Arbuscular mycorrhizal symbiosis is the most frequent and ancestral type of mycorrhizal symbiosis. It is estimated that at least 80% of terrestrial plant species are able to form a mutualistic relation with fungi. Consequently in the context of successful plant invasions, arbuscular mycorrhizal fungi may have a favourable if not a crucial role. The mycorrhizal status of 23 invasive species is reported here for the first time. This study also tested whether the intensity of mycorrhizal colonization of the roots of invasive species is related to that of the dominant species of invaded plant community. This is partly supported by our results when total percentages of mycorrhizal colonization were compared. In addition, the effect of habitat and community characteristics on the intensity of colonization of the roots of invasive species by arbuscular mycorrhizal fungi was tested and several significant correlations were revealed. At the among-species level, the total mycorrhizal colonization decreases and the relative arbuscular colonization increases in the roots of invasive species with increasing nitrogen availability in the habitat. Both these relations are significant after phylogenetic correction, which suggests this is an evolutionary adaptation. There are also negative correlations between the relative arbuscular colonization of invading species and the light and temperature demands of the species present in the community, and a positive correlation between the relative arbuscular colonization of the invaders and soil wetness. That all these relations are revealed at the within-species level possibly reflects differences among the habitats studied.
This study correlated the floristic composition of grassland communities with environmental variation in the Western Romanian Carpathians, focusing on the effect of grazing. Grasslands were sampled using 231 plots each 0.25 km2 in area. Vascular flora, altitude, aspect, slope, bedrock and grazing intensity were recorded for each plot. Data were processed using direct gradient analyses (CCA) and a generalized linear model. The results revealed three distinct communities associated with bedrock, landscape topography and grazing intensity. Grazing changes the floristic composition of grasslands on limestone more than on other types of bedrock. Specifically the floristic composition of the limestone-area plots subjected to low grazing pressure differ significantly from that of the plots of grassland on flysch and volcanic bedrock. When intensively grazed, the floristic composition of chalk grassland does not differ from that of the lightly grazed vegetation growing on flysch or volcanic bedrock. The reasons for this pattern and implications for management are discussed.