Invasive knotweed modifies predator–prey interactions in the soil food web

Abstract

Invasive plants often modify the structure of the community of native plants and animals, but their potential impact on the plant–soil interface is poorly studied. In this study, we looked at the impact of invasive knotweed (Reynoutria spp.) on the taxonomic and functional structure of three trophic levels (plants, detritivores and predators). We wanted to determine if knotweed had a cascading impact from plants to predators. The plants and soil invertebrates were sampled in seven sites in northern France in three knotweed cover classes (control, mid and high). Our results showed that knotweed had a low impact on invertebrate communities despite decreasing plant richness and functional diversity. However, we observed that the functional diversity of detritivores (based on palatability traits) and predators (based on feeding traits) were highly correlated in control sites without knotweed, but that this correlation was no longer present in knotweed invaded sites. This result suggests that feeding interactions are an important feature determining community structure in control plots, but that unidentified factors are more important in the presence of knotweed. Consequently, it can be hypothesised that the presence of knotweed disrupts functional linkages within the soil food web, which may ultimately modify ecosystem stability and functioning.