The impact of invasive plants on vegetation can vary greatly depending on the characteristics of the invaders and community invasibility. As to the factors that influence a plant's ability to invade, recent studies suggest that arbuscular mycorrhizal fungi (AMF) may be important regulators in plant invasions. To better understand the interactions of Helianthus tuberosus with co-occurring species in its native NorthAmerican and invaded European ranges,we carried out plot-based field surveys to determine whether the cover of H. tuberosus, its stem number and height, bare ground cover and amount of litter differ between ranges and how they interact with numbers of species in the plant community. To provide information aboutAMFcolonization of H. tuberosus,we evaluatedAMFcolonization in both ranges and tested the difference between continents, the effect of cover of H. tuberosus and their interaction with AMF. In the invaded range in Europe, H. tuberosus plants grew taller, had a greater stem density and there were fewer species in the invaded plant communities than in its native range in North America. In contrast, the cover of H. tuberosus and litter cover did not differ between the two continents. Plants of H. tuberosus were colonized by AMF in both ranges, but we found no statistical support for the potential effects of continent, the cover of H. tuberosus and their interaction with AMF. Overall, our study revealed that H. tuberosus exerts a negative impact on co-occurring species in the invaded European range, but not in North America where the species is native. To our knowledge, this is the first evaluation of AMF colonization of H. tuberosus at home and away and the results do not support either the degraded or enhanced mutualism hypotheses.

This report presents the European Weed Vegetation Database, a new database of vegetation plots documenting short-lived vegetation of arable and ruderal habitats from Europe and Macaronesia. The database comprises the phytosociological classes Papaveretea rhoeadis, Sisymbrietea, Chenopodietea and Digitario sanguinalis-Era-grostietea minoris. It is a gap-focused database containing mainly plots of this vegetation from the areas not yet represented in the European Vegetation Archive (EVA), to facilitate its accessibility for researchers to answer various questions. As of the end of 2018, it contained 24,734 plots, predominantly from Southern Europe. The data can be used for phytosociological studies, various kinds of interdisciplinary research as well as for studies for agronomy, nature management and biodiversity conservation.

The Carpathian Basin is one of the most important regions in terms of the invasion of the common ragweed (Ambrosia artemisiifolia) in Europe. The invasion history of this weed, however, seems to have been assessed differently in Austria and Hungary: Scientists in both countries assumed that this species had become abundant earlier and had caused more problems in their own than in other country. The goal of this study is to resolve the historical misunderstandings and scrutinize the related popular beliefs by a concise literature overview and an extensive analysis of the current patterns in ragweed infestations in crops in the borderlands in eastern Austria and western Hungary. The abundance of A. artemisiifolia was measured in 200 arable fields across the region, along with 31 background variables. Data were analysed using binomial generalized linear models (GLM), decision tree models and variation partitioning. Ambrosia artemisiifolia occurred more frequently in Hungary, but there were no significant differences in the proportion of larger cover values recorded in these two countries, and 'cover values > 10%' were even slightly more common in Austria.We found that previous crops of maize and soya bean and conventional farming were associated with the higher abundances in Austria, while organic farming was associated with relatively higher frequencies of heavy infestations in Hungarian fields. In the overall analysis crop cover was the most important variable with low crop cover associated with high ragweed abundance. Temperature and phosphorous fertilizer were negatively, while precipitation and soil phosphorous concentration positively associated with the abundance values. Land-use variables accounted for more of the variance in the abundance patterns of common ragweed than environmental variables. The current patterns in ragweed distributionmight indicate that a saturation process is still underway on the Austrian side. The saturation lag of 20-30 years is possibly due to several factors and the role of the Iron Curtain in determining cross-border exchange of propagules could be decisive. Nevertheless, the discrepancies uncovered in the accounts of the invasion of Hungarian and Austrian authors might also be seen as legacies of the Iron Curtain, which were caused by mutual limitations on access to national data and literature of the other country in a critical period of rapid ragweed spread. These discrepancies, that had a long-lasting effect on the work of scientific communities, are documented here in detail for the first time.

To better manage invasive populations, it is vital to understand the environmental drivers underlying spatial variation in demographic performance of invasive individuals and populations. The invasive common ragweed, Ambrosia artemisiifolia, has severe adverse effects on agriculture and human health, due to its vast production of seeds and allergenic pollen. Here, we identify the scale and nature of environmental factors driving individual performance of A. artemisiifolia, and assess their relative importance. We studied 39 populations across the European continent, covering different climatic and habitat conditions. We found that plant size is the most important determinant in variation of per-capita seed and pollen production. Using plant volume as a measure of individual performance, we found that the local environment (i.e. the site) is far more influential for plant volume (explaining 25% of all spatial variation) than geographic position (regional level; 8%) or the neighbouring vegetation (at the plot level; 4%). An overall model including environmental factors at all scales performed better (27%), including the weather (bigger plants in warm and wet conditions), soil type (smaller plants on soils with more sand), and highlighting the negative effects of altitude, neighbouring vegetation and bare soil. Pollen and seed densities varied more than 200-fold between sites, with highest estimates in Croatia, Romania and Hungary. Pollen densities were highest on arable fields, while highest seed densities were found along infrastructure, both significantly higher than on ruderal sites. We discuss implications of these findings for the spatial scale of management interventions against A. artemisiifolia.

Weed species loss due to intensive agricultural land use has raised the need to understand how traditional cropland management has sustained a diverse weed flora. We evaluated to what extent cultivation practices and environmental conditions affect the weed species composition of a small-scale farmland mosaic in Central Transylvania (Romania). We recorded the abundance of weed species and 28 environmental, management and site context variables in 299 fields of maize, cereal and stubble. Using redundancy analysis, we revealed 22 variables with significant net effects, which explained 19.2% of the total variation in species composition. Cropland type had the most pronounced effect on weed composition with a clear distinction between cereal crops, cereal stubble and maize crops. Beyond these differences, the environmental context of croplands was a major driver of weed composition, with significant effects of geographic position, altitude, soil parameters (soil pH, texture, salt and humus content, CaCO3, P2O5, K2O, Na and Mg), as well as plot location (edge vs. core position) and surrounding habitat types (arable field, road margin, meadow, fallow, ditch). Performing a variation partitioning for the cropland types one by one, the environmental variables explained most of the variance compared with crop management. In contrast, when all sites were combined across different cropland types, the crop-specific factors were more important in explaining variance in weed community composition.

The goal of this study was to identify factors determining weed species composition in soyabean crops in Hungary, where its expanding production faces difficult weed problems. The abundance of weed flora was measured in 262 fields across the country, along with 38 background variables. Using a minimal adequate model containing 24 terms with significant net effects, 21.6% of the total variation in weed species data could be explained. Plot location (edge vs core position, the single site variable in our analysis) was found to be the most important explanatory variable that was followed by a set of environmental (temperature, precipitation, altitude, soil texture, pH, Ca, K, Na and humus content), cultural (cultivar maturity, organic manure, fertiliser P and N, row spacing) and weed management (flumioxazin, pendimethalin, dimethenamid, propaquizafop, bentazone, quizalofop-p-ethyl, quizalofop-p-tefuril, linuron, thifensulfuron) factors. Variation partitioning revealed that environmental variables accounted for about four times more variance than cultural and about two and half times more than weed management variables. Chenopodium album, Ambrosia artemisiifolia, Hibiscus trionum, Echinochloa crus-galli and Convolvulus arvensis were the most dominant and frequent weeds, but their abundance was influenced by different factors. The responses of weed species to the studied variables provide new information about their ecological behaviour, and our findings also can be used to develop better weed management strategies.