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.

In the last decades in Hungary biotopes of Nanocyperion species have been reduced significantly according to the melioration and the declining of pasturing. Owing to the habitat loss more species such as the examined Lindernia procumbens, Eleocharis ovata, Centunculus minimus, Limosella aquatica, Juncus sphaerocarpus and Elatine triandra became endangered all over the country. During the researches site requirements of these species were analysed as well as their connection with the cultivated species and the soil cultivation carried out on the plough-lands. According to our experiences in West Hungary actual occurrences of Lindernia procumbens, Centunculus minimus, Juncus sphaerocarpus and Elatine triandra are related strongly to the plough-lands. Eleocharis ovata and Limosella aquatica occur on plough-lands less frequently, exist mainly on other pioneer moist habitats. It can be established in case of all the 6 examined species that their habitat spectrum has extended by the increasing in the territory of ploughs forming spacious convenient biotopes for these species. © Eugen Ulmer KG.

Inland water on soils with bad water balance can lead to serious yield losses. Soil management and plant protection is nearly impossible in these marshy vernal pools, wherefore very special vegetation develops. On the basis of 58 phytocoenological surveys made in South-Western Hungary the vegetation of the vernal pools will be characterised. From phytosociological point of view our surveys stand to Ranunculo sardoi-Alopecuretum geniculati and Myosuro-Ranunculetum sardoi associations the nearest, where the proportion of Nanocyperion elements is significant. The following endangered species occure in these vernal pools: Elatine alsinastrum, Limosella aquatica, Lindernia procumbens, Montia fontana, Peplis portula. However vernal pools in segetal fields are causing losses from economical aspects, they can contribute to increase agrobiodiversity and have an important role in maintaining numerous threatened and protected plant species (Red Data List, IUCN, Corine Biotopes Project, Bern Convention). © Eugen Ulmer KG.