatment options, to estimate the influence of increased management intensity. Our results indicate that all tested management techniques had negative impacts on S. gigantea density. Short‐term mowing did not appear to improve species diversity in the resident community; however, all long‐term options improved species diversity. Moreover, combining treatments with mowing varied in its effectiveness; mowing once increased the efficacy of flooding, but decreased the efficacy of grazing, while mowing twice decreased efficacy of flooding. We suspect this is due to the increased intensity of disturbance, which does not allow for the natural recovery of communities, and after management ceases, invasion is able to re‐occur. Our results indicate that for effective management, we need to combine management options which act via different mechanisms, leading to cumulative positive effects on the resident community when applied at moderate levels.

Some invasive plant species rapidly evolve greater size and/or competitive ability in their nonnative ranges. However, it is not well known whether these traits transfer back to the native range, or instead represent genotype-by-environment interactions where traits are context specific to communities in the new range where the evolution occurred. Insight into transferability vs. context specificity can be tested using experiments performed with individuals from populations from the native and nonnative ranges of exotic invasive species. Using a widespread invasive plant species in Europe, Solidago gigantea, we established reciprocal common garden experiments in the native range (Montana, North America; n = 4) and the nonnative range (Hungary, Europe; n = 4) to assess differences in size, vegetative shoot number, and herbivory between populations from the native and nonnative ranges. In a greenhouse experiment, we also tested whether the inherent competitive ability of genotypes from 15 native and 15 invasive populations differed when pitted against 11 common native North American competitors. In common gardens, plants from both ranges considered together produced five times more biomass, grew four times taller, and developed five times more rhizomes in the nonnative range garden compared to the native range garden. The interaction between plant origin and the common garden location was highly significant, with plants from Hungary performing better than plants from Montana when grown in Hungary, and plants from Montana performing better than plants from Hungary when grown in Montana. In the greenhouse, there were no differences in the competitive effects and responses of S. gigantea plants from the two ranges when grown with North American natives. Our results suggest that S. gigantea might have undergone rapid evolution for greater performance abroad, but if so, this response does not translate to greater performance at home.

Recent studies revealed that from various ecological factors influencing nectar yield and quality of a plant, soil properties can be as important as microclimatic features. To date, few studies have investigated the relationship of soil characters to nectar traits of bee pollinated plants growing in natural associations. Our study intended to reveal which soil properties had the most powerful impact on nectar variables of wild garlic (Allium ursinum L.). Specimens were collected from fourteen habitats in two different years, and were potted in their original soil under the same climatic conditions. Nectar volumes and sugar concentrations were measured and soil samples were analysed for fourteen parameters. Statistical analyses revealed that the number of nectar producing Allium flowers, as well as the nectar volume and sugar content of nectar in individual flowers were influenced by both year and habitat. The humus, iron and sulphate content of soil showed negative correlation with the number of flowers producing nectar, total nectar volumes were negatively correlated with humus and iron content, but positively affected by magnesium content of the soil. Our results suggest that in addition to the effect of microclimatic factors, certain soil properties can have significant impact on nectar traits.

Helianthus tuberosus L. (Jerusalem artichoke), a perennial plant native to North America, is one of the most dangerous invasive species in Europe. The fast spread of the plant may be enhanced by its allelopathic effects, through the release of chemical compounds into the environment. The goal of this work was to determine the allelopathic effect of different plant parts of H. tuberosus and to study the temporal changes of allelopathic factors throughout the vegetation period, based on germination bioassays, chemical analysis of allelochemicals, and greenhouse experiments. Bioassay results demonstrated differences in the effect of H. tuberosus extracts, depending on the concentration, the test species, the plant part used for extraction, and the time of the treatment. From the bioactive compounds salicylic acid, 2-OH-cinnamic acid and 4-OH-benzaldehyde showed characteristic distribution patterns throughout the vegetation period. In the competition experiment, the presence of H. tuberosus exerted a strong negative effect on all tested species, independently of their treatment with activated carbon. Based on our results, we concluded that H. tuberosus can interfere with other species through allelochemical interactions. Moreover, seasonal dynamics of allelochemicals could be more important than suspected in plant competition and is likely to play an important role in the spread of the invasive H. tuberosus into new areas.

We have yet to adequately quantify the impacts of invaders in their non-native ranges relative to their native ranges. Such biogeographical comparisons are crucial to better understand the role of invasive species in plant–plant interactions and in the evolution of community organization. Using Solidago canadensis, we conducted field surveys in the native range (North America) and non-native range (Europe) and correlated stem density and aboveground biomass of Solidago with associated plant species richness and diversity indices. We also conducted experiments to compare the competitive and allelopathic impact of Solidago on the growth of species from its native and non-native ranges. In the field, increasing stem density and biomass of Solidago correlated with more significant decreases in total species richness and two diversity indices in Europe than in North America. Solidago strongly suppressed both European species and North American species in competition experiments, but this competitive effect did not differ between species from the different ranges. However, root extracts from Solidago strongly suppressed the root growth of European species as a group, but not North American species as a group. Our results indicate that the biogeographic origin of species can have important effects on plant interactions and community organization.

Background: The adobe bricks of old buildings can preserve diaspores of cultivated and weed species associated with arable fields. Recovery of these plant remains can provide insight into historical agriculture, and former weed flora.Aims: This study aims to describe and evaluate the changes in the weed flora in south-western Hungary, based on archaeobotanical findings and contemporary plot surveys.Methods: Plant remains of 51 adobe bricks dating from 1850 to 1950 were identified in south-western Hungary and compared with the flora of 104 plots from the same region.Results: A total of 276 species were identified from the adobe bricks, while the present-day plot survey yielded 305 species. A significant difference was found between the historical (60- to 160-year-old) and current species richness of the weed flora. The proportion of rare and threatened species decreased by 38.1%. A total of 142 weed species identified from the adobe bricks have declined, and 40 of them even disappeared in comparison with t...