Abstract
The Asian knotweed species complex gathers some of the world’s most successful plant invaders including the Japanese knotweed (Reynoutria japonica), the giant knotweed (R. sachalinensis) and the hybrid of these two species, the Bohemian knotweed (R. × bohemica). Hybrid species often present higher competitive abilities compared to their parent species. While several studies have focused on the effects of knotweed invasion on plant communities, few have simultaneously considered (i) effects of the three taxa on native plant communities and (ii) effects on litter and soil faunal components. In this study, we compared the differential effects of three Asian knotweeds on vegetation and soil macroinvertebrates communities across seven sites on a regional scale in North Western France. All three knotweed species displayed similar negative effects on local plant species richness, while promoting the taxonomic richness of litter-dwelling macroinvertebrates. Belowground macroinvertebrate taxonomic richness appeared strongly reduced by the presence of the hybrid R. × bohemica, significantly more so than those of sites colonized by R. japonica or R. sachalinensis. These changes of belowground communities were correlated to associated changes of composition and richness within plant communities. This study provides new insight into the consequences of ecosystem invasion by these species, especially revealing the even further strength of impacts of the hybrid Bohemian knotweed on local vegetation and belowground macroinvertebrates than those of other Asian knotweeds, which points to the need for monitoring the spatial spread of R. × bohemica and describing further its effects on ecosystem properties.
Highlights
While sites invaded by R. japonica and R. ×bohemica displayed an overall increase of litter-dwelling macroinvertebrate richness
Invasion by hybrid R. ×bohemica leads to the strongest loss of plant richness amongst the three knotweed species, while impacts on the richness of invaded communities were weaker and similar for R. japonica and R. sachalinensis
Our study revealed that the three Asian knotweed taxa had negative effects on belowground macroinvertebrate richness and community composition, with a significantly higher impact of the hybrid R. ×bohemica than of R. japonica
Summary
Introduced into Europe during the 1840s [3] and into North America during the 1870s [4], they rapidly spread geographically and are recognized as noxious invaders, strongly modifying and reducing species richness of native plant communities [5,6,7,8,9], communities of litter-dwelling arthropods [7,10,11,12,13], and occasionally altering soil physicochemical properties [5,14,15,16]. Several examples of negative impacts of invasive plants on belowground fauna have been reported [22,23], but the intensity of these interactions seems to depend on the invasive species and the invaded communities [24,25]. Recent meta-analyses suggest the importance of both habitat structure and trophic level as drivers of invertebrate response to invasive plants [26,27,28]
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