Spatial patterns and effects of invasive plants on soil microbial activity and diversity along river corridors

Background and Aims Invasive species are a threat to the conservation of biological systems. In Central Europe, riparian ecosystems are especially susceptible to plant invasions, as waterflow mediates the spread of plant propagules, while invasive species may then affect soil including soil microbial communities. As waterflow also enhances connectivity among different segments of a river, spatial continuity of abiotic as well as biotic components of riparian ecosystems is expected. Methods We studied activity and functional diversity of microbial communities in three headwater streams in Central Europe. Plant diversity, soil properties and soil microbiota were assessed on 20 sample plots per river regularly distributed along the streams. Soil microbial activity and community-level physiological profiling were used to study the soil microbial community. Results Although the α-diversity of plants and soil microbiota was comparable, plant communities were substantially more differentiated than microbial communities. Richness in alien and invasive plants significantly differed among rivers, which was reflected in different spatial patterns and trends of microbial activity and diversity. A high level of spatial continuity and clearest longitudinal trends were observed in the Kysuca river with straightened riverbed and a high occurrence of artificial surfaces in the adjacent areas. The number of both alien and invasive plants significantly affects the composition of microbial functional groups of riverbed soils. Conclusion Continuity of processes in riparian ecosystems was confirmed also for headwater streams. However, the extent to which it applies to a particular stream strongly depends on particular environmental setting and stream characteristics.