Reynoutria japonica invasion negatively affects arbuscular mycorrhizal fungi communities regardless of the season and soil conditions

Reynoutria japonica (Japanese knotweed) is one of the most potent global invasive plant species; however, there is still insufficient knowledge on the impact of its invasion on arbuscular mycorrhizal fungi (AMF, Glomeromycota). The aim of our study was to assess the condition of AMF communities under the influence of R. japonica and determine the temporal and site-dependent variability of this influence. We studied AMF spore number, species richness, and composition as well as biomass in pairs of adjacent plots encompassing R. japonica and resident plant species. We established these pairs of plots in different habitat conditions (light and heavier soil conditions), and we sampled them four times (two spring and two summer seasons) to check if the potential impact of the invader on AMF communities is soil-and/or season-dependent. We found that the invasion reduced AMF spore number, species richness, and biomass, but had no effect on AMF species composition. AMF parameters varied over time (spore number, species composition and biomass) and depended on soil condition (species richness), but were barely affected by interactions between the studied factors. The lower performance of AMF communities in R. japonica plots was probably due to the displacement of resident mycorrhizal plant species. This displacement was not complete as some mycorrhizal plants, especially spring ephemerals, managed to survive the invasion. These were probably responsible for the maintenance of AMF communities in the patches of R. japonica. In conclusion, AMF communities are negatively affected by the invasion, but R. japonica does not entirely eliminate AMF, which is optimistic from the viewpoint of restoring sites invaded by this non-mycorrhizal alien plant species.

Automated summary

The invasion of Japanese knotweed has a negative impact on AMF communities, reducing spore number, species richness, and biomass, but not completely eliminating AMF. The performance of AMF communities varies over time and depends on soil conditions, with interactions between factors having minimal effect. The displacement of resident mycorrhizal plant species by the invader contributes to the lower performance of AMF communities, although some mycorrhizal plants are able to survive the invasion and maintain AMF communities.