Nematode communities indicate the negative impact of Reynoutria japonica invasion on soil fauna in ruderal habitats of tatra national park in Slovakia

Reynoutria japonica is a globally successful invasive plant that spreads rapidly after introduction, mainly along riparian or road corridors where dense stands often extend over several hundred square meters. Little is known, however, about the impacts of its spread in protected habitats of upland regions. This study was conducted to characterize the communities of plants and soil nematodes in ruderal forest habitats invaded and uninvaded by R. japonica in Tatra National Park, Slovakia. We hypothesized that invasion would reduce the diversity of native plant species, thereby affecting the nematode communities and their trophic structure. We found that invasion by R. japonica reduced the number and coverage of the native plant species and altered nematode communities and their structures. Total nematode abundance, species number and nematode biomass were significantly lower in invaded than uninvaded plots, but species diversity remained unaffected throughout the study. The overall abundance of all nematode trophic groups well represented the negative impact of R. japonica invasion on soil food webs, supported by low values of all maturity indices, a structural index and the Jaccard index of faunal similarity. A weighted faunal analysis similarly characterized the food webs of invaded plots as poorly developed or highly disturbed, with bacterial decomposition and a low C/N ratio. Our findings thus suggest that dense plots of knotweed simplify the structural complexity of the soil environment by reducing the richness of plant species, which may have contributed to the negative changes in the structures of the nematode communities.